1 stage of pregnancy

Stages of pregnancy | Office on Women's Health

Pregnancy lasts about 40 weeks, counting from the first day of your last normal period. The weeks are grouped into three trimesters.(TREYE-mess-turs) Find out what's happening with you and your baby in these three stages.

First trimester (week 1–week 12)

During the first trimester your body undergoes many changes. Hormonal changes affect almost every organ system in your body. These changes can trigger symptoms even in the very first weeks of pregnancy. Your period stopping is a clear sign that you are pregnant. Other changes may include:

Extreme tiredness
Tender, swollen breasts. Your nipples might also stick out.
Upset stomach with or without throwing up (morning sickness)
Cravings or distaste for certain foods
Mood swings
Constipation (trouble having bowel movements)
Need to pass urine more often
Headache
Heartburn
Weight gain or loss

As your body changes, you might need to make changes to your daily routine, such as going to bed earlier or eating frequent, small meals. Fortunately, most of these discomforts will go away as your pregnancy progresses. And some women might not feel any discomfort at all! If you have been pregnant before, you might feel differently this time around. Just as each woman is different, so is each pregnancy.

Second trimester (week 13–week 28)

Most women find the second trimester of pregnancy easier than the first. But it is just as important to stay informed about your pregnancy during these months.

You might notice that symptoms like nausea and fatigue are going away. But other new, more noticeable changes to your body are now happening. Your abdomen will expand as the baby continues to grow. And before this trimester is over, you will feel your baby beginning to move!

As your body changes to make room for your growing baby, you may have:

Body aches, such as back, abdomen, groin, or thigh pain
Stretch marks on your abdomen, breasts, thighs, or buttocks
Darkening of the skin around your nipples
A line on the skin running from belly button to pubic hairline
Patches of darker skin, usually over the cheeks, forehead, nose, or upper lip. Patches often match on both sides of the face. This is sometimes called the mask of pregnancy.
Numb or tingling hands, called carpal tunnel syndrome
Itching on the abdomen, palms, and soles of the feet. (Call your doctor if you have nausea, loss of appetite, vomiting, jaundice or fatigue combined with itching. These can be signs of a serious liver problem.)
Swelling of the ankles, fingers, and face. (If you notice any sudden or extreme swelling or if you gain a lot of weight really quickly, call your doctor right away. This could be a sign of preeclampsia.)

Third trimester (week 29–week 40)

You're in the home stretch! Some of the same discomforts you had in your second trimester will continue. Plus, many women find breathing difficult and notice they have to go to the bathroom even more often. This is because the baby is getting bigger and it is putting more pressure on your organs. Don't worry, your baby is fine and these problems will lessen once you give birth.

Some new body changes you might notice in the third trimester include:

Shortness of breath
Heartburn
Swelling of the ankles, fingers, and face. (If you notice any sudden or extreme swelling or if you gain a lot of weight really quickly, call your doctor right away. This could be a sign of preeclampsia.)
Hemorrhoids
Tender breasts, which may leak a watery pre-milk called colostrum (kuh-LOSS-struhm)
Your belly button may stick out
Trouble sleeping
The baby "dropping", or moving lower in your abdomen
Contractions, which can be a sign of real or false labor

As you near your due date, your cervix becomes thinner and softer (called effacing). This is a normal, natural process that helps the birth canal (vagina) to open during the birthing process. Your doctor will check your progress with a vaginal exam as you near your due date. Get excited — the final countdown has begun!

Your developing baby

First trimester (week 1-week 12)

At four to five weeks:

Your baby's brain and spinal cord have begun to form.
The heart begins to form.
Arm and leg buds appear.
Your baby is now an embryo and one-twenty-fifth inch long.

At eight weeks:

All major organs and external body structures have begun to form.
Your baby's heart beats with a regular rhythm.
The arms and legs grow longer, and fingers and toes have begun to form.
The sex organs begin to form.
The eyes have moved forward on the face and eyelids have formed.
The umbilical cord is clearly visible.
At the end of eight weeks, your baby is a fetus and looks more like a human. Your baby is nearly 1 inch long and weighs less than one-eighth ounce.

