During week 21 of pregnancy, a fetus will continue to mature and grow. Week 21 is no exception when it comes to developmental strides and bodily changes for both mother and child.

A fetus will now be using enough energy to warrant long periods of sleep, and will often need between 12 and 14 hours of sleep per day.

This MNT Knowledge Center feature is part of a series of articles on pregnancy. It provides a summary of this stage of pregnancy, what to expect, and insights into the development of your fetus.

Fast facts on pregnancy at 21 weeks

  • At 21 weeks pregnant, a woman may experience varicose veins, bleeding gums, and stretch marks.
  • Hormone levels can fluctuate at this stage and throughout pregnancy, causing mood swings and morning sickness.
  • A fetus may be tested for certain genetic abnormalities at this stage, such as Down’s syndrome.
  • Your child is the size of a banana at 21 weeks of pregnancy.
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Week 21 of pregnancy may see stretch marks begin to develop around the abdomen.

In addition to a growing belly and weight, a woman may continue to experience physical pregnancy symptoms at this stage.

These symptoms commonly include:

  • stronger nails and fuller hair
  • bloating and gas
  • increased appetite
  • fetal movement
  • varicose veins
  • a backache
  • bleeding gums
  • stretch marks

Be aware that pregnancy increases the risk of urinary tract infections (UTIs) from week 6 to week 24. If symptoms are not a result of the pregnancy and you suspect an infection, speak with a healthcare provider about treatment.

Some women notice that they look more “radiant” in the second semester of pregnancy, sometimes called the pregnancy “glow” or “bloom.”

Hormonal changes cause more blood to circulate, which can make the skin look pinker, or more “radiant.”

Moisture retention can also cause the skin to plump up, and this can smooth out wrinkles.

However, for some women, pregnancy can be trying on the skin, leading to:

  • spots and acne
  • sensitivity and itchiness
  • rashes
  • red veins on the cheeks
  • dark patches on the skin
  • puffiness due to water retention

These changes will not normally harm you or your baby, but if symptoms are severe, if there is blistering and inflammation, or if you are concerned about them, you should ask for health provider for advice.

Your baby is now the size of a banana, measuring nearly 7 inches and weighing nearly 11 oz.

Despite your baby’s increasing size, there is still plenty of room to allow for movement in the womb at this stage.

Other changes include:

  • rapid brain growth
  • cartilage converting to bone, the hardening of the skeleton, and the start of blood cell production in the bone marrow
  • the growth of soft head and body hair and eyebrows
  • the development of ovaries with primitive eggs and a formed uterus in females or testicular descent in males
  • the arms and legs becoming proportionate
  • fetal movement
  • the growth of taste buds
  • the swallowing of amniotic fluid.
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Genetic testing, to screen for genetic abnormalities, may not be recommended for everyone.

It is important to speak with your healthcare provider to determine if genetic testing and certain forms of prenatal screening are right for you.

Three blood tests are offered to women during their pregnancy to screen for a variety of genetic abnormalities: Down syndrome, Trisomy 18, and spina bifida. If a screen comes back positive, other tests will be carried out to diagnose or rule out the abnormality.

Since you are now in your second trimester, your healthcare provider may also recommend that you are examined for gestational diabetes. This test involves drinking a sugary liquid and checking blood glucose levels.

These tests include:

  • Sequential integrated screen: Between weeks 10 and 13, and again during weeks 15 to 20, this screening test may be recommended to test the blood for the six fetal proteins found in maternal blood circulation. This test can identify 92 percent of pregnancies that result in Down’s Syndrome. The first portion of this test is combined with a scan showing the amount of fluid under the skin behind the baby’s neck, known as the nuchal translucency ultrasound.
  • Serum integrated screen: This test looks for the same proteins as the sequential integrated screen and is carried out during the same period. A serum integrated screen is typically carried out in cases where a nuchal translucency ultrasound cannot be performed.
  • Quad marker screen: This is obtained between weeks 15 and 20. The quad marker screen tests maternal blood for four fetal proteins. Women who did not get the first portion of the serum and sequential tests are eligible to undergo this testing. This test is also the second test obtained during the sequential and serum screening tests.

Genetic amniocentesis is an additional test that is sometimes performed after 15 weeks pregnancy to evaluate for certain genetic abnormalities. This test is typically recommended for women with abnormal prenatal screening results, prior chromosomal abnormality, a family history of genetic abnormalities, a known genetic abnormality, or for women over the age of 35.

Between weeks 17 and 20 of pregnancy, a level 1 ultrasound is completed to evaluate the fetus for any congenital abnormalities that can be seen on ultrasound imaging. Any abnormal findings may lead to a level 2 scan.

As with earlier weeks, you will soon find out that there are many lifestyle modifications needed to adapt to pregnancy and life after delivery.

General health

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A prenatal vitamin regime may help to ensure that you and your baby receive vital nutrients.

During pregnancy, you will need to take care of yourself and your developing baby. Avoid alcohol, smoking, and all other toxic substances during this time. Exposure to strong smells, such as paint, can be volatile and also cause problems when inhaled.

If you are taking certain prescription medications, discuss these with your healthcare provider to ensure that it is safe to continue using them during pregnancy.

Eat a healthy diet and take a good prenatal vitamin regimen to nourish both yourself and your fetus.

Another way to maintain health during pregnancy is regular exercise. Speak with your healthcare provider about your current or desired exercise regimen to ensure safety.


While it is safe to eat fish during pregnancy, it is recommended that you limit intake to between 8 and 12 ounces (oz.) of fish and shellfish per week.

Examples of fish that are safe to consume during pregnancy include:

  • shrimp
  • salmon
  • canned light tuna, although mercury levels can vary from can to can
  • pollock
  • cod
  • catfish
  • anchovies

It is recommended that you limit consuming albacore tuna and tuna steak once per week. These fish contain higher levels of mercury than other types, and this poses a risk to your child. For the same reason, avoid eating shark, swordfish, tilefish, and king mackerel while pregnant.

If eating fish from a non-commercial source, such as a fish caught by yourself or your family, be sure to check with the local health authorities that the waters in which it was caught are safe.

Always make sure your food is fully cooked. Also avoid uncooked, smoked, or pickled fish. It is also important to avoid the following:

  • unpasteurized soft cheese
  • refrigerated pâté
  • raw or undercooked meat and poultry
  • cold cut deli meat
  • foods containing raw eggs
  • unpasteurized juice
  • milk
  • eggnog

It is safe to consume caffeine during pregnancy in moderation. Try to keep your daily caffeine consumption from all sources at or below 300 milligrams (mg).

Contact your healthcare provider with any questions or concerns about your pregnancy. It is also important to call your doctor if you are experiencing symptoms of an ectopic pregnancy or miscarriage, such as:

  • vaginal bleeding or passage of tissue
  • leaking vaginal fluid
  • feeling faint or dizzy
  • low blood pressure
  • rectal pressure
  • shoulder pain
  • severe pelvic pain or cramping

For information about other stages of pregnancy, please click on one of the following links:

First trimester: fertilization, implantation, week 5, week 6, week 7, week 8, week 9, week 10, week 11, week 12.

Second trimester: week 13, week 14, week 15, week 16, week 17, week 18, week 19, week 20.