Week 18 · Second trimester
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Week 18 fetal development and pregnancy guide — length about 14.2cm, weight 约190g (about the size of a a sweet pepper)

Your baby is now about 14.2cm and 约190g, about the size of a a sweet pepper.

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

View each day of week 18 →

Week 18 fetal development milestones: length / weight / ultrasound data

Key developmental changes during week 18:

  • The nervous system develops at a rapid pace; nerve fibres begin to myelinate, speeding up signal transmission.
  • The middle-ear bones (ossicles) begin to harden, making sound-signal transmission more efficient (but it still cannot hear clear outside sounds).
  • The lungs grow the bronchial tree, laying the groundwork for breathing after birth.
  • The baby develops a regular routine — alternating sleep and active cycles (about 20-40 minutes per round).
  • The bones keep ossifying and the long bones harden, with firmer joints.
  • It can suck its thumb, grasp, and turn around, with more coordinated movements.
  • Subcutaneous fat begins to build up noticeably and the body grows gradually rounder.
  • About 14.2cm long, about the size of a bell pepper, weighing about 190g.
  • The eyes can move, but the eyelids remain closed (they gradually open around weeks 26-28).
  • Taste receptors form, and it can sense differences among the tastes in the amniotic fluid.
Illustration of your baby about the size of a sweet pepper at week 18 (about 14.2cm/约190g)
Week 18 size: about the size of a a sweet pepper
BPD (biparietal diameter)40mmWidth across the head; reflects brain development
AC (abdominal circumference)126.3mmAbdomen circumference; reflects nutrient absorption
FL (femur length)25.4mmThigh bone length; tracks gestational age
Ultrasound parameters at week 18: BPD 40 mm, AC 126.3 mm, FL 25.4 mm (median reference)
Week 18 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 18 daily development

Your baby quietly grows every day of week 18. Tap any day to see fetal development, maternal changes, and daily guidance for that day.

120Day 1Today after dinner, lie on your side in bed, turn off the TV and phone, and press your hand lightly over the lower-belly area, staying quiet and feeling for 20 minutes. Around week 18, many first-time mothers first feel fetal movement — like a butterfly fanning its wing, a tiny fish bubbling, or a very faint bowel sound, easily overlooked. If you feel nothing today, that’s normal — mark this "detection date" so that when you finally do feel it, comparing with this day will be one of the warmest entries in your pregnancy diary.121Day 2Today remind yourself again: it’s not "eating for two"! The extra energy you need daily in the second trimester is only about 340 calories — which is roughly the total of a glass of milk (100 calories) + a boiled egg (70 calories) + a small handful of walnuts (110 calories) + an orange (60 calories). Photograph today’s lunch and look back at it in the evening — if the plate is as full as before, that’s exactly right. Pregnancy is not a licence to eat and drink freely.122Day 3Your baby already has its own sleep rhythm: sleeping about 20-40 minutes, being active for a few minutes, then sleeping again, repeated in many rounds a day. You can feel the baby’s activity at the same times (e.g. 3pm and 8pm); usually after blood sugar rises from meals, and at night when you quiet down, it is most lively. This is normal, not a "strange night owl", and it’s a forerunner of the biological clock it will have after birth.123Day 4Today have the routine prenatal visit: weight, blood pressure, fundal height, listening to the fetal heart (the Doppler picks up a fast da-da sound at about 110-160 beats per minute). Record the results in your pregnancy diary — especially the fundal height, which reflects the size of the uterus and the baby’s growth rate. The doctor will also confirm the mid-term screen or NIPT arrangements; if you’ve already done it, ask when the results will be back.124Day 5Today’s task for Dad-to-be: after dinner sit on the sofa or the bedside, place his palm gently on the most prominent part of your partner’s belly (wash hands first and warm the palm), and stay still for 5-10 minutes. At week 18 the fetal movement may already be faintly perceptible through the abdominal wall, and this gesture is also huge psychological support for your partner — "I’m not carrying this alone". If you don’t feel anything, saying "I’ll come back next week" is also tender company.125Day 6Do the prenatal cat-cow pose a few times each day: on all fours with hands under the shoulders and knees under the hips; on the inhale, let the back sink and lift the head (cow); on the exhale, arch the back up, lower the head and tuck the abdomen (cat). Repeat 5-8 times, slowly with the breath. This posture noticeably relieves mid-pregnancy lower-back soreness and pelvic stiffness — no jumping, no twisting, a purely natural mid-pregnancy starter yoga.126Day 7If the anomaly scan isn’t booked yet, open your phone calendar today: weeks 20-24 are the official window for the anomaly scan, but at good obstetric hospitals the actual slots are usually already full by weeks 14-16. Call now to book the obstetric ultrasound; if you’re told it’s "full", ask the clerk to put you on the waiting list, or ask whether the check can be done at another branch of the same hospital. Every day of delay adds risk.