At 12 weeks:

The nerves and muscles begin to work together. Your baby can make a fist.
The external sex organs show if your baby is a boy or girl. A woman who has an ultrasound in the second trimester or later might be able to find out the baby's sex.
Eyelids close to protect the developing eyes. They will not open again until the 28th week.
Head growth has slowed, and your baby is much longer. Now, at about 3 inches long, your baby weighs almost an ounce.

Second trimester (week 13-week 28)

At 16 weeks:

Muscle tissue and bone continue to form, creating a more complete skeleton.
Skin begins to form. You can nearly see through it.
Meconium (mih-KOH-nee-uhm) develops in your baby's intestinal tract. This will be your baby's first bowel movement.
Your baby makes sucking motions with the mouth (sucking reflex).
Your baby reaches a length of about 4 to 5 inches and weighs almost 3 ounces.

At 20 weeks:

Your baby is more active. You might feel slight fluttering.
Your baby is covered by fine, downy hair called lanugo (luh-NOO-goh) and a waxy coating called vernix. This protects the forming skin underneath.
Eyebrows, eyelashes, fingernails, and toenails have formed. Your baby can even scratch itself.
Your baby can hear and swallow.
Now halfway through your pregnancy, your baby is about 6 inches long and weighs about 9 ounces.

At 24 weeks:

Bone marrow begins to make blood cells.
Taste buds form on your baby's tongue.
Footprints and fingerprints have formed.
Real hair begins to grow on your baby's head.
The lungs are formed, but do not work.
The hand and startle reflex develop.
Your baby sleeps and wakes regularly.
If your baby is a boy, his testicles begin to move from the abdomen into the scrotum. If your baby is a girl, her uterus and ovaries are in place, and a lifetime supply of eggs have formed in the ovaries.
Your baby stores fat and has gained quite a bit of weight. Now at about 12 inches long, your baby weighs about 1½ pounds.

Third trimester (week 29-week 40)

At 32 weeks:

Your baby's bones are fully formed, but still soft.
Your baby's kicks and jabs are forceful.
The eyes can open and close and sense changes in light.
Lungs are not fully formed, but practice "breathing" movements occur.
Your baby's body begins to store vital minerals, such as iron and calcium.
Lanugo begins to fall off.
Your baby is gaining weight quickly, about one-half pound a week. Now, your baby is about 15 to 17 inches long and weighs about 4 to 4½ pounds.

At 36 weeks:

The protective waxy coating called vernix gets thicker.
Body fat increases. Your baby is getting bigger and bigger and has less space to move around. Movements are less forceful, but you will feel stretches and wiggles.
Your baby is about 16 to 19 inches long and weighs about 6 to 6½ pounds.

Weeks 37–40:

At 39 weeks, your baby is considered full-term. Your baby's organs are ready to function on their own.
As you near your due date, your baby may turn into a head-down position for birth. Most babies "present" head down.
At birth, your baby may weigh somewhere between 6 pounds 2 ounces and 9 pounds 2 ounces and be 19 to 21 inches long. Most full-term babies fall within these ranges. But healthy babies come in many different sizes.

All material contained on these pages are free of copyright restrictions and maybe copied, reproduced, or duplicated without permission of the Office on Women’s Health in the U.S. Department of Health and Human Services. Citation of the source is appreciated.

Page last updated: February 22, 2021

Pregnancy - week by week

The unborn baby spends around 38 weeks in the womb, but the average length of pregnancy (gestation) is counted as 40 weeks. This is because pregnancy is counted from the first day of the woman’s last period, not the date of conception, which generally occurs 2 weeks later.

Pregnancy is divided into three trimesters:

First trimester – conception to 12 weeks
Second trimester – 12 to 24 weeks
Third trimester – 24 to 40 weeks.

Conception

The moment of conception is when the woman’s ovum (egg) is fertilised by the man’s sperm. The gender and inherited characteristics are decided in that instant.

Week 1

This first week is actually your menstrual period. Because your expected birth date (EDD or EDB) is calculated from the first day of your last period, this week counts as part of your 40-week pregnancy, even though your baby hasn’t been conceived yet.

Week 2

Fertilisation of your egg by the sperm will take place near the end of this week.

