How does a single cell transform into a fully-formed baby. What are the key milestones in fetal development. When can you first hear the baby’s heartbeat. How does the fetus grow and change throughout pregnancy.

The Miraculous Beginning: From Conception to Implantation

The journey of fetal development begins with a single momentous event: fertilization. When sperm meets egg, they fuse to form a zygote, a single cell containing genetic material from both parents. This marks the official start of pregnancy, though many aren’t aware they’re pregnant at this early stage.

Within days, this zygote embarks on a remarkable transformation:

• By day 3: The zygote begins rapidly dividing into multiple cells
• Days 5-6: Now called a blastocyst, it reaches the uterus
• Days 6-10: The blastocyst attaches to the uterine wall in a process called implantation
• Days 10-12: The implanted cells are now referred to as an embryo

Early Embryonic Development

Once implantation occurs, the embryo wastes no time in laying the groundwork for future organ systems. By the end of week 4:

• Structures that will form the face and neck begin to develop
• The cardiovascular system, including the heart and blood vessels, continues to progress
• Initial formation of the lungs, stomach, and liver begins
• The placenta, vital for nourishing the growing fetus, starts to form

At this stage, a home pregnancy test may show a positive result, confirming the incredible changes happening within.

Weeks 6-8: Rapid Growth and Organ Development

The embryonic period is characterized by astonishing growth and differentiation. By week 8, the embryo measures just over half an inch in length, yet significant developments are underway:

• Eyelids and ears begin to form
• The tip of the nose becomes visible
• Arms and legs are well-defined
• Fingers and toes elongate and become more distinct

These weeks are crucial for organ development, with major systems laying their foundations. The neural tube, which will become the brain and spinal cord, is forming, and the heart begins to beat.

From Embryo to Fetus: A Milestone at Week 10

At the end of the 10th week of pregnancy, a significant terminology shift occurs: the embryo is now referred to as a fetus. This change reflects the transition from early formation to a period of growth and refinement of existing structures.

Key developments at this stage include:

• The fetus measures about 2 inches in length
• Independent movements begin, though they’re not yet felt by the mother
• The uterus may be palpable above the pubic bone
• Sex organs start to differentiate, though they may not be clearly visible on ultrasound yet

The Second Trimester: A Period of Rapid Growth and Sensation

As the second trimester begins, both mother and fetus enter a phase often described as the “golden period” of pregnancy. Morning sickness typically subsides, and the risk of miscarriage decreases significantly.

Weeks 13-16: Visible Progress

By week 16, the fetus has undergone remarkable changes:

• Length increases to about 4.3 to 4.6 inches
• Weight reaches approximately 3.5 ounces
• Eyes can blink
• The cardiovascular system is fully formed
• Unique fingerprints have developed

The top of the uterus is now typically about 3 inches below the belly button, and some mothers may begin to show a visible pregnancy bump.

Weeks 17-20: The Halfway Point

Reaching the halfway point of pregnancy brings exciting developments:

• The fetus weighs about 10 ounces and measures just over 6 inches
• Movement becomes more coordinated – sucking, yawning, and stretching are possible
• “Quickening” occurs – the first fetal movements felt by the mother
• A detailed anatomy scan ultrasound is typically performed

The 20-week ultrasound is a significant milestone. It allows doctors to check fetal development, assess the placenta’s health, and often determine the baby’s sex if desired.

Fetal Sensory Development: A World of Sound and Movement

As the pregnancy progresses into the latter part of the second trimester, the fetus becomes increasingly responsive to the world around it. By week 24:

• Weight increases to about 1.4 pounds
• The inner ear is fully developed, allowing for balance and positional awareness
• The fetus responds to external sounds by moving or increasing heart rate
• Hiccups may occur, felt as rhythmic jerking movements by the mother

This heightened sensory awareness marks a fascinating period of fetal development. The growing baby is now capable of perceiving and reacting to stimuli from the outside world, forming a deeper connection with its environment.

