The Third Trimester of Pregnancy

Written by Jacquelyn Cafasso | Published on October 6, 2014
Medically Reviewed by George Krucik, MD, MBA on October 6, 2014

What Is the Third Trimester?

A pregnancy lasts for about 40 weeks. The weeks are grouped into three trimesters. The third trimester includes weeks 28 through 40 of a pregnancy.

The third trimester can be both physically and emotionally challenging for a pregnant woman. The baby is considered full term at the end of week 37 and it’s only a matter of time before the baby will be born. Researching and understanding what to expect during the third trimester can help reduce any anxiety you may have during the final stages of your pregnancy.

What Happens to a Woman's Body During the Third Trimester?

In the third trimester a woman may experience more aches, pain, and swelling as she carries around her baby. A pregnant woman may also being to become anxious about her delivery.

Other events that occur during the third trimester include:

  • a lot of movement by the baby
  • occasional random tightening of the uterus called Braxton Hicks contractions. These are usually not painful and are completely random.
  • going to the bathroom more often
  • heartburn
  • swollen ankles, fingers, or face
  • hemorrhoids
  • tender breasts that may leak watery milk
  • difficulty sleeping

Call your doctor immediately if you experience:

  • painful contractions of increasing intensity and frequency
  • bleeding at any time
  • sudden decrease in activity by your baby
  • extreme swelling
  • rapid weight gain

What Happens to the Fetus During the Third Trimester?

At around week 32, your baby's bones are fully formed. The baby can now open and close its eyes and sense light. The baby's body will begin to store minerals like iron and calcium.

By week 36, the baby should be in a head down position. If the baby does not move into this position, your doctor may try to move the baby's position or recommend that you give birth by a cesarean section. This is when the doctor makes a cut in the mother's belly and uterus in order to deliver the baby.

After week 37, your baby is considered fell term and its organs are ready to function on their own. According to the Office on Women’s Health, the baby is now around 19 to 21 inches long and probably weighs between 6 and 9 pounds.

 

What Can Be Expected at the Doctor?

You will meet with your doctor more regularly during the third trimester. Around week 36, your doctor may perform a Group B strep test to test for a bacterium that can be very harmful to a baby. Your doctor will give you antibiotics if you test positive.

Your doctor will check you progress with a vaginal exam. Your cervix will become thinner and softer as you near your due date in order to help the birth canal open during the birthing process.

How Can You Stay Healthy During the Third Trimester?

It’s important to be aware of what to do and what to avoid as your pregnancy continues in order to take care of yourself and your developing baby.

What to Do:

  • Continue to take prenatal vitamins.
  • Stay active unless there is swelling or pain.
  • Work out your pelvic floor by doing kegel exercises.
  • Eat a diet high in fruits, vegetables, low-fat forms of protein, and fiber.
  • Drink lots of water.
  • Eat enough calories (about 300 calories more than normal).
  • Keep your teeth and gums healthy. Poor dental hygiene is linked to premature labor.
  • Get plenty of rest and sleep.

What to Avoid

  • strenuous exercise or strength training that could cause an injury to your stomach
  • alcohol
  • caffeine (no more than one cup of coffee or tea per day)
  • smoking
  • illegal drugs
  • raw fish or smoked seafood
  • shark, swordfish, mackerel, or white snapper fish (they have high levels of mercury)
  • raw sprouts
  • cat litter, which can carry a parasite that causes toxoplasmosis
  • unpasteurized milk or other dairy products
  • deli meats or hot dogs
  • the following prescription drugs: isotretinoin (Accutane) for acne, acitretin (Soriatane) for psoriasis, thalidomide (Thalomid), and ACE inhibitors for high blood pressure
  • long car trips and airplane flights, if possible. After 34 weeks, airlines may not let you board the plane because of the possibility of an unexpected delivery on the plane

If you must travel, stretch your legs and walk around at least every hour or two.

What Can You Do to Prepare for Birth During the Third Trimester?

If you haven't done this already, make a decision on where you plan to give birth to your child. These last-minute preparations can help make delivery go more smoothly:

  • Attend a parenting class if you haven't already. This is an opportunity to learn about what to expect during labor and the different options available for delivery.
  • Find a family member or friend who can care for your pets or other children.
  • Have an overnight bag packed and ready with items for you and your baby.
  • Plan the route and mode of transportation for getting to the hospital.
  • Have a car seat set up in your vehicle.
  • Develop a birth plan with your doctor. This may include deciding who you want in your labor room for support, concerns you have about hospital procedures, and pre-registering with your insurance information.
  • Arrange maternity leave with your employer.
  • Have a crib ready for your baby and double-check that it’s safe.
  • If you receive any "hand-me-down" equipment like cribs, strollers, and car seats, make sure they conform to current government safety standards.
  • Check that your smoke detectors and carbon monoxide detectors in your home are working properly.
  • Have emergency numbers, including poison control, written somewhere close to your phone.
  • Stock up on baby supplies, like diapers, wipes, and baby clothing in different sizes.
  • Celebrate your pregnancy with friends and family.
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