The third trimester is the final stage of pregnancy, spanning from week 29 through week 40. It covers the last three months before birth, during which your baby gains most of its weight, your body prepares for labor, and prenatal visits become more frequent. For many people, it’s the most physically demanding stretch of pregnancy.
When the Third Trimester Starts and Ends
Pregnancy is divided into three roughly equal stages called trimesters. The third trimester begins at week 29 and continues until delivery, which typically happens around week 40. Some pregnancies go a week or two past that date, but 40 weeks is considered full term. If you deliver before 37 weeks, the birth is classified as preterm.
How Your Baby Develops
Your baby enters the third trimester already looking like a newborn in miniature, but the organs still need significant maturing. By week 28, the nervous system can regulate body temperature and trigger practice breathing movements visible on ultrasound. Over the next several weeks, your baby becomes increasingly active and responsive: kicking, stretching, grasping, and opening its eyes wide by around week 30.
Sensory development accelerates rapidly. By week 33, your baby’s pupils can change size in response to light shining through the uterine wall. By week 37, the grip is strong enough to firmly hold objects. The brain is adding billions of neural connections during this entire period, which is one reason nutrition and rest matter so much in these final months.
Most babies settle into a head-down position between weeks 32 and 36. By around week 36, the head may drop lower into your pelvis, a shift called “lightening” or “engagement.” This repositioning is one of your body’s earliest preparations for delivery.
Physical Changes You Can Expect
The third trimester brings noticeable physical strain as your baby takes up more space. Shortness of breath is common because the growing uterus pushes up against your rib cage, reducing the room your lungs have to expand. Lying on your back can make this worse, so sleeping on your side often helps. Your lung capacity actually increases during pregnancy, but you may still feel winded more easily.
As the baby drops lower into your pelvis, pressure on your bladder increases. Frequent urination returns (if it ever left), and you may leak urine when you laugh, cough, sneeze, or lift something. This is normal and usually resolves after delivery.
Swelling in your ankles, hands, and face is another hallmark of the third trimester. Propping your legs up, wearing compression socks, and avoiding long stretches of standing or sitting with crossed legs can ease the discomfort. Mild swelling is expected, but sudden or severe swelling, especially in your face or hands, can signal a complication worth reporting to your provider.
Other common experiences include back pain, trouble sleeping, heartburn, and Braxton Hicks contractions, which are irregular practice contractions that come and go without a pattern.
Nutrition in the Final Months
Your calorie needs are modestly higher during the third trimester. Most people with a normal pre-pregnancy weight need about 2,400 calories per day, roughly 300 more than usual. The focus should be on nutrient-dense foods rather than simply eating more. Iron, calcium, and protein are especially important as your baby builds bone density and blood volume in these final weeks.
Prenatal Visits and Screenings
Expect your appointment schedule to pick up. During the third trimester, prenatal visits typically happen every two to four weeks, then shift to every one to two weeks starting at 36 weeks. These visits usually include blood pressure checks, urine tests, measuring your belly, and listening to the baby’s heartbeat.
One standard screening during this period is a test for group B strep, a common bacterium that’s harmless to you but can cause serious infection in a newborn during delivery. The test involves a simple swab of the lower vagina and anal area. If you test positive, you’ll receive antibiotics during labor to protect the baby.
Your provider may also ask you to track fetal movement at home, sometimes called “kick counts.” There are different methods, but the basic idea is paying attention to how often your baby moves during a set period each day. If movement feels noticeably reduced compared to your baby’s normal pattern, it’s worth calling your provider.
Warning Signs to Watch For
Most third-trimester discomfort is normal, but a few symptoms point to conditions that need prompt attention. Preeclampsia is one of the most serious. It involves high blood pressure (140/90 or above) combined with protein in the urine, and it develops after 20 weeks of pregnancy. Severe cases can cause intense headaches, blurred vision or seeing spots, upper abdominal pain, and nausea or vomiting. Sudden swelling of the face and hands can also be a sign. Preeclampsia can escalate quickly, so these symptoms warrant an immediate call to your provider.
Other reasons to reach out include vaginal bleeding, fluid leaking from the vagina (which could indicate your water breaking early), persistent contractions before 37 weeks, or a significant decrease in fetal movement.
How to Tell Real Labor From False Alarms
Distinguishing true labor from Braxton Hicks contractions is one of the biggest questions in the third trimester. True labor contractions follow a pattern: they get progressively closer together, last about 60 to 90 seconds each, grow stronger over time, and don’t stop when you change position. By the time active labor is underway, contractions are typically two to five minutes apart and intense enough that talking through them becomes difficult.
Before contractions begin, the cervix starts softening, shortening, and thinning in a process called effacement. It starts out about 3.5 to 4 centimeters long and needs to thin completely before vaginal delivery. You won’t feel this happening, but your provider will check for it at late-pregnancy appointments. Some people also notice a “bloody show,” a small amount of mucus tinged with blood, or a burst of energy in the days before labor begins.