The Importance of Maternal Voice and Music

Research suggests that exposure to voices, particularly the mother’s, and music during pregnancy can have positive effects on fetal development. While the fetus can’t understand words, it becomes attuned to the rhythms and tones of speech. This early auditory exposure may contribute to language development after birth.

Some interesting facts about fetal hearing:

• Low-frequency sounds are more easily transmitted through the amniotic fluid
• The fetus may show preference for familiar voices and music after birth
• Excessive noise exposure during pregnancy should be avoided, as it could potentially impact hearing development

The Third Trimester: Preparing for Birth

As pregnancy enters its final stage, the focus shifts to preparing both mother and baby for the upcoming birth. The third trimester brings significant growth and development for the fetus.

Weeks 28-32: Rapid Weight Gain

During this period, fetal weight increases dramatically:

• By week 28, the average fetus weighs about 2 pounds 6 ounces
• Survival rates for premature births at this stage are good with proper medical care
• The fetus changes position frequently
• Brain development accelerates

This is an ideal time for expectant parents to consider enrolling in childbirth education classes. These courses provide valuable information on labor, delivery, and newborn care.

Weeks 33-36: The Home Stretch

As the due date approaches, final preparations for birth occur:

• Fetal weight reaches nearly 4 pounds
• A layer of fat develops under the skin, giving the baby a less wrinkled appearance
• The fetus gains up to half its birth weight in this period
• Lung development nears completion

Expectant mothers may notice colostrum, a yellowish fluid, leaking from their breasts. This is a normal preparation for breastfeeding. Prenatal appointments typically increase to every two weeks during this stage.

Understanding Fetal Size and Position in Late Pregnancy

As the pregnancy nears its conclusion, the fetus reaches its final birth size and adopts the position for delivery. However, it’s important to note that fetal size can vary considerably based on factors such as genetics, maternal health, and whether it’s a multiple pregnancy.

Average Measurements at Full Term

While individual variations are normal, here are some average measurements for a full-term baby:

• Length: Approximately 18.5 inches
• Weight: Close to 6 pounds

In the final weeks, the fetus typically positions itself head-down in the pelvis, preparing for birth. This position, known as “vertex presentation,” is ideal for a vaginal delivery.

Brain and Lung Development in Late Pregnancy

Two critical systems continue to develop rapidly in the final stage of pregnancy:

1. Brain: Neurological development accelerates, with the brain increasing in size and complexity
2. Lungs: The respiratory system matures, preparing the baby to breathe independently after birth

These late-stage developments underscore the importance of carrying a pregnancy to term when possible.

Defining Full Term and Managing Post-Term Pregnancies

Understanding the terminology surrounding pregnancy duration is crucial for expectant parents and healthcare providers. The American College of Obstetricians and Gynecologists (ACOG) defines the following categories:

• Early Term: 37 weeks 0 days to 38 weeks 6 days
• Full Term: 39 weeks 0 days to 40 weeks 6 days
• Late Term: 41 weeks 0 days to 41 weeks 6 days
• Post Term: 42 weeks 0 days and beyond

The due date, marking the end of the 40th week, is calculated using the first day of the last menstrual period. Based on this calculation, a typical pregnancy can last anywhere from 38 to 42 weeks.

Managing Post-Term Pregnancies

When a pregnancy extends beyond 42 weeks, it’s considered post-term. However, it’s important to note that some post-term pregnancies may result from inaccurate due date calculations rather than truly prolonged gestation.

For safety reasons, most healthcare providers recommend delivery by 42 weeks at the latest. If labor doesn’t begin naturally, induction may be necessary. This decision is based on several factors:

• The health of the mother and baby
• The condition of the placenta
• The amount of amniotic fluid
• The size of the baby

Inducing labor involves using medications or other methods to stimulate contractions and initiate the birthing process. While it can be necessary for medical reasons, the decision to induce should be made carefully in consultation with a healthcare provider.

