Week 6 · First trimester
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Week 6 fetal development and pregnancy guide — length about 0.4cm, weight ＜1g (about the size of a a lentil)

Your baby is now about 0.4cm and ＜1g, about the size of a a lentil.

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

View each day of week 6 →

Week 6 fetal development milestones: length / weight / ultrasound data

Key developmental changes during week 6:

  • The primitive heart starts beating! A transvaginal ultrasound can usually observe the fetal heartbeat — this week’s milestone
  • The neural tube closes at both ends step by step, forming the basic structure of the brain and spinal cord
  • Primitive optic and otic vesicles appear on the sides of the head — the buds of the eyes and ears
  • Upper and lower limb buds appear, which will develop into arms and legs
  • Facial depressions begin to form, which will grow into the structures of the mouth and nose
  • The yolk sac is clearly visible, continuing to provide nutrition and blood formation
  • The circulatory system is established, and the embryo’s own blood circulation begins
  • The embryo is about 0.4cm — about the size of a small lentil — and still curved in a C shape
Illustration of your baby about the size of a lentil at week 6 (about 0.4cm/＜1g)
Week 6 size: about the size of a a lentil

* Values are medians from WHO/China standards; individual variation is normal. References: WHO INTERGROWTH-21st, China Prenatal & Pregnancy Care Guide, ACOG guidelines.

Week 6 daily development

Your baby quietly grows every day of week 6. Tap any day to see fetal development, maternal changes, and daily guidance for that day.

36Day 1The baby’s primitive heart has started beating! A transvaginal ultrasound at week 6 can usually show the flickering heartbeat — the most important milestone of early pregnancy. The heart rate is about 90-110 beats per minute, far faster than an adult’s. If you can’t yet see or clearly make out the heartbeat this week, don’t panic — the gestational age may be a little early or it may be an angle issue; a repeat scan in 1-2 weeks usually shows it clearly.37Day 2Sensitive to smells? Open the windows and stay away from kitchen fumes. Smell sensitivity is a common early-pregnancy annoyance — higher estrogen sharpens the smell receptors. Let family cook, ventilate often, and keep a bottle of lemon water to sniff when nausea hits. If a food you used to like now makes you want to throw up, switch to something else — at this stage “being able to eat” matters more than “eating balanced.”38Day 3Feeling especially sleepy? Take a nap; a 15-30 minute rest after lunch works best. Your body is busy building the placenta and supplying the embryo, and both metabolic rate and energy use rise sharply. For working moms, a short post-lunch rest can noticeably improve afternoon energy. Fatigue is the most underestimated “signal” of early pregnancy — it isn’t laziness, it’s your body making a huge investment.39Day 4Seeing the heartbeat on your first ultrasound is the most moving moment. If you have an ultrasound booked this week, just relax. Wear loose clothing that lets you expose the abdomen easily (a transvaginal scan needs an empty bladder; an abdominal scan may need a slightly full one). Go into the exam room with your partner and witness the moment — it’s your first “meeting.”40Day 5Record your current weight; weight management starts now. Early in the first trimester weight mostly stays level or rises slightly (about 1-2kg); if morning sickness is heavy it may even drop a little — all within the normal range. The total weight-gain goal depends on your pre-pregnancy BMI: for a standard BMI, roughly 11.5-16kg total. Take a belly photo as your “week 0 baseline” and one every 4 weeks to see changes.41Day 6Avoid the cat litter box! Toxoplasmosis is spread mainly through cat feces and raw meat, and infection in pregnancy can cause serious fetal problems. If you have a cat, from today let your partner clean the litter, wash hands thoroughly before meals and after touching the cat, and feed the cat cooked food rather than raw. Keeping a cat doesn’t mean you can’t be pregnant — just stay hygienic and there’s nothing to worry about.42Day 7Don’t tough out worsening morning sickness. Small, frequent meals (5-6 a day), ginger tea and lemon water, and vitamin B6 (with a doctor’s guidance) can ease mild-to-moderate nausea. If you cannot eat or drink at all, have little dark urine, or keep losing weight, it may be hyperemesis gravidarum and you must seek care and IV fluids — this isn’t being “dramatic,” it’s your body sending a distress signal.

Week 6 belly changes

Illustration of belly changes at week 6: uterine position and abdominal prominence

At week 6 (first trimester) your uterus still sits low in the pelvis, so there is little visible change and your abdomen circumference barely moves. Don't worry if you don't "show" yet.

