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Stages of Pregnancy - Weeks 13-27

Months 4, 5 and 6 will be your period of greatest weight gain. You may add 3-4 pounds each month. Your growing baby is also putting on weight. By the end of your second trimester, your baby will weigh about 1½ pounds.


Weeks 13-16: Growing legs are now supported by bones, not cartilage. The baby is 6-7 inches long and weighs about 5 ounces. Eyebrows have formed and there is a little hair on the head. Your baby is likely to be move around and kick more, whether sleeping or awake. Baby can also swallow and pass urine.

Weeks 17-20: Legs now are more in proportion to the rest of the baby's body. You are likely to feel your baby move. Vernix (a white layer of oil and cells) helps to protect the skin. Downy hair called lanugo covers the 20-week-old baby. By week 20, the baby is about 8-12 inches long and weighs from a half pound to a pound (8-16 ounces).

Weeks 21-25: The baby now has normal proportions and is gaining weight. By week 25, baby will weigh 1-1½ pounds and be 11-14 inches long.

Changes in you

By week 20, your uterus is much larger. If measured on the outside, it reaches to the level of your belly button. By week 24, the top of the uterus can be felt roughly an inch higher. By week 28, it will be 2 inches higher.

Your doctor will measure you in centimeters. For the first 36 weeks, the number of centimeters to the top of your uterus roughly equals the number of weeks you are pregnant. For example, at 30 weeks, you will probably measure between 28 and 32 centimeters. You may appear bigger than you would expect. It depends on:

  • Your body size
  • The size of your uterus
  • Baby position
  • Amount of amniotic fluid
  • Placement of the placenta

Breasts might not be as tender as before. They may enlarge more if you are gaining too much weight. You may not feel as tired. In fact, you may feel pretty good. You may still have to pass urine often – that may not change until you give birth.

Weight gain is encouraged. During the first 3 months, you should have gained 3-4 pounds. For the rest of your pregnancy, you should gain 3-4 pounds a month for a total of about 25 pounds. If you have questions about your weight gain, ask your doctor or nurse midwife. A prenatal registered dietitian could meet with you to discuss diet. You may be asked to take iron and/or vitamins.


Most women feel best during this part of the pregnancy. Stick with your normal routine as long as you are comfortable. Talk to your doctor or nurse midwife before starting an exercise program.

Feeling movement, hearing heartbeat

There is nothing quite like feeling your baby move or hearing his or her heartbeat. If this is your first baby, you are likely to feel your baby "quicken" (move for the first time that you notice) about week 19 or 20. If you have had a baby before, you may sense movement as early as week 16. You are likely to notice more aching and other pelvic discomfort if this is your second baby.

You and your provider may be able to hear a heartbeat as early as week 10 with a Doppler machine. Note: Heart rate gives no clue to whether the baby is a boy or girl. An active baby has a higher rate. A sleeping baby has a lower one.


Ultrasound: Between weeks 16 and 20, you are likely to have an ultrasound. This test helps confirm the baby's age in weeks, due date, how much amniotic fluid is in your uterus, placenta location and appearance, baby's anatomy and whether you have more than one baby.

Maternal serum screening: This blood test is offered between weeks 15 and 20. Results can show if there is an increased chance that your baby may have Down syndrome or a spinal defect. Discuss this test with your doctor or midwife.

Blood sugar testing: Most women have a glucose challenge test (GCT). It screens for gestational diabetes (diabetes you have when you are pregnant). You will drink a sweetened liquid and have a blood test one hour later.

Possible concerns - second trimester

You may have lower back pain as hormone levels shift and your body expands. To learn more about other common symptoms of this period, read Discomforts & Illnesses. Signs of early labor, leaking amniotic fluid and bleeding may be reasons to call your provider.

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