Week 3

Thirty hours after conception, the cell splits into two. Three days later, the cell (zygote) has divided into 16 cells. After two more days, the zygote has migrated from the fallopian tube to the uterus (womb). Seven days after conception, the zygote burrows itself into the plump uterine lining (endometrium). The zygote is now known as a blastocyst.

Week 4

The developing baby is tinier than a grain of rice. The rapidly dividing cells are in the process of forming the various body systems, including the digestive system.

Week 5

The evolving neural tube will eventually become the central nervous system (brain and spinal cord).

Week 6

The baby is now known as an embryo. It is around 3 mm in length. By this stage, it is secreting special hormones that prevent the mother from having a menstrual period.

Week 7

The heart is beating. The embryo has developed its placenta and amniotic sac. The placenta is burrowing into the uterine wall to access oxygen and nutrients from the mother’s bloodstream.

Week 8

The embryo is now around 1.3 cm in length. The rapidly growing spinal cord looks like a tail. The head is disproportionately large.

Week 9

The eyes, mouth and tongue are forming. The tiny muscles allow the embryo to start moving about. Blood cells are being made by the embryo’s liver.

Week 10

The embryo is now known as a fetus and is about 2. 5 cm in length. All of the bodily organs are formed. The hands and feet, which previously looked like nubs or paddles, are now evolving fingers and toes. The brain is active and has brain waves.

Week 11

Teeth are budding inside the gums. The tiny heart is developing further.

Week 12

The fingers and toes are recognisable, but still stuck together with webs of skin. The first trimester combined screening test (maternal blood test + ultrasound of baby) can be done around this time. This test checks for trisomy 18 (Edward syndrome) and trisomy 21 (Down syndrome).

Week 13

The fetus can swim about quite vigorously. It is now more than 7 cm in length.

Week 14

The eyelids are fused over the fully developed eyes. The baby can now mutely cry, since it has vocal cords. It may even start sucking its thumb. The fingers and toes are growing nails.

Week 16

The fetus is around 14 cm in length. Eyelashes and eyebrows have appeared, and the tongue has taste buds. The second trimester maternal serum screening will be offered at this time if the first trimester test was not done (see week 12).

Week 18-20

An ultrasound will be offered. This fetal morphology scan is to check for structural abnormalities, position of placenta and multiple pregnancies. Interestingly, hiccoughs in the fetus can often be observed.

Week 20

The fetus is around 21 cm in length. The ears are fully functioning and can hear muffled sounds from the outside world. The fingertips have prints. The genitals can now be distinguished with an ultrasound scan.

Week 24

The fetus is around 33 cm in length. The fused eyelids now separate into upper and lower lids, enabling the baby to open and shut its eyes. The skin is covered in fine hair (lanugo) and protected by a layer of waxy secretion (vernix). The baby makes breathing movements with its lungs.

Week 28

Your baby now weighs about 1 kg (1,000 g) or 2 lb 2oz (2 pounds, 2 ounces) and measures about 25 cm (10 inches) from crown to rump. The crown-to-toe length is around 37 cm. The growing body has caught up with the large head and the baby now seems more in proportion.

Week 32

The baby spends most of its time asleep. Its movements are strong and coordinated. It has probably assumed the ‘head down’ position by now, in preparation for birth.

Week 36

The baby is around 46 cm in length. It has probably nestled its head into its mother’s pelvis, ready for birth. If it is born now, its chances for survival are excellent. Development of the lungs is rapid over the next few weeks.

Week 40

The baby is around 51 cm in length and ready to be born. It is unknown exactly what causes the onset of labour. It is most likely a combination of physical, hormonal and emotional factors between the mother and baby.

Where to get help

Your GP (doctor)
Obstetrician
Midwife
Your maternal and child health nurse

what happens in 1, 2, 3 months

Wise nature endowed a woman with everything she needs to bear and give birth to a child. But this does not prevent expectant mothers from being interested in what is connected with conception, pregnancy and childbirth - asking important questions and looking for answers to them. They want to know what happens in the first trimester of pregnancy, how the baby develops, what processes take place in the body, what can and cannot be done. Let's talk about this in more detail.

