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Development of uterus during pregnancy
Anatomy of pregnancy and birth - uterus
Anatomy of pregnancy and birth - uterus | Pregnancy Birth and Baby beginning of content
What does the uterus look like?
One of the most recognised changes in a pregnant woman’s body is the appearance of the ‘baby bump’, which forms to accommodate the baby growing in the uterus. The primary function of the uterus during pregnancy is to house and nurture your growing baby, so it is important to understand its structure and function, and what changes you can expect the uterus to undergo during pregnancy.
The uterus (also known as the ‘womb’) has a thick muscular wall and is pear shaped. It is made up of the fundus (at the top of the uterus), the main body (called the corpus), and the cervix (the lower part of the uterus ). Ligaments – which are tough, flexible tissue – hold it in position in the middle of the pelvis, behind the bladder, and in front of the rectum.
The uterus wall is made up of 3 layers. The inside is a thin layer called the endometrium, which responds to hormones – the shedding of this layer causes menstrual bleeding. The middle layer is a muscular wall. The outside layer of the uterus is a thin layer of cells.
Illustration showing the female reproductive system.
The size of a non-pregnant woman's uterus can vary. In a woman who has never been pregnant, the average length of the uterus is about 7 centimetres. This increases in size to approximately 9 centimetres in a woman who is not pregnant but has been pregnant before. The size and shape of the uterus can change with the number of pregnancies and with age.
How does the uterus change during pregnancy?
During pregnancy, as the baby grows, the size of a woman’s uterus will dramatically increase. One measure to estimate growth is the fundal height, the distance from the pubic bone to the top of the uterus. Your doctor (GP) or obstetrician or midwife will measure your fundal height at each antenatal visit from 24 weeks onwards. If there are concerns about your baby’s growth, your doctor or midwife may recommend using regular ultrasound to monitor the baby.
Fundal height can vary from person to person, and many factors can affect the size of a pregnant woman’s uterus. For instance, the fundal height may be different in women who are carrying more than one baby, who are overweight or obese, or who have certain medical conditions. A full bladder will also affect fundal height measurement, so it’s important to empty your bladder before each measurement. A smaller than expected fundal height could be a sign that the baby is growing slowly or that there is too little amniotic fluid. If so, this will be monitored carefully by your doctor. In contrast, a larger than expected fundal height could mean that the baby is larger than average and this may also need monitoring.
As the uterus grows, it can put pressure on the other organs of the pregnant woman's body. For instance, the uterus can press on the nearby bladder, increasing the need to urinate.
How does the uterus prepare for labour and birth?
Braxton Hicks contractions, also known as 'false labour' or 'practice contractions', prepare your uterus for the birth and may start as early as mid-way through your pregnancy, and continuing right through to the birth. Braxton Hicks contractions tend to be irregular and while they are not generally painful, they can be uncomfortable and get progressively stronger through the pregnancy.
During true labour, the muscles of the uterus contract to help your baby move down into the birth canal. Labour contractions start like a wave and build in intensity, moving from the top of the uterus right down to the cervix. Your uterus will feel tight during the contraction, but between contractions, the pain will ease off and allow you to rest before the next one builds. Unlike Braxton Hicks, labour contractions become stronger, more regular and more frequent in the lead up to the birth.
How does the uterus change after birth?
After the baby is born, the uterus will contract again to allow the placenta, which feeds the baby during pregnancy, to leave the woman’s body. This is sometimes called the ‘after birth’. These contractions are milder than the contractions felt during labour. Once the placenta is delivered, the uterus remains contracted to help prevent heavy bleeding known as ‘postpartum haemorrhage‘.
The uterus will also continue to have contractions after the birth is completed, particularly during breastfeeding. This contracting and tightening of the uterus will feel a little like period cramps and is also known as 'afterbirth pains'.
Read more here about the first few days after giving birth.
The Royal Australian and New Zealand College of Obstetricians and Gynaecologists (Labour and birth), StatPearls Publishing (Anatomy, Abdomen and Pelvis), Department of Health (Clinical practice guidelines: Pregnancy care), Better Health Channel Victoria (Pregnancy stages and changes), Mater Mother's Hospital (Labour and birth information), Royal Australian and New Zealand College of Obstetricians and Gynaecologists (The First Few Weeks Following Birth), Queensland Health (Queensland Clinical Guidelines – maternity and neonatal), King Edward Memorial Hospital (Fundal height: Measuring with a tape measure), Royal Hospital for Women (Fetal growth assessment (clinical) in pregnancy), MSD Manual (Female internal genital organs)
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Last reviewed: October 2020
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Pregnancy is a state of having implanted products of conception located either in the uterus or elsewhere in the body. It ends through either spontaneous or elective abortion or delivery. During this time, the mother’s body goes through immense changes involving all organ systems to sustain the growing fetus. All medical providers must be aware of these alterations present in pregnancy to be able to provide the best possible care for both mother and fetus.
