Week 20 · Second trimester
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Week 20 fetal development and pregnancy guide — length about 16.4cm, weight 约300g (about the size of a a banana)

Your baby is now about 16.4cm and 约300g, about the size of a a banana.

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

View each day of week 20 →

Week 20 fetal development milestones: length / weight / ultrasound data

Key developmental changes during week 20:

  • Estimated by head-to-heel length (the birth-length measure) at about half of what it will be at birth, but its weight is only about one-tenth (it will catch up quickly later).
  • The taste buds are fully developed, able to distinguish different tastes (related to the mother’s diet).
  • Meconium (dark green) accumulates in the intestine, to be passed after birth.
  • The skin is thicker with more obvious layers, and the vernix continues to protect it.
  • Subcutaneous fat keeps increasing, and the body outline becomes softer.
  • It sucks, swallows and hiccups more expertly, with continued digestive rehearsal.
  • The bones keep ossifying and the long bones grow firmer.
  • About 16.4cm long, about the size of a banana, weighing about 300g.
  • The eyes can move, but the eyelids remain closed (they reopen only from around weeks 26-28).
  • Hearing is still developing; it grows more sensitive to outside sounds but cannot yet truly hear them.
Illustration of your baby about the size of a banana at week 20 (about 16.4cm/约300g)
Week 20 size: about the size of a a banana
BPD (biparietal diameter)46.1mmWidth across the head; reflects brain development
AC (abdominal circumference)149.6mmAbdomen circumference; reflects nutrient absorption
FL (femur length)31mmThigh bone length; tracks gestational age
Ultrasound parameters at week 20: BPD 46.1 mm, AC 149.6 mm, FL 31 mm (median reference)
Week 20 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 20 daily development

Your baby quietly grows every day of week 20. Tap any day to see fetal development, maternal changes, and daily guidance for that day.

134Day 1The pregnancy is officially half over (week 20 of about 40)! Congratulations on completing the first half, filled with morning sickness, drowsiness and anxiety. In the next 20 weeks the baby will race from 300g to about 3-3.5kg. Today write a short "halfway letter" to yourself and the baby: no need for beautiful prose, three lines will do — "Today is week 20; you’re as big as a banana. Halfway there; I made it through about 90% of those moments carried alone." This letter will help you revisit the whole journey on the night before delivery.135Day 2Today officially start sugar-control mode: clear the sugary drinks (cola, milk tea, fruit juices, flavoured yoghurt) out of the fridge and replace them with water plus lemon slices plus mint leaves. Change white-rice staples to half white rice and half brown rice or millet mixed and cooked; low-GI staples let blood sugar rise steadily and lower the GDM risk from second-trimester insulin resistance. Choose low-sugar, high-fiber fruit like strawberries, blueberries, cherries and kiwifruit, keeping the daily total at 200-350g in two servings.136Day 3Swollen legs? Raise your feet above heart level: after getting home from work, lie on the sofa or bed with two cushions under the calves so the ankles are above the knees and the knees above the heart, holding for 15-20 minutes. At the same time, lightly push with your fist along the back of the calf from the ankle toward the knee (the lymph-return direction), without massaging too deeply. If the swelling suddenly worsens above the mid-calf and won’t ease after plenty of rest, have your blood pressure checked to rule out preeclampsia.137Day 4Today’s ritual for Dad-to-be: cook a balanced, nutritious dinner (steamed fish + stir-fried vegetables + multigrain rice + fruit), then on a nice sheet of letter paper hand-write the first letter to the future baby — "Baby, you’re halfway here. When you come into the world, Dad wants to do these three things with you…". Put the letter into the pregnancy diary; when the baby is one month old, take it out and read it to him/her — a precious gift across time.138Day 5The anomaly scan is this week or next! Confirm the date and hospital address, the report time, and which building and department. If the baby isn’t cooperating during the check (facing inward or curled up), don’t be nervous — lie on your side for a few minutes, drink warm water, eat a small piece of chocolate, or walk a few steps so the baby changes position; the doctor will wait for it to turn around and continue. Bring your partner in; the wall screen shows the baby’s real-time ultrasound image.139Day 6Treat daily fetal education as "a ritual to relax yourself" rather than "a class for the baby". Play a soothing song you like (volume no more than 60 decibels), lie on your side on the sofa for 15 minutes, and cup the belly to feel the baby’s activity. Speak a couple of lines if you want, or stay quiet sensing the heartbeat and breath. You are not anxious, not forcing yourself — the more relaxed you are, the less stress hormone the baby feels in the womb.140Day 7This week is a key node for iron: blood volume is near its peak and red cells are diluted, so many women develop physiological anaemia between weeks 18-22. Today choose for lunch "red meat (lean beef/lean pork, about the palm-sized 80g) + vitamin C vegetables (broccoli/bell pepper/tomato) + multigrain rice", and after the meal skip fruit and strong tea — vitamin C aids iron absorption while tannic acid hinders it. Walk 10 minutes after the meal to promote circulation and iron transport.

