The third trimester of pregnancy begins at week 28 (the start of month seven) and lasts through week 40, or delivery. This final stretch covers roughly 13 weeks and is when the baby gains most of its birth weight, the lungs mature enough to breathe air, and your body begins preparing for labor.
When the Third Trimester Starts
Pregnancy is divided into three trimesters of roughly 13 weeks each. The first trimester runs from week 1 through week 12, the second from week 13 through week 27, and the third from week 28 through week 40. If you’re counting by months, the third trimester spans months seven through nine. A pregnancy that reaches 40 weeks is considered full term, though delivery anywhere from 39 to 40 weeks and 6 days falls into that category. Babies born before 37 weeks are considered preterm.
What’s Happening With the Baby
The third trimester is when your baby transforms from small and lean to the plump newborn you’ll hold at delivery. Between weeks 29 and 32, the skin begins to look smoother as fat accumulates underneath it. Starting around week 35, weight gain accelerates to roughly 8 to 12 ounces per week. Most babies weigh somewhere between 6 and 9 pounds at birth, and a large portion of that weight is packed on in these final weeks.
Lung development is one of the most critical milestones of this trimester. The lungs form the tiny air tubes that will carry oxygen in and out after birth, but they aren’t fully mature until close to 39 weeks. This is a key reason doctors avoid elective early deliveries when possible.
By weeks 29 to 32, the baby’s eyes can sense changes in light. The brain is growing rapidly, building the connections that will support breathing, temperature regulation, and feeding outside the womb. The baby also settles into a more predictable sleep-wake cycle, which is why you may notice movement patterns at certain times of day.
Tracking Fetal Movement
Starting around week 28, many providers recommend doing daily kick counts. The goal is to feel 10 movements, including kicks, flutters, swishes, or rolls, within two hours. Most babies hit that number well within an hour. Pick a time when your baby is usually active, sit or lie down, and count. If two hours pass without 10 movements, contact your provider. A sudden change in your baby’s usual pattern is worth a call even if the numbers technically look fine.
Physical Changes You’ll Notice
As the baby grows, so does the pressure on your body. The uterus pushes up against your diaphragm, which can make deep breaths feel harder. Later in the trimester, when the baby drops lower into your pelvis, breathing may get easier, but bladder pressure increases and you’ll likely need to urinate more often.
Braxton Hicks contractions become more noticeable in the third trimester. These are mild tightenings across the front of your belly that come and go without a regular pattern. They tend to show up in the afternoon or evening, after physical activity, or after sex, and they become more frequent as your due date approaches. They’re not a sign of labor on their own.
Prenatal Visits and Tests
Appointments become more frequent in the third trimester, typically every two weeks from 28 to 36 weeks, then weekly until delivery. Your blood pressure is checked at every visit, since rising blood pressure in late pregnancy can signal complications like preeclampsia.
Between weeks 36 and 37, your provider will do a Group B strep (GBS) test, a simple swab to check for a type of bacteria that’s harmless to you but could be passed to the baby during delivery. If the test is positive, you’ll receive antibiotics during labor to protect the baby. The CDC also recommends getting the Tdap vaccine between weeks 27 and 36, ideally on the earlier end, so your body has time to produce antibodies against whooping cough and pass them to the baby before birth.
Nutrition in the Final Weeks
Calorie needs increase modestly in the third trimester. Most normal-weight pregnant women need about 2,400 calories per day during this stage, roughly 300 more per day than before pregnancy. The extra energy supports the baby’s rapid weight gain, brain development, and fat storage. Protein, iron, and calcium matter most in these final weeks. If you’re already eating a balanced diet, you don’t need to overhaul anything, just add a couple of nutrient-dense snacks.
The Baby’s Position
Sometime in the third trimester, most babies rotate into a head-down position. When the baby’s head drops into the pelvis, it’s called engagement. Providers measure how deep the head sits using a scale from negative 5 to positive 5 (or negative 3 to positive 3, depending on the system). A station of zero means the head is fully engaged in the pelvis. First-time mothers often experience engagement a few weeks before labor starts, while those who’ve given birth before may not engage until labor is underway.
Telling Real Labor From False Labor
One of the trickiest parts of late pregnancy is figuring out whether contractions mean labor has started. Prodromal labor, sometimes called false labor, can feel surprisingly real. Contractions may come every five minutes and last up to 60 seconds each, but the defining feature is that they never get stronger or closer together. Pain or cramping stays at the same level, and the cervix doesn’t dilate.
True labor contractions follow a different pattern. They come less than five minutes apart, last longer than one minute each, and this continues for over an hour. They steadily increase in intensity and don’t ease up when you change position or rest. The only definitive way to confirm active labor is a cervical check, so if you’re unsure, calling your provider is always reasonable.