Issues of Concern
The female body goes through immense changes during a pregnancy that involve all organ systems in the body. These changes result in physiology that differs from that of a non-pregnant female. Additionally, abnormalities in the development of pregnancy can lead to further complications for both mother and fetus. With the maternal mortality rate in the United States reaching almost 18 deaths per 100,000 live births in 2009, a drastic increase from the 7.2 deaths per 100,000 in 1987, it has become more critical for all healthcare providers to understand the typical changes that accompany pregnancy, as well as recognize changes that go beyond typical pregnancy symptoms.
The fertilization of an egg with a sperm starts the process of embryogenesis. The fertilized egg goes through several divisions to form a blastocyst. This blastocyst then initiates implantation with the maternal endometrium. Implantation triggers the uterine stroma to undergo decidualization to accommodate the embryo. This decidua supports embryo survival and appears to act as a barrier against immunologic responses. Additionally, upon implantation, human chorionic gonadotropin (hCG) begins to be secreted, allowing the sustenance of pregnancy. The blastocyst then begins the process of forming three distinct germ layers, including the ectoderm, mesoderm, and endoderm. At this stage, the blastocyst then becomes an embryo. The embryo goes through a process known as organogenesis, in which the majority of the major organ systems develop. After 8 weeks from implantation, or 10 weeks gestational age, the embryo is then termed a fetus until birth.
The duration of pregnancy, from implantation of a fertilized ovum to birth, is taken as 266 days. However, as pregnancy dating is typically from the first day of the last menstrual period, the duration of pregnancy is considered to be 280 days on average. This duration is the amount of time by which approximately half of all women will deliver their babies. Babies born from 37 0/7 weeks gestation to 38 6/7 weeks are considered early term. Those born between 39 0/7 weeks and 40 6/7 weeks are labeled full term. Babies born 41 0/7 weeks through 41 6/7 weeks are titled late-term. Any baby born at 42 0/7 weeks gestation and beyond is deemed post-term.
Organ Systems Involved
Pregnancy induces a coordinated response of multiple organ systems to support both mother and fetus.
Female Reproductive System 
To accommodate a growing fetus, the uterus must undergo extreme structural changes and cellular hypertrophy. During this time, the uterus must maintain a passive noncontractile state; this occurs through elevated levels of progesterone, which act to relax smooth muscle—growth of the placenta results in uterine tissue and vascular remodeling. Hormonal signals, primarily estrogen, are responsible for initiating the uterine growth process during early pregnancy. The uterus increases from 70 g to 1100 g, with its volume capacity increasing from 10 mL to 5 L. Between weeks 12 and 16, the lower uterine corpus unfolds, allowing the uterus to become more spherical and giving room for amniotic sac expansion with minimal stretching of the uterus. When fetal growth rate begins to accelerate at 20 weeks, the uterus rapidly elongates, and the walls thin. The longitudinal diameter grows more rapidly than the left-right and anterior-posterior diameters, with the maximum rate of elongation happening between weeks 20 and 32. By 28 weeks, the maximum fetal growth rate has occurred, and the uterine tissue growth slows while continuing to stretch rapidly and become thin. Within several weeks of delivery, the uterus then returns to its pre-pregnancy structure.
During pregnancy, the cardiac output increases by 30 to 60%, with the majority of the increase occurring during the first trimester. The maximum output is reached between 20 and 24 weeks and is maintained until delivery. Initially, the increase in cardiac output is due to an increase in stroke volume. As the stroke volume decreases towards the end of the third trimester, an increase in heart rate acts to maintain the increased cardiac output.
Systemic vascular resistance decreases, resulting in decreased arterial blood pressure. Systolic blood pressure decreases by approximately 5 to 10 mm Hg, and diastolic blood pressure decreases by 10 to 15 mm Hg. This decrease reaches its lowest point at 24 weeks, at which point it slowly returns to pre-pregnancy levels. This decrease in arterial blood pressure is due to the elevated progesterone levels present during pregnancy. Progesterone leads to smooth muscle relaxation, thus decreasing vascular resistance.
Due to these physiological changes, bounding or collapsing pulses, as well as ejection systolic murmurs, are present in the majority of pregnant women. A third heart sound may be present, and ectopic beats and peripheral edema are also common. The changes in the position of the heart that occur as pregnancy progress lead to ECG changes that are considered normal findings in pregnancy. These include: atrial and ventricular ectopic beats, small Q waves and inverted T waves in lead III, ST-segment depression and T wave inversion in inferior and lateral leads, and left axis shift.
During pregnancy, the diaphragm elevates, resulting in a 5% decrease in total lung capacity (TLC). However, the tidal volume (TV) increases by 30 to 40%, thereby decreasing the expiratory reserve volume by 20%. Minute ventilation is similarly increased by 30 to 40%, owing to the fact that TV becomes increased while a constant respiratory rate is maintained.
The increase in minute ventilation that occurs during pregnancy allows for an increase in alveolar (PAO2) and arterial (PaO2) PO2 levels and a decrease in PACO2 and PaCO2. PaCO2 decreases from a pre-pregnancy level of 40 mm Hg to 30 mm Hg by 20 weeks. This decrease in PaCO2 creates an increased CO2 gradient between the fetus and mother, thus enhancing oxygen delivery and carbon dioxide removal in the fetus. This gradient is created by elevated progesterone levels, which appear to act to either increase the responsiveness of the respiratory system to CO2 or to be a primary stimulant. These changes are needed to accommodate the 15% increase in metabolic rate and the 20% increase in oxygen consumption that occurs during pregnancy.
