Fetal development: Month-By-Month Stages of Pregnancy
When does a pregnancy start?
The start of pregnancy is actually the first day of your last menstrual period. This is called the gestational age, or menstrual age. It’s about two weeks ahead of when conception actually occurs. Though it may seem strange, the date of the first day of your last period will be an important date when determining your due date. Your healthcare provider will ask you about this date and will use it to figure out how far along you are in your pregnancy.
How does conception work?
Each month, your body goes through a reproductive cycle that can end in one of two ways. You will either have a menstrual period or become pregnant. This cycle is continuously happening during your reproductive years — from puberty in your teen years to menopause around age 50.
In a cycle that ends with pregnancy, there are several steps. First, a group of eggs (called oocytes) gets ready to leave the ovary for ovulation (release of the egg). The eggs develop in small, fluid-filled cysts called follicles. Think of these follicles as small containers for each immature egg. Out of this group of eggs, one will become mature and continue on through the cycle. This follicle then suppresses all the other follicles in the group. The other follicles stop growing at this point.
The mature follicle now opens and releases the egg from the ovary. This is ovulation. Ovulation generally happens about two weeks before your next menstrual period begins. It’s generally in the middle of your cycle.
After ovulation, the opened (ruptured) follicle develops into a structure called the corpus luteum. This secretes (releases) the hormones progesterone and estrogen. Progesterone helps prepare the endometrium (lining of the uterus). This lining is the place where a fertilized egg settles to develop. If you don’t become pregnant during a cycle, this lining is what is shed during your period.
On average, fertilization happens about two weeks after your last menstrual period. When the sperm penetrates the egg, changes occur in the protein coating of the egg to prevent other sperm from entering.
At the moment of fertilization, your baby’s genetic make-up is complete, including its sex. The sex of your baby depends on what sperm fertilizes the egg at the moment of conception. Generally, women have a genetic combination of XX and men have XY. Women provide each egg with an X. Each sperm can be either an X or a Y. If the fertilized egg and sperm is a combination of an X and Y, it’s a boy. If there are two Xs, it’s a girl.
What happens right after conception?
Within 24 hours after fertilization, the egg begins rapidly dividing into many cells. It remains in the fallopian tube for about three days after conception. Then the fertilized egg (now called a blastocyte) continues to divide as it passes slowly through the fallopian tube to the uterus. Once there, its next job is to attach to the endometrium. This is called implantation.
Before implantation though, the blastocyte breaks out of its protective covering. When the blastocyte makes contact with the endometrium, the two exchange hormones to help the blastocyte attach. Some women notice spotting (slight bleeding) during the one or two days when implantation happens. This is normal and isn’t something you should worry about. At this point, the endometrium becomes thicker and the cervix (the opening between your uterus and birth canal) is sealed by a plug of mucus.
Within three weeks, the blastocyte cells ultimately form a little ball, or an embryo. By this time, the first nerve cells have formed.
Your developing fetus has already gone through a few name changes in the first few weeks of pregnancy. Generally, it's called an embryo from conception until the eighth week of development. After the eighth week, it's called a fetus until it’s born.
How early can I know I’m pregnant?
From the moment of conception, the hormone human chorionic gonadotrophin (hCG) will be present in your blood. This hormone is created by the cells that form the placenta (food source for the growing fetus). It’s also the hormone detected in a pregnancy test. Even though this hormone is there from the beginning, it takes time for it to build within your body. It typically takes three to four weeks from the first day of your last period for the hCG to increase enough to be detected by pregnancy tests.
When should I reach out to my healthcare provider about a new pregnancy?
Most healthcare providers will have you wait to come in for an appointment until you have had a positive home pregnancy test. These tests are very accurate once you have enough hCG circulating throughout your body. This can be a few weeks after conception. It’s best to call your healthcare provider once you have a positive pregnancy test to schedule your first appointment.
When you call, your healthcare provider may ask you if you are taking a prenatal vitamin. These supplements contain folic acid. It’s important that you get at least 400mcg of folic acid each day during a pregnancy to make sure the fetus's neural tube (beginning of the brain and spine) develops correctly. Many healthcare providers suggest that you take prenatal vitamins with folic acid even when you aren’t pregnant. If you weren’t taking prenatal vitamins before your pregnancy, your provider may ask you to start as early as possible.
What’s the timeline for fetal development?
The fetus will change a lot throughout a typical pregnancy. This time is divided into three stages, called trimesters. Each trimester is a set of about three months. Your healthcare provider will probably talk to you about fetal development in terms of weeks. So, if you are three months pregnancy, you are about 12 weeks.
