Week 23 · Second trimester
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Week 23 fetal development and pregnancy guide — length about 28.9cm, weight 约500g (about the size of a a big mango)

Your baby is now about 28.9cm and 约500g, about the size of a a big mango.

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

View each day of week 23 →

Week 23 fetal development milestones: length / weight / ultrasound data

Key developmental changes during week 23:

  • The vestibular system of the inner ear develops further, beginning to sense gravity and acceleration (the mother’s walking is like a "cradle" rocking).
  • The lungs begin to produce surfactant — the key to whether the alveoli can open smoothly and support spontaneous breathing after birth.
  • The kidneys can already filter blood and produce urine passed into the amniotic fluid, taking part in the dynamic balance of amniotic-fluid volume.
  • The activity and sleep cycles gradually become regular, and a sleep-wake cycle takes shape (increasingly in sync with the mother’s routine).
  • Hearing grows keener; a sudden loud sound may trigger a startle reaction.
  • The fingers can make a fist and grasp the umbilical cord, with more coordinated movements.
  • Blood vessels are clearly visible under the thin skin, and the skin is pinkish.
  • The nipples begin to show in the chest area.
  • The centre of blood-making has largely shifted to the bone marrow, and the liver and spleen’s blood-making function gradually weakens (echoing the bone marrow taking over at week 21).
  • About 28.9cm long, about the size of a large mango, weighing about 500g.
Illustration of your baby about the size of a big mango at week 23 (about 28.9cm/约500g)
Week 23 size: about the size of a a big mango
BPD (biparietal diameter)55.5mmWidth across the head; reflects brain development
AC (abdominal circumference)183.4mmAbdomen circumference; reflects nutrient absorption
FL (femur length)39.1mmThigh bone length; tracks gestational age
Ultrasound parameters at week 23: BPD 55.5 mm, AC 183.4 mm, FL 39.1 mm (median reference)
Week 23 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 23 daily development

Your baby quietly grows every day of week 23. Tap any day to see fetal development, maternal changes, and daily guidance for that day.

155Day 1Your baby’s vestibular system matures; when you walk, bend or lie on your side it can sense the direction of gravity — a single lap around the living room is a gentle "rocking" for it. This is why many mothers find the baby quietens during walks and gets active when you stop — regular movement is its lullaby. This evening, walk for 20 minutes after dinner — that is your baby’s natural sleeping prescription.156Day 2Lung surfactant is starting to be produced — the "lubricant" for whether the alveoli can open smoothly and take the first spontaneous breath after birth. Although it couldn’t survive outside the uterus yet, every day accumulates toward that crucial first breath. Today take 5 deep breaths: inhale 4 seconds → hold 2 seconds → exhale 6 seconds; your steady breathing and adequate oxygen support all the baby’s organs (including the lungs) as they keep developing.157Day 3Have a banana smoothie to add potassium and calcium: one ripe banana + 200ml milk + a small spoon of unsweetened yoghurt → blend for 15 seconds with no added sugar. Half an hour after drinking, go for a walk — potassium maintains muscle electrolyte balance and reduces cramps, and calcium supports pregnancy bone metabolism. If blood sugar runs high, halve the banana or swap to an avocado + unsweetened-yoghurt smoothie.158Day 4The belly suddenly tightens and hardens but is painless, resolves on its own within half a minute, and is eased by a change of position — this is a Braxton Hicks contraction, the uterus "rehearsing" for real delivery. Today if you feel one, record the time and duration; if it happens more than 4 times in an hour and turns regular, increasingly dense and painful or with lumbar heaviness, it’s not a rehearsal — contact your doctor immediately to rule out preterm labour.159Day 5This weekend list the hospital-bag items in your phone in three categories: mother (2 nursing bras, 10 maternity pads, 5 disposable underwear, maternity sanitary pads, travel-size toiletries), baby (30 NB diapers, 1 swaddle, 2 one-piece newborn suits, 1 pack of wipes, 3 small towels), and documents/miscellany (both ID cards, social-security card, prenatal records, power bank, small change). No need to buy everything now, but having the list ready means you can cope calmly.160Day 6OGTT is coming (weeks 24-28) — over the next couple of days there’s no need to deliberately change your diet; eat normally. But prepare a few things: fast from 8pm the night before (a little plain water is fine); arrive at the hospital fasting in loose clothes, bring a small snack (wholewheat crackers or nuts) to refuel right after; if you have a family history of diabetes, are overweight or are ≥35, this screen is especially important.161Day 7Today do 10 minutes of gentle prenatal yoga or stretching: cat-cow on all fours 5 times → seated butterfly opening the hips, hold 30 seconds → standing against a wall, arms raised stretching the side. The focus is pelvis and spine mobility with no pressure on the belly — even breathing, no jumping. These loosening moves relieve the lower-back soreness from long sitting and give the baby a flexible "uterus room".

