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Where is the fetus located


Your Body throughout Pregnancy

Your Body Before Pregnancy

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Your Body Before Pregnancy

Before pregnancy, most of the space in your abdomen is taken up by the large and small intestines. There is no real separation between the areas of your pelvis and abdomen.

In the picture here, you can see that the vagina is behind the bladder (sac that collects urine) and urethra (tube for moving urine out of bladder and body). In its normal position, your uterus is above and behind the bladder, with the cervix protruding into the vagina. The pelvic colon, rectum and anal canal are behind the vagina and uterus.

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Your Body at 6-7 Weeks of Pregnancy

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Your Body at 6-7 Weeks of Pregnancy

When you are between 6 and 7 weeks pregnant, you may be experiencing the early signs of pregnancy: your period has stopped and you may have nausea, breast tenderness and swelling, frequent urination and fatigue.

At this point, your uterus has begun to grow and become more egg-shaped. The pressure of the growing uterus on the bladder causes frequent urge to urinate.

In this image, you can see the beginnings of the placenta in the uterus. The embryo is about 1/4 inch to 1/2 inch long and weighs 1/1,000th of an ounce.

The embryo’s head is large in proportion to the rest of the body. The internal organs are forming and the heart has been beating since the end of the 4th week.

The embryo is floating in the amniotic sac. Buds for the arms and legs emerge in the 5th week and, by the 7th week, buds for fingers and toes also appear. The umbilical cord is lengthening and will continue to grow, allowing the fetus freedom to move. The 7th week represents a milestone in development: the embryo is now considered a fetus.

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Your Body at 12 Weeks of Pregnancy

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Your Body at 12 Weeks of Pregnancy

At the 12th week of pregnancy, the placenta is much larger. It now produces the hormones needed to sustain the pregnancy. Your uterus is the size of a grapefruit and completely fills the pelvis. It rises up into the area of the abdomen, as shown in the image. The fundus, the upper end of the uterus, is just above the top of the symphysis where the pubic bones join together. This upward growth of the uterus takes pressure off the bladder and decreases the need for frequent urination. The mucus plug, a barrier to protect the growing fetus, fills your cervical canal.

The fetus is now about 3 inches long and weighs about 1 ounce. By this week, the fetus has fingernails and toenails and can open and close the fingers. The fetus will start to move, but you will not feel it yet.

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Your Body at 20 Weeks of Pregnancy

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Your Body at 20 Weeks of Pregnancy

By the 20th week of pregnancy, your uterus can be felt at the level of your belly button (umbilicus). The pelvic colon and small intestines are crowded upward and backward. The ascending and descending colon maintain their usual positions.

At this point, your uterus is especially enlarged where the placenta attaches to it (usually on the front or back wall). This gives the uterus an uneven bulge. The wall of the uterus, which lengthens and thickens early in pregnancy, stretches as the fetus grows, and becomes thinner now – just 3 to 5 millimeters thick. Your bladder moves up but not as much as your uterus, which straightens as it moves up.

As your uterus moves up, it rests against the lower portion of the front of your abdominal wall, causing it to bulge forward noticeably by your 20th week. The size of the bulge depends on how strong your abdominal muscles are. If they are firm, the uterus may be pressed against the spinal column, and there will be no noticeable bulge; if they are weak, the pressure of the uterus against the inside wall makes a sizeable bulge.

At this point, you should be able to feel light movements of the fetus. This is called “quickening.” You may recognize this earlier if you have been pregnant before. The fetus sleeps and wakes at regular intervals, is more active, is about 9 inches long and weighs between a half-pound and a pound.

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At this point in pregnancy, the top of your uterus is about one-third of the distance between the bellybutton and the xiphoid cartilage at the lower end of your breastbone. Constipation is common because your uterus is pressing on your lower colon and hormones slow down your body’s excretion process. Between the growth of your uterus and general weight gain, you may be feeling fatigued. Some women also experience heartburn as your uterus presses against your stomach.

Your breasts are also changing to get ready for breastfeeding. First colostrum and then milk are produced by the grape-like clusters of tiny sacs (alveoli) deep within the breast tissue. Clusters of alveoli form lobules, which come together to form 15 to 20 lobes. Each lobe connects to a lactiferous duct for conveying milk. As the ducts extend toward the nipple and areola (darker area around the nipple), they widen into the lactiferous sinuses. These sinuses (or milk pools) release the milk through 15 to 20 tiny nipple openings in each breast when the baby nurses.

