At 30 weeks your baby is around 39.5 cm and 1.35 kg — roughly a large cabbage — with pupils that now react to light and movements that have shifted from gentle rolls to real jabs of elbows and knees as space runs short.
The short answer: the pupils can now constrict and dilate in response to light, a genuine reflex, and bone marrow has fully taken over red blood cell production. Movements feel stronger and sharper now that there is less room to move freely. For you, weight gain is often at its fastest pace, amniotic fluid has reached its peak volume, rib and back pain are common, and the first drops of colostrum may appear.
Your baby this week
Space has become tight enough that baby can no longer swim freely the way they could weeks ago — movements now feel like distinct jabs of elbows and knees rather than the fluid rolling of the second trimester. The pupils can now constrict when light is bright and dilate in the dark, a real, functioning reflex even though very little light actually reaches inside the uterus.
Bone marrow has fully taken over red blood cell production, a job the liver handled earlier in pregnancy — a real handover of function, not just growth. Weight is now around 1.35 kg, and the pace of gain from here is often the fastest of the whole pregnancy, both for baby and for you.
Your body this week
Your own weight gain may be at its fastest pace right now, which is expected rather than a sign anything is off track. Amniotic fluid volume has reached its maximum for the pregnancy and will gradually decrease from here to make more room for baby to grow — a normal part of the trajectory, not something that needs tracking.
Rib and back pain are common as the uterus presses higher against the ribcage; sitting upright rather than slumped and a supportive pregnancy belt both help. The first drops of colostrum may also appear from the breasts now — your body's early preparation for baby's first feeding, and entirely normal whether it shows up now, later, or not at all before birth.
Tests and appointments
Nothing is typically scheduled precisely at 30 weeks for most care pathways, though appointments continue becoming more frequent as the third trimester progresses.
✅ Worth doing this week
- Watch your posture — sitting upright eases rib pressure more than it seems like it would
- Consider a pregnancy support belt if back or rib pain is frequent
- Start the hospital bag list now — there is time to add to it gradually rather than rush later
- Don't worry about colostrum leaking or not — either is entirely normal at this stage
- Keep tracking baby's movement pattern daily as the third trimester continues
When to call your doctor
Call the same day if: rib or abdominal pain is severe or one-sided, or comes with shortness of breath, chest pain, or a headache with visual disturbance. Also call for reduced movement, bleeding, sudden swelling of the face or hands, regular tightenings before 37 weeks, or a temperature above 38°C.
FAQ — 30 weeks pregnant
Is it normal to leak colostrum at 30 weeks?
Yes — the first drops of colostrum, the antibody-rich fluid that comes before true milk, can appear from the breasts anywhere from the second trimester through birth, and 30 weeks is a common time to first notice it. Not everyone leaks any before birth, and that has no bearing on milk supply later, so its presence or absence at this stage is not a signal worth worrying about either way.
Why does rib pain start around 30 weeks?
The uterus has grown enough to press up against the lower ribs, and this pressure tends to increase as the weeks go on. Sitting up straight rather than slumped, propping yourself with pillows, and gently stretching the arm on the affected side can ease it. Pain that is severe, one-sided, or comes with shortness of breath, chest pain, or a headache needs same-day assessment rather than assumed to be routine rib pressure.
Why is amniotic fluid volume at its peak around 30 weeks?
Around this point amniotic fluid volume reaches its highest level of the pregnancy and then gradually decreases from here, partly because baby simply takes up more of the available space as they grow. This is a normal, expected part of the trajectory rather than something to track or worry about.
How big is the baby at 30 weeks?
Around 39.5 cm and 1.35 kg — roughly a large cabbage. The pupils can now constrict in bright light and dilate in the dark, a real reflex even though there is little light to detect inside the uterus, and bone marrow has fully taken over red blood cell production from the liver.
Week 30 at a glance
At 30 weeks your baby is around 39.5 cm and 1.35 kg, with pupils that react to light and movements that have shifted into real jabs as space tightens. For you, weight gain is often at its fastest pace, amniotic fluid has reached its peak, rib and back pain are common, and the first drops of colostrum may appear — all normal parts of the third trimester rather than signs anything is off.
Inside Baby Novum: the hospital bag checklist covers what you, your partner, and baby actually need, so ten weeks out is exactly the right time to start chipping away at it.