Week 23 belly changes

Illustration of belly changes at week 23: uterine position and abdominal prominence

At week 23 (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 23 maternal body changes and common symptoms

  • The uterine fundus is about 3cm above the navel.
  • Cumulative weight gain is about 5-8kg (about 0.4-0.5kg a week in the second trimester for a standard BMI).
  • Braxton Hicks contractions may appear (brief tightening and hardening of the abdomen that is painless and irregular).
  • Blood volume keeps increasing toward its peak; you may feel a faster heartbeat and fatigue more easily.
  • Swelling of the hands and feet and leg cramps may appear.
  • The breasts enlarge and may secrete a little colostrum.
  • Skin pigment and stretch marks may become more obvious.
  • Nasal congestion and gum bleeding may persist.

Week 23 nutrition advice and recommended recipes

This week blood volume keeps rising (about 40-50% more than before pregnancy by the end), so focus on water and potassium: drink about 1.5-2L of water daily and eat potassium-rich foods (banana, potato, red beans, spinach, orange) to maintain electrolyte balance and relieve oedema and cramps. Daily targets still follow authority guidance: 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 recipeBanana smoothie

Banana provides potassium, and milk provides calcium and protein; one cup tops up electrolytes and energy and is refreshing. Use ripe bananas plus low-fat milk; if blood sugar runs high, reduce the banana and use unsweetened yoghurt instead.

Week 23 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’s vestibular system matures and it can sense the rocking of your movement; moderate walking and prenatal yoga keep you fit and cheerful while the baby grows amid gentle rhythm — but this is "exercise makes Mum’s condition better", not "training" the baby. What you can do: walk daily or do 10-15 minutes of gentle prenatal yoga (avoid intense exercise and pressure on the abdomen); speak gently and lightly stroke the belly at a fixed time; choose soothing music to relax. A cheerful, relaxed mood is the best fetal education.

Week 23 partner's role

①Accompany your partner on walks or gentle prenatal exercise, combining fitness with bonding. ②Help her recognise Braxton Hicks contractions: when the abdomen tightens and hardens, help record the duration and frequency to distinguish true from false contractions. ③Talk or sing close to the belly at a fixed time daily to build a father’s voice the baby recognises. ④Remind and accompany her to drink more water and eat potassium-rich foods, helping relieve oedema and cramps.

Week 23 checkup reminders

Complete the anomaly scan (systematic ultrasound) before week 24 if not yet done — after 24 weeks the fetus grows and calcifies more, so some structures may be hidden. At the same time prepare for the GDM glucose-tolerance test (OGTT, usually at weeks 24-28): keep normal diet for the 3 days before, and start sugar-control habits now. If the mid-term screen/NIPT was abnormal, follow the genetic-counselling process with your doctor.

Week 23 key concerns

Complete the anomaly scan before week 24Prepare for OGTT (sugar-control habits)Supplement potassium and water to ease oedemaRecognise Braxton Hicks contractions30 minutes of moderate exercise daily (ACOG recommends 150 minutes a week across pregnancy)

Signs that need immediate care at week 23

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 false contractions becoming regular (once every 10 minutes or more often), with pain or lumbar heaviness/pressure (watch for preterm labour); ④ a fever over 38℃ that does not come down; ⑤ severe headache, blurred vision or severe upper-abdominal pain (watch for preeclampsia — risk rises after week 20; check blood pressure and urine protein); ⑥ itching all over, especially palms and soles, with no rash (watch for ICP); ⑦ swelling, warmth or pain in one leg (watch for a clot, different from ordinary cramping); ⑧ clearly reduced fetal movement.

