The third trimester spans weeks 28 through 40 and brings the most rapid changes of your entire pregnancy. Your baby will roughly triple in weight during these final months, and your body will shift dramatically to accommodate that growth. Here’s what’s actually happening, what feels normal, and what deserves attention.
How Your Baby Grows
At week 28, your baby measures about 10 inches from head to tailbone and weighs around 2¼ pounds. By week 32, they’re closer to 11 inches and 3¾ pounds. By week 40, they’ll reach roughly 14 inches crown to rump and about 7½ pounds. Most of that weight gain is fat, which helps regulate body temperature after birth.
The lungs are one of the last organs to fully mature. A key substance that keeps the air sacs open (preventing them from collapsing with each breath) typically appears in adequate amounts around week 35, and clinical lung maturity is generally present after 36 weeks. This is one reason every additional week in the womb matters for babies born near the boundary of “early term.” The brain also undergoes rapid development throughout the third trimester, building the neural connections that support breathing, feeding, and temperature regulation outside the womb.
Physical Changes You’ll Notice
Shortness of breath is one of the most common complaints. As the baby grows, the uterus pushes up against your rib cage, reducing the space your lungs have to expand. At the same time, your lungs actually increase their total air capacity during pregnancy, so you breathe a bit faster and get winded more easily. Lying on your back can make this worse. Many people find relief by propping themselves up with pillows or sleeping on their side.
Swelling in the feet, ankles, and hands tends to increase as the weeks go on, especially by the end of the day. Elevating your legs and staying moderately active can help. Heartburn, back pain, and the frequent need to pee also intensify as the baby takes up more room and presses on your bladder and digestive organs.
You’ll likely start noticing Braxton Hicks contractions if you haven’t already. These feel like a tightening across your belly that comes and goes without a regular pattern. They’re more common in the afternoon or evening, after exercise, or after sex, and they become more frequent as your due date approaches. They’re not a sign of labor on their own, but knowing how they feel will help you recognize the real thing later.
Sleep Gets Harder
Between the belly size, the bathroom trips, and the general discomfort, quality sleep becomes elusive. Side sleeping is the most practical position in late pregnancy. Researchers have found that back sleeping may compress major blood vessels (the aorta and the vein that returns blood from the lower body to the heart), potentially reducing blood flow to the placenta. A pillow between your knees and another supporting your belly can make side sleeping more comfortable. If you wake up on your back, simply roll over. There’s no need to stress about every position shift during the night.
Prenatal Visits Pick Up
During the third trimester, you’ll typically have appointments every two to four weeks. Starting at 36 weeks, that increases to every one to two weeks until delivery. These visits check your blood pressure, measure your belly, and monitor the baby’s heart rate and position.
Two specific things happen during this stretch. First, you’ll be tested for group B strep, a common bacterium that’s harmless to you but can pose risks to the baby during delivery. If you test positive, you’ll receive antibiotics during labor. Second, the CDC recommends getting the Tdap vaccine between weeks 27 and 36, ideally on the earlier end. This protects your newborn against whooping cough by passing antibodies through the placenta before birth. The recommendation applies to every pregnancy, even if your pregnancies are close together.
Tracking Your Baby’s Movement
Kick counts become an important daily habit in the third trimester. The standard method is to pick a time when your baby is usually active, sit or lie down, and count how long it takes to feel 10 movements. Kicks, rolls, flutters, and swishes all count. You’re looking for 10 movements within two hours. Most people reach that number much faster.
The specific number matters less than the pattern. You’ll get to know your baby’s routine. If movements suddenly change, slow down dramatically, or stop, that’s worth a call to your provider. Don’t wait until the next scheduled visit.
Baby’s Position Before Birth
By the mid-30s in weeks, your provider will start paying attention to whether the baby is head-down. Most babies settle into this position on their own, but some remain breech (bottom or feet first) or lie sideways. If your baby is still breech after 36 weeks, your provider may offer a procedure called external cephalic version, where they use their hands on your abdomen to gently guide the baby into a head-down position. If the baby can’t be turned, you’ll discuss delivery options, which often means a planned cesarean.
Telling Real Labor From Practice Contractions
One of the biggest third trimester anxieties is figuring out whether contractions are the real deal. The key differences are pattern, persistence, and progression. True labor contractions come at regular intervals and get closer together over time. Each one lasts about 60 to 90 seconds. They continue no matter what you’re doing, whether you walk around, lie down, or change positions.
Braxton Hicks contractions have no predictable pattern. They don’t get steadily closer together, and they often stop if you rest, walk, or drink water. A simple test: time your contractions while resting and hydrating. If they go away, it’s not labor yet.
Warning Signs That Need Attention
Preeclampsia is the complication most specific to the third trimester. It’s defined by blood pressure at or above 140/90 along with protein in the urine, and it can develop even if your blood pressure has been normal throughout pregnancy. The symptoms to watch for include a severe headache that won’t go away, visual changes like blurred vision or seeing spots, pain in the upper abdomen (especially on the right side), and sudden swelling in the hands or face. Nausea and vomiting that appear for the first time after the first trimester can also be a sign.
Other reasons to contact your provider promptly: vaginal bleeding, fluid leaking from the vagina (which could mean your water broke), a decrease in fetal movement, or contractions coming regularly before 37 weeks.
Nutrition in the Final Stretch
Your calorie needs increase by about 300 per day during pregnancy, bringing the total to roughly 2,400 calories daily in the third trimester for most people at a normal pre-pregnancy weight. The emphasis isn’t just on eating more but on eating well. Iron supports the increased blood volume your body is maintaining. Calcium and vitamin D support your baby’s rapidly hardening bones. Protein helps build muscle and tissue during this period of fastest growth. Fiber and plenty of water help with the constipation that tends to worsen as the uterus crowds the digestive tract.
Small, frequent meals often feel better than large ones, especially as heartburn and a compressed stomach make big portions uncomfortable.