Decreased PaCO2 levels, increased tidal volume, and decreased total lung capacity combine to result in dyspnea of pregnancy in approximately 60% to 70% of pregnant patients. This feeling is a subjective sensation of breathlessness with no hypoxia present. It is most common during the third trimester but can start at any time.
Elevated levels of estrogen, progesterone, and human chorionic gonadotropin (hCG) combine to bring about nausea and vomiting, commonly termed morning sickness. Hypoglycemia can be an additional cause of nausea. Morning sickness develops in over 70% of pregnancies and can occur at any time of day. It typically resolves by weeks 14 to 16 but persists beyond week 20 in about 10-20% of pregnant patients. If nausea and vomiting are severe enough to lead to ketosis and weight loss greater than or equal to 5% of pre-pregnancy weight, the term for this is hyperemesis gravidarum. In these patients, intravenous fluid and vitamin substitution may be necessary.
Elevated progesterone levels induce smooth muscle relaxation, leading to prolonged gastric emptying time. When combined with decreased gastroesophageal sphincter tone and upwards displacement of the stomach, reflux often occurs. Progesterone-mediated smooth muscle relaxation also leads to decreased motility in the large bowel, resulting in increased water absorption and constipation.
The renin-angiotensin-aldosterone system is activated in early pregnancy, consequently increasing sodium reabsorption. However, an increased glomerular filtration rate (GFR) acts to maintain sodium plasma levels. Additionally, elevated progesterone and prostacyclin, along with angiotensin I receptor modification in pregnancy, leads to a relative resistance to angiotensin II. This state acts to balance the vasoconstrictive effect of angiotensin and allows for vasodilation of the renal arteries mediated by relaxin stimulation of endothelium to synthesize nitric oxide.
Due to renal vasodilation, both the GFR and renal plasma flow increase. The GFR increases 50% starting in early pregnancy, and this increase remains until delivery. The decrease in systemic vascular resistance results in both afferent and efferent arterioles experiencing decreased vascular resistance, thus maintaining glomerular hydrostatic pressure—the resulting increased renal blood flow results in an increase in kidney size. Progesterone acts to reduce ureteral tone, peristalsis, and contraction pressure, thereby dilating the ureters.
The elevation in GFR acts to decrease blood urea nitrogen and creatinine by 25%. The elevated GFR, combined with increased glomerular capillary permeability to albumin, results in an increase of fractional excretion of protein to as much as 300 mg/day. Less effective tubular reabsorption of both glucose and urea results in increased excretion rates.
In pregnancy, the RBC volume increases by 20% to 30%, while the plasma volume increases by 45 to 55%. This disproportionate volume increase leads to dilutional anemia with decreased hematocrit. WBC count increases to 6 to 16 million/mL and can be as high as 20 million/mL during and shortly after labor. Platelet concentration decreases slightly due to the increased plasma volume but typically stays within normal limits. A small proportion of women (5 to 10%) will have platelet levels between 100 and 150 billion/L without any pathology present. Fibrinogen and factors VII – X levels increase, but the clotting and bleeding times remain unchanged. However, increased venous stasis and damaged vessel endothelium result in higher rates of thromboembolic events during pregnancy. The increase in the risk of thromboembolic events starts in the first trimester and continues at least 12 weeks postpartum.
The increased levels of estrogen in pregnancy result in a stimulation of thyroid-binding globulin, which then increases levels of thyroxine (T4) and tri-iodothyronine (T3). Free T3 and T4 levels are slightly altered, but remain relatively constant, with a slight decrease in the second and third trimesters. TSH levels decrease somewhat in the first trimester due to the weakly stimulating effect of hCG on the thyroid but increase again by the end of the first trimester. Despite the changes, pregnancy is considered to be a euthyroid state.
During pregnancy, there is an increase in hormone production by the adrenal glands. The reduced vascular resistance and blood pressure stimulate the RAA system, resulting in a three-fold increase in aldosterone by the end of the first trimester and a ten-fold increase by the end of the third trimester. There is also an increase in the production of cortisol, adrenocorticotropic hormone (ACTH), corticosteroid-binding globulin (CGB), and deoxycorticosterone, resulting in a hyper cortisol state. By the end of the third trimester, total cortisol levels are three times higher than in non-pregnant women. By the end of pregnancy, the placenta contributes to the increased cortisol state due to its production of corticotropin-releasing hormone, thus helping to trigger labor.
The increased levels of estradiol in pregnancy result in an increase in prolactin, with serum prolactin levels increasing ten-fold by the end of pregnancy. This increased production induces growth in the pituitary gland caused by the proliferation of cells in the anterior lobe. Oxytocin levels, produced by the posterior pituitary, increase throughout pregnancy and peak at term. Elevated estrogen, progesterone, and inhibin act to inhibit the production of follicle-stimulating hormone (FSH) and luteinizing hormone (LH), making these levels undetectable.