Week 23 frequently asked questions

What do Braxton Hicks contractions feel like?
The abdomen suddenly tightens and hardens, lasts seconds to 30 seconds, then loosens on its own; it is painless and irregular and disappears with movement or a change of position — the uterus "warming up" for delivery. Drinking water, resting and changing position can ease it, and it is a common phenomenon.
How do I tell false vs. true contractions/preterm labour?
False contractions: irregular, not growing stronger, disappear with rest or a change of position, usually painless. True contractions/preterm-labour signals: regular (e.g. once every 10 minutes or more often), growing stronger and more frequent, not eased by rest, possibly with lumbar heaviness/pressure, vaginal bleeding or fluid leakage. If the latter appears, seek care immediately.
What is the latest I can have the anomaly scan?
The best window for the anomaly scan is weeks 20-24; week 23 is near the last-call window, so complete it as soon as possible and don’t let it pass week 24. After week 24 the fetus grows and calcifies more, and some structures may be obscured by its body or the placenta, affecting interpretation.
How should I prepare for OGTT?
The OGTT (glucose-tolerance test) is usually done at weeks 24-28. Keep a normal diet for the 3 days before (no deliberate dieting or carb-loading), fast for 8-12 hours the night before (a little plain water is fine), and arrive at the hospital fasting. The whole process takes about 2-3 hours with several blood draws; you can bring a healthy small snack to refuel afterwards.
How to read the week-23 ultrasound report?
The three measurements at 23 weeks: BPD (biparietal diameter) about 55.5mm, AC (abdominal circumference) about 183.4mm, and FL (femur length) about 39.1mm, 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 gain is normal at week 23?
For a standard BMI, about 0.4-0.5kg a week in the second trimester, with a cumulative gain of roughly 5-8kg by week 23 being common. Watch the overall trend — use a weight-gain calculator to manage by BMI — and discuss with the doctor if it’s too fast or too slow.
How much water should I drink and do I need potassium at week 23?
Blood volume rises in pregnancy; drink about 1.5-2L of water daily as recommended (little and often). Potassium-rich foods in the everyday diet such as banana, potato, red beans, spinach and orange are usually enough, so you don’t need a potassium supplement. Supplementing water and potassium helps relieve oedema and leg cramps.
What about leg cramps at week 23?
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.
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 23?
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 should I note about my sleeping position at week 23?
Practise sleeping on your left side to increase uterine-placental blood flow, using a pregnancy pillow for support; you don’t need to stay that way all night — comfort and good sleep matter; avoid prolonged lying on your back and face-down on the belly.
What about lower-leg oedema at week 23?
Mild oedema 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 spreads from the ankle up the calf and won’t ease with rest, or comes with headache/vision changes, check blood pressure to rule out preeclampsia.
What should I avoid eating at week 23?
Avoid raw or undercooked meat, fish and eggs, high-mercury large fish, unpasteurised dairy, alcohol, caffeine over 200mg a day, and excess animal liver. Fully cooked, well-heated food is safer.
Can I fly during pregnancy at week 23?
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 wear compression stockings to prevent clots; ask your doctor first if you have bleeding, pain or placenta problems.
My heart beats faster and I get tired easily at week 23 — is that normal?
In the second trimester blood volume rises and the heart works harder, so a slightly faster heartbeat and easy fatigue on activity are common. Slow your pace, rest more, and don’t take on too much at once. If you develop obvious palpitations, chest tightness, shortness of breath, dizziness or fainting, seek care to rule out anaemia and heart-rhythm problems.
Is increased discharge normal at week 23?
Higher oestrogen increases white discharge; milky-white or clear and odourless is normal. Watch out 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 constipation at week 23?
Eat more coarse grains, fruit and vegetables for dietary fiber, drink 1.5-2L of water daily, walk after meals, and toilet on a regular schedule without squatting long. In serious cases consult a doctor for a pregnancy-safe laxative rather than buying a stimulant laxative yourself.
⚡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 23 daily focus

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

Day 1Your baby’s vestibular system matures; when you walk, bend or lie on your side it can sense the direction of gravity — a single lap around the living room is a gentle "rocking" for it. This is why many mothers find the baby quietens during walks and gets active when you stop — regular movement is its lullaby. This evening, walk for 20 minutes after dinner — that is your baby’s natural sleeping prescription.Day 2Lung surfactant is starting to be produced — the "lubricant" for whether the alveoli can open smoothly and take the first spontaneous breath after birth. Although it couldn’t survive outside the uterus yet, every day accumulates toward that crucial first breath. Today take 5 deep breaths: inhale 4 seconds → hold 2 seconds → exhale 6 seconds; your steady breathing and adequate oxygen support all the baby’s organs (including the lungs) as they keep developing.Day 3Have a banana smoothie to add potassium and calcium: one ripe banana + 200ml milk + a small spoon of unsweetened yoghurt → blend for 15 seconds with no added sugar. Half an hour after drinking, go for a walk — potassium maintains muscle electrolyte balance and reduces cramps, and calcium supports pregnancy bone metabolism. If blood sugar runs high, halve the banana or swap to an avocado + unsweetened-yoghurt smoothie.Day 4The belly suddenly tightens and hardens but is painless, resolves on its own within half a minute, and is eased by a change of position — this is a Braxton Hicks contraction, the uterus "rehearsing" for real delivery. Today if you feel one, record the time and duration; if it happens more than 4 times in an hour and turns regular, increasingly dense and painful or with lumbar heaviness, it’s not a rehearsal — contact your doctor immediately to rule out preterm labour.Day 5This weekend list the hospital-bag items in your phone in three categories: mother (2 nursing bras, 10 maternity pads, 5 disposable underwear, maternity sanitary pads, travel-size toiletries), baby (30 NB diapers, 1 swaddle, 2 one-piece newborn suits, 1 pack of wipes, 3 small towels), and documents/miscellany (both ID cards, social-security card, prenatal records, power bank, small change). No need to buy everything now, but having the list ready means you can cope calmly.Day 6OGTT is coming (weeks 24-28) — over the next couple of days there’s no need to deliberately change your diet; eat normally. But prepare a few things: fast from 8pm the night before (a little plain water is fine); arrive at the hospital fasting in loose clothes, bring a small snack (wholewheat crackers or nuts) to refuel right after; if you have a family history of diabetes, are overweight or are ≥35, this screen is especially important.Day 7Today do 10 minutes of gentle prenatal yoga or stretching: cat-cow on all fours 5 times → seated butterfly opening the hips, hold 30 seconds → standing against a wall, arms raised stretching the side. The focus is pelvis and spine mobility with no pressure on the belly — even breathing, no jumping. These loosening moves relieve the lower-back soreness from long sitting and give the baby a flexible "uterus room".

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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