Week 18 belly changes

Illustration of belly changes at week 18: uterine position and abdominal prominence

At week 18 (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 18 maternal body changes and common symptoms

  • The uterine fundus roughly reaches the level of the navel.
  • First-time mothers usually begin to feel fetal movement around this week.
  • The appetite increases, but beware the trap of "eating for two" — you only need about 340kcal extra a day (ACOG).
  • The breasts keep enlarging and a suitable bra is needed.
  • Back pain and pelvic discomfort may worsen.
  • Nasal congestion and gum bleeding are possible.
  • Pigmentation (pregnancy mask, abdominal line) becomes more obvious.
  • A few women feel round-ligament tugging pain.

Week 18 nutrition advice and recommended recipes

Key reminder: in the second trimester you only need about 340kcal extra a day (ACOG, roughly a glass of milk plus an egg plus a small handful of nuts) — not "eating for two"! Excess intake is what causes rapid weight gain and raises the risk of gestational diabetes and a large baby. Daily targets: about 70g of quality protein, calcium 1000mg, iron 27mg, DHA 200-300mg, folate 400-800μg (recommended through the whole pregnancy), iodine 230μg, fiber 25-30g. Choose high-protein, high-fiber foods for a fuller feeling, and give up sugary drinks and snacks. Avoid alcohol, raw or unpasteurised milk products, high-mercury fish, and keep caffeine to ≤200mg a day.

DHA200-300mgBrain & vision development
Recommended recipeAvocado egg wholewheat sandwich

Avocado’s healthy fats plus folate, the egg’s quality protein, and wholewheat bread’s fiber make the perfect pregnancy breakfast/snack — filling without exceeding calories. Add a slice of low-fat cheese for calcium; if your blood sugar runs high, halve the avocado and add more vegetables.

Week 18 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: the traditional idea of shining a torch on the belly has limited evidence — the baby’s eyelids reopen only around weeks 26-28, so light can hardly reach the retina, and there’s no need to deliberately shine a light (or to chase "visual fetal education"). This week the baby’s routine is become more regular, so what you can do: talk gently for 5-10 minutes at a fixed time daily and lightly stroke the belly, enjoying the parent-child connection; choose soothing music/white noise at ≤60 decibels for 15-20 minutes a day for your own relaxation. Understanding fetal education as "looking after Mum’s mood" is the most practical.

Week 18 partner's role

①Mom-to-be may start to feel fetal movement now! Put your hand quietly on her belly for a few minutes and you may feel the baby’s "kicking". 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 the "eating for two" appetite: prepare healthy high-protein, high-fiber snacks and take evening walks together. ④Accompany her to routine prenatal visits and record the fetal heartbeat.

Week 18 checkup reminders

Weeks 18-20: routine prenatal visit (weight, blood pressure, fundal height, abdominal circumference, listening to the fetal heart). If you haven’t booked the anomaly scan (weeks 20-24 systematic ultrasound), make sure to book it this week — popular hospitals have tight slots that often need weeks of lead time. If you still feel no fetal movement at all at week 20, tell the doctor and have an ultrasound assessment.

Week 18 key concerns

Feel and record fetal movementControl the rate of weight gain (don’t eat for two)Balanced dietBook/prepare for the anomaly scan30 minutes of exercise daily (ACOG recommends 150 minutes a week across pregnancy)

Signs that need immediate care at week 18

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, which usually occurs after week 20 — still rare at week 18 but must be checked if it appears); 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 sudden obvious oedema or a sudden week of rapid weight gain.

