Week 37 · Third trimester
EN
中文ZHहिन्दीHIBahasa IndonesiaIDPortuguêsPTРусскийRU日本語JAEspañolES

Week 37 fetal development and pregnancy guide — length about 48.6cm, weight 约2859g (about the size of a chards)

Your baby is now about 48.6cm and 约2859g, about the size of a chards.

Medical references: WHO INTERGROWTH-21st · China Prenatal & Pregnancy Care Guide · ACOG

View each day of week 37 →

Week 37 fetal development milestones: length / weight / ultrasound data

Key developmental changes during week 37:

  • At week 37 the baby reaches the "term" standard (early-term).
  • The organs are mature and can work independently.
  • Large turning is hard and the position is basically fixed.
  • Meconium has filled the bowel and will be passed in the first stool after birth.
  • Subcutaneous fat reserves are ample and the body is full and rounded.
  • The lungs are mature and can breathe independently.
  • The brain is mature and can regulate complex physiological reflexes.
  • The immune system has stored ample maternal antibodies (IgG).
  • Fetal-movement amplitude eases a little but the count stays.
  • The nails have grown past the fingertips.
  • Pulmonary surfactant is ample, so even if born prematurely the risk of respiratory distress is already low.
  • Subcutaneous fat shifts the skin colour from red to pink and reduces puckering, so the appearance is closer to a newborn.
Illustration of your baby about the size of chards at week 37 (about 48.6cm/约2859g)
Week 37 size: about the size of a chards
BPD (biparietal diameter)89.9mmWidth across the head; reflects brain development
AC (abdominal circumference)327.2mmAbdomen circumference; reflects nutrient absorption
FL (femur length)68.3mmThigh bone length; tracks gestational age
Ultrasound parameters at week 37: BPD 89.9 mm, AC 327.2 mm, FL 68.3 mm (median reference)
Week 37 three core ultrasound parameters (median; varies by individual)

* Values are medians from WHO/China standards; individual variation is normal. References: WHO INTERGROWTH-21st, China Prenatal & Pregnancy Care Guide, ACOG guidelines.

Week 37 daily development

Your baby quietly grows every day of week 37. Tap any day to see fetal development, maternal changes, and daily guidance for that day.

253Day 1Full term! From today, onset at any time, any night, is a normal birth — you don’t need to wait anymore, and the baby doesn’t either. This is the most worth-remembering day of the whole pregnancy: you have walked through all 37 weeks, every prenatal visit, every fetal-movement count, every sleepless (转辗) night — now the finish line is in sight, and everything you prepared will be delivered in the days ahead.254Day 2Carve the 511 rule into memory (even stick it by the head of the bed): contractions every 5 minutes, each lasting over 1 minute, and this regularity lasting 1 hour — that is the clear signal to go to hospital. More importantly, three things intersect: rupture of membranes takes priority — whether or not contractions have reached 511, the moment membranes break, lie flat with the hips raised and go to hospital; a small amount of bloody show without regular contractions can be observed at home first; heavy bright-red bleeding, with or without contractions, is immediate medical care.255Day 3Have a "face-to-face talk" with the father: sit comfortably together, place both your hands on the belly and tell the baby in a gentle, everyday tone "This world has birdsong outside the window, the warm yellow of lights, Dad’s guitar, the picture book Mum has read 100 times — we’re all ready to meet you. No rush; pick the most comfortable day." This isn’t a ritualised "labour declaration" — it genuinely lets both of you shift attention from "preparing" to "waiting".256Day 4Pelvic measurement is usually done at the week-37 visit — mainly assessing the transverse and anteroposterior diameter of the pelvic outlet to judge whether the baby can pass through the birth canal smoothly. The result is judged together with estimated fetal weight, position and cord position to decide delivery mode. If the doctor doesn’t mention it, you can ask "do I need a pelvic measurement?" — you have the right to understand your body and the birth-method options ahead of you.257Day 5Do the water-break drill again today: if lying in bed or sitting on the sofa you suddenly feel an uncontrollable flow of warm fluid from the vagina that your perineal muscles can’t stop — lie flat immediately (don’t sit, stand or walk around), put two pillows under your hips so the hips are higher than the chest, and have family call obstetrics or 120, telling the operator you "suspect waters broken" and your current gestational week. Don’t shower, don’t insert anything, don’t pace on the way to hospital — every step done lying down.258Day 6Pack a labour energy kit into the hospital bag: ①3-4 energy gels (marathon-style small packs, easily absorbed without bloating), ②two small boxes of coconut water (natural electrolytes), ③4-5 wholemeal biscuits, ④a small bag of raisins. You likely won’t have an appetite for a full meal during labour, but these light, high-energy foods quickly replenish you between contractions — far more reliable than the hospital vending machine’s sugary drinks and snacks.259Day 7Bloody show (pink or blood-streaked snot-like mucus) is the sign of the cervix softening and beginning — first-time mums usually go into labour within 24-48 hours, and mothers of a previous child may be quicker. If it’s just a little bloody show with no regular contractions and no rupture, you can shower, put on clean underwear, eat a normal meal and re-check the hospital bag; but if after bloody show you get 511 regular contractions, or the bleeding exceeds a menstrual flow or is bright red, go to hospital immediately.

