Week 27 · Second trimester
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Week 27 fetal development and pregnancy guide — length about 36.6cm, weight 约875g (about the size of a a cauliflower)

Your baby is now about 36.6cm and 约875g, about the size of a a cauliflower.

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

View each day of week 27 →

Week 27 fetal development milestones: length / weight / ultrasound data

Key developmental changes during week 27:

  • More sulci and gyri appear on the cerebral cortex, the surface area increases and neurons proliferate rapidly.
  • The lungs keep maturing, and surfactant approaches the level needed to sustain breathing on its own.
  • The immune system matures gradually — a large amount of maternal IgG passes through the placenta in the third trimester to give the baby early protection after birth.
  • Regular rapid-eye-movement (REM) sleep appears, so the baby may be "dreaming".
  • Hearing matures and the baby can tell the parents’ different voices.
  • Subcutaneous fat keeps accumulating and the body gradually rounds out.
  • The lungs rhythmically practise breathing movements (drawing in and out amniotic fluid).
  • The hand and foot movements are strong, and fetal movements can be seen from outside the belly.
  • Hair keeps growing, and the eyebrows and eyelashes are more obvious.
  • About 36.6cm long, about the size of a cauliflower, weighing about 875g (the last week of the second trimester).
Illustration of your baby about the size of a cauliflower at week 27 (about 36.6cm/约875g)
Week 27 size: about the size of a a cauliflower
BPD (biparietal diameter)67.7mmWidth across the head; reflects brain development
AC (abdominal circumference)225.8mmAbdomen circumference; reflects nutrient absorption
FL (femur length)49mmThigh bone length; tracks gestational age
Ultrasound parameters at week 27: BPD 67.7 mm, AC 225.8 mm, FL 49 mm (median reference)
Week 27 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 27 daily development

Your baby quietly grows every day of week 27. Tap any day to see fetal development, maternal changes, and daily guidance for that day.

183Day 1REM (rapid-eye-movement) sleep has appeared this week — which may mean your baby is "dreaming"! Though we can’t know what the baby dreams about, REM sleep is crucial for consolidating and developing the brain’s neural networks. Your normal sleep and routine today, producing melatonin and circadian rhythm, are also helping the baby build its own day-night rhythm — your routine is your baby’s routine.184Day 2Weigh yourself, take out your pregnancy weight record (or phone memo), and review the gain trend from week 13 to 27: a standard-BMI woman gains about 8-11kg cumulatively, about 0.4-0.5kg a week. If you’re on track — congratulations, you’ve given your baby a stable and precise growing environment. If gain is too fast or too slow, send the data to your prenatal-care doctor and start adjusting diet and exercise from the third trimester — next week officially enters the third trimester, and today is your last tuning window.185Day 3Shortness of breath isn’t panic — it’s the uterus pressing the diaphragm. As the baby grows, it pushes the diaphragm up, reducing the lungs’ room to expand, so you gasp after a little movement. Ways to relieve it: sit up straight with the chest out to give your lungs more room, prop your back up 15-30 degrees when sleeping, and eat smaller meals more often so your stomach doesn’t swell and press the diaphragm further. If breathing difficulty comes with chest pain, fever or blue lips, seek care immediately to rule out pulmonary embolism.186Day 4Make a "second-trimester memoir" — combine your belly photos from weeks 13 to 27, ultrasound images, weight records, prenatal reports and a few lines from your pregnancy diary into a simple electronic album, or print and clip it into your diary. This time capsule will be repeatedly flipped through on the night before delivery and at the baby’s one-month celebration — it’s the most real record of life.187Day 5Mark on the calendar that prenatal visits (from week 28) change to every two weeks — from next week you enter a higher-frequency rhythm of visits: checking blood pressure, weight, fundal height, abdominal circumference, fetal heart and urine protein so that gestational hypertension and preeclampsia are caught early. At the same time start researching the booking path for the 30-32-week small-scan ultrasound; don’t put it off until next month.188Day 6Do a 5-minute deep-breathing practice with soothing music daily: inhale 4 seconds → hold 2 seconds → exhale 6 seconds, repeating 5-8 rounds. This is the base movement of the Lamaze delivery breathing technique; start getting familiar with the rhythm now and add more variations after week 28. Imagine breathing out bodily tension and anxiety with each exhale, and breathing in calm and endurance with each inhale — you’re building the "breathing muscles" for delivery.189Day 7Make steamed fish with mixed vegetables today: choose low-mercury fish (sea bass/cod/salmon) topped with ginger and scallion, steam 8-10 minutes, and serve with lightly stir-fried broccoli and bell pepper — DHA + quality protein + vitamin C all in one meal. The DHA in fish is vital for your baby’s brain development and retinal maturation in these final weeks; eat it 2-3 times a week. Don’t steam the fish too long — it’s tenderest just as the flesh turns white and cooked through.

