Pictures of Fetal Development Month by Month

Reviewed by Traci C. Johnson, MD on May 09, 2023

Are you curious about what’s going on in your uterus during pregnancy? Take a peek inside to see all that’s happening with your fetus and your body — and what to expect as your pregnancy progresses.

When a sperm joins with an egg, the two form a single cell called a zygote that contains DNA from both parents. This is fertilization, also called conception. Within about 3 days, the zygote begins dividing into more cells. By about 5-6 days, it has traveled through the fallopian tube into the uterus. At this stage, it’s called a blastocyst. It attaches, or implants, to the uterus walls. By day 10-12, the zygote has become an embryo. 

At this point, the embryo is developing the structures that will eventually form the face and neck. The heart and blood vessels continue to develop. And the lungs, stomach, and liver start to develop. The placenta, which will nourish the fetus, is forming. A home pregnancy test could show up positive now.

The embryo is now a little over half an inch in size. Eyelids and ears are forming, and you can see the tip of the nose. The arms and legs are well formed. The fingers and toes grow longer and more distinct. At the end of the 10th week of pregnancy, the embryo is considered a fetus. That’s what doctors call it until birth. 

The fetus measures about 2 inches and starts to make its own movements. You may start to feel the top of your uterus above your pubic bone. Your doctor may hear the heartbeat with special instruments. The sex organs should start to become clear. At the end of the 12th week, the first trimester is over.

The fetus now measures about 4.3 to 4.6 inches and weighs about 3.5 ounces. You should be able to feel the top of your uterus about 3 inches below your belly button. The fetus’ eyes can blink and the heart and blood vessels are fully formed. Its fingers and toes have fingerprints.

The fetus weighs about 10 ounces and is a little more than 6 inches long. Your uterus should be at the level of your belly button. The fetus can suck its thumb, yawn, stretch, and make faces. Soon — if you haven’t already — you’ll feel it move, which is called “quickening.”

An ultrasound is usually done at 20 weeks. During this ultrasound, the doctor will make sure that the placenta is healthy and attached normally and that your fetus is growing properly. You can see the heartbeat and movement of its body, arms, and legs on the ultrasound. You can usually find out whether it’s a boy or a girl at 20 weeks.

Shown here is a 2D ultrasound (inset) contrasted with a 4D ultrasound, both at 20 weeks.

The fetus weighs about 1.4 pounds now and responds to sounds by moving or increasing their pulse. You may notice jerking motions if they hiccup. With the inner ear fully developed, it may be able to sense being upside down in the womb.

The fetus weighs about 2 pounds and 6 ounces and changes position often at this point in pregnancy. If you had to deliver prematurely now, there is a good chance it would survive. Ask your doctor about preterm labor warning signs. With the third trimester beginning, now is the time to register for birthing classes. They prepare you for many aspects of childbirth, including labor and delivery and taking care of your newborn. 

The fetus weighs almost 4 pounds and moves often. It has fewer wrinkles as a layer of fat starts to form under the skin. Between now and delivery, your fetus gains up to half its birth weight. Think about how you plan to feed your baby. You may notice a yellowish fluid leaking from your breasts. That’s colostrum, and it happens to prepare your breasts for making milk. Most people go to the doctor every 2 weeks at this stage. 

A fetus’ size depends on things like gender, the parents’ size, and whether it’s a multiple. On average, it’s about 18.5 inches and weighs close to 6 pounds. The brain has been developing rapidly. Lungs are almost fully developed. The head is usually positioned down into the pelvis. A baby is considered early-term if born between 37-39 weeks, at term at 39-40 weeks, and late term at 41-42 weeks.

Your due date marks the end of your 40th week. The delivery date is calculated using the first day of your last period. Based on this, pregnancy can last between 38 and 42 weeks. Some post-term pregnancies — those lasting more than 42 weeks — aren’t actually late. The due date may just may not have been accurate. For safety reasons, most babies are delivered by 42 weeks. Sometimes the doctor may need to induce labor to make that happen.

IMAGES PROVIDED BY:

(1) Copyright © LookatSciences / Phototake – All rights reserved.

