Pregnancy › Week by Week › Week 31
At 31 weeks your baby is about the size of a coconut, with all five senses up and running and a brain that is forming new connections at a remarkable pace.
Size
A coconut
head to heel
Length
16.2 in
about 41.1 cm
Weight
3.3 lb
about 1500 g
Your baby at 31 weeks
All five senses are working, the brain is wiring up fast, and a stretch of quick weight gain is underway.
Your baby is not just growing bigger now, but growing more aware. The brain and senses are developing quickly, and your baby is taking in far more of the world inside the womb than you might expect.
Senses. All five senses are now working. Your baby can hear your voice and the muffled sounds of your body and the world outside, can taste the flavors that pass into the amniotic fluid from what you eat, and can feel touch. The eyes can sense light and dark, and your baby will often turn toward a bright light shone on your belly, which is one of the first signs of the vision that keeps developing after birth.
Brain. The brain is making connections at an astonishing rate, wiring together the networks it will use to process everything it senses. Your baby can take in information, and can process signals from all those working senses, which is part of why sleep and wake cycles are becoming more defined.
Weight gain. A phase of rapid weight gain begins around now. Your baby is laying down fat under the skin, smoothing out the wrinkles and building the reserves that help with warmth and energy after birth. Much of your baby’s remaining growth happens in these final weeks.
How big is your baby at 31 weeks?
About 16.2 inches (41.1 cm) head to heel and around 3.3 pounds (1500 g).
Your baby is measured head to heel now that the legs have stretched out. This is the start of a real growth spurt, with weight climbing quickly over the coming weeks as fat builds up, so those strong movements you feel are a busy, growing baby with less and less room to move.
Your body at 31 weeks
Braxton Hicks get more noticeable, colostrum may start to leak, and backache and bathroom trips are common company.
The practice contractions called Braxton Hicks often become easier to notice this week, a painless tightening across your bump that lasts a short while and eases off. They are normal and are not labor. You may also spot your breasts leaking small amounts of a thick, yellowish fluid called colostrum, the first milk your body makes. It is a normal sign your body is getting ready to feed your baby, and a nursing pad tucked into your bra handles any leaks.
The extra weight out front changes your posture and pulls on your lower back, so backache is common now. Gentle movement, good support when you sit, and taking care with how you lift all help. And with your baby pressing low again, you are probably making more trips to the bathroom, and may notice a little leaking when you laugh or sneeze, which is normal as everything shifts to make room.
What is normal, and when to call your provider
Practice contractions and third trimester aches are normal, but call your doctor or midwife the same day, or go in, if you have any of these:
- A clear drop in your baby’s movement, or a pattern that feels off to you, movement counts matter now, so call the same day rather than waiting
- Any vaginal bleeding
- A severe headache, changes in your vision, or sudden swelling of your face or hands, which can be signs of preeclampsia
- A gush or a steady leak of fluid, which can mean your waters have broken
- Regular painful contractions before 37 weeks, which can be a sign of preterm labor
- A fever over 100.4°F (38°C)
Your week 31 checklist
- Keep up your kick counting, watch your baby’s movement pattern, and call if it changes
- Tuck a nursing pad in if colostrum starts to leak, and keep taking your prenatal vitamin
- Mind your posture and try gentle stretches to ease backache
- Think about the calm end of the nursery, a white noise machine can help newborn sleep
- Get the safe sleep space sorted, a bassinet keeps baby close for the first months
Appointments and tests around 31 weeks
Every two week visits continue, with the same growth and blood pressure checks each time.
Your prenatal visits are most likely every two weeks now. Each one covers your blood pressure, weight, and urine, a fundal height measurement to check your baby is growing on track, and a listen to the heartbeat. Your provider will ask about your baby’s movements and about any swelling, headaches, or vision changes, all part of watching for preeclampsia. If your fundal height, your history, or your baby’s position raises a question, your provider may order an ultrasound to check growth and how your baby is lying. This is a good time to start your birth plan and sign up for any classes you want before things get busier.
A few things worth having on hand now
A note for your partner
Your baby can hear now, and knows your voice too. Reading a few lines aloud, playing a song, or just chatting to the bump is a real way to start bonding before birth, and many babies clearly respond with a kick. On the practical side, backache is settling in, so a few minutes rubbing the lower back at the end of the day, or taking over the tasks that mean bending and lifting, goes a long way.
You are not alone this week
Thirty one weeks can feel like a lot of body all at once, the aches, the leaks, the endless bathroom trips. All of it is your body doing exactly what it should to grow and feed your baby. Let yourself slow down, take the joy where you find it, and know that the strange and uncomfortable bits are shared by just about everyone at this stage.
31 weeks pregnant, common questions
Can my baby really hear me at 31 weeks?
Yes. Your baby’s hearing is working now and picks up your voice, your heartbeat, and sounds from outside your body, though everything is muffled by fluid and tissue. Talking, reading, and playing music are lovely ways to connect, and many babies grow calmer at a familiar voice or song after birth.
Why am I leaking a yellowish fluid from my breasts?
That is colostrum, the rich first milk your body makes to feed your baby in the earliest days. Leaking it in the third trimester is a normal sign your body is preparing. A nursing pad in your bra handles it. Not leaking is also normal and does not say anything about how nursing will go later.
How do I tell Braxton Hicks from real contractions?
Braxton Hicks are usually irregular, do not get stronger or closer together, and ease if you change position or drink some water. Real labor contractions grow more regular, stronger, and closer over time. If tightenings become regular and painful before 37 weeks, or come with the warning signs above, call your provider.
What can I do about the back pain?
Try to stand and sit tall, sleep on your side with a pillow between your knees, and avoid standing for long stretches. Gentle movement, prenatal stretches or yoga, a warm compress, and comfortable supportive shoes all help. If back pain is severe, comes in a rhythmic wave, or is paired with any warning sign, call your provider.
Sources
- American College of Obstetricians and Gynecologists (ACOG), third trimester fetal development and care guidance.
- Mayo Clinic, Fetal development: the 3rd trimester.
- MedlinePlus, National Library of Medicine (NIH), Fetal development and the senses.
Medical disclaimer: This page is for information and education only and is not a substitute for professional medical advice. Every pregnancy is different. Always follow the guidance of your doctor, midwife, or qualified provider, and contact them with any concerns.