What is the step 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

How to correctly calculate the gestational age and determine the date of delivery

It often comes as a surprise to first-time pregnant women that in obstetrics the gestational age is determined not in months, but in weeks. But the surprises do not end there - the fact is that the obstetric period is calculated not from conception, but from the first day of the last menstruation.

In fact, pregnancy occurs two weeks after the start of the obstetric period, at the time of ovulation, when the sperm meets the egg. Thus, the age of the embryo, or gestational age, differs from the obstetric one by 2 weeks down. nine0003

How long does pregnancy last?

The obstetric term of a term pregnancy is 40 weeks, or 280 days. It is on the basis of the obstetric gestational age that the doctor will prescribe tests and examinations for you, determine the date of maternity leave and calculate the EDD (estimated date of birth).

Doctors use the Negele formula to calculate the EDD. According to this formula, if we add nine months and seven days to the first day of the last menstruation, we get the estimated date of birth. nine0003

Unfortunately, determining the gestational age from the first day of the last menstrual period is not a very accurate method. It is well suited for women with a stable 28-day cycle, but if your cycle is slightly longer or shorter, then the date of ovulation shifts, respectively, and the actual obstetric gestational age will differ from the established one.

The most accurate way to calculate the EDD is to add 266 days to the date of the last ovulation (if you know it).

How to confirm pregnancy, determine the duration of pregnancy and the date of delivery nine0007

By itself, a delay in the start of a new menstrual cycle does not necessarily indicate pregnancy - failures can be explained by diseases, excessive physical exertion or stress. Pregnancy must be confirmed with an hCG test or examination on a gynecological chair. 1) Blood test for hCG cycle or the woman will feel the first symptoms. Also, an analysis of the level of hCG in the blood allows you to determine the gestational age with an accuracy of about two weeks. nine0003

2) Home pregnancy test

Home pregnancy tests also work by measuring hCG levels, but they are less sensitive than blood tests. The most modern of them can not only confirm the presence of pregnancy a few days before the delay, but also indicate (not too accurately) an approximate date.

Tests of the old generation will show a more or less accurate result only after a delay, that is, after 2-4 weeks from conception. nine0003

3) Gynecological examination

A qualified gynecologist-obstetrician can diagnose pregnancy during an examination starting 3-4 weeks after conception, focusing on changes in the shape and size of the uterus, as well as other signs.

4) Ultrasound

Ultrasound is the most accurate way to diagnose pregnancy. With the help of ultrasound with a transvaginal sensor, it is possible to determine the presence of a fetal egg in the uterus already 1-2 weeks after conception (3-4 obstetric weeks), but fetal heartbeats can only be detected for a period of 5-6 obstetric weeks. It is possible to determine the gestational age with high accuracy (up to 2-3 days!) With the help of ultrasound only from 6-7 weeks. nine0003

If the delay, as well as the result of an hCG test or blood test, indicate that you will soon become a mother, do not rush to get an ultrasound right away. Wait another 2-3 weeks, then by ultrasound you will not only be accurately determined by the period, but will also be allowed to listen to the baby's heartbeat.

If you did not do an early ultrasound to confirm pregnancy, then for the first time you will encounter this study at the 10-14th week. At the same time, the exact gestational age and PDR will be established or corrected for you. During pregnancy, you will need to undergo such an examination at least twice more. This will happen at 20-24 and 30-34 weeks. However, it is worth saying that ultrasound in the 2nd and 3rd trimesters may have an error in determining the gestational age. The PDR established according to them may differ from the real one by 2-3 weeks. That is why it is so important not to miss the first screening and do an ultrasound on time. nine0003

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How to determine the gestational age | Center for Fetal Medicine at Chistye Prudy

Methods for determining the duration of pregnancy
Embryonic term
Obstetric term
By last menstrual period
By ovulation date or conception date
According to the size of the uterus
Ultrasonography
According to the level of hCG in the blood
According to the first movement of the fetus