Week 20 belly changes

Illustration of belly changes at week 20: uterine position and abdominal prominence

At week 20 (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 20 maternal body changes and common symptoms

  • The uterine fundus reaches the level of the navel.
  • Lower-back pain may become more obvious (forward centre of gravity, relaxed ligaments).
  • Leg oedema appears after long standing or sitting.
  • The abdomen bulges clearly and clothes grow tight.
  • The breasts keep enlarging and a suitable bra is needed.
  • Nasal congestion and gum bleeding are possible.
  • Pigmentation (pregnancy mask, abdominal line, areolae) becomes more obvious.
  • A few women have round-ligament pain or leg cramps.

Week 20 nutrition advice and recommended recipes

From this week look ahead to controlling blood sugar. Insulin sensitivity falls during pregnancy, and GDM is usually screened at weeks 24-28; build good habits now: cut down on sugary drinks, replace sweets with fruit (about 200-350g a day in portions), mix coarse grains into staples, and control refined carbohydrates. Daily targets: about 340kcal extra (ACOG), calcium 1000mg, iron 27mg, DHA 200-300mg, folate 400-800μg (recommended through the whole pregnancy), iodine 230μg, fiber 25-30g, about 70g of quality protein. Avoid alcohol, raw or unpasteurised milk products, high-mercury fish, and keep caffeine to ≤200mg a day.

DHA200-300mgBrain & vision development
Recommended recipeBrown rice with steamed vegetables

Brown rice is low-GI, filling and steadies blood sugar; steamed vegetables keep their nutrients with less oil, making it a good staple pairing during blood-sugar control. You can add soy products or lean meat for protein; if your blood sugar runs high, watch the total staple amount — don’t overeat just because it is "healthy".

Week 20 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 stimulation makes the baby smarter. On light stimulation: shining a torch on the belly for "visual/five-sense fetal education" has limited evidence — the baby’s eyelids reopen only around weeks 26-28, so light barely reaches the retina, and there’s no need to deliberately shine a light. This week you can: talk gently for 5-10 minutes at a fixed time daily and lightly stroke the belly to build the parent-child connection; choose soothing music/white noise at ≤60 decibels for 15-20 minutes a day for your own relaxation; and keep a mood diary as a pregnancy keepsake. Understanding fetal education as "looking after Mum’s mood" is the most practical; don’t chase "all-round sensory training".

Week 20 partner's role

①You’ve passed the halfway point! Plan a "halfway ceremony": cook a nutritious dinner, write a letter to the future baby, review the pregnancy diary. ②Talk and sing close to the belly at a fixed time daily to build a father’s voice the baby recognises. ③Help your partner control blood sugar: prepare low-GI healthy snacks and take evening walks together. ④Accompany/confirm the anomaly scan (weeks 20-24) and record the check time and results.

Week 20 checkup reminders

Weeks 20-24: the anomaly scan (systematic ultrasound), the most comprehensive malformation check — make sure to complete it on time (popular hospitals need advance booking). At the same time look ahead to the GDM screen (glucose tolerance, usually at weeks 24-28), starting blood-sugar-control habits this week. If the mid-term screen/NIPT was not done, confirm with the doctor in good time whether to catch it up.