(2) Dr. David M. Phillips / Visuals Unlimited / Getty Images
(3) 3D4Medical.com / Getty Images
(4) Copyright © Scott Camazine / Phototake — All rights reserved.
(5) Copyright © LookatSciences / Phototake – All rights reserved.
(6) Nestle / Petit Format / Photo Researchers, Inc.
(7) © Lennart Nilsson Photography AB. All rights reserved worldwide.
(8) a) Dr.Benoit/Mona Lisa. Copyright © LookatSciences / Phototake — All rights reserved. b)Vincenzo Lombardo / Photographer’s Choice / Getty Images
(9) Dr. Benoit/Mona Lisa. Copyright © LookatSciences / Phototake — All rights reserved.
(10) © Lennart Nilsson Photography AB. All rights reserved worldwide.
(11) Jose Manuel Gelpi Diaz / iStockphoto
(12) © Lennart Nilsson Photography AB. All rights reserved worldwide.
(13) © Yoav Levy / Phototake — All rights reserved.

SOURCES:

American Academy of Family Physicians.

Cleveland Clinic: “Fetal Development.”

Mayo Clinic: “Fetal development: The 1st trimester,” “Blastocyst.”

Merck Manual: “Stages of Development of the Fetus.”

University of Rochester Medical Center: “Anatomy of the Male and Female Pelvis.”American College of Obstetricians and Gynecologists: “Definition of Term Pregnancy,” “How Your Baby Grows During Pregnancy.”

KidsHealth.org: “Pregnancy Calendar.”

March of Dimes: “Prenatal Care – Ultrasound,” “What Is Full-Term?”

U.S. Department of Health and Human Services Office of Women’s Health: “Pregnancy: Breast Changes. “

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How the belly grows – articles from the specialists of the clinic “Mother and Child”

Bagriy Alexander Tarasovich

Anesthesiologist-resuscitator

Clinical hospital “AVICENNA” GC “Mother and Child”

Let’s say right away that how the belly looks and grows during pregnancy depends on many reasons: the physique of a woman, the structure of the pelvis, the state of the muscles, height uterus and baby, the amount of amniotic fluid. Therefore, for some, the belly grows faster, for some it is slower, for some mothers it is large, for others it can be almost invisible. But still, there are some general patterns of growth and size of the abdomen during pregnancy.

Growth rate

1st trimester

As a rule, in the early stages of pregnancy, the belly does not increase in size or increases very slightly. This is due to the fact that the uterus is still very small and takes up little space in the pelvis. So, for example, by the end of 4th week the uterus reaches only the size of a chicken egg, by the 8th week increases to the size of a goose, but most importantly, at this time it still does not reach the pubic articulation (located in the lower abdomen ). That is why in the early stages no increase in the abdomen is visible. And only after 12th week (end of the first trimester of pregnancy) the fundus of the uterus begins to rise above the womb.

II trimester

At this time, the child is rapidly gaining height and weight, and the uterus is also growing rapidly. That is why, at a period of 12-16 weeks, an attentive mother will see that the stomach has already become noticeable. True, others will pay attention to the woman’s new position at about 20-q weeks, especially if she wears tight-fitting things.

III trimester

By the beginning of the third trimester, no one doubts pregnancy. The abdomen is clearly visible even if the woman is wearing loose clothing.

Sharp, round, various

Approximately from the second trimester of pregnancy, during each examination, the obstetrician-gynecologist determines the height of the uterine fundus and measures the circumference of the abdomen at the level of the navel. Why does the doctor so carefully monitor the increase in mother’s tummy? The fact is that this is the easiest way to control the growth and development of the unborn baby.

One of the formulas for estimating fetal weight by fundal height (FHH): the shape of the abdomen often tried to determine the sex of the child. It was believed that a round belly portends a girl, and an elongated, oblong, “sharp” one portends a boy. However, these predictions did not always come true, since the shape and size of the abdomen do not depend at all on the sex of the child.

1. In large, tall women, the belly may be small and not very noticeable until advanced pregnancy, and in thin, petite women (especially with a narrow pelvis or large baby), the belly seems very large.
2. Significant influence on the shape of the abdomen has a state of muscle tone of the anterior abdominal wall and uterus. During the first pregnancy and good muscle tone, the abdomen may look more “tight” than in subsequent pregnancies. In addition, with repeated pregnancies as a result of reduced muscle tone of the anterior abdominal wall, the child does not take the final position until the last month of pregnancy. Because of this, the shape of the abdomen can also be “stretched”.
3. If a woman is expecting twins, her belly will be larger than with a single pregnancy.
4. And often the belly can be large simply because a woman ceases to limit herself in nutrition, eats “for two.”
5. If the baby grows quickly or is large, then the mother’s belly can grow faster and be larger.
6. Babies are located in the uterus in different ways. With some types of presentation, the stomach will be less noticeable, with others it will begin to grow earlier and will appear larger.