Excursion to obstetrics

First, let's define some terminology.

The entire pregnancy (gestation) of a woman lasts 40 weeks (280 days). These data are conditional, because normally, childbirth can begin at almost any time for a period of 37-42 weeks. This entire period is divided into three trimesters. The first trimester of pregnancy lasts from the first day of the last menstrual period until the end of the 13th week.

The division of pregnancy into weeks and trimesters is accepted in obstetrics. But women more often measure this period by months. This is not entirely correct, because one month includes 4 or 5 weeks. Therefore, in the article we will focus specifically on the obstetric weeks of gestation, but we will also correlate them with the months familiar to many women. nine0003

What happens in the first trimester of pregnancy

Obstetricians calculate the gestational age from the first day of the last menstruation. This is convenient - after all, most women keep a calendar and know this date. However, there is still no fetus during this period. Conception happens later - during ovulation, after about two weeks. It would be possible to count the gestational age from the moment of conception, but this date is difficult to calculate. In addition, ovulation may not occur in the middle of the cycle, but much earlier or later - and then it will be even more difficult to calculate it. nine0003

So, there are two stages of pregnancy:

Obstetric - from the first day of the last menstruation.
Embryonic - from the moment of conception.

We will focus on the obstetric period

In the article we will divide this period into weeks, not stages. Conventionally, the first trimester of pregnancy can also be divided into three months.

First month of pregnancy

The 1st month of pregnancy is the period from the 1st to the 4-5th week. nine0003

No baby in the first two weeks. During this period, the woman's body is preparing for a possible pregnancy. Follicles mature in the ovaries, one (rarely two or more) dominant follicles stand out among them. If ovulation occurs, the egg is released from the follicle. When it meets sperm, fertilization occurs and new life is born.

In the third week of gestation, the fertilized egg moves through the fallopian tubes. Its task is to get into the uterine cavity and attach to its wall. This happens on the 7-8th day after conception - by the beginning of the 4th week. After implantation, the development of the fetal egg, the new life in it, continues. By the way, a child in early pregnancy is called an embryo, and after a full 8 weeks it will be called a fetus. nine0003

At the 3rd week, the embryo is a multitude of cells that are constantly dividing and developing. By the end of the first month of pregnancy, it already begins to influence the hormonal background of a woman due to the production of its own hormone - hCG (human chorionic gonadotropin). It is by the concentration of the hormone that it is possible to determine whether conception occurred in this menstrual cycle.

In the 1st month of gestation, the woman's well-being practically does not change. And only at the end of the 4th week toxicosis can develop. It is manifested by nausea, vomiting, increased salivation and weakness. Many women do not have toxicosis - and this is also a variant of the norm. The belly in the first month of pregnancy is not yet visible. nine0003

Second month of pregnancy

The 2nd month of gestation is the period from 4-5 to 8-9 weeks.

In the early stages of pregnancy, the active development of the embryo continues. It still has a C-shape. By the end of the 4th week, limb rudiments are formed, a circulatory system and a two-chamber heart rudiment appear. At the 6th week, the heart begins to beat - and it can be heard during an ultrasound.

At the beginning of the 5th week, further development of the nervous system of the embryo takes place. The rudiment of the brain is isolated, conditions are created for its further differentiation. nine0003

On the 6th week of the 1st trimester, the organs of vision develop, the rudiments of the genital organs appear. The heart becomes three-chambered. At the 8th week, the sex of the embryo is determined - but it cannot yet be seen on ultrasound. As a result of all these transformations, in the second month of pregnancy, the fetus acquires a clear human appearance.

A woman's feelings change in the middle of the 1st trimester. Symptoms appear, which are usually called characteristic signs of pregnancy:

Nausea, vomiting, increased salivation - this is how toxicosis manifests itself. nine0022
General weakness, fatigue.
Sudden mood swings.
Frequent urination.
Breast augmentation and enhancement of its sensitivity.
Increased sensitivity to odors.
Predilection or aversion to certain foods.

The belly is not yet visible in early pregnancy. The uterus is already growing, but so far it is completely in the pelvic cavity and does not go beyond the womb. But the breasts in the 2nd month of pregnancy already noticeably increase, become sensitive or even slightly painful. nine0003

The third month of pregnancy

The 3rd month is the period from the 8th-9th to the 12th-13th week.