Week 20 key concerns

Complete the anomaly scanStart blood-sugar management (sugar-control habits)Limit salt to prevent oedemaHalfway ceremony30 minutes of exercise daily (ACOG recommends 150 minutes a week across pregnancy)

Signs that need immediate care at week 20

If any of the following occurs, contact your obstetrician or seek medical help promptly: ① persistent spotting or brown discharge; ② sudden leakage of fluid from the vagina (possible preterm rupture of membranes); ③ persistent or severe abdominal pain, with fever, or regular contraction-like tightening; ④ a fever over 38℃ that does not come down; ⑤ severe headache, blurred vision or severe upper-abdominal pain (watch for pregnancy high blood pressure/preeclampsia — the risk begins to rise after week 20; if it appears, have blood pressure and urine protein checked); ⑥ painful urination, frequent/urgent urination or blood in the urine (urinary-tract infection); ⑦ swelling, warmth or pain in one leg (watch for a clot); ⑧ oedema spreading from the ankle up the calf that does not ease with rest, or with headache/vision changes (watch for preeclampsia).

Week 20 frequently asked questions

Can the anomaly scan detect everything?
It can screen for most structural malformations, but not all (such as small heart defects, functional problems, metabolic diseases). The overall detection rate is about 60-80%, depending on the type of malformation and the hospital’s level; low risk is not the same as zero risk.
Can the anomaly scan see the baby’s face?
Yes, the check looks at facial structures (cleft lip, cleft palate, etc.). Some hospitals provide 3D/4D photos (possibly charged extra). A poor baby position may prevent seeing them, needing movement or a rescheduled re-check.
What should I note about blood-sugar control at week 20?
GDM is usually screened at weeks 24-28. Look ahead now: cut sugary drinks, eat fruit 200-350g a day in portions, mix coarse grains into staples, control refined carbs, and walk after meals. Don’t blindly diet and starve yourself — a balanced, portioned approach is steadier.
What should I note about the halfway point at week 20?
The pregnancy is exactly half done! The focus is regular prenatal visits, balanced weight control, consistent exercise and a good mood. You can use a "halfway ceremony" to record your feelings and write the baby a letter, both as a keepsake and to help you relax.
How to read the week-20 ultrasound report?
The three measurements at 20 weeks are BPD (biparietal diameter) about 46mm, AC (abdominal circumference) about 150mm, and FL (femur length) about 31mm. If the three are in step, the head, abdomen and legs are developing well; a single slight deviation isn’t necessarily abnormal — go by the doctor’s overall assessment.
Weight at week 20?
For a standard BMI, about 0.4-0.5kg a week in the second trimester, with a cumulative gain of roughly 4-6kg by week 20 being common. Watch the trend — you can use a weight-gain calculator to manage it by BMI — and ask your doctor if it’s too fast or too slow.
Fetal movement at week 20?
Most first-time mothers feel movement at 18-22 weeks; by this week you should be able to feel it (like bubbles or a small fish bubbling). If you still feel none at all, have the week-20 ultrasound confirm; afterwards you can gradually learn to count movements.
Can I get a massage during pregnancy?
Yes; the second trimester is a good window. Choose a therapist with pregnancy-massage qualifications, use the side-lying position, avoid direct pressure on the abdomen and the acupoints near the ankles, and avoid deep leg massage (clot risk).
Is there a recommended exercise duration in pregnancy?
ACOG advises 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 20?
If there’s no placenta praevia, bleeding or cervical insufficiency, 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.
Lower-back pain obvious at week 20?
The forward centre of gravity and relaxed ligaments make lumbar pain common. Avoid standing or sitting too long, wear low supportive shoes, sleep on your side with a pregnancy pillow, do prenatal yoga and pelvic-floor exercises, and apply local heat. Severe pain on one side, or with bleeding or fever, needs medical attention.
Swollen lower legs at week 20?
Mild oedema after long standing or sitting is common; raise your legs, lie on your left side, walk to promote return flow, and limit salt. If the swelling spreads up the calf and doesn’t ease with rest, or comes with headache or vision changes, have your blood pressure checked to rule out preeclampsia.
Constipation at week 20?
Eat more fiber-rich fruit and vegetables, drink 1.5-2L of water daily, walk after meals, and toilet on a regular schedule. In serious cases consult a doctor for a pregnancy-safe laxative.
What should I avoid eating at week 20?
Avoid raw or undercooked meat, fish and eggs, high-mercury large fish, unpasteurised dairy, alcohol, caffeine over 200mg/day, and excess liver.
Can I fly during pregnancy at week 20?
Flying is more comfortable in the second trimester; most airlines don’t require a certificate before 32 weeks and need one after 32 weeks (most prohibit flying after 36 weeks). Choose an aisle seat, stay hydrated, and use compression stockings; ask your doctor first if you have bleeding, pain or placenta problems.
Do I need calcium and iron supplements at week 20?
ACOG recommends about 1000mg calcium and 27mg iron in the second trimester. Give priority to food sources; if prenatal checks show a deficiency, add supplements on the doctor’s advice, taking iron apart from calcium for better absorption.
Increased discharge at week 20?
Higher oestrogen increases white discharge; milky-white, clear and odourless is normal. Yellow-green, foul-smelling, itchy discharge or large amounts of watery leakage needs medical attention; wear cotton underwear and don’t douche.
Stretch marks at week 20?
About 50-90% of pregnant women get them, related to genetics and the speed of weight gain. Steady weight gain, moisturising massage and moderate exercise can reduce them, but they can’t be fully avoided; most fade after delivery.
Abdominal tightening at week 20?
Occasional brief tightening is usually a sensitive uterus or ligament tugging and is common if it resolves on its own. If it becomes regular (every 10 minutes), or comes with pain/bleeding/leakage, seek medical attention.
⚡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 20 daily focus