Feeling the belly

The belly of the expectant mother changes not only externally. From the 20th week of pregnancy, the mother begins to feel movements of the baby . At first, they look like light flutters, over time, the movements become more intense, because by the end of pregnancy, the mass and size of the child increase, and now it is not as spacious in the uterus as before. The number of movements gradually decreases, but their strength grows.

The movements of the crumbs, especially intense ones, can cause unpleasant sensations in a woman, especially in the right or left hypochondrium .

This is explained by the fact that during cephalic presentation (the baby is located in the uterus head down), the blows of the baby’s legs are projected into the region of the mother’s internal organs: the liver, stomach, intestines and spleen. Such sensations and even pains are natural and do not require treatment.

And sometimes pains appear in the lateral sections of the abdomen.

They occur due to the fact that during pregnancy the ligaments that support the uterus and ovaries are stretched.

In addition, changes occur in the fallopian tubes (they thicken, blood circulation increases in them), in the ovaries (they increase slightly in size, cyclic processes stop in them, and the position of the ovaries changes due to an increase in the size of the uterus). Slight pain in the lower abdomen may occur several times during the day, but, as a rule, they quickly disappear if the woman takes a position that is comfortable for her. Sometimes periodic discomfort in the lower lateral parts of the abdomen appear with constipation, which is also common in pregnant women: during pregnancy, hormones are produced that relax the uterus, they have a similar effect on the intestines: its peristalsis is disturbed, resulting in constipation.

The belly can be large or small, bulging forward or as if swollen, low or high – everything will depend on the individual characteristics of the pregnancy.

How the belly grows and looks during pregnancy depends on many factors: the physique of the woman, the structure of the pelvis, the condition of the muscles, the growth of the uterus and the baby, the amount of amniotic fluid.

Most often, the belly begins to grow after the 12th week of pregnancy, and others will be able to notice the woman’s interesting position only from the 20th week. However, everything is strictly individual, there is absolutely no exact definition of the timing of the appearance of the abdomen, it is simply impossible to predict.

Don’t be upset if the shape or size of your belly does not match the average, because everyone is different. Focus on your constitution, the work of your body and the development of the baby.

REFERENCE

At 4 weeks, the uterus reaches the size of a hen’s egg.

Goose egg at 8 weeks.

At 12 weeks, the uterus reaches the upper edge of the pubic bone. The belly is not visible yet.

At 16 weeks, the abdomen is rounded, the uterus is in the middle of the distance between the pubis and the navel.

At 20 weeks, the abdomen is visible to others, the fundus of the uterus is 4 cm below the navel.

At 24 weeks, the fundus of the uterus is at the level of the navel.

At 28 weeks, the uterus is already above the navel.

At 32 weeks, the navel begins to smooth out. Abdominal circumference – 80-85 cm.

At 40 weeks, the navel protrudes noticeably. Abdominal circumference 96-98 cm

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Physiological changes in the body during pregnancy

From the very first days of pregnancy, a woman’s body undergoes profound transformations. These transformations are the result of the coordinated work of almost all body systems, as well as the result of the interaction of the mother’s body with the child’s body. During pregnancy, many internal organs undergo significant restructuring. These changes are adaptive in nature, and, in most cases, are short-lived and completely disappear after childbirth. Consider the changes in the basic systems of the vital activity of a woman’s body during pregnancy.

The respiratory system works hard during pregnancy. The respiratory rate increases. This is due to an increase in the need of the mother and fetus for oxygen, as well as in the limitation of the respiratory movements of the diaphragm due to an increase in the size of the uterus, which occupies a significant space of the abdominal cavity.