Week 6 maternal body changes and common symptoms

  • Morning sickness often worsens this week (vomiting, nausea, smell sensitivity) from rapidly rising hCG; the degree varies
  • The breasts keep enlarging and the areolas darken as the glands prepare for breastfeeding
  • Fatigue and sleepiness are obvious — the body is working hard to support embryo development and placenta formation; rest is needed
  • Frequent urination continues, from pelvic congestion and the growing uterus pressing the bladder
  • Saliva may increase and taste changes; some people develop likes or dislikes for certain foods
  • Mood rises and falls, easily crying or irritating, linked to hormone swings; family should be understanding
  • Mild dizziness may occur (blood pressure and blood sugar adjustments); rise slowly and carry a small snack
  • A few people have very light spotting; light amounts can be observed, but bright-red increases or pain need care

Week 6 nutrition advice and recommended recipes

Morning sickness is often hardest this week, so prioritize “eat what you can and avoid vomiting,” and catch up on balanced nutrition once it eases. Key points: ①continue folic acid 400-800μg; ②eat smaller, frequent, plain meals of easily digestible porridge, noodles, steamed eggs and fruit; ③ensure fluids — drink small amounts often or eat water-rich foods to prevent dehydration; ④protein — try to have eggs, milk, fish or lean meat daily; ⑤for severe morning sickness, vitamin B6 can help under a doctor’s guidance. Avoid greasy, spicy and strongly-smelling foods; avoid alcohol, cold-raw unpasteurized milk and high-mercury fish; caffeine ≤200mg/day.

Recommended recipeSteamed sea bass

Fish is tender, easy to digest and rich in DHA and high-quality protein; steaming it lightly is lean and not greasy, good for the morning-sickness phase. Score the fish, lay on ginger and scallion, and steam 8 minutes to remove fishiness; if nausea is severe you can drink a little of the broth and eat a little fish.

Week 6 prenatal education guide

At week 6 the baby’s heart has begun beating, but it has no hearing or vision yet, so this stage doesn’t need deliberate music, light or “training” — those methods have no real effect on such a small embryo. The best “prenatal care” now is taking care of the mother: ①stay relaxed and cheerful so the hormone environment is more stable; ②keep a regular routine and sleep well to carry you through morning sickness and fatigue; ③talking gently to your belly is completely fine — it’s a way to build the mother-baby bond and reassure yourself. Don’t be held hostage by “falling behind at the starting line” anxiety; getting through early pregnancy calmly is the best thing for your baby.

Week 6 partner's role

①Take on cooking and housework, handling strong-smelling dishes yourself and keeping your partner away from cooking fumes; ②Keep warm lemon water, soda crackers and ginger candy by the bed, ready for morning sickness; ③Go with her to the first ultrasound at 6-8 weeks to witness the heartbeat together; ④Be tolerant of mood swings, spend time and listen, and quit smoking yourself while keeping the home smoke- and odor-free.

Week 6 checkup reminders

Weeks 6-8 are the recommended window for the first ultrasound: confirm an intrauterine pregnancy, the sac size, the heartbeat and the number of embryos (singleton/twins). If you don’t yet see a heartbeat this week, don’t panic — your doctor will usually suggest a repeat scan in 1-2 weeks. Meanwhile, start learning the file-establishing process and required documents at target hospitals, in preparation for building your file at weeks 8-12.

Week 6 key concerns

Book or complete the first ultrasound at weeks 6-8Keep taking folic acid 400-800μg dailyEat small, frequent meals to cope with morning sickness; stay hydrated to prevent dehydrationGet enough sleep and avoid overexertionSeek care promptly if you have severe vomiting or bleeding with abdominal pain

Signs that need immediate care at week 6

Please see a doctor promptly if any of the following occurs: ①severe vomiting that keeps you from eating or drinking at all, little dark urine, and obvious weight loss (be alert for hyperemesis gravidarum — you may need fluids); ②vaginal bleeding with abdominal pain (be alert for threatened miscarriage); ③persistent severe pain on one side of the lower abdomen with bleeding or dizziness (be alert for ectopic pregnancy); ④fever above 38°C with chills; ⑤severe headache or blurred vision; ⑥painful urination, frequent/urgent urination, or blood in the urine (urinary tract infection); ⑦heavy gush of fluid from the vagina; ⑧sudden fainting with pale face (be alert for internal bleeding).