You will see distinct changes in the fetus, and yourself, during each trimester.
Traditionally, we think of a pregnancy as a nine-month process. However, this isn’t always the case. A full-term pregnancy is 40 weeks, or 280 days. Depending on what months you are pregnant during (some are shorter and some longer) and what week you deliver, you could be pregnant for either nine months or 10 months. This is completely normal and healthy.
Once you get close to the end of your pregnancy, there are several category names you might hear regarding when you go into labor. These labels divide up the last few weeks of pregnancy. They’re also used to look out for certain complications in newborns. Babies that are born in the early term period or before may have a higher risk of breathing, hearing or learning issues than babies born a few weeks later in the full term time frame. When you’re looking at these labels, it’s important to know how they’re written. You may see the week first (38) and then you’ll see two numbers separated by a slash mark (6/7). This stands for how many days you currently are in the gestational week. So, if you see 38 6/7, it means that you are on day 6 of your 38th week.
The last few weeks of pregnancy are divided into the following groups:
Early term: 37 0/7 weeks through 38 6/7 weeks.
Full term: 39 0/7 weeks through 40 6/7 weeks.
Late term: 41 0/7 weeks through 41 6/7 weeks.
Post term: 42 0/7 weeks and on.
Talk to your healthcare provider about any questions you may have about gestational age and due date.
Stages of Growth Month-by-Month in Pregnancy
The first trimester will span from conception to 12 weeks. This is generally the first three months of pregnancy. During this trimester, the fertilized egg will change from a small grouping of cells to a fetus that is starting to have a baby’s features.
Month 1 (weeks 1 through 4)
As the fertilized egg grows, a water-tight sac forms around it, gradually filling with fluid. This is called the amniotic sac, and it helps cushion the growing embryo.
During this time, the placenta also develops. The placenta is a round, flat organ that transfers nutrients from the mother to the fetus, and transfers wastes from the fetus. Think of the placenta as a food source for the fetus throughout your pregnancy.
In these first few weeks, a primitive face will take form with large dark circles for eyes. The mouth, lower jaw and throat are developing. Blood cells are taking shape, and circulation will begin. The tiny "heart" tube will beat 65 times a minute by the end of the fourth week.
By the end of the first month, the fetus is about 1/4 inch long – smaller than a grain of rice.
Month 2 (weeks 5 through 8)
Facial features continue to develop. Each ear begins as a little fold of skin at the side of the head. Tiny buds that eventually grow into arms and legs are forming. Fingers, toes and eyes are also forming.
The neural tube (brain, spinal cord and other neural tissue of the central nervous system) is well formed now. The digestive tract and sensory organs begin to develop too. Bone starts to replace cartilage.
The head is large in proportion to the rest of the body at this point. At about 6 weeks, a heartbeat can usually be detected.
After the 8th week, healthcare providers refer to it as a fetus instead of an embryo.
By the end of the second month, the fetus is about 1 inch long and weighs about 1/30 of an ounce.
Month 3 (weeks 9 through 12)
The arms, hands, fingers, feet and toes are fully formed. At this stage, the fetus is starting to explore a bit by doing things like opening and closing its fists and mouth. Fingernails and toenails are beginning to develop and the external ears are formed. The beginnings of teeth are forming under the gums. The reproductive organs also develop, but sex is still difficult to distinguish on ultrasound.
By the end of the third month, the fetus is fully formed. All the organs and limbs (extremities) are present and will continue to develop in order to become functional. The circulatory and urinary systems are also working and the liver produces bile.
At the end of the third month, the fetus is about 4 inches long and weighs about 1 ounce.
Since the most critical development has taken place, your chance of miscarriage drops considerably after three months.
This middle section of pregnancy is often thought of as the best part of the experience. By this time, any morning sickness is probably gone and the discomfort of early pregnancy has faded. The fetus will start to develop facial features during this month. You may also start to feel movement as the fetus flips and turns in the uterus. During this trimester, many people find out whether their baby will be designated male or female at birth. This is typically done during an anatomy scan (an ultrasound that checks physical development) around 20 weeks.
Month 4 (weeks 13 through 16)
The fetal heartbeat may now be audible through an instrument called a doppler. The fingers and toes are well-defined. Eyelids, eyebrows, eyelashes, nails and hair are formed. Teeth and bones become denser. The fetus can even suck his or her thumb, yawn, stretch and make faces.
