Quick answer: Week 37: Early term vs full term vs late term, lung maturity, natural induction myths.
Week 37 — you’re in the third trimester, the final stretch. Your baby is gaining weight rapidly, your body is working harder than ever, and the finish line is in sight. It’s completely normal to feel a mix of excitement, anxiety, and ‘let’s just get this done.’
Baby Development This Week
At week 37, your baby is approximately the size of a winter melon — measuring around 19.1 in / 48.6cm. Full term. Lungs are mature and baby is ready for life outside. Growth and final organ maturation are the priorities now. Your baby gains approximately half a pound per week from week 28 onward, laying down the fat deposits that will regulate body temperature after birth.
Symptoms You May Feel
Third trimester week 37 commonly brings: shortness of breath as the uterus presses against the diaphragm (improves when baby drops lower, usually weeks 36–38 for first pregnancies), heartburn at its peak as the stomach is compressed, frequent urination returning with a vengeance, swollen ankles and feet from fluid retention and venous compression, pelvic pressure and occasional ‘lightning crotch’ (sharp nerve pain), Braxton Hicks becoming more frequent and sometimes intense, carpal tunnel syndrome from fluid pressing on wrist nerves, and sleep disruption from physical discomfort and frequent waking.
Early term vs full term vs late term, lung maturity, natural induction myths
Early term (37–38+6) versus full term (39–40+6) versus late term (41–42) carries clinical significance. Babies born at 37–38 weeks have slightly higher rates of breathing difficulties, NICU admission, and breastfeeding challenges than babies born at 39+ weeks — which is why elective procedures before 39 weeks are generally avoided without medical indication. Lung maturity in late preterm babies is variable; the surfactant system isn’t fully mature until approximately 34–36 weeks in most babies. Natural labor induction methods with evidence: membrane sweep (offered from week 39–40, success rate ~24%); sexual intercourse (prostaglandins in semen are cervix-ripening). Nipple stimulation and spicy food lack meaningful evidence.
How do I know if I’m in labor at week 37?
Week 37 is full term — labor at this point is normal and expected. Signs that labor is approaching or beginning: Braxton Hicks becoming more regular and intense; loss of mucus plug (clear, pink, or bloody discharge — can happen days before labor or simultaneously); contractions that are regular (every 5 minutes), last 60 seconds, and don’t ease with movement; and rupture of membranes. The 5-1-1 rule: contractions every 5 minutes, lasting 1 minute, for 1 hour — go to the hospital. If membranes rupture, go immediately regardless of contractions.
Practical Tips for Week 37
- Sleep on your left side — it optimizes blood flow to the placenta and reduces vena cava compression.
- Start kick counts from week 28 — 10 movements in 2 hours is the standard guideline; call your provider if concerned.
- Pack your hospital bag by week 35 — babies don’t always wait until their due date.
- Practice perineal massage from week 34 to reduce tearing risk at birth.
- Attend all prenatal appointments — monitoring frequency increases in the third trimester for good reason.
- Discuss your birth preferences with your provider before week 36.
When to Call Your Midwife or OB
In the third trimester, call your provider immediately for: fewer than 10 fetal movements in 2 hours, regular painful contractions before 37 weeks, severe persistent headache with visual changes or facial swelling (preeclampsia warning signs), any bleeding, signs of water breaking, or any gut feeling that something isn’t right. From week 37, always err on the side of calling — your team would always rather you check in unnecessarily than miss something important.
Frequently Asked Questions
How do I know if I’m in labor?
True labor contractions are regular, progressively stronger, longer, and closer together — and they don’t stop with rest, hydration, or position changes (unlike Braxton Hicks). They typically start every 10–15 minutes and intensify over hours. Other labor signs include: bloody show (pink-tinged mucus from the cervical plug), your water breaking, and lower back pain that radiates to the front. The 5-1-1 rule for hospital: contractions every 5 minutes, lasting 1 minute, for 1 hour.
Is extreme fatigue normal at week 37?
Absolutely. Third trimester fatigue combines extra physical weight, disrupted sleep, frequent urination, and the enormous metabolic cost of a baby gaining half a pound weekly. Your cardiac output is 30–50% above baseline, your kidneys filter 50% more blood, and your body produces extra blood, hormones, and nutrients continuously. Rest is not laziness at this stage — it is medically appropriate preparation.
What is the mucus plug and when does it come out?
The mucus plug is a thick collection of cervical mucus that seals the cervix throughout pregnancy to protect against infection. It can come out days or even weeks before labor, or during early labor itself. It may be clear, white, yellow, or tinged with pink or brown blood. Losing it doesn’t mean labor is imminent, but it does mean your cervix is beginning to prepare. Any bright red bleeding should always be reported to your provider.
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Related Reading
- 20 weeks pregnant: halfway there – anatomy scan guide
- The exhaustion of being everything to everyone – and asking for help
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