In the third month of pregnancy, the further development of the child continues. Now it is called fruit. Its head, rudiments of limbs, torso, rudiments of eyes, nose and mouth are clearly visible. The fruit reaches the size of a goose egg.

On the 9-10th week, the cerebral cortex differentiates in the fetus, and the development of the nervous system continues. By the 12th week, foci of hematopoiesis appear in the bone marrow, and the first cells appear in the blood. At the 13th week, the formation of all organs of the fetus is completed, and the placenta is formed. nine0003

The placenta in early pregnancy is usually low, near the cervix. It provides the baby with everything necessary - oxygen and nutrients, and removes metabolic products. It connects to the fetus through the umbilical cord, in which two arteries and one vein pass. Gradually, the placenta migrates and by the end of the second trimester, as a rule, takes the correct position.

The feelings of a woman in the 3rd month of pregnancy remain the same. As before, she feels weakness, mood swings, changes in taste preferences. There may be signs of toxicity. But some women do not notice significant changes in their well-being - and this is also the norm. nine0003

The belly is not visible at the 3rd month. Only on the 12-13th week the uterus goes beyond the womb. A slight rounding of the abdomen will be visible only at the 14-16th week.

What problems can be in the first trimester of pregnancy

The expectant mother should be alerted by the appearance of such symptoms: There are no periods during pregnancy. Seek medical attention if bleeding occurs.

Drawing pains in the lower abdomen. If the stomach slightly pulls in the early stages, this is normal. The uterus grows, the ligamentous apparatus of the pelvis changes, unpleasant sensations appear. But you should see a doctor in any case - in order to exclude pregnancy complications. If the lower abdomen is strongly pulled, especially against the background of spotting, the help of a gynecologist is needed immediately. nine0022

Unusual vaginal discharge. From the first trimester of pregnancy, the discharge changes - it becomes plentiful, milky. But there should not be itching, burning or other discomfort.

If you experience any unusual sensations and symptoms, you should contact your doctor as soon as possible!

What examinations are needed in the early stages of pregnancy

To confirm the fact of pregnancy, you can donate blood for hCG as early as the 1st month. This hormone rises 8-10 days after conception - after the implantation of the embryo. It is recommended to donate blood for hCG immediately after a missed period. nine0003

If hCG is positive, you need to contact a gynecologist and get registered. To clarify the diagnosis, the doctor may refer you to an ultrasound scan. With ultrasound in the 1st trimester, from the 3rd-4th week, you can see the fetal egg, from the 6th week, you can hear the fetal heartbeat. The next ultrasound, if there are no other indications, is carried out for a period of 11-14 weeks. This will be the first screening where you can assess the condition of the fetus and placenta, make sure that there are no malformations and other complications.

In the first trimester of pregnancy, all women are recommended to be screened:

Pass blood and urine tests (the list will be issued by the attending physician).
Get checked out by a dentist and an ophthalmologist.
If necessary, visit other specialists (for example, an endocrinologist - if there is a thyroid disease).
Make an ECG and consult a therapist.

All this is necessary in order to make sure that the expectant mother is healthy, can bear and give birth to a child.

Many women wonder how to behave if the pregnancy is less than a month old. Here are some recommendations:

In the first trimester of pregnancy, all women are advised to be screened:

Give up alcohol and quit smoking if you did not do so before conception.
Do not take medicines without a doctor's prescription.
Avoid overheating and hypothermia.
Do not take X-rays, MRIs, or similar procedures unless you have a strong indication and a referral from a doctor.
Do not overexert yourself, reduce physical activity, including in sports. nine0022
Avoid stressful situations.

In the following weeks of the first trimester, the recommendations remain the same, and nutritional advice is added:

Eat often, in small portions, 5-6 times a day.
Eat only fresh produce.
Avoid foods that increase the symptoms of toxicosis and provoke constipation.
Avoid feeling hungry, but don't overeat either.

