At 31 weeks pregnant, your baby is about the size of a coconut, roughly 16 inches long and weighing around 3.3 pounds. This is a period of rapid brain development and steady weight gain for your baby, while your body manages increasing pressure from a growing uterus. Here’s what’s happening for both of you this week.
Your Baby’s Brain Is Processing More
Week 31 marks a significant leap in brain activity. Your baby can now process more information and respond to stimuli from the outside world, including light, sound, and touch. The five senses are all functioning to some degree at this point. You may notice your baby reacting to loud noises or shifting position when a bright light shines on your belly.
Sleep-wake cycles are becoming more defined, and you can probably identify distinct patterns in when your baby is active versus quiet. Many parents notice a predictable rhythm: stretches of vigorous movement followed by longer periods of stillness. These cycles reflect a maturing nervous system that’s organizing itself for life outside the womb.
What Your Body Is Doing
The third trimester brings a collection of symptoms that are all connected to one thing: your baby is getting bigger, and your organs are running out of room.
Shortness of breath is common as your uterus pushes up against your rib cage. You may get winded doing things that felt easy a few weeks ago, like climbing stairs or talking while walking. Lying on your back can make it worse, so resting on your side helps. Good posture also gives your lungs a bit more space to expand.
Heartburn tends to intensify around this time because your digestive system is compressed and hormones relax the valve between your stomach and esophagus. Eating smaller, more frequent meals helps. Avoid lying down right after eating, and steer clear of fried foods, citrus, chocolate, spicy dishes, and carbonated drinks.
Pelvic pressure and frequent urination increase as the baby settles deeper into your pelvis. The pressure on your bladder means more trips to the bathroom, and you may leak urine when you laugh, cough, sneeze, or bend over. This is normal and almost universal in late pregnancy. Pelvic floor exercises can reduce the severity.
You may also notice colostrum leaking from your breasts. Colostrum is the thick, yellowish first milk your body starts producing as early as the second trimester, though leaking typically begins sometime in the third trimester. Not everyone experiences this, but if you do, it’s a sign your body is preparing to feed your baby. Colostrum is packed with antibodies that protect your newborn’s gut and help build their immune system. It will be ready the moment your baby starts nursing after birth.
Weight Gain at This Stage
During the third trimester, the general guideline is to gain about 1 pound per week until delivery. If you started pregnancy at a higher weight, the recommendation drops to about half a pound per week. These are averages, not rigid targets. Some weeks you’ll gain more, others less. What matters is the overall trend, not any single weigh-in. Much of the weight at this stage goes toward your baby’s growth, increased blood volume, amniotic fluid, and the placenta.
Tracking Your Baby’s Movement
By week 31, your provider may suggest doing regular kick counts if you haven’t started already. There are two common approaches: count the number of kicks you feel in one hour, or time how long it takes to feel 10 movements. Lying on your left side maximizes blood flow to the uterus and makes it easier to notice movement. If you don’t reach 10 movements in an hour, try extending the count to two hours before calling your provider.
The goal isn’t to hit a specific number every single time. It’s to learn your baby’s normal pattern so you can recognize a meaningful change. A baby who is usually active after dinner but suddenly goes quiet for an extended stretch is worth paying attention to. Consistent daily tracking gives you a reliable baseline.
Prenatal Visits and Vaccines
At this point in pregnancy, you’re typically seeing your provider every two to four weeks. These visits usually include blood pressure checks, urine tests, belly measurements, and listening to the baby’s heartbeat. Starting at 36 weeks, visits increase to every one to two weeks.
If you haven’t already received the Tdap vaccine (which protects against whooping cough), the recommended window is between 27 and 36 weeks. Getting it during this period allows your body to produce antibodies that cross the placenta and give your baby some protection during the first few months of life, before they can be vaccinated themselves.
Signs of Preterm Labor
At 31 weeks, your baby still has important growing to do, so it’s worth knowing the warning signs of preterm labor. The key signals include contractions that come every 10 minutes or more frequently, a change in vaginal discharge (especially fluid leaking or any bleeding), and persistent lower back pain or pelvic pressure that doesn’t go away with rest. Six or more contractions in one hour is not normal at this stage, even if they feel mild.
Braxton Hicks contractions are common in the third trimester and feel like a tightening across your belly that comes and goes without a regular pattern. The difference is that true preterm labor contractions have a rhythm, get closer together, and don’t stop when you change position or drink water. If you’re unsure which you’re experiencing, timing the contractions for an hour gives you useful information to share with your provider.