At 31 weeks your baby is about 40.5 cm and 1.5 kg — roughly a coconut — with a brain forming billions of new neural connections and lungs and digestive system that are nearly ready for independent function.
The short answer: the brain is developing at a striking pace, and baby now genuinely processes input from all five senses rather than responding only by reflex. The lungs and digestive system are nearly ready for life outside the uterus, though a little more fat is still needed. For you, the uterus has risen high enough to make breathlessness a common companion, and breasts often feel heavier with colostrum starting to leak.
Your baby this week
The brain is developing at an incredible pace this week, with billions of nerve cells forming new connections every day. Baby can now genuinely process input from all five senses — sight, hearing, taste, smell, and touch — rather than responding only by reflex as in earlier weeks, though sight remains the least developed since there is very little to actually see inside the uterus.
Despite the increasingly tight space, baby is actively turning their head from side to side. The lungs and digestive system are nearly ready for independent function outside the womb, though a little more subcutaneous fat still needs to build up before that readiness is complete — one reason the final weeks of pregnancy matter even once a baby would technically be viable if born early.
Your body this week
The uterus has risen about 11 cm above the navel by now, which leaves the lungs less room to expand fully with each breath — a mechanical limit rather than a sign of anything wrong, and one that typically eases once baby's head engages lower into the pelvis later on. Breathing exercises help manage it now and double as a genuinely useful tool for labour later, so practising them is not wasted effort either way.
Breasts often feel noticeably heavier around now, and colostrum leaking from the nipples is common — the first antibody-rich food baby will get after birth, and breast pads can help manage it comfortably if it happens.
Tests and appointments
Most care pathways have nothing scheduled precisely at 31 weeks, though appointments continue becoming more frequent through the rest of the third trimester.
✅ Worth doing this week
- Keep practising deep, slow breathing — it helps now and becomes a real labour tool later
- Check the hospital bag for your documents and essentials, even if it is not fully packed yet
- Try breast pads if colostrum leaking is noticeable or uncomfortable
- Move between sitting and standing regularly to ease breathlessness during the day
- Keep tracking baby's movement pattern daily as space continues to tighten
When to call your doctor
Call the same day if: breathlessness is sudden, severe, or comes with chest pain or a rapid heartbeat — this needs assessment rather than being assumed routine. Also call for reduced movement, bleeding, a severe headache with visual disturbance, sudden swelling of the face or hands, or a temperature above 38°C.
FAQ — 31 weeks pregnant
What does it mean that baby processes all five senses at 31 weeks?
The neural pathways for sight, hearing, taste, smell, and touch are now developed enough that baby genuinely registers and responds to input through each of them, not just reflexively as in earlier weeks. Sight is the least developed of the five, since there is very little to see inside the uterus, while hearing and touch are the most functionally mature at this stage.
Why does breathlessness get worse at 31 weeks?
The uterus has risen about 11 cm above the navel by now, leaving the lungs less room to expand fully with each breath — a mechanical limit rather than a sign of a breathing problem. It typically eases once the baby's head engages lower into the pelvis later in the third trimester. Breathlessness that is sudden, severe, or comes with chest pain or a rapid heartbeat needs same-day assessment rather than assumed to be routine.
Is heavier, leaking colostrum from the breasts normal at 31 weeks?
Yes — breasts commonly feel heavier and fuller from around now, and colostrum leaking from the nipples is common and not a sign of anything unusual. It is the first antibody-rich food baby will receive after birth, and breast pads can help manage any leaking comfortably in the meantime.
How big is the baby at 31 weeks?
About 40.5 cm and 1.5 kg — roughly a coconut. The lungs and digestive system are nearly ready for independent function, though a little more subcutaneous fat is still needed, and baby is actively turning their head from side to side despite the increasingly tight space.
Week 31 at a glance
At 31 weeks your baby is about 40.5 cm and 1.5 kg, with a brain forming billions of new connections and genuine processing across all five senses, while the lungs and digestive system near readiness for life outside the womb. For you, the uterus sitting 11 cm above the navel makes breathlessness common, and heavier breasts with leaking colostrum are a normal part of the third trimester.
Inside Baby Novum: breathing techniques that ease breathlessness now double as real tools for labour later, so the practice you build this week keeps paying off.