Musculoskeletal and Dermatologic 
The shift in the center of gravity that occurs with pregnancy results in increased lordosis of the lower back and flexion in the neck. This shift in posture can cause lower back strain that worsens as the pregnancy progresses. Increased mobility and widening of the sacroiliac joints and pubic symphysis occur, as well as joint laxity in the lumbar spine. Carpal tunnel syndrome is a common occurrence in pregnancy due to compression of the median nerve.
Increased estrogen levels result in spider angiomata and palmar erythema. Elevated melanocyte-stimulating hormones and steroid hormones lead to hyperpigmentation of the face, nipples, perineum, abdominal line, and umbilicus.
The placenta produces human placental lactogen (hPL), which acts to supply nutrition to the fetus. It induces lipolysis to increase free fatty acids, which are preferentially used by the pregnant mother for fuel. It also acts as an insulin antagonist to induce a diabetogenic state. This activity prompts hyperplasia of pancreatic beta-cells to create increased insulin levels and protein synthesis. In early pregnancy, maternal insulin sensitivity increases, followed by resistance in the second and third trimesters.
Total serum cholesterol and triglyceride levels increase during pregnancy due to increased synthesis in the liver and decreased activity of lipoprotein lipase. LDL cholesterol increases throughout pregnancy, with a 50% increase by term. HDL cholesterol increases during the first half of pregnancy and then falls in the third trimester while still staying above non-pregnant levels. The increase in triglycerides is essential for supplying the mother’s energy while sparing glucose for the fetus. The increased LDL levels are crucial for placental steroidogenesis.
There are increased caloric and nutritional requirements during pregnancy, including increased requirements for protein, iron, calcium, folate, and other vitamins and minerals. The protein requirement in pregnancy increases from 60 g/day to 70 to 75 g/day, as the amino acids are transported to the developing fetus. The calcium requirement increases to 1.5 g/day, due to the fetus's requirement of 30 g of calcium. Maternal serum levels of calcium are maintained in pregnancy, with fetal needs being met by increased intestinal absorption starting at week 12.
The primary function of pregnancy is to allow for the growth and development of the fetus. All changes that occur within the mother’s body are intended to allow for this growth, as well as for the development of the placenta to nourish the fetus and sustain the pregnancy.
The menstrual cycle ranges from 26 to 35 days, with 28 days being the average duration. Menstrual bleeding begins on the first day of the menstrual cycle, and the heaviest flow occurs, on average, on day 2. The beginning of the menstrual cycle comprises the follicular phase, during which FSH from the pituitary gland stimulates the development of a primary ovarian follicle. This follicle induces estrogen production, allowing the uterine lining to proliferate. A spike in LH, triggered by the estrogen surge, stimulates ovulation and begins the luteal phase. The greatest probability of conception occurs in the follicular phase, one day before ovulation. However, the fertile phase spans the time between 5 days before and the day of ovulation. After ovulation, the corpus luteum secretes progesterone, maintaining the endometrial lining for a fertilized ovum. If fertilization does not occur or the fertilized ovum does not implant into the endometrial lining, then the corpus luteum degenerates, progesterone levels fall, and the endometrial lining sloughs off to begin the menstrual cycle again. 
If a fertilized ovum successfully implants into the endometrium, the trophoblast cells proliferate into syncytiotrophoblast cells and begin to produce hCG. This sustains the corpus luteum to maintain the secretion of progesterone and estrogen, allowing the pregnancy to develop. The syncytiotrophoblast, along with the cytotrophoblast and extraembryonic mesoderm, goes on to form the placenta. The primary purpose of the placenta is to sustain the pregnancy and meet the demands of the fetus. The placental membrane allows for the exchange of nutrients and gases between the fetus and the mother’s body, acting as the fetal respiratory, gastrointestinal, endocrine, renal, hepatic, and immune systems. 
Pregnancy ends with the delivery of the fetus. There are several theories as to how labor initiates. Some studies show that labor becomes triggered by the withdrawal of progesterone and mechanical stretch experienced by the uterine wall. Other studies suggest that inflammatory mediators, such as prostaglandins, are vital in initiating uterine contractions. Oxytocin then goes on to sustain contractions during labor and delivery.
Indications for testing to confirm pregnancy, either through urine or serum sample, include a female of child-bearing age with amenorrhea, dysmenorrhea, pelvic pain, abdominal pain, syncope, lightheadedness, dizziness, hypotension, tachycardia, nausea or vomiting, vaginal discharge, or urinary symptoms. Levels of hCG in a viable intrauterine pregnancy double approximately every 48 hours in early pregnancy. Levels peak around 10 to 12 weeks gestation, then decline to a steady state after 15 weeks. Ultrasound confirmation of early pregnancy is utilized when an individual has a positive pregnancy test along with pelvic pain, abdominal pain, or vaginal bleeding. 
Confirmation of a viable pregnancy occurs with an ultrasound, which shows a gestational sac on transvaginal ultrasound at five weeks or with an hCG level of 1,500 to 2,000 mIU/mL. Fetal heart motion is visible on transvaginal ultrasound at six weeks or with hCG levels starting at 5,000 to 6,000 mIU/mL.