The Importance of Full-Term Pregnancies

While it may be tempting to consider early delivery, especially in the uncomfortable final weeks of pregnancy, there are significant benefits to allowing a pregnancy to reach full term naturally:

• Brain Development: The fetal brain undergoes crucial growth in the final weeks of pregnancy
• Lung Maturation: The respiratory system continues to develop, reducing the risk of breathing problems after birth
• Weight Gain: The baby adds important fat stores in the last few weeks
• Reduced NICU Admissions: Full-term babies are less likely to require intensive care after birth

Unless there are medical reasons to deliver earlier, waiting until at least 39 weeks allows the baby to gain the maximum benefit from the full gestational period.

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. “

© 2023 WebMD, LLC. All rights reserved. View privacy policy and trust info

4 Weeks Pregnant: Symptoms, Cramping & More

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Highlights this week

Pregnancy testing

If you haven’t already, test now to confirm you’re pregnant. For the most accurate results, wait until a few day after you miss your period before you take a pregnancy test, use your first morning pee so hCG levels are more concentrated, and follow the directions on your test carefully. If you get a negative pregnancy test but your period hasn’t come, wait a few days and test again.

Your due date

Our Due Date Calculator can determine your due date based on the date of your last menstrual period or the date of conception. Keep in mind that a due date is just a guess – only 1 out of 20 women actually delivers on her due date. You’re just as likely to go into labor any day during the two weeks before or after.

From blastocyst to embryo

Your baby-to-be will soon transform from a ball of cells called a blastocyst to an embryo the size of a poppy seed. (Once your amniotic sac forms, 10 to 12 days after fertilization, your baby becomes an official embryo.) Over the next six weeks, your baby’s nervous system, connective tissue, and organs will start to develop.

Baby development at 4 weeks

Growing fast

Cells are multiplying rapidly and taking on different functions. Your little embryo consists of two layers called the hypoblast and the epiblast, from which all of the organs will begin to develop over the next six weeks. This is the time when your baby will be most vulnerable to anything that might interfere with development, so be sure to steer clear of alcohol, smoking, drugs, and unsafe chemicals.

Also, watch out for overheating. High temperatures, especially early in pregnancy, have been associated with increased risk of neural tube defects. That’s why saunas, steam baths, and hot tubs aren’t recommended during pregnancy.

Primitive placenta

Your embryo’s outer cells are tunneling into the lining of your uterus. Spaces form within this layer for your blood to flow into so that you’ll be able to provide nutrients and oxygen to your growing baby.

Amniotic sac and yolk sac

There’s now an amniotic sac surrounding your embryo – it contains amniotic fluid and will cushion your baby as they grow. Your tiny embryo also has a yolk sac, which temporarily provides nourishment and makes cells that turn into the umbilical cord, gastrointestinal system, and reproductive organs.

Having twins?

It’s too soon to know. But it’s still fun to see what fraternal twins look like in the womb this week. You can also learn about your likelihood of having twins or more.

Your baby at 4 weeks

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Your baby is about the size of a poppy seed

Pregnancy symptoms during week 4

No pregnancy symptoms?

Don’t worry. Many women don’t feel anything yet this week. By next week, about half of women will experience symptoms, but most early pregnancy symptoms don’t start until about 6 weeks.

Tender, swollen breasts

Breast tenderness can be one of the first signs of pregnancy. It usually starts around 4 to 6 weeks and lasts through the first trimester. You may notice your breasts growing or your nipples darkening. Some women also see prominent blue or purple veins develop on their breasts in early pregnancy.

Fatigue

For many women, exhaustion is one of the early signs of pregnancy. Pregnancy fatigue affects almost all expecting moms in the first trimester, likely due to a dramatic rise in progesterone.

Nausea or vomiting

Despite the misleading name, morning sickness can strike at any time of day. It usually starts around 6 weeks of pregnancy but can begin as early as 4 weeks. Up to 80 percent of expecting moms experience nausea during pregnancy, and about half have both nausea and vomiting.