Week 27 belly changes

Illustration of belly changes at week 27: uterine position and abdominal prominence

At week 27 (second trimester) the uterus rises from the pelvis into the abdomen and most mums start to "show" — a gentle bump. First-time mums usually show a little later than mums who've been pregnant before; the fundal height sits between the navel and pubic bone.

Week 27 maternal body changes and common symptoms

  • The uterine fundus is about 7cm above the navel.
  • Cumulative weight gain is about 8-11kg.
  • Breathing may become quicker (the growing uterus pushes the diaphragm upward).
  • Fetal movements are strong and regular with obvious active periods.
  • Lower-back pain, pelvic pain and pubic-bone pain may worsen.
  • Heartburn, bloating, constipation and haemorrhoids may appear.
  • Swelling of the hands and feet, leg cramps, and varicose veins.
  • The breasts enlarge, colostrum is secreted, and Braxton Hicks contractions may increase.

Week 27 nutrition advice and recommended recipes

The last week of the second trimester — review your current weight against pre-pregnancy to see if it’s in the recommended range (about 11.5-16kg over the whole pregnancy for a standard BMI). Prepare for the third trimester: protein needs rise (about 85g a day), so keep calcium, iron and DHA ample. Daily targets: quality protein about 70-80g, calcium 1000mg, iron 27mg, DHA 200-300mg, fiber 25-30g, iodine 230μg. Keep controlling sugar (especially with GDM). Avoid alcohol, raw or unpasteurised milk products, high-mercury fish, caffeine ≤200mg a day.

DHA1000mgBrain & vision development
Recommended recipeSteamed fish with mixed vegetables

Steamed low-mercury fish (sea bass, sole) keeps the original flavour and provides DHA and quality protein; served with seasonal vegetables, low in oil and salt, it’s a balanced, easy-to-digest third-trimester meal. Make sure the fish is fully cooked and free of bones; eat in moderation if you have gout.

Week 27 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. With the third trimester near, you can add "breathing practice" to your routine: play soothing music and do deep breathing (such as inhale 4 seconds → hold 2 seconds → exhale 6 seconds) — this is both good relaxation and groundwork for the later Lamaze delivery breathing; the main beneficiary is you (relieving tension and steadying mood). What you can do: talk gently 5-10 minutes at a set time daily and stroke the belly; do deep breathing with music for 5-10 minutes. Cheerful, relaxed feelings are the best fetal education.

Week 27 partner's role

①Review the 14 weeks of the second trimester with your partner: gather photos, a diary, ultrasound results and fetal-movement records and make a "second-trimester memoir" to give the future baby. ②Learn delivery knowledge together and practise deep-breathing relaxation with her. ③Help her relieve shortness of breath and back pain: remind her to slow down, prepare cushion support and gently massage. ④Plan the third trimester: prenatal visits change to every two weeks, so arrange your accompanying time ahead.

Week 27 checkup reminders

The last week of the second trimester. From week 28 you enter the third trimester: prenatal visits change from monthly to every two weeks, and you begin formally counting fetal movements every day. If the 24-28-week OGTT hasn’t been done, complete it as soon as possible. Book the 30-32-week small scan (anomaly-late ultrasound) ahead to assess fetal growth, amniotic-fluid volume, placental position and maturity, fetal position, and umbilical blood flow.

Week 27 key concerns

Complete the OGTT (if not done)Summarise second-trimester weight gainPrepare for the third trimesterArrange two-weekly prenatal visits30 minutes of moderate exercise daily (ACOG recommends 150 minutes a week across pregnancy)

Signs that need immediate care at week 27

If any of the following occurs, contact your obstetrician or seek care promptly: ① persistent vaginal bleeding or brown discharge; ② sudden leakage of fluid from the vagina (possible premature rupture of membranes); ③ regular contractions (once every 10 minutes or more often) with lumbar heaviness/downward pressure (watch for preterm labour — at 27 weeks the survival rate under care is already fairly high, so prompt care is key); ④ a fever over 38℃ that does not come down; ⑤ severe headache, blurred vision or severe upper-abdominal pain (watch for preeclampsia — check blood pressure and urine protein); ⑥ itching all over, especially palms and soles with no rash (watch for ICP); ⑦ sudden shortness of breath, chest pain or blue lips (watch for pulmonary embolism — seek care immediately); ⑧ clearly reduced fetal movement or swelling, warmth and pain in one leg (watch for a clot).