As the purpose of the placenta is to support and maintain the pregnancy, any abnormality in placenta formation can result in adverse outcomes for both mother and fetus. Abnormalities can be in the form of the structure of the placenta, the location of the placenta, and the implantation of the placenta.
Preeclampsia appears to involve both maternal and fetal factors, leading to abnormal development of the vasculature in the placenta; this ultimately leads to under-perfusion, resulting in hypoxia and growth restriction. Maternal endothelial dysfunction, believed to be due to antiangiogenic factors, leads to increased vascular permeability, with activation of the coagulation cascade, vasoconstriction, and microangiopathic hemolysis. These factors lead to the clinical manifestations of preeclampsia, including hypertension, proteinuria, seizure, cerebral hemorrhage, DIC, renal failure, pulmonary edema, uteroplacental insufficiency, placental abruption, premature delivery, and increased rate of cesarean section deliveries. Preeclampsia falls into two categories, preeclampsia without severe features and preeclampsia with severe features. To be diagnosed without severe features, third-trimester blood pressure greater than 140/90 mm Hg on two occasions at least 6 hours apart is needed, as well as proteinuria over 300 mg/24 hours or protein to creatinine ratio greater than 0.3. Women with preeclampsia without severe features are managed with delivery at 37 weeks. If diagnosed before 37 weeks, they are closely monitored as inpatients, although outpatient monitoring can be utilized if there are no other comorbidities. To be diagnosed as preeclampsia with severe features, blood pressure must be greater than 160/110 mm Hg in addition to proteinuria. Alternatively, blood pressure can be greater than 140/90 mm Hg on two occasions with at least one other feature, including renal insufficiency, thrombocytopenia, pulmonary edema, impaired liver function, or cerebral or visual disturbances. These patients should be delivered at 34 weeks and should receive treatment with magnesium sulfate for seizure prophylaxis. If blood pressure is greater than 160/110 mm Hg, antihypertensives should be used to decrease the risk of stroke.
Approximately 10% of patients with preeclampsia with severe features will go on to develop HELLP syndrome—these patients present with hemolysis, elevated liver enzymes, and low platelets. Hypertension and proteinuria do not need to be present in these patients. These patients diagnosed after 34 0/7 weeks should be delivered once stabilized. If diagnosed before 34 weeks, these women should be delivered 24 to 48 hours after betamethasone administration. They should also be administered magnesium sulfate until 24 hours postpartum. 
Eclampsia is diagnosed when grand mal seizures occur in a preeclamptic patient. It can occur in women both with and without severe features. Eclampsia appears to occur when there is a breakdown in autoregulation of cerebral circulation due to endothelial dysfunction, hyperperfusion, and brain edema. Treatment includes seizure management and prophylaxis, blood pressure control, and delivery once the patient has been stabilized and convulsions controlled.
Placenta previa occurs with abnormal implantation of the placenta covering the internal cervical os. It can be considered complete, in which the internal os is completely covered by the placenta, partial previa, with the placenta covering a portion of the internal os, or marginal previa, where the edge of the placenta approaches the margin of the os. The placenta is considered low-lying when it is in the lower uterine segment but does not extend to the internal os. During the third trimester, the lower uterine segment begins thinning, leading to disruption in the placental attachment and painless bleeding. This bleeding irritates the uterus, stimulating uterine contractions that cause further separation and bleeding. As the cervix dilates and effaces during labor, placental separation and unavoidable bleeding occur, which may result in hemorrhage and shock. These patients are managed with pelvic rest after 20 weeks, decreased physical activity, and cesarean delivery between 36 and 37 weeks.
Placenta accreta occurs when the placenta invades into the uterine wall during implantation. If the invasion extends to the myometrium, the term for the condition is placenta increta. If the invasion extends further through the myometrium and into the serosa, this is considered placenta percreta. Placenta percreta may also invade into surrounding organs, such as the bladder or rectum. In these conditions, the placenta is unable to separate from the uterine wall properly, which can lead to hemorrhage and shock. As such, this condition can lead to the need for a hysterectomy at the time of delivery. 
Understanding changes that occur during pregnancy is critical for the proper management of pregnant patients. They encounter many physical changes that can create physical, mental, and emotional strain for the patient. It is essential to remain sensitive to these changes when providing care.
In addition to remaining sensitive to providing compassionate care, knowing the physiologic changes of pregnancy are essential when determining whether an apparent pathology is indeed pathological versus a normal finding in a pregnant patient. Many lab value limits are adjusted in pregnancy due to the changes in hormones and organ functioning. Hypotension and tachycardia become more prevalent throughout pregnancy, requiring careful considerations in the treatment of a pregnant trauma patient.
Overall, understanding the physiology of pregnancy allows all providers, not only OB/GYNs, to provide the best possible care.
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Child development by week | Regional Perinatal Center
Expectant mothers are always curious about how the fetus develops at a time when it is awaited with such impatience. Let's talk and look at the photos and pictures of how the fetus grows and develops week by week.
What does the puffer do for 9 whole months in mom's tummy? What does he feel, see and hear?