Week 6 frequently asked questions

Can the fetal heartbeat be seen at week 6? What if it isn’t visible yet?
A transvaginal ultrasound can usually see the fetal heartbeat at this point, while an abdominal scan may not yet. If it isn’t visible yet, the gestational age may be slightly smaller or ovulation/implantation later than thought, and your doctor will usually suggest a repeat scan in 1-2 weeks — no need to panic immediately. Assessing it together with the HCG trend over time is more accurate.
Is it normal for morning sickness to be stronger at week 6?
Yes. HCG usually peaks at weeks 8-10, and morning sickness often gradually worsens from week 6 — nausea, sleepiness and smell sensitivity are all common. Small, frequent meals and bland food can help; if you cannot eat or drink at all and lose weight noticeably, it may be hyperemesis gravidarum and you should seek care.
How should I read HCG and progesterone at week 6?
In early pregnancy the dynamic doubling trend of HCG matters more than any single value; good doubling usually suggests normal development. Progesterone fluctuates a lot day to day and varies greatly between individuals, so one low reading is no reason for excessive anxiety. Whether medication is needed should be decided by your doctor based on HCG and ultrasound — never self-prescribe to “protect” the pregnancy.
Are brown discharge or bleeding at week 6 a concern?
Small amounts of brown discharge are common with a sensitive cervix or hormone swings; if only a little and without pain, you can observe first and avoid exertion and intercourse. If bleeding turns bright red, increases, or comes with sharp lower-abdominal pain, seek care immediately to rule out threatened miscarriage and ectopic pregnancy.
Is abdominal pain at week 6 normal? How is it different from ectopic pregnancy?
Mild lower-abdominal ache or fullness is usually from uterine growth and ligament stretching — a common symptom. Ectopic pregnancy is classically a constant or tearing severe pain on one side, often with bleeding, and in serious cases dizziness, shoulder pain or fainting. If you have severe one-sided pain or obvious bleeding, seek care right away.
What if morning sickness stops me from eating at week 6?
Prioritize eating whatever you can. Eat small, frequent, bland, easily digestible meals, have a soda cracker before getting up, and avoid greasy food and strong smells; ginger, lemon water and vitamin B6 (under a doctor’s guidance) help some people. Short-term under-eating is usually fine, but if you consistently cannot eat or drink and have little dark urine, seek care for fluids.
Do I still need folic acid at week 6? Are other supplements needed?
Keep taking folic acid 400-800μg daily through week 12. If your diet is balanced, other supplements need not be stacked blindly; if morning sickness is severe or eating is poor, your doctor may suggest a multivitamin or vitamin B6. Focused iron and calcium supplementation usually begins after the second trimester.
Can I have sex at week 6?
If there is no bleeding, abdominal pain, history of miscarriage, or low-lying placenta as a contraindication, gentle sex is usually fine — move carefully and avoid pressure on the abdomen. If there is bleeding, pain, or your doctor advises against it, pause.
Can I exercise and work at week 6?
Yes — you can work normally and do walking, prenatal yoga and other gentle exercise, while avoiding prolonged standing, overexertion and heavy lifting. If your job is high-stress or involves radiation or chemical exposure, discuss adjustments with your doctor and employer. Rest and seek care if you have pain or bleeding.
Can I take medicine for a cold or fever at week 6?
Do not self-medicate. Rest, drink plenty of fluids and eat bland food; if fever is above 38°C or symptoms are obvious, see a doctor promptly and tell them you are pregnant, so they can choose medications that are relatively safe in pregnancy. High fever in early pregnancy may itself affect the embryo — do not just tough it out.
Can I drink coffee or milk tea at week 6?
A little is okay, but keep caffeine under 200mg/day (about one medium americano or two cups of weak tea). Milk tea also contains a lot of sugar and trans fats, so it is best to limit it. Avoid alcohol entirely — no amount is safe.
Can I fly or take long trips at week 6?
If there are no complications, travel in early pregnancy is usually fine, but move around often, drink water to prevent blood clots, and wear your seatbelt (belt under the abdomen). If you have bleeding, pain, or a history of miscarriage, consult your doctor before traveling.
Do I need to build my maternity file now at week 6?
Generally not this early. File-building is usually done after the intrauterine pregnancy is confirmed, around weeks 8-12. For now you can call target hospitals about their process and required documents (often both ID cards, marriage certificate, household register, ultrasound report), then complete the file once intrauterine pregnancy is confirmed.
