👶 Antenatal Guide — Weeks 27–40
Third Trimester Guide
The third trimester is the final stretch — your baby grows from about 900g at 27 weeks to 3.0–3.5 kg at term. This is the time for growth monitoring, pre-eclampsia surveillance, birth planning, and knowing exactly when to go to the hospital.
Key Milestones
🌱 Weeks 27–32: Rapid growth and lung maturation
The baby gains approximately 200g per week. Lung surfactant production — which allows the lungs to expand at birth — develops between 28–36 weeks. A baby born at 32 weeks has an excellent prognosis with appropriate neonatal care. The baby opens its eyes around 28 weeks.
🌱 Weeks 32–36: Baby positions head-down
Most babies naturally rotate to a head-down (cephalic) position by 32–36 weeks. A baby remaining breech (bottom-down) after 36 weeks may require an external cephalic version (ECV) attempt or planned caesarean section. Your obstetrician will assess position from 32 weeks.
🌱 Weeks 36–37: Term approaches
From 37 weeks, the pregnancy is "term" — the baby is mature and ready for birth. This is the time for a final growth scan, confirmation of baby's position, and finalising your birth plan.
🌱 Week 40: Due date — and beyond
Only 5% of babies arrive exactly on their due date. Most arrive between 38–42 weeks. If pregnancy continues beyond 41 weeks, induction of labour is typically recommended — the risk of stillbirth rises slightly after 41–42 weeks. Your obstetrician will discuss the timing with you.
Essential Tests & Scans
Third Trimester Growth Scan
⏱ Weeks 28–32 and 36–38
Measures baby's head circumference, abdominal circumference, and femur length to estimate fetal weight and assess growth along the expected trajectory. Identifies intrauterine growth restriction (IUGR) — a baby smaller than expected for its gestational age.
Umbilical Artery Doppler
⏱ Weeks 28–38 if indicated
Ultrasound assessment of blood flow through the umbilical cord. In IUGR pregnancies, abnormal Doppler flow (absent or reversed end-diastolic flow) indicates fetal compromise and guides timing of delivery. Routine Doppler is added to growth scans in high-risk pregnancies.
Biophysical Profile (BPP)
⏱ From 32 weeks in high-risk pregnancies
A 30-minute ultrasound assessment scoring: fetal breathing movements, gross body movements, fetal tone, and amniotic fluid volume — each scored 0 or 2. A score of 8/8 is normal; below 6 triggers further management.
Group B Streptococcus (GBS) Swab
⏱ Weeks 35–37
A vaginal and rectal swab for Group B Streptococcus — a bacterium that 10–30% of women carry harmlessly but which can cause serious infection in the newborn during birth. A positive swab leads to IV antibiotics during labour.
Blood Pressure and Urine Protein (every visit)
⏱ Every antenatal visit
Pre-eclampsia risk is highest in the third trimester. BP above 140/90 with proteinuria after 20 weeks = pre-eclampsia. If severe features develop (headache, visual disturbance, RUQ pain, BP above 160/110), hospital admission is required.
Frequently Asked Questions
What is the difference between Braxton Hicks and real contractions?
Braxton Hicks (practice contractions) are irregular, do not increase in frequency or intensity over time, usually resolve with movement or a change in position, and are not painful — just a tightening. True labour contractions are regular (come every 5–10 minutes), progressively closer together and longer, do not resolve with movement, and increase in intensity over time. If you are unsure, time 3–4 contractions with a watch — if they are regular and consistent, go to the hospital.
My baby is breech at 34 weeks — what can I do?
Most breech babies turn spontaneously before 36 weeks — at 34 weeks, do not worry yet. From 36 weeks, your obstetrician may offer an external cephalic version (ECV) — a manual procedure done in hospital where the doctor tries to turn the baby from outside the abdomen. ECV has a 50–70% success rate. If unsuccessful or declined, a planned caesarean section is arranged. Positions like hands-and-knees (all-fours) from 30–32 weeks may encourage the baby to rotate but have limited evidence.
Is it safe to have sex in the third trimester?
Yes, for uncomplicated pregnancies. Sex does not trigger labour in a normal pregnancy — prostaglandins in semen may soften the cervix slightly but only if the cervix is ready. Avoid sex if placenta praevia is diagnosed, membranes have ruptured, or your obstetrician has specifically advised against it. Positions that are comfortable change as the bump grows — side-lying or woman-on-top positions are usually best.
When should I go to the hospital in labour?
For first-time mothers: when contractions are regular every 5 minutes, lasting 1 minute each, for at least 1 hour (5-1-1 rule). For women who have given birth before: every 7–10 minutes, or when contractions are becoming intense — second labours progress faster. Go immediately if: membranes rupture, there is any bleeding, you feel fewer movements, or any third trimester warning sign is present.