The mother’s circulatory system has to pump more blood during pregnancy to ensure an adequate supply of nutrients and oxygen to the fetus. In this regard, during pregnancy, the thickness and strength of the heart muscles increase, the pulse and the amount of blood pumped by the heart in one minute increase. In addition, the volume of circulating blood increases. In some cases, blood pressure increases. The tone of blood vessels during pregnancy decreases, which creates favorable conditions for increased supply of tissues with nutrients and oxygen. During pregnancy, the network of vessels of the uterus, vagina, and mammary glands decreases sharply. On the external genitalia, in the vagina, lower extremities, there is often an expansion of the veins, sometimes the formation of varicose veins. Heart rate decreases in the second half of pregnancy. It is generally accepted that the rise in blood pressure over 120-130 and a decrease to 100 mm Hg. signal the occurrence of pregnancy complications. But it is important to have data on the initial level of blood pressure.

And changes in the blood system. During pregnancy, blood formation increases, the number of red blood cells, hemoglobin, plasma and bcc increases. BCC by the end of pregnancy increases by 30-40%, and erythrocytes by 15-20%. Many healthy pregnant women have a slight leukocytosis. ESR during pregnancy increases to 30-40. Changes occur in the coagulation system that contribute to hemostasis and prevent significant blood loss during childbirth or placental abruption and in the early postpartum period.

Kidneys work hard during pregnancy. They secrete decay products of substances from the body of the mother and fetus (the waste products of the fetus pass through the placenta into the mother’s blood).

Changes in the digestive system are represented by increased appetite (in most cases), craving for salty and sour foods. In some cases, there is an aversion to certain foods or dishes that were well tolerated before the onset of pregnancy. Due to the increased tone of the vagus nerve, constipation may occur.

The most significant changes, however, occur in the genitals of a pregnant woman. These changes prepare the woman’s reproductive system for childbirth and breastfeeding.

The uterus of a pregnant woman increases significantly in size. Its mass increases from 50 g – at the beginning of pregnancy to 1200 g – at the end of pregnancy. The volume of the uterine cavity by the end of pregnancy increases by more than 500 times! The blood supply to the uterus is greatly increased. In the walls of the uterus, the number of muscle fibers increases. The cervix is ​​filled with thick mucus that clogs the cavity of the cervical canal. The fallopian tubes and ovaries also increase in size. In one of the ovaries, there is a “corpus luteum of pregnancy” – a place for the synthesis of hormones that support pregnancy. Walls vaginas will loosen and become more elastic. External genitalia (labia minor and major), also increase in size and become more elastic. The tissues of the perineum are loosened. In addition, there is an increase in mobility in the joints of the pelvis and a divergence of the pubic bones. The changes in the genital tract described above are of extremely important physiological significance for childbirth. Loosening the walls, increasing the mobility and elasticity of the genital tract increases their throughput and facilitates the movement of the fetus through them during childbirth.

Skin in the genital area and in the midline of the abdomen usually becomes darker in color. Sometimes “stretch marks” form on the skin of the lateral parts of the abdomen, which turn into whitish stripes after childbirth.

Mammary glands increase in size, become more elastic, tense. When pressing on the nipple, colostrum (first milk) is released.

Changes of the bone skeleton and muscular system . An increase in the concentration of the hormones relaxin and progesterone in the blood contributes to the leaching of calcium from the skeletal system. This helps to reduce the rigidity of the joints between the bones of the pelvis and increase the elasticity of the pelvic ring. Increasing the elasticity of the pelvis is of great importance in increasing the diameter of the internal bone ring in the first stage of labor and further reducing the resistance of the birth tract to fetal movement in the second stage of labor. Also, calcium, washed out of the mother’s skeletal system, is used to build the skeleton of the fetus.

It should be noted that calcium compounds are washed out of all bones of the maternal skeleton (including the bones of the foot and spine). As shown earlier, a woman’s weight increases during pregnancy by 10 -12 kg. This additional load against the background of a decrease in bone stiffness can cause foot deformity and the development of flat feet. A shift in the center of gravity of the body of a pregnant woman due to an increase in the weight of the uterus can lead to a change in the curvature of the spine and the appearance of pain in the back and pelvic bones. Therefore, for the prevention of flat feet, pregnant women are advised to wear comfortable shoes with low heels. It is advisable to use insoles that support the arch of the foot. For the prevention of back pain, special physical exercises are recommended that can unload the spine and sacrum, as well as wearing a comfortable bandage. Despite an increase in calcium loss by the bones of the skeleton of a pregnant woman and an increase in their elasticity, structure and bone density (as is the case with osteoporosis in older women).

Changes in the nervous system .