Week 18 frequently asked questions

Why do I still not feel fetal movement?
Completely normal. Most first-time mothers clearly feel movement only at 18-22 weeks; mothers who’ve given birth before feel it a little earlier; heavier builds, placenta praevia or an anterior placenta also delay the sensation. The week-20 ultrasound can confirm, so don’t worry about "not feeling anything".
My appetite has surged at week 18 — how do I control weight?
You only need about 340kcal extra a day (ACOG, roughly a glass of milk plus an egg plus a small handful of nuts), not eating for two. Choose high-protein, high-fiber foods for a fuller feeling, give up sugary drinks and snacks, and walk after meals. Gaining too fast raises the risk of GDM and a large baby.
Can I shine a torch on my belly for visual fetal education at week 18?
It’s not advised. The baby’s eyelids reopen only around weeks 26-28, so light barely reaches the retina; the evidence for "visual fetal education" with a torch is limited and it could even stimulate the uterus. Relaxing, talking and light music are safer as fetal education.
What does fetal movement feel like at week 18?
The first sensation is like a butterfly fanning its wings, a small fish bubbling, a gurgle in the gut or a tiny flutter, easily mistaken for intestinal gas. It’s felt most after meals in a quiet time and in the evening. Recording it helps for later kick counting.
Weight gain at week 18?
For a standard BMI, about 0.4-0.5kg a week in the second trimester, with a cumulative gain of roughly 3-5kg by week 18 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.
How to read the week-18 ultrasound report?
The three measurements at 18 weeks are BPD (biparietal diameter) about 40mm, AC (abdominal circumference) about 126mm, and FL (femur length) about 25mm. 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.
What does the week-18 routine prenatal visit check?
Weight, blood pressure, fundal height, abdominal circumference, listening to the fetal heart (Doppler about 110-160 beats per minute); some hospitals also run routine blood and urine tests. These are the regular items for assessing the basic condition of mother and baby.
Sleeping position at week 18?
Practise sleeping on your left side to increase uterine-placental blood flow, using a pregnancy pillow; comfort is the priority, brief right-side or flat positions are fine, and avoid lying face-down on the belly.
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 18?
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.
Back pain at week 18?
The forward centre of gravity and relaxed ligaments make lumbar soreness and back 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.
Constipation at week 18?
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 rather than buying a stimulant laxative yourself.
What should I avoid eating at week 18?
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 18?
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.
Should I book the anomaly scan at week 18?
Absolutely. The anomaly scan is done at weeks 20-24 with tight slots that often need weeks of lead time; book this week to avoid missing the best window.
Iron-deficiency anaemia at week 18?
Build it up with red meat, liver (≤50g a week) and spinach paired with vitamin C; once diagnosed, the doctor will prescribe an iron supplement, taken apart from calcium tablets and dairy for better absorption.
Increased discharge at week 18?
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.
Preventing stretch marks at week 18?
About 50-90% of pregnant women get stretch marks, related to genetics and the speed of weight gain. Slow 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 18?
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 18 daily focus

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

Day 1Today after dinner, lie on your side in bed, turn off the TV and phone, and press your hand lightly over the lower-belly area, staying quiet and feeling for 20 minutes. Around week 18, many first-time mothers first feel fetal movement — like a butterfly fanning its wing, a tiny fish bubbling, or a very faint bowel sound, easily overlooked. If you feel nothing today, that’s normal — mark this "detection date" so that when you finally do feel it, comparing with this day will be one of the warmest entries in your pregnancy diary.Day 2Today remind yourself again: it’s not "eating for two"! The extra energy you need daily in the second trimester is only about 340 calories — which is roughly the total of a glass of milk (100 calories) + a boiled egg (70 calories) + a small handful of walnuts (110 calories) + an orange (60 calories). Photograph today’s lunch and look back at it in the evening — if the plate is as full as before, that’s exactly right. Pregnancy is not a licence to eat and drink freely.Day 3Your baby already has its own sleep rhythm: sleeping about 20-40 minutes, being active for a few minutes, then sleeping again, repeated in many rounds a day. You can feel the baby’s activity at the same times (e.g. 3pm and 8pm); usually after blood sugar rises from meals, and at night when you quiet down, it is most lively. This is normal, not a "strange night owl", and it’s a forerunner of the biological clock it will have after birth.Day 4Today have the routine prenatal visit: weight, blood pressure, fundal height, listening to the fetal heart (the Doppler picks up a fast da-da sound at about 110-160 beats per minute). Record the results in your pregnancy diary — especially the fundal height, which reflects the size of the uterus and the baby’s growth rate. The doctor will also confirm the mid-term screen or NIPT arrangements; if you’ve already done it, ask when the results will be back.Day 5Today’s task for Dad-to-be: after dinner sit on the sofa or the bedside, place his palm gently on the most prominent part of your partner’s belly (wash hands first and warm the palm), and stay still for 5-10 minutes. At week 18 the fetal movement may already be faintly perceptible through the abdominal wall, and this gesture is also huge psychological support for your partner — "I’m not carrying this alone". If you don’t feel anything, saying "I’ll come back next week" is also tender company.Day 6Do the prenatal cat-cow pose a few times each day: on all fours with hands under the shoulders and knees under the hips; on the inhale, let the back sink and lift the head (cow); on the exhale, arch the back up, lower the head and tuck the abdomen (cat). Repeat 5-8 times, slowly with the breath. This posture noticeably relieves mid-pregnancy lower-back soreness and pelvic stiffness — no jumping, no twisting, a purely natural mid-pregnancy starter yoga.Day 7If the anomaly scan isn’t booked yet, open your phone calendar today: weeks 20-24 are the official window for the anomaly scan, but at good obstetric hospitals the actual slots are usually already full by weeks 14-16. Call now to book the obstetric ultrasound; if you’re told it’s "full", ask the clerk to put you on the waiting list, or ask whether the check can be done at another branch of the same hospital. Every day of delay adds risk.

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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