Let's start the story about the development of the fetus by weeks from the very beginning - from the moment of fertilization. A fetus up to 8 weeks old is called embryo , this occurs before the formation of all organ systems.
Embryo development: 1st week
The egg is fertilized and begins to actively split. The ovum travels to the uterus, getting rid of the membrane along the way.
On the 6th-8th days, implantation of eggs is carried out - implantation into the uterus. The egg settles on the surface of the uterine mucosa and, using the chorionic villi, attaches to the uterine mucosa.
Embryo development: 2-3 weeks
Picture of embryo development at 3 weeks.
The embryo is actively developing, starting to separate from the membranes. At this stage, the beginnings of the muscular, skeletal and nervous systems are formed. Therefore, this period of pregnancy is considered important.
Embryo development: 4–7 weeks
Fetal development by week in pictures: week 4
Fetal development by week photo: week 4
Photo of an embryo before the 6th week of pregnancy.
The heart, head, arms, legs and tail are formed in the embryo :) . Gill slit is defined. The length of the embryo at the fifth week reaches 6 mm.
Fetal development by week photo: week 5
At the 7th week, the rudiments of the eyes, stomach and chest are determined, and fingers appear on the handles. The baby already has a sense organ - the vestibular apparatus. The length of the embryo is up to 12 mm.
Fetal development: 8th week
Fetal development by weeks photo: weeks 7-8
The face of the fetus can be identified, the mouth, nose, and auricles can be distinguished. The head of the embryo is large and its length corresponds to the length of the body; the fetal body is formed. All significant, but not yet fully formed, elements of the baby's body already exist. The nervous system, muscles, skeleton continue to improve.
Fetal development in the photo already sensitive arms and legs: week 8
The fetus developed skin sensitivity in the mouth (preparation for the sucking reflex), and later in the face and palms.
At this stage of pregnancy, the genitals are already visible. Gill slits die. The fruit reaches 20 mm in length.
Fetal development: 9–10 weeks
Fetal development by week photo: week 9
Fingers and toes already with nails. The fetus begins to move in the pregnant woman's stomach, but the mother does not feel it yet. With a special stethoscope, you can hear the baby's heartbeat. Muscles continue to develop.
Weekly development of the fetus photo: week 10
The entire surface of the fetal body is sensitive and the baby develops tactile sensations with pleasure, touching his own body, the walls of the fetal bladder and the umbilical cord. It is very curious to observe this on ultrasound. By the way, the baby first moves away from the ultrasound sensor (of course, because it is cold and unusual!), And then puts his hands and heels trying to touch the sensor.
It's amazing when a mother puts her hand to her stomach, the baby tries to master the world and tries to touch with his pen "from the back".
The development of the fetus: 11–14 weeks
Development of the fetus in the photo of the legs: weeks 11
The baby, legs and eyelids are formed, and the genitals become distinguishable (you can find out the gender (you can find out the gender child). The fetus begins to swallow, and if something is not to its taste, for example, if something bitter got into the amniotic fluid (mother ate something), then the baby will begin to frown and stick out his tongue, making less swallowing movements.
Fruit skin appears translucent.
Fruit development: Week 12
Photo of the fetus 12 weeks per 3D Uzi
Development of the fetus for weeks: Week 14 9000 9000
buds are responsible for production for production urine. Blood forms inside the bones. And hairs begin to grow on the head. Moves more coordinated.
Fetal development: 15-18 weeks
Fetal development by weeks photo: week 15
The skin turns pink, the ears and other parts of the body, including the face, are already visible. Imagine, a child can already open his mouth and blink, as well as make grasping movements. The fetus begins to actively push in the mother's tummy. The sex of the fetus can be determined by ultrasound.
Fetal development: 19-23 weeks
Fetal development by week photo: week 19
Baby sucks his thumb, becomes more energetic. Pseudo-feces are formed in the intestines of the fetus - meconium , kidneys begin to work. During this period, the brain develops very actively.
Fetal development by weeks photo: week 20
The auditory ossicles become stiff and now they are able to conduct sounds, the baby hears his mother - heartbeat, breathing, voice. The fetus intensively gains weight, fat deposits are formed. The weight of the fetus reaches 650 g, and the length is 300 mm.
The lungs at this stage of fetal development are so developed that the baby can survive in the artificial conditions of the intensive care unit.
Fetal development: 24-27 weeks
Lungs continue to develop. Now the baby is already falling asleep and waking up. Downy hairs appear on the skin, the skin becomes wrinkled and covered with grease. The cartilage of the ears and nose is still soft.
Fetal development by week photo: week 27
Lips and mouth become more sensitive. The eyes develop, open slightly and can perceive light and squint from direct sunlight. In girls, the labia majora do not yet cover the small ones, and in boys, the testicles have not yet descended into the scrotum. Fetal weight reaches 900–1200 g, and the length is 350 mm.
9 out of 10 children born at this term survive.
Fetal development: 28-32 weeks
The lungs are now adapted to breathe normal air. Breathing is rhythmic and body temperature is controlled by the CNS. The baby can cry and responds to external sounds.
Child opens eyes while awake and closes during sleep.
