Pregnancy: Your Third Trimester

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Your Third Trimester

The third trimester of pregnancy spans from week 28 to the birth. Although your due date marks the end of your 40th week, a full-term pregnancy can deliver between the 38th and 42nd weeks of pregnancy. During this final trimester, your fetus grows larger and the body organs mature. The fetus moves frequently, especially between the 27th and 32nd weeks.

In the final 2 months of pregnancy, a fetus becomes too big to move around easily inside the uterus and may seem to move less. At the end of the third trimester, a fetus usually settles into a head-down position in the uterus. You will likely feel some discomfort as you get close to delivery.

See illustrations of the fetus at 32 and 40 weeks of development .

Normal symptoms you may experience during the third trimester of pregnancy include:

• Braxton Hicks contractions, which are "warm-up" contractions that do not thin and open the cervix (do not lead to labor).
• Fatigue.
• Back pain.
• Pelvic ache and hip pain.
• Hemorrhoids and constipation.
• Heartburn (a symptom of gastroesophageal reflux disease, or GERD).
• Hand pain, numbness, or weakness (carpal tunnel syndrome).
• Breathing difficulty, since your uterus is now just below your rib cage, and your lungs have less room to expand.
• Mild swelling of your feet and ankles (edema). Pregnancy causes more fluid to build up in your body. This, plus the extra pressure that your uterus places on your legs, can lead to swelling in your feet and ankles.
• Difficulty sleeping and finding a comfortable position. Lying on your back interferes with blood circulation, and lying on your stomach isn't possible. Sleep on your side, using pillows to support your belly and between your knees. Later in your pregnancy, it is best to lie on your left side. When you lie on your right side or on your back, the increasing weight of your uterus can partly block the large blood vessel in front of your backbone.
• Frequent urination, caused by your enlarged uterus and the pressure of the fetus's head on your bladder.

Signs that labor is not far off include the following:

• The fetus settles into your pelvis. Although this is called dropping, or lightening, you may not feel it.
• Your cervix begins to thin and open (cervical effacement and dilatation). Your health professional checks for this during your prenatal examinations.
• Braxton Hicks contractions become more frequent and stronger, perhaps a little painful. You may also feel cramping in the groin or rectum or a persistent ache low in your back.
• Your "water" may break (rupture of the membranes). In most cases, rupture of the membranes occurs after labor has already started. In some women, this happens before labor starts. Call your health professional immediately or go to the hospital if you think your membranes have ruptured.

Last updated:	November 30, 2006
Author:	Shannon Erstad, MBA/MPH
Reviewed By:	Renée M. Crichlow, MD - Family Medicine, Kirtly Jones, MD - Obstetrics and Gynecology
Editors:	Kathleen M. Ariss, MS, Pat Truman, MATC