Here the pregnancy test showed the coveted two strips, the expectant mother is in a hurry to register in the antenatal clinic. The first thing that an obstetrician-gynecologist determines when registering is the gestational age. This indicator is extremely important in order to understand whether the pregnancy is proceeding correctly and the baby is developing, when it is necessary to take tests and undergo additional examinations, when to go on maternity leave and wait for the baby to be born. nine0003

It is also very important to know the exact gestational age for screening for the presence of genetic abnormalities in the fetus (ultrasound and blood tests), since these examinations are carried out strictly at certain times of pregnancy.

Learn more about the services:

1st trimester ultrasound
Appointment and consultation with a gynecologist

Turning to an obstetrician-gynecologist, many expectant mothers begin to worry about the difference in terms of pregnancy - what the doctor calculated and the woman herself. In order not to worry in vain, you need to know that there are 2 stages of pregnancy - obstetric and embryonic. nine0003

Fetal term

This is the true gestational age from conception, it usually lags behind the obstetric term by about 2 weeks.

Obstetric period

Doctors determine it from the first day of the last menstruation before pregnancy. It should be remembered that all doctors use only the obstetric term, all test results, the size of the fetus, the timing of examinations, maternity leave and the term of delivery are calculated taking into account only the obstetric term of pregnancy. nine0003

There are several ways to determine the gestational age.

Determination of the gestational age by the date of the last menstrual period

This is the most common method of calculating the gestational age. However, it can only be used if a woman's menstruation comes regularly at the same interval.

It is not always possible to accurately calculate the duration of pregnancy, guided only by the date of the last menstruation. This happens in cases where a woman has irregular menstruation or in those patients who have a regular but long menstrual cycle. For example, if a woman has a typical cycle length of 35 days (and not 26 - 28, like most women), then most likely she will only be able to conceive on about the 21st day of the cycle (and not on the 14th, as on a 28 day cycle). Accordingly, the period calculated by menstruation will exceed the “real” obstetric gestational age by a week. nine0003

According to the date of ovulation or the date of conception

If the date of conception is known, two weeks must be added to this date - we will get the obstetric gestational age. However, it must be remembered that even if a woman knows exactly the date of ovulation or the date of sexual intercourse, after which pregnancy occurred, this does not mean that she absolutely knows the date of conception.

A spermatozoon that has entered the female body is capable of fertilization within 4-5 days, sometimes even within a week, and a mature egg retains the ability to conceive for 2 days after ovulation. Therefore, even knowing exactly the date of sexual intercourse or ovulation, it is impossible to say with accuracy that fertilization occurred on that day. It could have happened later. Therefore, the period calculated by ovulation or the date of conception cannot be considered completely accurate. nine0003

Doctors calculate the gestational age in a slightly different way in cases where pregnancy has occurred as a result of IVF. In this case, the fertilization of the egg by the spermatozoon is carried out "in vitro" by the embryologist. Embryos develop in the laboratory for 3-5 days, after which they are transferred to the uterus.

Doctors calculate the true duration of pregnancy after IVF from the date of ovarian puncture, that is, the stage of the procedure, when the follicular fluid and the follicles contained in it are taken with a special needle for subsequent fertilization “in vitro”, and to determine the “usual” obstetric period , add 2 weeks in the date of ovarian puncture. nine0003

If the transfer of the embryo into the uterus was preceded by its cryopreservation (that is, freezing in liquid nitrogen), to determine the exact gestational age, doctors add 5 days to the transfer date (this is the number of days the embryo develops before freezing), and to determine the obstetric period to the received true date add 2 weeks.