At week 28, the fetus is about 16 inches long and weighs two to three pounds. The skin is wrinkled but will become less so as more fat builds up under the skin in the next few weeks. Fine, downy hair called lanugo, and a waxy white protective substance covering the skin called vernix, are on the fetus’ body. Its eyes are open, and eyebrows and eyelashes were formed in the fourth month. The fetus sucks its thumb and its taste buds have developed. It kicks, stretches and moves frequently in your uterus—you’ll feel it moving around and others might even be able to see these movements!

Fetal organs and systems are quite well developed by the 28th week of pregnancy, but the final two months of gestation are important for further maturation of all body systems and organs.

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Your Body at 36 Weeks of Pregnancy

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Your Body at 36 Weeks of Pregnancy

By the end of the 36th week of pregnancy, your enlarged uterus almost fills the space within your abdomen. The fetus is inside the membrane sac within the uterus and high within the abdomen. The muscles of your abdomen support much of its weight.

During this week, the top of the uterus is at the tip of the xiphoid cartilage at the lower end of the breastbone, which is pushed forward.

The change in the position of the heart and the upward pressure of the diaphragm may make it hard to breathe at this point. The crowding of your stomach and intestines may contribute to discomfort after eating.

Your cervix is long, thick and filled with the mucous plug. By the 36th week, your vagina and urethra are elongated and all the tissues in the perineum (area between vaginal and anal openings) are enlarged. The swollen perineum projects outward in the last weeks of pregnancy and readily expands during labor.

The brain of the fetus is growing rapidly, but bones in the skull are soft so that he or she will fit through your vagina at birth. The lungs are still forming. You will likely feel the fetus kicking and may be aware of rhythmic movements, which could be hiccups or thumb sucking. Another possible sensation, sudden movement, may be a startle response.

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Your Body at 40 Weeks of Pregnancy (Internal)

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Your Body at 40 Weeks of Pregnancy (Internal)

At full term, or 40 weeks of pregnancy, the fetus’ head has generally lowered into your pelvis, where it takes up most of the space. This is called “lightening.” In first pregnancies, this may happen a few weeks before labor. In repeat pregnancies, this can happen at the time of labor. The canal of the broad, enlarged cervix is still filled with the plug of mucous. If this is your first pregnancy, the small opening at the bottom of your cervix is usually not dilated, whereas if you have given birth before, it will often be open as wide as two fingers some time before labor begins.

At this point, you may be experiencing frequent urination, increased constipation, edema (water retention) and aching legs or vulva. Varicose veins in the vulva, rectum and legs are also possible. This is because of the position of the uterus, the pressure of the baby's head and a loss of muscle tone as the hormone relaxin loosens your tissues in preparation for birth. Other changes at this time include increased development of blood vessels and increased amount of blood.

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Your Body at 40 Weeks of Pregnancy (External)

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Your Body at 40 Weeks of Pregnancy (External)

You can see that the round ligament is long and enlarged. It is also farther forward because of the twisting of the uterus. The enlarged uterosacral ligament is shown stretched taut by the enlarged uterus. Backaches in late pregnancy may be due to the stress of the weight of your uterus on the ligaments that connect it to your spine.

Because your uterus dropped a bit, you may be able to breathe and eat more comfortably near the end of your pregnancy.

At this time, the lungs of the fetus are likely fully mature and ready to begin breathing. The fetus gains about a half pound every week at the end of pregnancy, for a birth weight of roughly 7 pounds, and is growing longer for a birth length of about 18 to 21 inches.

Labor starting on its own around week 40 is a sign that your body is ready to give birth and your baby is ready to be born.

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Anatomy of pregnancy and birth - uterus

Anatomy of pregnancy and birth - uterus | Pregnancy Birth and Baby beginning of content

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What does the uterus look like?

One of the most recognised changes in a pregnant woman’s body is the appearance of the ‘baby bump’, which forms to accommodate the baby growing in the uterus. The primary function of the uterus during pregnancy is to house and nurture your growing baby, so it is important to understand its structure and function, and what changes you can expect the uterus to undergo during pregnancy.