Week 27 frequently asked questions

What’s different at week 27?
This is the last week of the second trimester; next week you enter the third trimester. The baby shows REM sleep and may be "dreaming", the lungs are close to breathing on their own, and the immune system starts receiving antibodies from the mother. For you, prepare for the third trimester: visits change to every two weeks, start counting fetal movements, and get the hospital bag ready.
Can a baby born at week 27 survive?
The survival rate of a 27-week preterm baby under NICU care is already fairly high (about 80%-90%, though it varies between hospitals) and the risk of severe disability is clearly lower than for babies born earlier. But it’s still not an ideal delivery time — keeping the pregnancy to term is best for the baby; seek care promptly at preterm-labour signs (regular contractions, broken waters, bleeding).
Is shortness of breath at week 27 normal?
Yes. The growing uterus pushes the diaphragm up, and pregnancy oxygen demand rises, so it’s easy to feel breathless. Slow your movements, sit up straight with the chest out to give your lungs more room, and prop your upper body up a little when sleeping. If breathing difficulty comes on suddenly with chest pain or blue lips, seek care immediately to rule out pulmonary embolism.
What changes in prenatal visits after week 28?
After entering the third trimester at week 28, visits change from monthly to every two weeks (with more frequent weekly visits after week 36), and you start counting fetal movements daily. The third trimester also arranges the small scan (weeks 30-32), GBS screening (weeks 35-37) and NST fetal-heart monitoring (generally from week 34).
How do I read the week-27 ultrasound report?
The three measurements at 27 weeks: BPD (biparietal diameter) about 67.7mm, AC (abdominal circumference) about 225.8mm, and FL (femur length) about 49.0mm, reflecting head, abdomen and leg development. If the three are in step, growth is good; a single slight deviation isn’t necessarily abnormal — go by your obstetrician’s overall assessment.
How much weight should I gain by week 27 / in the second trimester?
A cumulative gain of about 8-11kg by week 27 is common. For a standard BMI, the whole pregnancy recommends about 11.5-16kg, with the second and third trimesters at about 0.4-0.5kg a week. Watch the overall trend and manage by BMI with a weight-gain calculator.
Do I need to start counting fetal movements at week 27?
Nearly. Systematic counting usually starts from week 28: pick one hour in the morning, afternoon and evening each, count fetal movements while lying on your left side or sitting; normally ≥10 times within 2 hours. This week you can first become familiar with the method and your baby’s routine. Seek care any time if movement clearly decreases.
What about lower-back and pubic-bone pain at week 27?
They come from a forward centre of gravity and relaxin loosening the ligaments and pelvic joints. Avoid long standing or sitting, wear supportive low-heeled shoes, side-sleep with a pregnancy pillow, use a belly-support belt, do prenatal yoga and pelvic-floor exercise, and apply local warmth. Sharp pain on one side or with bleeding and fever needs care.
Is there a recommended exercise duration in pregnancy?
ACOG advises women without complications about 150 minutes of moderate-intensity exercise accumulated weekly (walking, prenatal yoga, swimming), split over 5 days at about 30 minutes a day. Avoid intense exercise and pressure on the abdomen; stop and seek care for pain or bleeding.
Should I get the flu vaccine in pregnancy?
It’s recommended. The CDC and ACOG recommend that pregnant women receive the inactivated flu vaccine: pregnant women are at higher risk of severe flu, the vaccine protects mother and baby, and it is safe at every stage. During flu season (September to April) you can get vaccinated; tell them you’re pregnant.
Can I have sex at week 27?
If there’s no placenta praevia, bleeding, cervical insufficiency or threatened preterm labour, gentle sex is fine using positions that don’t press on the belly and with gentle movements. Pause if you feel unwell or the doctor advises against it; see a doctor for post-sex bleeding or pain.
What if I sleep poorly at week 27?
A growing belly, frequent urination and trouble turning over affect sleep. Use a pregnancy pillow for support, sleep on your left side, soak your feet before bed to relax, reduce evening fluids to cut night urination, and exercise moderately during the day. Avoid screens before bed and caffeinated drinks.
What about leg cramps at week 27?
When a cramp hits, flex the foot and massage the calf. Prevention: supplement calcium and magnesium, drink water, stretch before bed, wear support stockings, and avoid long standing or sitting. If cramps are frequent with weakness and numbness, check blood calcium, magnesium and electrolytes at a prenatal visit.
What should I avoid eating at week 27?
Avoid raw or undercooked meat, fish and eggs, high-mercury large fish, unpasteurised dairy, alcohol, caffeine over 200mg a day, and excess animal liver. If you have GDM, strictly control refined sugar and sugary drinks as well.
What about constipation and haemorrhoids at week 27?
Eat more coarse grains and vegetables for dietary fiber, drink 1.5-2L of water daily, walk after meals, and toilet regularly without squatting long; soak in warm water for haemorrhoids. In serious cases consult a doctor about a pregnancy-safe medication; discuss with your doctor if iron worsens constipation.
What about heartburn at week 27?
Eat smaller meals more often and chew slowly, sit or stand for 30 minutes after meals before lying down, avoid eating in the 2-3 hours before bed, avoid spicy, greasy, overly sweet food and carbonated drinks, and prop up your upper body when sleeping. In serious cases, use a pregnancy-safe antacid under a doctor’s guidance.
Is more discharge at week 27 normal?
Higher oestrogen increases white discharge; milky-white or clear and odourless is normal. Watch for turning yellow-green, foul-smelling, with itching (infection), or a sudden large amount of watery leakage (rupture of membranes) — seek care the moment these appear. Wear cotton underwear and don’t douche.
What about swelling at week 27?
Mild swelling after long standing or sitting is common; raise your legs, lie on your left side, walk to promote return flow, and moderately limit salt. If the swelling suddenly worsens, spreads to the face and hands, or comes with headache or vision changes, check your blood pressure to rule out preeclampsia.
⚡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 27 daily focus