Gas and bloating

Increased progesterone levels may be slowing down your digestion and causing gas and bloating. Even weeks before you begin to show, you may burp or pass gas much more often, or have to unbutton your pants to relieve bloating.

Cramping

Cramps during pregnancy are often nothing to worry about. In early pregnancy, some women feel implantation cramps (and can have some spotting) when the fertilized egg implants in the uterus. However, first trimester cramps along with other symptoms (such as bleeding) can signal a problem such as an ectopic pregnancy or miscarriage. Find out when to call your doctor or midwife about cramping during pregnancy.

Mood swings

Hormones, stress, and exhaustion all contribute to mood swings during pregnancy, which can be strongest in the first trimester. Emotional upheaval is normal right now. But if your mood swings are becoming more frequent or more intense, or if they last longer than two weeks, talk to your provider. You may be among the one in 10 women who battle mild to moderate depression during pregnancy.

Your body at 4 weeks

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Pregnancy checklist at 4 weeks pregnant

Make a prenatal appointment

Once you get a positive pregnancy test, call your doctor or midwife and make your first prenatal appointment. Many healthcare providers will schedule your first visit for when you’re about 8 weeks pregnant. Some will see you sooner, particularly if you have a medical condition, have had problems with a pregnancy in the past, or are having symptoms such as vaginal bleeding, abdominal pain, or severe nausea and vomiting.

Make sure your medicine is pregnancy-safe

Always check with your provider before you take any kind of medicine during pregnancy – prescription medicine or even an over-the-counter (OTC) product. If you take medication currently, ask your provider whether it’s a safe medicine for pregnancy. Your doctor or midwife can help you find a good alternative if it isn’t.

Soothe your digestive system

If you’re plagued by gas, bloating, or an uncomfortable sensation in your gut, try eating smaller meals throughout the day. Eat slowly and chew your food well, don’t drink too much water during meals, and avoid carbonated beverages, gum, and the artificial sweetener sorbitol. Exercise, like walking or prenatal yoga, can also provide relief.

Find out what’s in store throughout pregnancy

You’re pregnant! Now what? Get a sneak peek at the months ahead with our quick pregnancy overview.

4 weeks pregnant bellies

Though you just found out you’re pregnant, you may already feel the button on your pants digging into your belly. That’s due to bloating, which can make your clothes uncomfortable even this early in your pregnancy journey.

It will be a few months before you need maternity clothes, but until then you’ll probably appreciate things that are loose-fitting at the waist, like leggings, joggers, sweats, and maxi dresses. You’ll be glad you have them as your body starts to change more.

There may be a period where your regular clothes don’t fit, but you’re not ready to wear maternity clothes yet either – that’s normal. This in-between phase is a good time to shop your closet with an eye for soft knits, athleisure, loose-fitting blouses, oversize cardigans, and roomy dresses. These items can also be helpful if you aren’t ready to announce your pregnancy yet, and want to keep well-meaning-but-curious friends and colleagues at bay.

This week’s video

Kate Marple

Kate Marple is a writer and editor who specializes in health, pregnancy, and parenting content. She’s passionate about translating complicated medical information into helpful pregnancy and parenting advice that’s easy to understand. She lives in San Francisco with her family.

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3 weeks 5 weeks

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Pregnancy 4 weeks description and photo – Euromedclinic 24

This week the baby’s growth is from 0. 36 mm to 1 mm. The period of development that began at week 4 is called “embryonic”, it will last until the beginning of the eleventh week of your pregnancy. The fourth week is extremely important for the unborn baby, now all his organs are beginning to form, and some of them will even begin to function! Embryonic petals begin to form, which will subsequently develop into various tissues and organs. The inner layer, or endoderm, serves as the basis for the formation of the lungs, digestive system, liver and pancreas. The middle layer, or mesoderm, will be transformed into the bone, muscle and circulatory systems, heart and kidneys. The outer layer, or ectoderm, will develop further into hair, skin, nervous system, eye lenses, tooth enamel. The head of the embryo also begins to form. Now it is a small droplet, tender and transparent.