Week 37 belly changes

Illustration of belly changes at week 37: uterine position and abdominal prominence

At week 37 (third trimester) the uterine fundus keeps rising closer to the sternum. Your belly is clearly rounded and your waistline and fundal height grow quickly, so pay more attention to balance and safety in daily movement.

Week 37 maternal body changes and common symptoms

  • Full term! From today it is normal for labour to start at any time.
  • Weight may plateau or even dip slightly (stomach-space changes after engagement).
  • Vaginal discharge increases (the cervix softens and the mucus plug may pass), preparing for delivery.
  • Bloating and heartburn largely ease as the baby engages and the stomach space frees up, but overeating still causes reflux.
  • If lower-limb swelling and cramps suddenly worsen at term or come with headache, check blood pressure to rule out preeclampsia.
  • Sleep worsens from anticipation and frequent urination; a regular routine plus a pregnancy pillow help.
  • Itchy abdominal skin, stretch marks and urine leaking, with more frequent false contractions (one of the pre-labour signals at term).
  • The breasts enlarge and colostrum is secreted; you can start preparing nursing bras and nursing pads.

Week 37 nutrition advice and recommended recipes

Pre-labour, prepare small high-carb + electrolyte meals (such as banana-oat porridge or coconut water) to store easily used energy and fluids; after labour, eat as the hospital directs (a vaginal birth generally allows progressive eating soon after). Daily targets still follow authority guidance: quality protein about 80-90g, iron about 27-29mg, calcium 1000mg, DHA 200-300mg, fiber 25-30g, iodine 230μg. Avoid alcohol, raw or unpasteurised milk products, high-mercury fish, caffeine ≤200mg a day.

DHA200-300mgBrain & vision development
Recommended recipeRed-date longan congee

Red dates supplement iron and longan calms the nerves; congee is easy to digest and a traditional warm, gentle food, suitable before labour and the confinement month. If blood sugar runs high or in GDM, control the red dates and longan and add no sugar; you can switch to a sugar-free multigrain congee.

Week 37 prenatal education guide

The core of "fetal education" is still to help the mother-to-be relax and go with the flow; there is no strong evidence that any specific stimulation makes the baby smarter. This week the baby is full term; you can sit down with the father, place your hands on the belly and have a "face-to-face talk" with the baby — tell it what Mum and Dad look like, what their voices sound like and what home is like. This is a warm parent-child bond and a way to relax, helping you steady your own mood, chasing no "training effect". Enjoy the final time together.

Week 37 partner's role

①Be fully on call: check every preparation — hospital bag by the door, route to hospital, full tank of fuel, leave approved, confinement-nanny phone number and the family notification list. ②Never keep your phone on silent; be on stand-by at all times. ③Talk or sing close to the belly at a set time daily to build a father’s voice the baby recognises. ④Help ease pre-labour anxiety: be present, listen, do relaxing exercises together and stay calm.