How many months pregnant am I at week 6? How big is the baby?
Week 6 is just over one month; it is still the first trimester. The baby is about 0.4cm, about the size of a small lentil; the heart has begun beating, but the belly is not yet visibly growing.
What signs might a twin pregnancy have at week 6?
Twin pregnancies often have higher HCG, stronger morning sickness and a larger uterus, but none of these confirms twins. Whether it is twins must be determined by ultrasound (two sacs or two heartbeats visible at weeks 6-8) — do not rely on symptoms alone.
Can the baby’s sex be seen at week 6?
No. The external genitalia have not yet differentiated, so neither ultrasound nor folk methods can determine the sex accurately. It is usually only possibly clearly distinguished by ultrasound after about 18 weeks, and in China sex identification is not performed unless medically needed.
What if morning sickness suddenly stops and the breasts feel less full at week 6?
Early-pregnancy symptoms naturally come and go, and a brief easing is usually normal. But if previously clear symptoms vanish suddenly together with abdominal pain or bleeding, seek care so HCG and ultrasound can rule out a stopped pregnancy — do not draw conclusions from symptoms alone.
Is it a problem to be around cats or pets at week 6?
The main risk is toxoplasmosis (spread mostly through cat feces and raw meat). You do not need to rehome your cat, but avoid cleaning the litter box yourself (let family do it), feed the cat cooked food, and wash hands carefully before meals and after handling raw meat. If needed, ask at a prenatal visit about a TORCH screen.
⚡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 6 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 primitive heart has started beating! A transvaginal ultrasound at week 6 can usually show the flickering heartbeat — the most important milestone of early pregnancy. The heart rate is about 90-110 beats per minute, far faster than an adult’s. If you can’t yet see or clearly make out the heartbeat this week, don’t panic — the gestational age may be a little early or it may be an angle issue; a repeat scan in 1-2 weeks usually shows it clearly.Day 2Sensitive to smells? Open the windows and stay away from kitchen fumes. Smell sensitivity is a common early-pregnancy annoyance — higher estrogen sharpens the smell receptors. Let family cook, ventilate often, and keep a bottle of lemon water to sniff when nausea hits. If a food you used to like now makes you want to throw up, switch to something else — at this stage “being able to eat” matters more than “eating balanced.”Day 3Feeling especially sleepy? Take a nap; a 15-30 minute rest after lunch works best. Your body is busy building the placenta and supplying the embryo, and both metabolic rate and energy use rise sharply. For working moms, a short post-lunch rest can noticeably improve afternoon energy. Fatigue is the most underestimated “signal” of early pregnancy — it isn’t laziness, it’s your body making a huge investment.Day 4Seeing the heartbeat on your first ultrasound is the most moving moment. If you have an ultrasound booked this week, just relax. Wear loose clothing that lets you expose the abdomen easily (a transvaginal scan needs an empty bladder; an abdominal scan may need a slightly full one). Go into the exam room with your partner and witness the moment — it’s your first “meeting.”Day 5Record your current weight; weight management starts now. Early in the first trimester weight mostly stays level or rises slightly (about 1-2kg); if morning sickness is heavy it may even drop a little — all within the normal range. The total weight-gain goal depends on your pre-pregnancy BMI: for a standard BMI, roughly 11.5-16kg total. Take a belly photo as your “week 0 baseline” and one every 4 weeks to see changes.Day 6Avoid the cat litter box! Toxoplasmosis is spread mainly through cat feces and raw meat, and infection in pregnancy can cause serious fetal problems. If you have a cat, from today let your partner clean the litter, wash hands thoroughly before meals and after touching the cat, and feed the cat cooked food rather than raw. Keeping a cat doesn’t mean you can’t be pregnant — just stay hygienic and there’s nothing to worry about.Day 7Don’t tough out worsening morning sickness. Small, frequent meals (5-6 a day), ginger tea and lemon water, and vitamin B6 (with a doctor’s guidance) can ease mild-to-moderate nausea. If you cannot eat or drink at all, have little dark urine, or keep losing weight, it may be hyperemesis gravidarum and you must seek care and IV fluids — this isn’t being “dramatic,” it’s your body sending a distress signal.

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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