The skin becomes thicker, smoother and pinkish. Starting from this period, the fetus will actively gain weight and grow rapidly. Almost all babies born prematurely at this time are viable. The weight of the fetus reaches 2500 g, and the length is 450 mm.
Fetal development: 33-37 weeks
Fetal development by week photo: week 36
The fetus reacts to a light source. Muscle tone increases and the baby can turn and raise his head. On which, the hairs become silky. The child develops a grasping reflex. The lungs are fully developed.
Fetal development: 38-42 weeks
The fetus is quite developed, prepared for birth and considered mature. The baby has mastered over 70 different reflex movements. Due to the subcutaneous fatty tissue, the baby's skin is pale pink. The head is covered with hairs up to 3 cm.
Fetal development by weeks photo: week 40
The baby perfectly mastered the movements of his mother , knows when she is calm, excited, upset and reacts to this with her movements. During the intrauterine period, the fetus gets used to moving in space, which is why babies love it so much when they are carried in their arms or rolled in a stroller. For a baby, this is a completely natural state, so he will calm down and fall asleep when he is shaken.
The nails protrude beyond the tips of the fingers, the cartilages of the ears and nose are elastic. In boys, the testicles have descended into the scrotum, and in girls, the large labia cover the small ones. The weight of the fetus reaches 3200-3600 g, and the length is 480-520 mm.
After the birth, the baby longs for touching his body, because at first he cannot feel himself - the arms and legs do not obey the child as confidently as it was in the amniotic fluid. Therefore, so that your baby does not feel lonely, it is advisable to carry him in your arms, press him to you while stroking his body.
And one more thing, the baby remembers the rhythm and sound of your heart very well . Therefore, you can comfort the baby in this way - take him in your arms, put him on the left side and your miracle will calm down, stop crying and fall asleep. And for you, finally, the time of bliss will come :) .
1-4 weeks of pregnancy
From a tiny fetus to a small person, a child's body develops in just 9 months. What changes are happening to the expectant mother and what changes are observed inside her during this difficult and joyful period of life?
Each new life begins with the union of the egg and sperm. Conception is the process by which a sperm enters an egg and fertilizes it.
It should be noted that the embryonic and obstetric terms are different. The thing is that among specialists it is customary to consider the period from the first day of the last menstruation, that is, the obstetric period includes the period of preparation for pregnancy. So it turns out that the embryo has just appeared, and the gestation period is already two weeks. It is the obstetric period that is indicated in all the documents of a woman and is the only reporting period for specialists.
Until the moment of the meeting, the spermatozoon and the ovum lived for a certain time, being in the stage of development and maturation. The development of the future fetus significantly depends on the quality of these processes.
Growth and maturation of the egg starts from the first day of the cycle. A mature egg contains 23 chromosomes as the genetic material for the future embryo, and also contains all the nutrients necessary to start its development. It contains reserves of carbohydrates, proteins and fats, designed to support the embryo during the first days after its occurrence.
A certain number of eggs are laid in each ovary of a girl before she is born. During the childbearing period, they only grow and develop, the process of their formation does not occur. By the time a girl is born, the number of cells from which eggs can develop in the future reaches a million, but this number decreases significantly over the course of life. So, by the time of puberty, there are several hundred thousand of them, and by maturity - about 500.
The ovary each month gives the opportunity to develop most often one egg, the maturation of which occurs inside a vesicle with a liquid called a follicle. From the first day of the cycle, the uterine mucosa begins to prepare for a possible pregnancy. For implantation, i.e., the introduction of the resulting embryo into the wall of the uterus, an optimal environment is created. To do this, due to the influence of hormones, the endometrium thickens, it becomes covered with a network of vessels and accumulates the nutrients necessary for the future embryo.
Male reproductive cells are formed in the gonads - in the testicles or testes. The maturation of spermatozoa occurs in the epididymis, into which they move after formation. The liquid structure of semen is formed due to the secretion of the seminal vesicles and the prostate gland. A liquid medium is necessary for storing mature spermatozoa and creating favorable conditions for their life.
The number of spermatozoa is quite large: tens of millions in one milliliter. Despite such a significant number, only one of them will be able to fertilize the egg. In spermatozoa, there is exclusively genetic material - 23 chromosomes, which are necessary for the appearance of the embryo.
Spermatozoa are characterized by high motility. Once in the female genital tract, they begin their movement towards the egg. Only half an hour or an hour passes from the moment of ejaculation, when sperm enter the uterine cavity. It takes one and a half to two hours for spermatozoa to penetrate into the widest part, which is called the ampulla. Most spermatozoa die on the way to the egg, meeting the folds of the endometrium, getting into the vaginal environment, cervical mucus.
In the middle of the cycle, the egg fully matures and leaves the ovary. It enters the abdominal cavity. This process is called ovulation. With a regular cycle of 30 days, ovulation occurs on the fifteenth. The egg is unable to move on its own. When she leaves the follicle, the fimbriae of the fallopian tube ensure her penetration inside. The fallopian tubes are characterized by longitudinal folding, they are filled with mucus. The muscular movements of the tubes have a wave-like character, which, with a significant number of cilia, creates optimal conditions for transporting the egg.