Week 37 checkup reminders

Weeks 37-40: weekly prenatal visits + NST fetal-heart monitoring. This week or soon, pelvic measurement is done to assess pelvic size and delivery mode (one reference for vaginal/cesarean). Keep counting fetal movements daily. Learn the signs of labour: bloody show, rupture of membranes and regular contractions (the 511 rule), and seek care as soon as they appear.

Week 37 key concerns

Pelvic measurement to assess delivery modeReady for labour at any timeDelivery notification planPostpartum-month diet plan30 minutes of moderate exercise daily (ACOG recommends 150 minutes a week across pregnancy)

Signs that need immediate care at week 37

If any of the following occurs, contact your obstetrician or seek medical help promptly: ① rupture of membranes → regardless of contractions, lie flat immediately with the hips raised and seek care; ② regular contractions (the 511 rule: every 5 minutes, each lasting over 1 minute, for over 1 hour) → go to hospital; ③ clearly reduced fetal movement (fewer than 10 in 2 hours or less than half the usual); ④ persistent severe headache, blurred vision or severe upper-abdominal pain with raised blood pressure or sudden oedema (watch for preeclampsia); ⑤ itching all over, especially the palms and soles with no rash (watch for ICP); ⑥ a fever over 38℃ that does not come down; ⑦ one leg swollen, hot and painful, or sudden breathlessness and chest pain (watch for a clot/pulmonary embolism); ⑧ a large amount of bright-red vaginal bleeding (watch for placenta praevia) or bloody show with regular contractions.

