Week 39 · Third trimester
Week 39 fetal development and pregnancy guide — length about 50.7cm, weight 约3288g (about the size of a a small watermelon)
Your baby is now about 50.7cm and 约3288g, about the size of a a small watermelon.
Medical references: WHO INTERGROWTH-21st · China Prenatal & Pregnancy Care Guide · ACOG
View each day of week 39 →Week 39 fetal development milestones: length / weight / ultrasound data
Key developmental changes during week 39:
- All systems needed for life outside the womb are ready.
- Fetal-movement amplitude decreases as space shrinks (not the number of movements).
- The hair has clearly grown longer.
- The head’s biparietal diameter is about 9.2cm — the greatest challenge when passing the birth canal.
- Subcutaneous fat is thick and the body is full and firm.
- Each organ system is mature and can operate independently.
- Hearing is acute, with a clear response to the parents’ voices.
- Fetal-movement amplitude is small but the frequency is normal.
- The nails are long and will extend beyond the fingertips at birth, needing trimming.
- Meconium fills the bowel, preparing for the first stool after birth.
- Maternal-antibody (IgG) transfer is complete, taking effect from the first months after birth.
- The thermoregulatory centre matures with thickening subcutaneous fat, giving better warmth retention after birth.
BPD (biparietal diameter)92.1mmWidth across the head; reflects brain development
AC (abdominal circumference)344.5mmAbdomen circumference; reflects nutrient absorption
FL (femur length)71.1mmThigh bone length; tracks gestational age
* Values are medians from WHO/China standards; individual variation is normal. References: WHO INTERGROWTH-21st, China Prenatal & Pregnancy Care Guide, ACOG guidelines.
Week 39 daily development
Your baby quietly grows every day of week 39. Tap any day to see fetal development, maternal changes, and daily guidance for that day.
267Day 1The baby’s hair is clearly longer — at birth your first glance will see the fine newborn hair on its head’s crown. After engagement the hair lies against the head, and ultrasound sometimes faintly shows strands floating in the amniotic fluid. Subcutaneous fat is in place in every corner; the face is full and rounded. Today’s baby is already entirely the look of a newborn — you no longer need to imagine; this is the little person you will soon be holding.268Day 2Don’t try any folk labour-inducing remedies: castor oil (can cause severe diarrhoea and dehydration), spicy foods (they irritate the bowel without helping contractions), excessive stair-climbing (unstable centre of gravity in late pregnancy risks falls), and self-nipple stimulation (may trigger unmanageable over-strong contractions). Truly safe induction is done in hospital with evidence-based methods — cervical-balloon dilation, artificial rupture of membranes and oxytocin infusion — all under strict obstetric monitoring.269Day 3Do 10 minutes of mindful meditation daily: sit in a quiet dim room, close your eyes, put a hand on your chest to feel your heartbeat → shift attention to the abdomen to feel the baby’s slight movements → say softly to yourself "my body knows how to give birth, the baby knows how to be born" → breathe deeply five times. From this week to week 41 every day may be a wait, and this mindful practice turns "the anxiety of waiting" into "the calm of expectation" — a skill you can also use during labour.270Day 4Dad-to-be, this week focus on learning two labour-support skills: ①how to help her count contraction frequency (phone stopwatch, from the start of this contraction to the start of the next, recording each interval); ②when a contraction comes, help her count the breathing rhythm in a low, calm voice: "in — out — in — out", while slowly circling a palm on her lower back (lumbosacral soreness is the most uncomfortable spot for many women). Neither needs a medical background — just your focused presence.271Day 5Bloody show — you find pale pink or blood-streaked mucus on the tissue when using the toilet; this is the cervical plug falling off, usually signalling onset within 24-48 hours. What you can do now: notify the father, take a warm shower, put on clean underwear, eat a normal meal, move the hospital bag from the door to hand, and set the obstetrics quick-call on the phone. Don’t rush to hospital — bloody show alone without contractions or rupture will send you home again, and the energy of the round trip is better spent in comfortable home waiting.272Day 6From today, keep your phone 24/7, un-silenced and at least 70% charged, and set a dedicated labour ringtone (distinct from everyday calls so you identify it in a second at a critical moment). Set the father’s phone the same way. Place a power bank and cable by the bed, in the living room and the bathroom — so you can grab one and stuff it into the bag anytime. When real contractions come, you won’t have time to hunt for a charger.273Day 7At 39 completed weeks, with a clear medical indication (breech / placenta praevia / oligohydramnios / fetal distress, etc.), an elective cesarean can be arranged. Without an indication, the best choice is to await natural onset — babies born naturally at 39-40 weeks have their lungs, brain and thermoregulation at the best maturity. Don’t press the doctor to operate early because you "can’t wait" — every minute of patience you give in the final week repays you with more mature baby organs.