Through the tubes, the egg enters their widest part, which is called the ampulla. This is where fertilization takes place. If there is no meeting with the sperm, the egg dies, and the female body receives the appropriate signal to start a new cycle. There is a rejection of the mucous membrane, which was created by the uterus. The manifestation of such rejection is bloody discharge, which is called menstruation.
The waiting period for fertilization by the egg is short. On average, it takes no more than a day. Fertilization is likely on the day of ovulation and maximum on the next. Sperm have a longer lifespan, averaging three to five days, in some cases seven. Accordingly, if a spermatozoon enters the female genital tract before ovulation, there is a possibility that it will be able to wait for the appearance of an egg.
When the egg is in a state of waiting for fertilization, certain substances are released that are designed to detect it. If spermatozoa find an egg, they begin to secrete special enzymes that can loosen its shell. As soon as one of the spermatozoa penetrates the egg, the others can no longer do this due to the restoration of the density of its shell. Thus, one egg can only be fertilized by one sperm.
After fertilization, the chromosome sets of the parents merge - 23 chromosomes from each. As a result, one cell is formed from two different cells, which is called a zygote. The sex of the unborn child depends on which of the chromosomes, X or Y, was in the sperm. Eggs contain only X chromosomes. When XX is combined, girls are born. If the spermatozoon contains a Y chromosome, that is, with a combination of XY, boys are born. As soon as a zygote is formed in the body, a mechanism is launched in it aimed at maintaining pregnancy. There are changes in the hormonal background, biochemical reactions, immune mechanisms, and the receipt of nerve signals. The female body creates all the necessary conditions for the safe development of the fetus.
As soon as a day has passed after the formation of the embryo, he will need to make his first journey. The movements of the cilia and the contraction of the muscles of the tube direct it into the uterine cavity. During this process, inside the egg, fragmentation into identical cells occurs.
After four days, the appearance of the egg changes: it loses its round shape and becomes vine-shaped. This stage is called morula, embryogenesis begins - an important stage in the development of the embryo, during which the formation of the rudiments of organs and tissues occurs. Cleavage of cells continues for several days, on the fifth day their complexes are formed, which have different functions. The central cluster forms directly the embryo, the outer one, called the trophoblast, is designed to melt the endometrium - the inner layer of the uterus.
It takes 5-7 days for the embryo to reach the uterus. When implantation occurs in its mucous membrane, the number of cells reaches one hundred. The term implantation refers to the process of implantation of the embryo into the endometrial layer.
After fertilization on the seventh or eighth day, implantation takes place. The first critical period of pregnancy is this stage, since the embryo will have to demonstrate its viability for the first time.
During implantation, the outer cells of the embryo actively divide, and the process itself takes about forty hours. The number of cells outside the embryo increases dramatically, they stretch, they penetrate into the uterine mucosa, and the thinnest blood vessels are formed inside, which are necessary for the supply of nutrients to the embryo. Time will pass, and these vessels will be transformed first into the chorion, and subsequently into the placenta, which will be able to supply the fetus with everything necessary until the baby is born.
The embryo at this stage of life is called a blastocyst. It contacts with the endometrium, melts the cells of the endometrium with its activity, creates a path for itself to the deeper layers. The blood vessels of the embryo intertwine with the mother's body, which allows it to immediately begin to extract useful and necessary substances for development. This is vital, because by this time the stock that the mature egg carried in itself is exhausted.
Next, the production of the trophoblast cells, i.e., the outer cells of human chorionic gonadotropin, the hCG hormone, begins. The distribution of this hormone throughout the body notifies it of the onset of pregnancy, which causes the launch of active hormonal changes and the beginning of corresponding changes in the body.
After fertilization and before the start of hCG, it usually takes eight or nine days. Therefore, already from the tenth day after fertilization, it becomes possible to determine this hormone in the mother's blood. Such an analysis is the most reliable confirmation of the onset of pregnancy. The tests that are offered today to determine pregnancy are based on the detection of this hormone in the urine of a woman. After the first day of delayed menstruation with its regular cycle, it is already possible to determine pregnancy using a test on your own.
What happens to a woman in the third week of pregnancy
If a woman is planning a pregnancy, 21-24 days, subject to a regular cycle, should be important for her. This is a period of possible implantation, when you should pay special attention to your own lifestyle. During this period, thermal effects and excessive physical exertion are undesirable, and the influence of various kinds of radiation should also be prevented.
The woman does not feel anything at this stage, because implantation has no external signs. If you adjust your lifestyle in accordance with the simple rules listed above, you will be able to create optimal conditions for successful implantation.
In the fourth obstetric week or the second week of the fetus's life, its body consists of two layers. Endoblast - cells of the inner layer - will become the beginning of the digestive and respiratory systems, ectoblast - cells of the outer layer - will start the development of the nervous system and skin.
The size of the embryo at this stage is 1.5 mm. The flat arrangement of the cells determined the name of the embryo of this age - the disc.
The fourth week is characterized by intensive development of extra-embryonic organs. Such organs should surround the embryo and create the most favorable conditions for its development.