In addition, on the 4th week there is an active development of extra-embryonic organs – amnion, chorion, yolk sac. It is these organs that will provide breathing, nutrition, protection and support for your baby. The amnion will become the basis for the development of the fetal bladder, and the chorion – the placenta. In general, the most important weeks in the development of an unborn child are from 1 to 12, at which time not only internal organs are formed, but also the placenta, which plays a huge role in providing the baby with nutrition, oxygen, and also in the production of hormones.

What is the “yellow body” and what is its role?

The ovum leaves the ovary after ovulation, and in the place where the ruptured follicle remained, a corpus luteum, or corpus luteum, is formed. Outwardly, it looks like a small bubble or sac, which contains liquid and is located on the wall of the ovary. The corpus luteum rapidly develops blood vessels designed to produce hormones, in particular progesterone. The hormones will keep the pregnancy going early until the placenta separates.

Physicians have not yet come to a consensus on the role of the corpus luteum. There is a point of view that it plays an important role at the beginning of pregnancy, supplying the body with progesterone. Starting from 8-12 weeks, the placenta begins to supply progesterone, and the corpus luteum, as a rule, functions for about 6 months. However, there are cases when the corpus luteum persisted until childbirth. In addition, there are a number of cases when the corpus luteum had to be removed during the implantation period due to a ruptured cyst, while the pregnancy proceeded and ended quite successfully.

Changes in a woman’s body

You should have started your period by the end of this week. The delay confuses you, you start to suspect something. And then he also feels a little nauseous, and for some reason the temperature rises for no apparent reason. Yes, and she became irritable … Have you still not bought a pregnancy test? Then now is the time!

What to do in the fourth week of pregnancy

If you want, take a blood test for the hormone hCG (chorionic gonadotropin), its level in the blood rises already 10 days after fertilization. This analysis will be the most informative and will definitely let you know whether you are pregnant or not.

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Ultrasound photo during pregnancy, fetal photo during ultrasound during pregnancy

4-5 weeks

Photo ultrasound of the fetus during pregnancy 4-5 weeks

The earliest period at which a fetal egg in the uterine cavity can be seen using transvaginal ultrasound is the 30th day of gestation, or 4-5 obstetric weeks of pregnancy. The level of hCG blood in this case should be at least 1000 mU / ml. At this time, neither the embryo nor the yolk sac is visible. When visualizing two fetal eggs, it can be argued that this is a dichorionic multiple pregnancy. When visualizing one fetal egg, it can be argued that this is a monochorionic pregnancy. But at this time, we still cannot say how many embryos are in each fetal egg. In addition, during a single ultrasound, we still cannot tell if this pregnancy is progressing, since the embryo does not yet have a heartbeat. The average inner diameter (SID) of the fetal egg at this time is 2-10 mm.

The conclusion will indicate: Uterine pregnancy of a short term.

More about ultrasound in early pregnancy

5-6 weeks

Photo ultrasound of the fetus during pregnancy 5-6 weeks

At this time, a white ring appears inside the fetal egg – this is the yolk sac.

Foci of erythropoiesis form in the wall of the yolk sac, which form a capillary network, supplying erythroblasts (nuclear erythrocytes) to the primary circulatory system of the fetus. The yolk sac is a source of primary germ cells that migrate from its wall to the anlage of the gonads of the embryo. Until the 6th week after fertilization, the yolk sac, playing the role of the “primary liver”, produces many important proteins for the embryo – alpha-fetoprotein, transferrins, alpha2-microglobulin. By the end of the first trimester of pregnancy, this provisional organ ceases to function and is reduced.

The normal size of the yolk sac is 2-6 mm. If two yolk sacs are visualized in the fetal egg, then this is a monochorionic multiple pregnancy. But if one yolk sac is visible inside the fetal egg, and the embryo is not yet clearly visualized, then this may still be monochorionic monoamniotic twins.

