The Third Trimester of Pregnancy: Weight Gain and Other Changes

Medically reviewed by Debra Rose Wilson, PhD, MSN, RN, IBCLC, AHN-BC, CHT on May 16, 2017Written by the Healthline Editorial Team

The 3rd trimester of pregnancy

Your baby changes most rapidly during your third trimester of pregnancy. Your body will also go through significant changes to support your growing fetus. You may have some of the same changes and symptoms you had during your first and second trimesters, but they are often worse in the third trimester, as you get closer to your baby’s arrival.

Rapid weight gain

During the final months of pregnancy, your baby gains the most weight. In fact, according to the , a fetus weighs around 2 pounds at 27 weeks, 4 to 4 ½ pounds by 32 weeks, and grows up to between 6 ¾ pounds to 10 pounds, if you have a full-term delivery. Your baby will also grow an average of six more inches during the third trimester.

In addition to baby weight, your body will also gain weight from:

  • fluids
  • more blood
  • amniotic fluid
  • a larger uterus
  • the placenta
  • fat stores

All of these will add a few extra pounds. That’s one reason why doctors and midwives stress that women try not to gain too much weight during the first two trimesters of pregnancy.

While you certainly don’t want to lose weight during the third trimester, it’s also important not to give in to unhealthy food cravings and to be as active as possible. Doing both will help you prevent unnecessary weight gain. The total amount of weight you should gain depends on how much you weighed pre-pregnancy. Complications of too much weight gain can show up during the third trimester, and may include:

  • gestational diabetes
  • high blood pressure
  • premature birth (baby is born at 37 weeks or earlier)
  • heavy birth weight

Leg veins and swelling

Natural weight gain from pregnancy can cause your legs and ankles to swell. The problem can be worse with extra fluid retention, so make sure to drink plenty of water and avoid salty foods. The extra pressure in your lower extremities may lead to spider veins and varicose veins. Take pressure off of your legs by resting with your feet up when you can. You may also consider wearing support stockings if the swelling causes pain.

Minor fluid retention is normal, but rapid and painful swelling in your legs and ankles could be a cause for concern. Tell your doctor about any sudden swelling, so they can rule out a potentially life-threatening condition called preeclampsia. It’s marked by extremely high blood pressure, protein in the urine, and sometimes headache and upper-right abdominal pain.

Breast and vaginal changes

It’s normal for breasts to grow larger and more tender during the final weeks of pregnancy. In fact, the estimates that women gain an average of 2 pounds of tissue in the breasts during pregnancy. By the third trimester, your breasts may leak colostrum, which is early breast milk that’s yellow in color.

During pregnancy, any significant vaginal changes could be a cause for concern. There’s a small exception during the third trimester. As you near the end of your pregnancy, you may notice some vaginal discharge that looks like mucous and has a spot or two of blood in it. This is a result of your cervix softening to help prepare you for labor. You should call your doctor if you notice:

  • excessive discharge
  • a discharge that is thick, yellow, green, or cheesy, since this might indicate an infection
  • any blood from the vagina

Aches and pains

Your growing baby is starting to get cramped in your belly, so you might start feeling more kicks and other movements. Some of these might be painful from time to time—perhaps your baby is a future soccer star! A growing fetus can cause more body aches for you because of the extra weight you’re carrying. Aches and pains in the back, knees, and neck are common during the third trimester. Rest and put your feet up when you can, and alternate between ice packs and heating pads to ease the pain.

Frequent urination

During the first and second trimesters, you might have needed to urinate more often because of hormonal changes. Now that you’re in the third trimester, it may seem like you have to pee every hour. That’s because all the weight your baby’s gaining puts extra pressure on your bladder. Avoid drinking too many fluids at night to avoid disrupting your sleep.

To prepare for labor, your baby settles into your pelvis. This is called lightening. Once this happens, you might notice being able to breathe more deeply or to eat a bit more food. But your baby’s head is now pushing down even more on your bladder.

Aside from the annoyance, frequent bathroom visits aren’t usually a cause for concern. However, if you notice any blood in your urine or have back pain, call your doctor right away. Both could be signs of a urinary tract infection.

Trouble sleeping at night

Early in your pregnancy you may have wanted to sleep all the time. In your third trimester, you’re more likely to have insomnia. General discomfort is the primary reason why pregnant women can’t sleep. That discomfort can be from needing to urinate or a kicking baby. To make sure you prepare yourself and your bedroom for a good night’s sleep.

  • Avoid exercise in the late afternoon and evening.
  • Keep your bedroom cool and dark.
  • Avoid late naps or naps longer than an hour.
  • Layer your bedding in case you get hot.
  • Consider putting a fan at the bedside.
  • Leave the TV off in the bedroom. (Even with the sound off, the flickering light can disturb sleep cycles.)
  • Take a warm bath before bed.
  • Meditate or practice deep breathing exercises.
  • Use extra pillows to support your belly.

Other changes

Some mothers-to-be have other changes during the third-trimester, including:

Final preparations for baby

Perhaps the most significant changes you’ll have towards the end of your pregnancy are contractions. Unlike Braxton Hicks contractions, true labor progresses by contractions becoming longer, stronger, and closer together. Congratulations — this is your cue to call your midwife or birth center to prepare for the arrival of your baby!

CMS Id: 15920