Week 23 is a significant week for your baby's lungs. The cells lining the air sacs are beginning to produce surfactant — a substance that will be essential for breathing at birth. Without surfactant, the tiny air sacs in the lungs collapse on themselves every time the baby exhales. Its gradual development over the coming weeks is one of the main factors that determines survival in cases of very preterm birth.
Your baby is also becoming more aware of the outside world. Sound, light, and your voice are all registering in a more meaningful way now.
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Key Takeaways
- Your baby has reached 500 grams — the half-kilogram mark — and measures about 28.9 cm
- Surfactant production begins this week: the lung substance critical for breathing at birth
- Your baby can now distinguish your voice from other voices and will recognize it at birth
- Swollen feet and ankles are very common by week 23 — elevation and daily walks help
- The gestational diabetes glucose screening is typically scheduled between weeks 24 and 28
Your Baby This Week
Size: Grapefruit — about 28.9 cm (head to toe)
Weight: About 500 grams
Your baby has reached the half-kilogram mark. Here's what's developing this week:
- Surfactant production begins. Type II pneumocytes — specialized lung cells — are starting to produce surfactant, a soap-like substance that reduces surface tension in the alveoli (air sacs). This production will increase steadily through the third trimester. Babies born very early often need synthetic surfactant delivered via a breathing tube to survive.
- The vestibular system is functional. The inner ear structures that detect movement and balance are now developed. Your baby can sense when you are moving, sitting, or lying down. This is why babies often become more active when you stop moving — your stillness is no longer rocking them.
- The skin is turning less transparent. Fat hasn't filled in yet, but the skin is becoming less see-through. It still has a reddish appearance due to developing blood vessels visible beneath.
- Hearing is sharp. Your baby can now hear your heartbeat, digestive sounds, your voice, and sounds from outside your body. Research suggests babies can distinguish their mother's voice from other voices by this point in pregnancy.
- Bone density is increasing. The skeleton continues to calcify, requiring a steady supply of calcium from your diet.
- Fingernails are growing. Those tiny nails are extending toward the fingertips.
Your Body This Week
- Linea nigra. The dark line running from your navel to your pubic bone — and sometimes extending up to your sternum — is common and caused by increased melanin production. It fades after birth.
- Swollen feet and ankles. Edema in the lower legs is very common in the second trimester, especially by the end of the day. It's caused by increased blood volume and the uterus pressing on veins that return blood from the legs. Elevating your feet and staying active helps.
- Braxton Hicks contractions may be more noticeable. They're harmless practice contractions and become more frequent as pregnancy progresses.
- Trouble sleeping. Between a growing belly, leg cramps, heartburn, and increased bathroom trips, many people find sleep disrupted from mid-pregnancy onward. A good pregnancy pillow is one of the most effective investments you can make right now.
- Itchy skin. As the belly skin stretches, itchiness is common. Moisturizing regularly helps. Severe, widespread itching — especially on the palms and soles of the feet, and worse at night — should always be reported to your provider (see "When to Call Your Doctor" below).
- Increased appetite. The second trimester hunger is often most pronounced around now. Focus on protein-rich, nutrient-dense foods.
Tips for Week 23
1. Talk and sing to your baby. Your voice is the one your baby will recognize most at birth. This isn't just sentimentality — it's science. Newborns have measurably different physiological responses to their mother's voice versus a stranger's. Read aloud, narrate your day, or simply talk.
2. Prepare for glucose screening. The standard gestational diabetes screening (glucose challenge test) is typically scheduled between 24 and 28 weeks. Ask your provider when yours is planned, and know that it requires no fasting in the standard one-hour version. If you have risk factors, yours may already be scheduled.
3. Support your calcium intake. Your baby is building bone fast. The recommended calcium intake during pregnancy is 1,000 mg per day (WHO). Dairy, fortified plant milks, almonds, leafy greens, and canned salmon with bones are all good sources.
4. Walk every day. Even a 20-minute walk supports circulation, reduces leg swelling, helps with back pain, and improves mood. Walking is one of the safest and most effective forms of exercise throughout pregnancy.
5. Research your leave options. If you haven't started thinking about parental leave, now is a reasonable time to review your workplace policies and entitlements. Knowing the timeline takes one stressor off your plate.
When to Call Your Doctor
Certain symptoms at this stage need prompt medical attention:
- Severe, widespread itching — especially on the palms and soles of feet, and worse at night. This can be a sign of intrahepatic cholestasis of pregnancy (ICP), a liver condition that requires monitoring and management.
- Signs of preterm labor: Regular contractions, pelvic pressure, a low backache that comes and goes, or a change in vaginal discharge (watery, mucusy, or bloody) before 37 weeks
- Reduced fetal movement: By 23 weeks, most people feel movement daily. If your baby has been active and you notice significantly less movement, contact your provider.
- Severe headache, visual changes, or sudden swelling in your face or hands — these are possible signs of preeclampsia and need immediate evaluation
- Pain or burning with urination — UTIs are more common and more serious in pregnancy
Frequently Asked Questions
How big is my baby at 23 weeks pregnant?
At 23 weeks, your baby measures about 28.9 cm (11.4 inches) from head to toe and weighs approximately 500 grams (1.1 lbs). Reaching the half-kilogram mark is a significant milestone. Your baby's skin is still thin and reddish, as subcutaneous fat has not yet built up.
What is surfactant and why does it matter at 23 weeks?
Surfactant is a substance produced by specialized lung cells (type II pneumocytes) that reduces surface tension in the alveoli — the tiny air sacs in the lungs. Without it, the air sacs collapse every time the baby exhales. Surfactant production begins around week 23–24 and increases through the third trimester. Babies born very early often need synthetic surfactant administered through a breathing tube to survive and breathe independently.
Can my baby hear me at 23 weeks?
Yes. The inner ear is developed and hearing is active by 23 weeks. Your baby can hear your heartbeat, digestive sounds, your voice, and external sounds. Research suggests babies can distinguish their mother's voice from other voices by this stage of pregnancy. Talking, singing, and reading aloud to your baby is not just sentimentality — newborns show measurable recognition responses to their mother's voice at birth.
Why are my feet and ankles swelling at 23 weeks?
Swelling (edema) in the lower legs is very common in the second trimester and tends to worsen toward the end of the day. It is caused by increased blood volume and by the growing uterus pressing on veins that return blood from the legs. Elevating your feet when resting, wearing compression socks, and staying active with daily walking all help reduce swelling. Sudden, severe swelling — especially in the face or hands — should be reported to your provider.
When is the gestational diabetes test scheduled?
The standard glucose challenge test (GCT) for gestational diabetes is typically scheduled between weeks 24 and 28. It does not require fasting for the one-hour version. If results are elevated, a follow-up three-hour glucose tolerance test is used to confirm a diagnosis (ACOG). If you have risk factors for gestational diabetes, your provider may schedule screening earlier.
Related Tools & Articles
- Due Date Calculator — Track your estimated due date
- Pregnancy Week-by-Week Overview — full 40-week timeline
- Milestone Tracker — monitor your baby's development
- Hospital Bag Checklist — start planning ahead