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

Day 1The pregnancy is officially half over (week 20 of about 40)! Congratulations on completing the first half, filled with morning sickness, drowsiness and anxiety. In the next 20 weeks the baby will race from 300g to about 3-3.5kg. Today write a short "halfway letter" to yourself and the baby: no need for beautiful prose, three lines will do — "Today is week 20; you’re as big as a banana. Halfway there; I made it through about 90% of those moments carried alone." This letter will help you revisit the whole journey on the night before delivery.Day 2Today officially start sugar-control mode: clear the sugary drinks (cola, milk tea, fruit juices, flavoured yoghurt) out of the fridge and replace them with water plus lemon slices plus mint leaves. Change white-rice staples to half white rice and half brown rice or millet mixed and cooked; low-GI staples let blood sugar rise steadily and lower the GDM risk from second-trimester insulin resistance. Choose low-sugar, high-fiber fruit like strawberries, blueberries, cherries and kiwifruit, keeping the daily total at 200-350g in two servings.Day 3Swollen legs? Raise your feet above heart level: after getting home from work, lie on the sofa or bed with two cushions under the calves so the ankles are above the knees and the knees above the heart, holding for 15-20 minutes. At the same time, lightly push with your fist along the back of the calf from the ankle toward the knee (the lymph-return direction), without massaging too deeply. If the swelling suddenly worsens above the mid-calf and won’t ease after plenty of rest, have your blood pressure checked to rule out preeclampsia.Day 4Today’s ritual for Dad-to-be: cook a balanced, nutritious dinner (steamed fish + stir-fried vegetables + multigrain rice + fruit), then on a nice sheet of letter paper hand-write the first letter to the future baby — "Baby, you’re halfway here. When you come into the world, Dad wants to do these three things with you…". Put the letter into the pregnancy diary; when the baby is one month old, take it out and read it to him/her — a precious gift across time.Day 5The anomaly scan is this week or next! Confirm the date and hospital address, the report time, and which building and department. If the baby isn’t cooperating during the check (facing inward or curled up), don’t be nervous — lie on your side for a few minutes, drink warm water, eat a small piece of chocolate, or walk a few steps so the baby changes position; the doctor will wait for it to turn around and continue. Bring your partner in; the wall screen shows the baby’s real-time ultrasound image.Day 6Treat daily fetal education as "a ritual to relax yourself" rather than "a class for the baby". Play a soothing song you like (volume no more than 60 decibels), lie on your side on the sofa for 15 minutes, and cup the belly to feel the baby’s activity. Speak a couple of lines if you want, or stay quiet sensing the heartbeat and breath. You are not anxious, not forcing yourself — the more relaxed you are, the less stress hormone the baby feels in the womb.Day 7This week is a key node for iron: blood volume is near its peak and red cells are diluted, so many women develop physiological anaemia between weeks 18-22. Today choose for lunch "red meat (lean beef/lean pork, about the palm-sized 80g) + vitamin C vegetables (broccoli/bell pepper/tomato) + multigrain rice", and after the meal skip fruit and strong tea — vitamin C aids iron absorption while tannic acid hinders it. Walk 10 minutes after the meal to promote circulation and iron transport.

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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