At the beginning of the 5th week, the embryo is practically indistinguishable on the wall of the yolk sac, but by the end of the week, the coccyx-parietal size (CTE) of the embryo reaches 3 mm.

SVD of the ovum 11-16 mm.

Read also: Is ultrasound harmful during pregnancy? Is ultrasound dangerous? How often can an ultrasound be done?

6 – 7 weeks

Photo ultrasound of the fetus during pregnancy 6-7 weeks

Inside the fetal egg, we see a “ringlet with a precious stone” 🙂 – this is the yolk sac and already a well-defined embryo, located nearby. The heart of the embryo begins to beat at the beginning of the 6th obstetric week of pregnancy. It is the presence of a heart pulsation that is a reliable ultrasound sign of a progressing pregnancy. With CTE ≥6 mm and the absence of heart pulsation, a conclusion is made about stopping the development of this embryo. Normal heart rate (HR) of the embryo at the very beginning of the 6th week 70-90 beats per minute, but by the end of the week it becomes more than 100 beats. in min. In the early stages of pregnancy, it is not the heart rate that matters, but the presence or absence of heart contractions as such. Sometimes, with a non-developing pregnancy, you can see the reflection of the pulsation of the mother’s vessels inside the embryo and take them for the baby’s heartbeat. But in this case, the pulsation frequency will be identical to the mother’s heart rate.

The presence of one yolk sac, one embryo and one pulsating heart in most cases indicates a singleton pregnancy. But in very rare cases, it may later turn out to be unseparated twins.

SVD of the ovum 13-23 mm. Embryo KTR 4-9 mm.

Read also: “I don’t want an ultrasound, I want a baby!”. Why is ultrasound during pregnancy necessary?

7 – 8 weeks

Photo ultrasound of the fetus during pregnancy 7-8 weeks

The distance between the embryo and the yolk sac gradually increases and the yolk duct (ductus vitellinus), which connects the yolk sac and the intestines of the embryo, becomes clearly visible. Just like the yolk sac, the duct becomes empty and resolves at a later date, but if this does not happen for some reason, then a blind protrusion of the ileum wall is formed in a person – Meckel’s diverticulum.

Until this time, the chorion has an annular shape, surrounds the fetal egg from all sides, and it is still impossible to say which wall of the uterus the embryo has attached to.

In the case of monochorionic twins, no amniotic membranes are yet visible, and in the presence of two yolk sacs, it is still impossible to tell whether this pregnancy is mono or diamniotic. If the gestational sac contains two yolk sacs and two fetuses with cardiac activity, the subsequent number of amniotic cavities may be greater than the number of placentas (monochorial diamniotic) or the same (monochorial monoamniotic). In this case, it is possible to accurately determine amnionality after 8 weeks, when the amniotic membranes begin to be clearly visualized.

Embryo heart rate 130-160 beats per minute.

SVD of the ovum 24-30 mm, CTE of the embryo 9-15 mm.

8 – 9 weeks

Photo ultrasound of the fetus during pregnancy 8-9 weeks

During the ultrasound of the embryo, it is already possible to clearly distinguish individual segments – the head, trunk, limbs. The first movement appears. The amniotic membranes become clearly visible and we can already talk about the number of amniotic sacs in multiple pregnancies. The chorion is differentiated into a smooth one, facing the uterine cavity, and a branched one, from which the placenta will subsequently form, so that we can already talk about the predominant location of the chorion along the anterior or posterior wall of the uterus.

The heart rate of the embryo increases to 160-180 beats per minute.

SVD of the ovum 31-37 mm. Embryo KTR 16-22 mm.

9 – 10 weeks

Photo ultrasound of the fetus during pregnancy 9-10 weeks

The development of the embryo continues. The handles of the legs are already clearly visible, and on a good device, sometimes you can even see the fingers and toes.