Week 37 frequently asked questions

What is the 511 rule?
The 511 rule: contractions every 5 minutes, each lasting over 1 minute, continuing for over 1 hour (5-1-1). Meeting 511 is basically a reliable sign of labour — go to hospital immediately. But if membranes break, there is bleeding or movement clearly drops, seek care promptly regardless of 511.
Is week 37 considered full term?
Yes. Week 37 reaches the "term" standard (early-term baby), and from today labour starting at any time is a normal term birth. That said, birth at 39-40 weeks is more ideal; without a medical indication there is no need to induce at 37 weeks.
How much weight gain is normal at week 37?
A cumulative gain of about 12-16kg by week 37 is common. In the third trimester a standard-BMI mum gains about 0.4-0.5kg a week, with about 11.5-16kg recommended across the whole pregnancy. Weight may plateau or dip a little at term — normal; watch the overall trend.
Do I need a pelvic measurement at week 37?
Pelvic measurement is usually done around week 37 to assess pelvic size and shape, as one reference for delivery mode (vaginal/cesarean), judged together with the baby’s size, position and cervical condition. Follow your prenatal doctor’s arrangement.
How to read the week-37 ultrasound report?
The three measurements at 37 weeks: BPD (biparietal diameter) about 89.9mm, AC (abdominal circumference) about 327.2mm, and FL (femur length) about 68.3mm, reflecting head, abdomen and leg development respectively. If the three are in step, growth is good; a single slight deviation isn’t necessarily abnormal — go by your obstetrician’s overall assessment.
Is fetal movement regular at week 37?
At term, amplitude may ease as space shrinks, but the count should not clearly drop. Since week 28 count daily: one hour morning, noon and evening, with ≥10 in 2 hours normal; if clearly under 10 in 2 hours or less than half the usual, seek care immediately.
Bloody show, ruptured membranes or contractions — which and which order?
Ruptured membranes (colourless fluid leaking continuously) → lie flat immediately with the hips raised and seek care; regular contractions meeting 511 → go to hospital; bloody show (mucus with blood streaks) can be observed at home first, waiting for regular contractions. Contact obstetrics if unsure.
Is there a recommended exercise duration in pregnancy?
ACOG recommends about 150 minutes of moderate-intensity exercise accumulated weekly. At week 37 (term), still favour walking, stretching and prenatal yoga, avoiding intense exercise and pressure on the abdomen; if regular contractions (511), rupture of membranes, bleeding or clearly reduced movement appear, stop immediately and seek care — labour may have begun.
Do I still need vaccinations at week 37?
The CDC and ACOG recommend the Tdap (pertussis) vaccine at weeks 27-36; the inactivated flu vaccine can also be given in flu season — both are pregnancy-safe, and this week is at the end of the window, so tell the provider you are pregnant before vaccination.
Can I have sex at week 37?
After term, sex may trigger contractions, so caution or avoidance is generally advised. With no contraindications and the doctor’s permission, very gentle sex in a non-pressing position can be acceptable; see a doctor immediately for bleeding, pain or fluid leakage after sex. Most doctors advise pausing before labour.
What about leg cramps and oedema at week 37?
For a cramp, flex the foot and massage the calf; prevention centres on calcium, magnesium, water and stretching before bed. Oedema after long standing/sitting is clearer at term: raise the legs, lie on your left side, walk to promote return flow and moderately limit salt; if swelling suddenly worsens, spreads to the face and hands or comes with headache/vision changes, check blood pressure to rule out preeclampsia.
What should I avoid eating at week 37?
Even at term, avoid raw or undercooked meat, fish and eggs, high-mercury large fish, unpasteurised dairy, alcohol, caffeine up to 200mg a day, and excess animal liver. The Tdap window is at its end this week; GDM mums strictly control sugar. No need to specially "supplement" or try labour-inducing foods just to trigger birth.
What about heartburn and bloating at week 37?
At term, after the baby engages, the stomach space frees up and heartburn mostly eases, but one overfull meal still brings reflux. Eat small frequent meals, chew slowly, stay sitting 30 minutes after a meal before lying down, don’t eat within 2-3 hours before bed, avoid spicy, greasy, overly sweet food and fizzy drinks, and prop up the upper body; in severe cases use a pregnancy-safe antacid as directed.
What about constipation and haemorrhoids at week 37?
Eat more coarse grains, fruit and vegetables for fiber, drink 1.5-2L of water daily, walk after meals and toilet on a regular schedule without squatting long; warm-water sitz baths help haemorrhoids. Iron supplements can worsen constipation — discuss adjusting them with your doctor; at term choose a pregnancy-safe medication for severe cases and avoid stimulating laxatives to prevent discomfort before labour.
What about lower-back and pubic-bone pain at week 37?
At term the forward centre of gravity and relaxin loosening the pelvic joints may worsen back or pubic pain. Avoid long standing or sitting, wear supportive low shoes, use a belly-support belt, side-sleep with a pregnancy pillow, do prenatal yoga and pelvic-floor exercises and apply local heat; sharp pain on one side, or with bleeding or fever, needs medical care.
Can’t sleep well and anxious at week 37?
Anticipation and pre-labour anxiety coexisting at term is normal. Use a pregnancy pillow for support, side-sleep, soak your feet before bed, exercise moderately in the day and communicate more with your partner; remembering the 511 rule and having the hospital bag at the door raises your sense of control and eases anxiety; if it is marked, talk to your doctor.
Are frequent false contractions at week 37 normal?
Frequent false contractions at term are fairly common: brief tightening, painless, irregular, resolving with rest. If they become regular, painful or come with lumbar heaviness (meeting 511), seek care to rule out the onset of labour.
What should the hospital bag contain?
Three categories: maternal items (postnatal pads, nursing bra, toiletries, straw cup), baby items (NB nappies, swaddling, going-home clothes, small hat) and documents (ID, social-security card, prenatal record). In the first week of term, confirm it is packed and at the door, phone charged, and route and obstetrics number at hand.
What signals precede the pain of labour?
Common precursor signs: lightening (easier breathing, worse urination), bloody show (mucus plug passing, possible onset within 24-48 hours) and stronger irregular contractions. The true signs of labour are regular contractions (511) or rupture of membranes — seek care promptly.
⚡The gestational-development data on this tool is compiled from the WHO INTERGROWTH-21st fetal growth standards, ACOG (American College of Obstetricians and Gynecologists), and the Chinese Medical Association's Guidelines for Pre-conception and Prenatal Care, and is reviewed for consistency by obstetrics consultants against those authoritative standards. Daily developmental tips, maternal changes, and nutrition advice follow an evidence-based approach. Note that fetal length is measured differently by week: crown–rump length (CRL) at or before week 20, and crown–heel length (CHL) from week 21 — values either side of week 21 are not directly comparable, which is a normal measurement change.