Week 39 belly changes
At week 39 (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 39 maternal body changes and common symptoms
- Intense anticipation and anxiety coexist — both normal.
- Weight may stop increasing (common after term).
- Contractions may increase but aren’t yet regular enough for labour.
- If bloating, heartburn and constipation persist, keep light, easily digestible food and avoid overeating before labour.
- Lower-limb swelling, cramps and varicose veins — sudden one-leg swelling/pain needs checking for a clot.
- Sleep difficulty and back or pubic-bone pain are more grinding during the waiting period; a warm bath relaxes.
- Itchy abdominal skin, stretch marks and urine leaking, with frequent false contractions needing the 511 check.
- The breasts enlarge and colostrum is secreted; near breastfeeding you can consult a lactation adviser.
Week 39 nutrition advice and recommended recipes
No "labour-inducing" food is recommended to try (such as castor oil, spicy foods, etc.) — they may cause diarrhoea or discomfort with no reliable induction evidence. Keep a normal balanced diet and adequate fluids to store energy for onset at any time. 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 recipeOat-banana energy bowl
Oats provide durable energy and banana provides potassium to prevent cramps, gently topping up energy before labour without filling the stomach. Add a few nuts for DHA and magnesium; GDM mums control the banana amount and sugar.
Week 39 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 do 5-10 minutes of mindful meditation daily: close your eyes, breathe deeply, focus on the abdomen to feel fetal movement — without expectation, worry or rushing, enjoying the final together time. This mainly helps you steady your emotions and reduce pre-labour tension — the most practical "fetal education".
Week 39 partner's role
①Labour-support prep: learn about epidural analgesia, perineal massage, labour positions and the birthing ball; a prepared companion beats an empty one. ②Talk or sing close to the belly at a set time daily to build a father’s voice the baby recognises. ③Confirm all contacts and transport to hospital, and keep the phone fully charged. ④Help ease your partner’s anxiety: be present, listen, do relaxing exercises together and stay calm.
Week 39 checkup reminders
Week 39: weekly prenatal visit + NST fetal-heart monitoring. At 39 completed weeks, elective cesarean is possible (if medically indicated, such as breech, placenta praevia or fetal distress). Without an indication, generally await natural onset, or follow the doctor’s arrangement for induction before week 41. Keep counting fetal movements daily.
Week 39 key concerns
Signs that need immediate care at week 39
If any of the following occurs, contact your obstetrician or seek medical help promptly: ① bloody show (mucus with blood streaks) with no contractions can be observed at home first, waiting for regular contractions; ② rupture of membranes → lie flat immediately with the hips raised and seek care; ③ regular contractions (the 511 rule) → go to hospital; ④ clearly reduced fetal movement (fewer than 10 in 2 hours or less than half the usual); ⑤ severe headache, blurred vision or severe upper-abdominal pain with raised blood pressure or sudden oedema (watch for preeclampsia); ⑥ itching all over, especially the palms and soles with no rash (watch for ICP); ⑦ a fever over 38℃ that does not come down; ⑧ one leg swollen, hot and painful, or sudden breathlessness and chest pain (watch for a clot/pulmonary embolism).
Week 39 frequently asked questions
Bloody show vs rupture of membranes?
