31 weeks pregnant: your baby & body
Your baby this week
About 39.9 cm and 1300 g — around the size of a cabbage. Every baby grows a little differently.
How your baby is developing
- The fetus can typically turn its head, and rapid brain development continues.UNSW Embryology (CC-BY)
- The kidneys are typically fully developed, and the lungs continue maturing.UNSW Embryology (CC-BY)
How you may feel
- Sleep can become more difficult as the bump grows; frequent urination and Braxton Hicks contractions commonly continue.NHS
Nutrition this week
When to reach out
- Heavy vaginal bleeding or passing clots.ACOG
- Severe or persistent abdominal or pelvic pain.ACOG
- Severe, persistent nausea or vomiting that prevents keeping any fluids down (possible hyperemesis gravidarum).NHS
- Fever of 38°C (100.4°F) or higher, or chills.WHO
- Severe dizziness, fainting, or a racing/irregular heartbeat.NHS
- Pain or burning when urinating (possible urinary tract infection).NHS
- A severe or persistent headache that doesn't improve.ACOG
- Sudden swelling of the face, hands, or feet.ACOG
- Visual disturbances — blurring, flashing lights, or spots.ACOG
- Regular contractions, pelvic pressure, or low back pain before 37 weeks (possible signs of preterm labor).ACOG
- Fluid leaking or gushing from the vagina (possible ruptured membranes).NHS
- Persistent pain in the upper abdomen, especially under the ribs on the right side.ACOG
- A noticeable reduction in the baby's usual movements, or no movement felt — contact your midwife or doctor promptly rather than waiting; do not wait until the next appointment.ACOG
- Regular, painful contractions before 37 weeks, or any contraction pattern that concerns you near term.ACOG
- Waters breaking, or blood-stained ('bloody show') discharge — a normal sign labor may be starting at term, but call your midwife or doctor to be checked.NHS
These apply to this week specifically. See the full list of urgent warning signs the CDC publishes for pregnancy and the year after birth.
Part of the Third trimester (weeks 28–42).
Educational reference only — not medical advice. Typical/average figures; every pregnancy differs. Always consult your doctor or midwife. Seek urgent care for any warning sign.