Data sources & notes

This tool provides algorithm-based estimates from the authoritative standards above for pregnancy time planning and general reference. It does not replace a doctor's diagnosis or individualized medical advice; follow your obstetrician for all prenatal care decisions.

Week 37 daily focus

Key daily tips for this week; tap any item to view the full development and guidance for that day.

Day 1Full term! From today, onset at any time, any night, is a normal birth — you don’t need to wait anymore, and the baby doesn’t either. This is the most worth-remembering day of the whole pregnancy: you have walked through all 37 weeks, every prenatal visit, every fetal-movement count, every sleepless (转辗) night — now the finish line is in sight, and everything you prepared will be delivered in the days ahead.Day 2Carve the 511 rule into memory (even stick it by the head of the bed): contractions every 5 minutes, each lasting over 1 minute, and this regularity lasting 1 hour — that is the clear signal to go to hospital. More importantly, three things intersect: rupture of membranes takes priority — whether or not contractions have reached 511, the moment membranes break, lie flat with the hips raised and go to hospital; a small amount of bloody show without regular contractions can be observed at home first; heavy bright-red bleeding, with or without contractions, is immediate medical care.Day 3Have a "face-to-face talk" with the father: sit comfortably together, place both your hands on the belly and tell the baby in a gentle, everyday tone "This world has birdsong outside the window, the warm yellow of lights, Dad’s guitar, the picture book Mum has read 100 times — we’re all ready to meet you. No rush; pick the most comfortable day." This isn’t a ritualised "labour declaration" — it genuinely lets both of you shift attention from "preparing" to "waiting".Day 4Pelvic measurement is usually done at the week-37 visit — mainly assessing the transverse and anteroposterior diameter of the pelvic outlet to judge whether the baby can pass through the birth canal smoothly. The result is judged together with estimated fetal weight, position and cord position to decide delivery mode. If the doctor doesn’t mention it, you can ask "do I need a pelvic measurement?" — you have the right to understand your body and the birth-method options ahead of you.Day 5Do the water-break drill again today: if lying in bed or sitting on the sofa you suddenly feel an uncontrollable flow of warm fluid from the vagina that your perineal muscles can’t stop — lie flat immediately (don’t sit, stand or walk around), put two pillows under your hips so the hips are higher than the chest, and have family call obstetrics or 120, telling the operator you "suspect waters broken" and your current gestational week. Don’t shower, don’t insert anything, don’t pace on the way to hospital — every step done lying down.Day 6Pack a labour energy kit into the hospital bag: ①3-4 energy gels (marathon-style small packs, easily absorbed without bloating), ②two small boxes of coconut water (natural electrolytes), ③4-5 wholemeal biscuits, ④a small bag of raisins. You likely won’t have an appetite for a full meal during labour, but these light, high-energy foods quickly replenish you between contractions — far more reliable than the hospital vending machine’s sugary drinks and snacks.Day 7Bloody show (pink or blood-streaked snot-like mucus) is the sign of the cervix softening and beginning — first-time mums usually go into labour within 24-48 hours, and mothers of a previous child may be quicker. If it’s just a little bloody show with no regular contractions and no rupture, you can shower, put on clean underwear, eat a normal meal and re-check the hospital bag; but if after bloody show you get 511 regular contractions, or the bleeding exceeds a menstrual flow or is bright red, go to hospital immediately.

Content sources & notes

This guide references WHO INTERGROWTH-21st standards, the China Prenatal & Pregnancy Care Guide, ACOG clinical guidelines and BabyCenter (medically reviewed).

This page is educational pregnancy information for general reference and does not replace the diagnosis or advice of a licensed healthcare provider.

View the full fetal BPD/AC/FL reference table (weeks 14–42) →

Related pregnancy tools

Pregnancy Weight Gain CalculatorCheck whether this week's gain is within a healthy rangeBMI CalculatorLearn your pre-pregnancy BMI and pregnancy adviceSafe Period CalculatorTrack your cycle to plan conception and contraceptionPregnancy CalculatorEnter your last period to see your exact week