The uterus (also known as the ‘womb’) has a thick muscular wall and is pear shaped. It is made up of the fundus (at the top of the uterus), the main body (called the corpus), and the cervix (the lower part of the uterus ). Ligaments – which are tough, flexible tissue – hold it in position in the middle of the pelvis, behind the bladder, and in front of the rectum.

The uterus wall is made up of 3 layers. The inside is a thin layer called the endometrium, which responds to hormones – the shedding of this layer causes menstrual bleeding. The middle layer is a muscular wall. The outside layer of the uterus is a thin layer of cells.

Illustration showing the female reproductive system.

The size of a non-pregnant woman's uterus can vary. In a woman who has never been pregnant, the average length of the uterus is about 7 centimetres. This increases in size to approximately 9 centimetres in a woman who is not pregnant but has been pregnant before. The size and shape of the uterus can change with the number of pregnancies and with age.

How does the uterus change during pregnancy?

During pregnancy, as the baby grows, the size of a woman’s uterus will dramatically increase. One measure to estimate growth is the fundal height, the distance from the pubic bone to the top of the uterus. Your doctor (GP) or obstetrician or midwife will measure your fundal height at each antenatal visit from 24 weeks onwards. If there are concerns about your baby’s growth, your doctor or midwife may recommend using regular ultrasound to monitor the baby.

Fundal height can vary from person to person, and many factors can affect the size of a pregnant woman’s uterus. For instance, the fundal height may be different in women who are carrying more than one baby, who are overweight or obese, or who have certain medical conditions. A full bladder will also affect fundal height measurement, so it’s important to empty your bladder before each measurement. A smaller than expected fundal height could be a sign that the baby is growing slowly or that there is too little amniotic fluid. If so, this will be monitored carefully by your doctor. In contrast, a larger than expected fundal height could mean that the baby is larger than average and this may also need monitoring.

As the uterus grows, it can put pressure on the other organs of the pregnant woman's body. For instance, the uterus can press on the nearby bladder, increasing the need to urinate.

How does the uterus prepare for labour and birth?

Braxton Hicks contractions, also known as 'false labour' or 'practice contractions', prepare your uterus for the birth and may start as early as mid-way through your pregnancy, and continuing right through to the birth. Braxton Hicks contractions tend to be irregular and while they are not generally painful, they can be uncomfortable and get progressively stronger through the pregnancy.

During true labour, the muscles of the uterus contract to help your baby move down into the birth canal. Labour contractions start like a wave and build in intensity, moving from the top of the uterus right down to the cervix. Your uterus will feel tight during the contraction, but between contractions, the pain will ease off and allow you to rest before the next one builds. Unlike Braxton Hicks, labour contractions become stronger, more regular and more frequent in the lead up to the birth.

How does the uterus change after birth?

After the baby is born, the uterus will contract again to allow the placenta, which feeds the baby during pregnancy, to leave the woman’s body. This is sometimes called the ‘after birth’. These contractions are milder than the contractions felt during labour. Once the placenta is delivered, the uterus remains contracted to help prevent heavy bleeding known as ‘postpartum haemorrhage‘.

The uterus will also continue to have contractions after the birth is completed, particularly during breastfeeding. This contracting and tightening of the uterus will feel a little like period cramps and is also known as 'afterbirth pains'.

Read more here about the first few days after giving birth.

Sources:
The Royal Australian and New Zealand College of Obstetricians and Gynaecologists (Labour and birth), StatPearls Publishing (Anatomy, Abdomen and Pelvis), Department of Health (Clinical practice guidelines: Pregnancy care), Better Health Channel Victoria (Pregnancy stages and changes), Mater Mother's Hospital (Labour and birth information), Royal Australian and New Zealand College of Obstetricians and Gynaecologists (The First Few Weeks Following Birth), Queensland Health (Queensland Clinical Guidelines – maternity and neonatal), King Edward Memorial Hospital (Fundal height: Measuring with a tape measure), Royal Hospital for Women (Fetal growth assessment (clinical) in pregnancy), MSD Manual (Female internal genital organs)

Learn more here about the development and quality assurance of healthdirect content.

Last reviewed: October 2020


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Related pages

  • Anatomy of pregnancy and birth
  • Anatomy of pregnancy and birth - abdominal muscles
  • Anatomy of pregnancy and birth - cervix
  • Anatomy of pregnancy and birth - pelvis
  • Anatomy of pregnancy and birth - perineum and pelvic floor

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