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

Day 1REM (rapid-eye-movement) sleep has appeared this week — which may mean your baby is "dreaming"! Though we can’t know what the baby dreams about, REM sleep is crucial for consolidating and developing the brain’s neural networks. Your normal sleep and routine today, producing melatonin and circadian rhythm, are also helping the baby build its own day-night rhythm — your routine is your baby’s routine.Day 2Weigh yourself, take out your pregnancy weight record (or phone memo), and review the gain trend from week 13 to 27: a standard-BMI woman gains about 8-11kg cumulatively, about 0.4-0.5kg a week. If you’re on track — congratulations, you’ve given your baby a stable and precise growing environment. If gain is too fast or too slow, send the data to your prenatal-care doctor and start adjusting diet and exercise from the third trimester — next week officially enters the third trimester, and today is your last tuning window.Day 3Shortness of breath isn’t panic — it’s the uterus pressing the diaphragm. As the baby grows, it pushes the diaphragm up, reducing the lungs’ room to expand, so you gasp after a little movement. Ways to relieve it: sit up straight with the chest out to give your lungs more room, prop your back up 15-30 degrees when sleeping, and eat smaller meals more often so your stomach doesn’t swell and press the diaphragm further. If breathing difficulty comes with chest pain, fever or blue lips, seek care immediately to rule out pulmonary embolism.Day 4Make a "second-trimester memoir" — combine your belly photos from weeks 13 to 27, ultrasound images, weight records, prenatal reports and a few lines from your pregnancy diary into a simple electronic album, or print and clip it into your diary. This time capsule will be repeatedly flipped through on the night before delivery and at the baby’s one-month celebration — it’s the most real record of life.Day 5Mark on the calendar that prenatal visits (from week 28) change to every two weeks — from next week you enter a higher-frequency rhythm of visits: checking blood pressure, weight, fundal height, abdominal circumference, fetal heart and urine protein so that gestational hypertension and preeclampsia are caught early. At the same time start researching the booking path for the 30-32-week small-scan ultrasound; don’t put it off until next month.Day 6Do a 5-minute deep-breathing practice with soothing music daily: inhale 4 seconds → hold 2 seconds → exhale 6 seconds, repeating 5-8 rounds. This is the base movement of the Lamaze delivery breathing technique; start getting familiar with the rhythm now and add more variations after week 28. Imagine breathing out bodily tension and anxiety with each exhale, and breathing in calm and endurance with each inhale — you’re building the "breathing muscles" for delivery.Day 7Make steamed fish with mixed vegetables today: choose low-mercury fish (sea bass/cod/salmon) topped with ginger and scallion, steam 8-10 minutes, and serve with lightly stir-fried broccoli and bell pepper — DHA + quality protein + vitamin C all in one meal. The DHA in fish is vital for your baby’s brain development and retinal maturation in these final weeks; eat it 2-3 times a week. Don’t steam the fish too long — it’s tenderest just as the flesh turns white and cooked through.

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) →

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