According to the size of the uterus

Examining a woman in a gynecological chair, an obstetrician-gynecologist uses both hands to determine the size of the uterus. In this case, you can also determine the approximate gestational age. nine0003

This method is most accurate in early pregnancy, up to about 12 weeks. The earliest period that can be determined by the size of the uterus is 5 weeks of pregnancy. By this time, the uterus is slightly enlarged, softened and becomes rounded. At later dates, the size of the uterus may vary slightly depending on the size of the fetus, the amount of amniotic fluid, and the structure of the woman's pelvis. For example, it is believed that at 16 weeks the bottom of the uterus is located in the middle of the distance between the pubis and the navel, at 24 weeks of pregnancy the bottom of the uterus is at the level of the navel. nine0003

Ultrasound

In the early stages of pregnancy, by measuring the size of the ovum and embryo, the gestational age can be determined with great accuracy.

At 4-5 weeks in the uterus with ultrasound, a small “black circle” is determined - this is a fetal egg, in which an embryo will appear a little later. At about 6-7 weeks, the embryo appears in the form of a small “stripe” and you can see its heartbeat. More accurate is the period calculated by measuring the KTP of the embryo (KTP is the coccygeal-parietal size, that is, the maximum distance from the head end of the fetus to its tailbone), and not by the diameter of the fetal egg. nine0003

After 12 weeks, the gestational age during ultrasound is determined according to the so-called fetometry, that is, measurements of various sizes of the head and abdomen of the fetus, length of arms, legs, heart sizes, etc. are used to calculate the term.

Up to 9-10 weeks of pregnancy, the embryo grows proportionally, and its size in all women with the same gestational age will be approximately identical. In the future, the size of the fetus will differ in expectant mothers of different nationalities, with different body weights, the weight of the mother and father at birth will matter, and so on. That is, in the later stages of pregnancy, normally developing children of the same term may have different sizes (fluctuations can be about 2 weeks, sometimes more), and in such a situation, it is impossible to reliably determine the gestational age according to ultrasound data. In the later stages, the determination of the gestational age by ultrasound is only clarifying. In addition, the lag in the size of the fetus during ultrasound at long gestations is most often regarded by doctors as a developmental disorder due to the fact that the placenta does not transport oxygen and nutrients well enough. nine0003

At the Fetal Medicine Center in Moscow, all types of ultrasound during pregnancy, including ultrasound in early pregnancy, are performed at an expert level.

Our center is organized in such a way that the whole range of services is concentrated in one place, where a woman receives the results of various types of examinations, including ultrasound, biochemical, and specialist consultation within 1-1. 5 hours.

According to the level of hCG in the blood

HCG (human chorionic gonadotropin) is a hormone that is released during pregnancy by the placenta. It begins to be produced with the onset of pregnancy, gradually its amount increases, until about the 11th week of pregnancy, and then begins to decrease slightly. nine0003

Determining the concentration of hCG in the blood in the early stages of pregnancy helps to accurately determine the period. Having received the results of a blood test for hCG, it is worth paying attention that in the laboratory tables of the correspondence of the hormone level to the gestational age, the embryonic period is often indicated, that is, to determine the usual obstetric gestational age, 2 weeks should be added to the result.

Recently, tests have appeared to determine the duration of pregnancy by urine. They also determine the concentration of the hCG hormone in the urine of a pregnant woman and, in addition to confirming the very fact of pregnancy, show what period the hormone content corresponds to. The only thing to remember is that urine tests also show the fetal gestational age. nine0003

The Fetal Medicine Center performs all types of tests for pregnant women.

Determining the term of pregnancy by the first movement of the fetus

This method of determining the term has recently been used less and less. It is based on the fact that nulliparous women begin to feel the first movements of the baby at 20 weeks of gestation, multiparous women a little earlier - at 18 weeks. That is why obstetrician-gynecologists recommend that a woman remember the date of the first movement of the fetus and enter this data into the exchange card. nine0003

However, this method of determining gestational age is often erroneous.

A mother who is expecting her first child, indeed, most often begins to feel the movements of the fetus a little later than a multiparous woman. This is due to the fact that "experienced" mothers know how the movements of the crumbs are felt at first and what they should feel.

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