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.
Track your timeline with our Due Date Calculator.
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
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