The nervous system is starting to function. The reproductive organs and genitalia are now fully developed, and your doctor can see on ultrasound if the fetus will be designated male or female at birth.
By the end of the fourth month, the fetus is about 6 inches long and weighs about 4 ounces.
Month 5 (weeks 17 through 20)
At this stage, you may begin to feel the fetus moving around. The fetus is developing muscles and exercising them. This first movement is called quickening and can feel like a flutter.
Hair begins to grow on the head. The shoulders, back and temples are covered by a soft fine hair called lanugo. This hair protects the fetus and is usually shed at the end of your baby's first week of life.
The skin is covered with a whitish coating called vernix caseosa. This "cheesy" substance is thought to protect fetal skin from the long exposure to the amniotic fluid. This coating is shed just before birth.
By the end of the fifth month, the fetus is about 10 inches long and weighs from 1/2 to 1 pound.
Month 6 (weeks 21 through 24)
If you could look inside the uterus right now, you would see that the fetus's skin is reddish in color, wrinkled and veins are visible through translucent skin. The finger and toe prints are visible. In this stage, the eyelids begin to part and the eyes open.
The fetus responds to sounds by moving or increasing the pulse. You may notice jerking motions if the fetus hiccups.
If born prematurely, your baby may survive after the 23rd week with intensive care.
By the end of the sixth month, the fetus is about 12 inches long and weighs about 2 pounds.
Month 7 (weeks 25 through 28)
The fetus continues to mature and develop reserves of body fat. At this point, hearing is fully developed. The fetus changes position frequently and responds to stimuli, including sound, pain and light. The amniotic fluid begins to diminish.
If born prematurely, your baby would be likely to survive after the seventh month.
At the end of the seventh month, the fetus is about 14 inches long and weighs from 2 to 4 pounds.
This is the final part of your pregnancy. You may be tempted to start the countdown till your due date and hope that it would come early, but each week of this final stage of development helps the fetus prepare for birth. Throughout the third trimester, the fetus gains weight quickly, adding body fat that will help after birth.
Remember, even though popular culture only mentions nine months of pregnancy, you may actually be pregnant for 10 months. The typical, full-term pregnancy is 40 weeks, which can take you into a tenth month. It’s also possible that you can go past your due date by a week or two (41 or 42 weeks). Your healthcare provider will monitor you closely as you approach your due date. If you pass your due date, and don’t go into spontaneous labor, your provider may induce you. This means that medications will be used to make you go into labor and have the baby. Make sure to talk to your healthcare provider during this trimester about your birth plan.
Month 8 (weeks 29 through 32)
The fetus continues to mature and develop reserves of body fat. You may notice more kicking. The brain developing rapidly at this time, and the fetus can see and hear. Most internal systems are well developed, but the lungs may still be immature.
The fetus is about 18 inches long and weighs as much as 5 pounds.
Month 9 (weeks 33 through 36)
During this stage, the fetus continues to grow and mature. The lungs are close to being fully developed at this point.
The fetus has coordinated reflexes and can blink, close the eyes, turn the head, grasp firmly, and respond to sounds, light and touch.
The fetus is about 17 to 19 inches long and weighs from 5 ½ pounds to 6 ½ pounds.
Month 10 (Weeks 37 through 40)
In this final month, you could go into labor at any time. You may notice that less movement because space is tight. At this point, The fetus's position may have changed to prepare for birth. Ideally, it's head down in your uterus. You may feel very uncomfortable in this final stretch of time as the fetus drops down into your pelvis and prepares for birth.
Your baby is ready to meet the world at this point. They are about 18 to 20 inches long and weigh about 7 pounds.
Baby Development Month By Month
Baby Development Month by Month
A baby grows and develops an amazing amount in just nine months. Here’s a short summary of how your baby’s development occurs during pregnancy. Be sure to sign up for our pregnancy week by week newsletter for pregnancy changes and baby development updates to your inbox weekly!
Month 1 – Week 1-4
After an egg has been fertilized and implants into the uterine lining, a sac grows around it. This becomes the amniotic sac and will hold the amniotic fluid and cushion the embryo. The placenta also forms during this month. This will bring nutrition and support to the baby from the mother. The face and eyes begin to develop, and the heart begins to beat. By the end of the 4th week, your baby will slightly smaller than a grain of rice! B vitamins play a crucial role in you and your baby’s development and your health during pregnancy. Vitamin B6 and Folic Acid (Vitamin B9) are especially important for early development, so make sure you are getting the right amounts of these.
