Pregnancy Week by Week
Pregnancy is counted in weeks from the first day of the last period, which means the first two weeks are counted before conception. Forty weeks is the full term, and the three trimesters divide it into thirteen-week stretches with quite different concerns.
Reviewed by Dr. Mohan Gayenlast reviewed
Antenatal care is not optional and this page does not replace any part of it. Regular check-ups exist to catch the problems that have no symptoms until they are dangerous — pre-eclampsia in particular.
Numbers are listed for 55 countries and can change — if your country is not here, or you are not sure, 112 reaches emergency services across the European Union and works from a mobile in much of the world. Do not drive yourself.
Get medical help immediately for any of these
- Vaginal bleeding at any stage.
- A gush or steady leak of fluid before 37 weeks.
- Severe or persistent headache, blurred vision or flashing lights, or sudden swelling of the face and hands — possible pre-eclampsia.
- Severe pain in the upper abdomen, especially on the right.
- A noticeable reduction in the baby’s movements after 28 weeks. Do not wait until morning and do not try to provoke movement with cold drinks — call the maternity unit.
- Fever with chills, or burning on passing urine with back pain.
- Persistent vomiting that stops you keeping fluids down.
- Regular painful contractions before 37 weeks.
First trimester — weeks 1 to 13
All the major organs form in this period, which is why it is the most sensitive to medicines, alcohol, smoking, infections and radiation. By the end of it the baby is about 7–8 cm long and every organ system is present in outline.
- Book antenatal care as early as you can — the first visit and the first scan matter.
- Start folic acid, ideally before conception and through at least the first twelve weeks. It substantially reduces neural tube defects.
- Nausea and tiredness are usual. Nausea severe enough to stop you keeping fluids down is not, and needs treatment.
- Check EVERY medicine, including over-the-counter and traditional remedies, with a doctor or pharmacist.
- No alcohol and no smoking. There is no established safe amount of either.
- A dating scan is usually done between 11 and 14 weeks.
Second trimester — weeks 14 to 27
Usually the most comfortable stretch. Nausea settles, energy returns, and the first movements are felt — between about 18 and 22 weeks in a first pregnancy, often earlier afterwards.
- The anomaly scan, around 18–22 weeks, checks the baby’s structure in detail.
- Screening for gestational diabetes is usually done around 24–28 weeks.
- Haemoglobin and blood pressure are checked at every visit — anaemia is very common and very treatable.
- Td or Tdap vaccination is given in this period in most schedules.
- Start noticing the pattern of movements. What matters later is a change from YOUR baby’s normal pattern, not a fixed number of kicks.
Third trimester — weeks 28 to 40+
The baby gains most of its weight now, and the lungs mature. Visits become more frequent because this is when pre-eclampsia and growth problems appear.
- MONITOR MOVEMENTS DAILY. A reduction is the single most important warning sign in late pregnancy. Call the maternity unit the same day — every time, even if you have called before.
- Blood pressure and urine protein are checked at every visit, specifically to catch pre-eclampsia, which often has no symptoms at first.
- Heartburn, breathlessness, back pain, swollen ankles and disturbed sleep are common. Sudden or severe swelling is not.
- Learn the difference between practice (Braxton Hicks) contractions and real labour: real ones get longer, stronger and closer together and do not settle with rest.
- Have a birth plan and a bag ready by about 36 weeks, and know how you will get to hospital at 3 a.m.
Signs that labour has started
| Sign | What it means |
|---|---|
| Regular contractions getting stronger and closer | Labour is establishing. Time them: contact the unit when they are roughly 5 minutes apart, lasting a minute, for an hour. |
| A "show" — plug of blood-stained mucus | The cervix is changing. Labour may still be days away. Fresh bleeding is different and needs a call. |
| Waters breaking | Call the unit. Note the time and the colour — green or brown fluid needs urgent assessment. |
| Backache with a rhythm, or period-like cramps | Often early labour, particularly if it builds. |
This is general health information for education, not medical advice, and not a diagnosis. It cannot see you, your history, your allergies or your medicines. Never use it to start, stop or change a treatment, and never let it delay you seeking care. If you are worried about symptoms, speak to a qualified doctor; if they are severe or sudden, seek emergency help.
Where this comes from: General antenatal information consistent with widely published maternal health guidance.
Where this is written from: This site is written from Indian clinical practice. Drug availability and brand names, vaccination schedules, national health programmes and some reference cut-offs differ between countries — a schedule or a threshold that is standard here may not be standard where you are. If you are reading outside India, check anything on this page against your own country’s guidance before you act on it.
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What is happening, and what to watch for, trimester by trimester.