Bloody show = a little blood-streaked or pink mucus in the discharge (like the end of a period); with no contractions you can observe at home first. Ruptured membranes = colourless clear fluid leaking continuously and uncontrollably. Bloody show can wait for regular contractions; ruptured membranes need immediate lying flat with raised hips and medical care.
What labour signals are there at week 39?
Common signals: ①regular contractions (the 511 rule); ②rupture of membranes; ③bloody show (mucus plug passing, possible onset within 24-48 hours); ④a sense of diarrhoea or lumbar soreness (the body preparing for birth). Contact obstetrics if unsure.
How much weight gain is normal at week 39?
A cumulative gain of about 12-16kg by week 39 is common. Weight may plateau or dip a little at term — normal; the recommended total gain is about 11.5-16kg (standard BMI), so watch the overall trend.
How to read the week-39 ultrasound report?
The three measurements at 39 weeks: BPD (biparietal diameter) about 92.1mm, AC (abdominal circumference) about 344.5mm, and FL (femur length) about 71.1mm. If the three are in step, growth is good; a single slight deviation isn’t necessarily abnormal — go by your obstetrician’s overall assessment.
Can I have an elective cesarean at week 39?
At 39 completed weeks, with a clear medical indication (such as breech, placenta praevia, fetal distress or a previous cesarean), elective cesarean can be arranged. Without an indication, generally awaiting natural onset or inducing before week 41 is advised, and an elective cesarean is preferably not before 39 weeks.
Is a smaller fetal-movement amplitude normal at week 39?
After term, as space shrinks, the amplitude (force/range of kicks) can decrease, but the count should not clearly drop. Count fetal movements 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.
How big is the baby’s head at week 39?
At 39 weeks the baby’s biparietal diameter is about 9.2cm — the largest part passing through the birth canal. Judge with your obstetrician based on the femur length and pelvic assessment.
Is there a recommended exercise duration in pregnancy?
ACOG recommends about 150 minutes of moderate-intensity exercise accumulated weekly. At week 39 labour could start at any time; favour walking and stretching, avoiding intense exercise and pressure on the abdomen; walking also helps engagement and cervical ripening. Seek care immediately for regular 511 contractions, rupture of membranes, bleeding or clearly reduced movement.
Can I have sex at week 39?
After term, sex may trigger contractions and is generally advised against. With no contraindications and the doctor’s permission, very gentle sex could be acceptable, but most doctors advise pausing; see a doctor immediately for bleeding, pain or fluid leakage after sex.
What about leg cramps and oedema at week 39?
For a cramp, flex the foot and massage the calf; prevention centres on calcium, magnesium, water and stretching before bed. Continued oedema and cramps: raise the legs, lie on your left side, walk to promote return flow and limit salt; if the 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 39?
Still 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; GDM mums strictly control sugar, and especially avoid castor oil and other "labour-inducing foods" — no reliable evidence and they may cause diarrhoea and discomfort; induction is done properly in hospital.
What about heartburn and bloating at week 39?
At term the stomach space frees up and heartburn mostly eases, but one overfull meal before labour still brings reflux and affects comfort while counting movements. 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 39?
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. Iron supplements can worsen constipation — discuss adjusting them with your doctor; choose a pregnancy-safe medication for severe constipation and avoid stimulating laxatives to prevent pre-labour discomfort.
What about lower-back and pubic-bone pain at week 39?
At term, forward centre of gravity and relaxin loosening the pelvic joints make back/pubic pain more grinding while waiting to start. 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 39?
Anticipation and anxiety before labour are common, and the more anxious the harder to sleep. Use a pregnancy pillow for support, side-sleep, soak your feet before bed, do mindful meditation and walk in the day; communicate more with your partner; remember a relaxed mood helps natural oxytocin secretion; if anxiety is marked, talk to the doctor and an NST confirming all is well reassures you.
Are frequent false contractions at week 39 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 labour; even past the due date, keep counting movements daily and go to the doctor for anything that feels "off".
After bloody show, how soon will I give birth?
After bloody show (mucus plug passing), most women start regular contractions within 24-48 hours, but some start days later. With no contractions you can observe at home and rest; seek care immediately if regular contractions, rupture of membranes or reduced movement appear.