It is worth noting that the nutrition of the expectant mother affects not only her, but also the baby, and it is worth taking a responsible approach to this. Yes, a special universal diet has not been developed, but the doctor may recommend that the expectant mother adhere to a certain diet after the examination (add certain foods to the diet if any elements are missing, etc.). nine0003

It is recommended to follow the general principles of a healthy diet:

Eat more fresh vegetables, fruits and greens - up to 5 servings per day.
Limit salt and added sugar intake.
Reduce the proportion of animal fats in the diet.
Refuse fried, spicy, salty foods, sausages and smoked meats.
Prefer whole grains.

If you need to follow a special diet for health reasons, you should discuss this with your doctor. nine0003

Most of the questions in the early stages arise in women during their first pregnancy. Everything is unusual and incomprehensible, what can and cannot be done, and how to maintain health - one's own and the child's. If you have any questions, you can consult with a gynecologist. A doctor observing a woman knows all the nuances and will tell you how to behave in the first trimester of pregnancy.

1. Normal pregnancy. Clinical recommendations, 2019.

2. Obstetrics: national guidance.: Ailamazyan E.K., Savelyeva G.M., Radzinsky V.E.

3. S. Yu. Vinogradov, S. V. Dindiaev. Introduction to embryology and human embryonic histogenesis..

1st trimester of pregnancy: what happens to the fetus

1st trimester: 1st-12th weeks

The gestational age is calculated from the first day of the last menstruation, since it is difficult to determine the exact day of conception. Since conception usually occurs in the middle of the menstrual cycle, you are not actually pregnant during the first two weeks, but this period is counted as the beginning of pregnancy. nine0003

As soon as the fertilization of the egg takes place around the 3rd week, the hormones begin to produce changes in your body little by little. As a result, you may experience some of the following symptoms:

Morning sickness. As a result of rising levels of hormones characteristic of pregnancy, up to 80% of women in the 1st trimester experience morning sickness with symptoms such as nausea and vomiting. The idea that such malaise is observed only in the morning is a common misconception. In fact, symptoms can appear at any time of the day or night. Up to 1 in 5 women experience morning sickness in the 2nd trimester of pregnancy and can sometimes persist throughout pregnancy. nine0002 If you experience morning sickness, avoid foods that make you sick, eat little and often, avoid fatty and spicy foods, drink more water. If you experience severe symptoms or symptoms that bother you, see your doctor.
Breast changes. The mammary glands will begin to increase in size, soreness may appear. The nipples will increase in size, become darker and more protruding.
Fatigue. High levels of the hormone progesterone can make you feel tired and sleepy. Rest as often as possible in a horizontal position with your legs up and eat as well as possible, which is not easy if you are experiencing morning sickness! nine0022
Increased emotionality. A higher level of emotionality, manifested as a result of an increase in hormone levels, is a normal phenomenon. Understanding and patience on the part of your partner and loved ones is very important here.
Food likes and dislikes. You may find yourself intolerant of one food and addicted to another. This is usually not a problem, unless you feel like eating weird foods like chalk. If you are concerned about the situation, contact your doctor. nine0022
Frequent urination. As your fluid levels increase and your uterus puts pressure on your bladder, you will become more likely to visit the toilet. Go to the toilet as soon as you feel the need - this minimizes the pressure on the bladder.
Feeling of dizziness. Sometimes you may feel a little dizzy (this is due to hormonal changes). Try not to stay on your feet for a long time and slowly rise from a sitting or lying position. If you experience severe dizziness, contact your doctor immediately. nine0022
Heartburn and constipation. Your digestive system will slow down to allow more time for food to be absorbed. This can lead to heartburn and constipation. To help manage heartburn, try to eat small meals at regular intervals and avoid fried or spicy foods and carbonated drinks. Constipation is helped by eating a diet rich in fiber, maintaining physical activity and drinking plenty of water.

1st trimester milestones

Approximately 7 days after fertilization, the embryo implants in the uterine wall. The placenta, umbilical cord and amniotic sac will begin to form to provide nourishment and protection to the embryo.
By the end of the first 12 weeks of pregnancy, the uterus is palpable through the wall of the abdomen, the abdomen will begin to grow.

Child development in the 1st trimester of pregnancy

By the end of the 1st trimester: