Quick answer: Week 15: AFP, hCG, estriol, inhibin A explained, false positive rates, next steps.
Week 15 puts you in the second trimester — often called the golden period of pregnancy, and for good reason. Energy typically improves, nausea subsides, and the pregnancy becomes physically and emotionally more comfortable for most women.
Baby Development This Week
At week 15, your baby is approximately the size of a apple — measuring around 4.0 in / 10cm. Baby is squirming constantly, though you likely can’t feel it yet. All organs are now formed and the focus has shifted entirely to growth and maturation. Your baby is increasingly responsive to sound, light, and touch.
Symptoms You May Feel
Common week 15 second trimester symptoms include: round ligament pain (sharp, brief twinges on the sides of your abdomen as the uterus grows rapidly), Braxton Hicks contractions (occasional irregular tightening — harmless practice contractions), back pain as your center of gravity shifts forward, nasal congestion from increased blood volume, skin changes including the linea nigra (dark line down the abdomen) and possible chloasma (facial darkening), and for many women, a welcome increase in energy and libido compared to the first trimester.
AFP, hCG, estriol, inhibin A explained, false positive rates, next steps
The quad screen (AFP, hCG, estriol, inhibin A) is offered at 15–20 weeks as a second trimester screening option for neural tube defects and chromosomal conditions. A high AFP (alpha-fetoprotein) raises the risk of open neural tube defects such as spina bifida; a low AFP combined with low estriol and high hCG suggests trisomy 21 risk. The false positive rate is approximately 5% — meaning 5% of women who do not have an affected pregnancy will get an abnormal result. A positive quad screen leads to an offer of diagnostic testing (amniocentesis from 16 weeks). If you’ve had NIPT (which screens for chromosomal conditions but not neural tube defects), a targeted AFP test at 15–20 weeks covers the neural tube aspect.
When should I feel the baby move at week 15?
A small percentage of women — particularly those who have been pregnant before or who are slender — may feel early movement at week 15, described as a flutter, bubble, or tapping sensation low in the abdomen. For most first-time mothers, it’s still too early. The fetus at 15 weeks is approximately 10cm; bones are hardening, and the skin is covered in lanugo (fine hair) that helps regulate temperature until fat deposits develop. This is a good week to research prenatal classes if you haven’t already — popular classes fill up early.
Practical Tips for Week 15
- Start pelvic floor exercises (Kegels) now — 3 sets of 10-second holds, 3 times daily pays dividends postpartum.
- Consider a pregnancy pillow as your bump grows — better sleep protects energy and mood.
- Book prenatal/childbirth classes early — good ones fill up months in advance.
- Continue prenatal vitamins and increase iron-rich foods as blood volume expands significantly.
- Walk 30 minutes daily — the evidence for maternal and fetal benefits is consistent and strong.
- Begin researching your birth plan options and discussing preferences with your provider.
When to Call Your Midwife or OB
Contact your provider for: regular contractions before 37 weeks (more than 4 per hour), decreased fetal movement, severe headache with visual changes, sudden swelling of the face or hands, any bleeding, or fever above 101°F / 38.3°C. Trust your instincts — if something feels different or wrong, call.
Frequently Asked Questions
When should I feel the baby move at week 15?
First movements (quickening) are typically felt between weeks 16–25. First-time mothers usually notice them later than those who’ve been pregnant before. Early movements feel like flutters, bubbles, or light taps — easily confused with gas. They become unmistakable kicks and rolls as the weeks progress. If you have an anterior placenta (at the front of the uterus), it cushions movement and you may feel it later than expected.
Is lower back pain normal in the second trimester?
Very much so — it affects around 50% of pregnant women. Your growing uterus shifts your center of gravity forward, your ligaments loosen from relaxin, and your posture compensates in ways that strain the lumbar spine. Prenatal yoga, swimming, a maternity support belt, and sleeping with a pillow between your knees all provide significant relief. If pain is severe, radiates down the leg, or is accompanied by numbness or tingling, mention it to your provider.
When should I start buying baby gear?
Week 15 is a reasonable time to start researching — particularly big-ticket items like strollers, car seats, and cribs that may need to be ordered months in advance. Most parents wait until after the 20-week anatomy scan (when risk drops significantly) before major purchases. Baby showers are typically held in the third trimester, so let that guide the timing of purchases you expect as gifts.
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Related Reading
- 14 weeks pregnant: can you feel the baby yet?
- 16 weeks pregnant: anatomy scan coming up
- How do I know if my baby is getting enough breast milk?
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