Week 31 is dominated by one thing: brain connections. Your baby's neural network is growing at a pace that will never be matched again in their lifetime. Billions of neurons are firing and wiring, forming the synaptic connections that underpin every thought, emotion, and skill your child will ever have. It's an invisible, extraordinary process happening right now, inside you.
Your baby also weighs 1.5 kilograms this week — half the weight of a typical newborn.
Track your progress with our Due Date Calculator.
Your Baby This Week
Size: Coconut — about 41.1 cm (head to toe)
Weight: About 1.5 kilograms
Here's what's happening this week:
- Brain connections are forming at extraordinary speed. The brain is not only producing neurons but also building the synapses that connect them. This synaptogenesis is particularly rapid in the third trimester, laying down the neural architecture for sensory processing, emotion, and learning. Research in developmental neuroscience shows that stimulation — including your voice, music, and gentle touch — actively shapes this wiring.
- The digestive system is nearly mature. The gut is capable of processing breast milk, and the digestive enzymes needed for newborn feeding are in place. The system will complete its final preparation in the remaining weeks.
- The lungs are more functional. Surfactant production is now sufficient that a baby born at 31 weeks would have a very high survival rate in a NICU, with a good prognosis for normal development. The lungs are not fully mature, but they are functional.
- The baby is practicing breathing movements. Rhythmic chest movements that pull amniotic fluid in and out of the lungs are strengthening the respiratory muscles for the work of breathing at birth.
- All five senses are active. Your baby can see (light vs. dark), hear (voices, music, internal body sounds), taste (amniotic fluid flavors), feel (touch, movement), and smell (though the olfactory system completes development after birth).
- Sleep is still the dominant state. Your baby sleeps around 85-95% of the time, alternating between REM and non-REM cycles. They're active during their wake windows, which you'll notice as bursts of movement.
Your Body This Week
Nine weeks to go. Here's what's common at 31 weeks:
- More frequent urination. The baby's head may be pressing on the bladder now, making bathroom trips more frequent and sometimes urgent. Reducing evening fluid intake slightly can help with nighttime trips, but don't restrict overall hydration.
- Swollen hands and feet. Normal, moderate edema is expected. Your rings may not fit. Removing jewelry proactively — before it gets stuck — is sensible now.
- Colostrum leaking. Your breasts may begin producing and leaking the early milk (colostrum). This is completely normal and is not a sign of early labor. Nursing pads can help with any leaking.
- Pelvic pressure. The baby's weight is pressing downward. This can cause a persistent heavy sensation in the pelvis, pressure on the bladder, and sometimes sharp pains when the baby presses on nerves.
- Heartburn. With the stomach compressed, heartburn and reflux often peak in the third trimester. Eating small, frequent meals, avoiding lying down after eating, and elevating the head of the bed slightly are the most effective measures. Your provider can also recommend safe antacids.
- Braxton Hicks contractions. These should still be irregular and painless. Any pattern of regularity — even if mild — warrants a call to your provider.
Tips for Week 31
1. Play music or read aloud. Your baby can hear you clearly, and exposure to language and music in utero has been associated with newborn recognition and responsiveness to familiar sounds after birth. This isn't homework — make it enjoyable.
2. Finalize your birth plan. You have about nine weeks left, and your provider should have a copy of your preferences before your 36-week appointment. Cover your key priorities: your approach to pain management, your thoughts on interventions, who you want present, and your plans if a cesarean becomes necessary.
3. Research your feeding options. Whether you plan to breastfeed, formula-feed, or use a combination, understanding the basics before birth is valuable. If breastfeeding, a prenatal consultation with a lactation consultant can address questions and concerns early.
4. Set up the nursery — or at least the essentials. A safe sleep space (firm, flat, bare mattress), a place to change diapers, and a few clothing basics are what you actually need. Everything else can wait.
5. Check your iron levels. If your provider hasn't checked your blood count recently, ask at your next appointment. Iron-deficiency anemia peaks in the third trimester and causes fatigue that makes an already demanding time harder. It's easily treated.
When to Call Your Doctor
- Reduced fetal movement. Less than 10 movements in 2 hours at a time your baby is typically active — call your provider. Don't wait.
- Signs of preeclampsia: severe headache, visual changes, sudden significant swelling in face or hands, pain under the right rib cage. These need same-day evaluation — this condition can escalate quickly.
- Regular contractions before 37 weeks. More than 4-6 per hour, especially if accompanied by pelvic pressure, low back pain, or changes in discharge.
- Water breaking or significant fluid leakage. Call immediately, regardless of how many weeks pregnant you are.
- Sudden severe abdominal pain at any intensity — rule out placental abruption.
Related Tools & Articles
- Due Date Calculator — Nine weeks to go
- Contraction Timer — Be ready
- Hospital Bag Checklist — Have it packed and by the door
- Pregnancy Week-by-Week Overview — Full timeline
- Milestone Tracker — Track your baby's development