Month 2 – Week 5-9
At two months pregnant, your baby’s face continues its development. Buds that will eventually be limbs begin to develop. Organs such as the brain, sensory organs, and the digestive tract begin to take shape. The cartilage in the embryo begins to be replaced by bone. By the end of the second month, your baby is about 1 inch long! After about 6 weeks, your baby’s heartbeat can be detected with an ultrasound. It is never too soon to start taking prenatal vitamins and omega 3’s and fish oil to help your baby have a healthy development. The American Pregnancy Association recommends Nordic Naturals’ selection of supplements including:
Children’s DHA Xtra
Artic-D Cod Liver Oil
Month 3 – Week 10-14
The limbs, as well as the hands, feet, fingers, and toes, become well developed. The fingernails and toenails begin to form. The external ears and teeth begin their development as well. Though reproductive organs haven begun to form, they can’t yet be determined on an ultrasound or sonogram. By the end of the 3rd month, your baby is fully formed (with all organs and extremities present), he or she weighs about an ounce and is 4 inches long! After the 3rd month of development, the chance of miscarriage drops considerably.
Month 4 – Week 15-19
Hair, eyelids, eyelashes, and nails become well developed. The heartbeat is now clearly audible through a Doppler instrument. The teeth become denser, and the baby begins to stretch, yawn and make other movements. The reproductive organs are now visible on an ultrasound. Your baby can now stretch, suck their thumb, yawn, and make super cute faces.
This is the month that his or her nervous system develops. Their reproductive system also fully develops meaning your doctor can tell you whether you are having a girl or boy via ultrasound. By the end of the 4th month, your baby is about 6 inches long and weighs 4 ounces!
Month 5 – Week 20-24
This month you may start to feel the baby move. Hair growth continues on the baby’s head and body. The shoulders and back become covered with a thin hair called lanugo. A thick substance, called vernix caseosa, covers the skin to keep it protected from the exposure to amniotic fluid. This layer will shed before the baby is born. At the end of month 5, your baby is about 10 inches long and can weigh anywhere from .5 lbs – 1 lb! If your baby is born prematurely after the 23rd week, he or she will be kept in the NICU for a better chance of survival.
Month 6 – Week 25-30
The skin is still translucent yet reddish and wrinkled. His or her fingerprints and toe prints become well developed. The baby’s eyelids become parted, and the eyes can be opened. Your baby will respond to external stimuli such as sounds by increasing their pulse or moving. This is when you may experience your baby’s hiccups in jerk-like motions. At the end of month 6, your baby is about 12 inches long and can weigh close to 2 lbs!
Month 7 – Week 26-29
During this month, your baby will continue to grow and develop the existing organs and systems. In addition, a layer of fat will begin to be stored. At this stage, hearing is fully developed. He or she will react to sound, pain, and light and often changes position. The amount of amniotic fluid that cushions the baby begins to decrease as the baby grows larger. At the end of this month, your baby is about 14 inches long and can weigh between 2 – 4 lbs! If born prematurely after week 27, your baby has a better chance of survival.
Month 8 – Week 30-34
The baby continues to mature during this month, adding to fat stores and experiencing a rapid development of the brain. The baby can see at this stage and will begin to kick more. Most of the internal organs and systems are fully developed, but the lungs still need time to mature. By month 8, your baby is close to 18 inches long and can weigh close to 5 lbs!
Month 9 – Week 35-40+
The lungs become mature during this time in preparation for birth. Reflexes become more coordinated, allowing the baby to respond to sounds, blink, grasp, and turn his or her head. The baby may move less during the last few weeks and will move into a position for birth, with the head down near the birth canal. Your baby is now about 18-20 inches long and can weigh at least 7 lbs!
A Happy Momma = A Happy Baby
Pregnancy is such an exciting time for mom and baby. Getting plenty of rest, maintaining a healthy, balanced diet and avoiding stress is especially important for you and baby. You can start bonding with your baby during pregnancy in several ways now. Below are some recommended books for you to learn more about how your body changes while your baby develops inside throughout pregnancy. Remember, a happy momma makes for a happy baby.
Recommended Books On Baby Development Month By Month and Pregnancy:
Before Birth: A week-by-week guide to your baby’s development during pregnancy
In the Womb: Witness the Journey from Conception to Birth with Astonishing 3D Images
A Child Is Born: Fourth Edition of the Beloved Classic–Completely Revised and Updated
Pregnancy Day By Day
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 week photo: week 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.