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). By week 39 it should be at the door, phone charged, and the route and obstetrics number at hand — ready to go.
What labour-inducing preparations can I make at week 39?
Safe practices: walking (promotes engagement and cervical ripening) and staying relaxed. Don’t try castor oil, spicy foods or nipple stimulation on your own — they may bring risks and need doctor guidance. Real induction is done in hospital with standard methods (such as a balloon catheter or oxytocin).
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
- Guidelines for Pre-conception and Prenatal Care (Chinese Society of Obstetrics and Gynecology)
- ACOG Methods for Estimating the Due Date (Committee Opinion No.700)
- WHO INTERGROWTH-21st fetal growth standards
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 39 daily focus
Key daily tips for this week; tap any item to view the full development and guidance for that day.
Day 1The baby’s hair is clearly longer — at birth your first glance will see the fine newborn hair on its head’s crown. After engagement the hair lies against the head, and ultrasound sometimes faintly shows strands floating in the amniotic fluid. Subcutaneous fat is in place in every corner; the face is full and rounded. Today’s baby is already entirely the look of a newborn — you no longer need to imagine; this is the little person you will soon be holding.Day 2Don’t try any folk labour-inducing remedies: castor oil (can cause severe diarrhoea and dehydration), spicy foods (they irritate the bowel without helping contractions), excessive stair-climbing (unstable centre of gravity in late pregnancy risks falls), and self-nipple stimulation (may trigger unmanageable over-strong contractions). Truly safe induction is done in hospital with evidence-based methods — cervical-balloon dilation, artificial rupture of membranes and oxytocin infusion — all under strict obstetric monitoring.Day 3Do 10 minutes of mindful meditation daily: sit in a quiet dim room, close your eyes, put a hand on your chest to feel your heartbeat → shift attention to the abdomen to feel the baby’s slight movements → say softly to yourself "my body knows how to give birth, the baby knows how to be born" → breathe deeply five times. From this week to week 41 every day may be a wait, and this mindful practice turns "the anxiety of waiting" into "the calm of expectation" — a skill you can also use during labour.Day 4Dad-to-be, this week focus on learning two labour-support skills: ①how to help her count contraction frequency (phone stopwatch, from the start of this contraction to the start of the next, recording each interval); ②when a contraction comes, help her count the breathing rhythm in a low, calm voice: "in — out — in — out", while slowly circling a palm on her lower back (lumbosacral soreness is the most uncomfortable spot for many women). Neither needs a medical background — just your focused presence.Day 5Bloody show — you find pale pink or blood-streaked mucus on the tissue when using the toilet; this is the cervical plug falling off, usually signalling onset within 24-48 hours. What you can do now: notify the father, take a warm shower, put on clean underwear, eat a normal meal, move the hospital bag from the door to hand, and set the obstetrics quick-call on the phone. Don’t rush to hospital — bloody show alone without contractions or rupture will send you home again, and the energy of the round trip is better spent in comfortable home waiting.Day 6From today, keep your phone 24/7, un-silenced and at least 70% charged, and set a dedicated labour ringtone (distinct from everyday calls so you identify it in a second at a critical moment). Set the father’s phone the same way. Place a power bank and cable by the bed, in the living room and the bathroom — so you can grab one and stuff it into the bag anytime. When real contractions come, you won’t have time to hunt for a charger.Day 7At 39 completed weeks, with a clear medical indication (breech / placenta praevia / oligohydramnios / fetal distress, etc.), an elective cesarean can be arranged. Without an indication, the best choice is to await natural onset — babies born naturally at 39-40 weeks have their lungs, brain and thermoregulation at the best maturity. Don’t press the doctor to operate early because you "can’t wait" — every minute of patience you give in the final week repays you with more mature baby organs.
Content sources & notes
This guide references WHO INTERGROWTH-21st standards, the China Prenatal & Pregnancy Care Guide, ACOG clinical guidelines and BabyCenter (medically reviewed).
View the full fetal BPD/AC/FL reference table (weeks 14–42) →