A typical pregnancy lasts around 40 weeks from the first day of your last menstrual period, divided into three trimesters. The NHS schedules around 10 antenatal appointments for a first pregnancy, including two routine ultrasound scans at 12 and 20 weeks.
Pregnancy is dated from the first day of your last menstrual period (LMP), not from conception. Your due date is calculated as 40 weeks (280 days) from your LMP. According to the NHS, only about 4% of babies arrive on their due date.
By the end of week 12, every major organ system has begun to form. Your baby has a beating heart, and tiny fingers and toes are visible on ultrasound.
The fertilised egg implants in the uterine lining around day 6 to 12. By week 4, the embryo is about the size of a poppy seed.
The neural tube is forming, which is why the NHS recommends 400 micrograms of folic acid daily. By week 6, the heart beats at around 110 bpm. By week 8, the embryo is about 1.6 cm long.
From week 9, your baby is officially called a foetus. By week 12, your baby is about 6 cm long and weighs around 18 grams. Your NHS booking appointment typically happens between weeks 8 and 12.
Nausea typically eases as the placenta takes over hormone production. By week 16, your baby is about 12 cm long.
Most women feel their baby move between weeks 18 and 20. The 20-week anomaly scan checks your baby's organs and structures.
By week 24, your baby reaches viability. By week 27, your baby weighs approximately 900 grams and responds to sounds.
At your 28-week appointment, your midwife checks blood pressure and offers blood tests. If you are Rhesus negative, you will be offered an anti-D injection.
Lungs are maturing and producing surfactant. By week 36, most babies are head-down.
Per ACOG, full term is 39 to 40 weeks. NICE guideline NG207 recommends offering induction at 41 weeks.
| When | Appointment | What happens |
|---|---|---|
| 8-12 weeks | Booking | Medical history, blood tests, BMI |
| 11-14 weeks | Dating scan | Confirms due date, combined screening |
| 18-21 weeks | Anomaly scan | Detailed check of development |
| 28 weeks | Midwife | Blood tests, anti-D if Rhesus negative |
| 36 weeks | Midwife | Check baby position, discuss labour |
| 38-41 weeks | Weekly | Membrane sweep from 39 weeks, induction discussion |
Full term is 39 to 40 weeks. Babies born at 37-38 weeks are early term, 41 weeks is late term, 42+ is post-term.
The dating scan is offered between 11 and 14 weeks. The anomaly scan is at 18 to 21 weeks.
Most women feel movement between 18 and 20 weeks. From 28 weeks, monitor your baby's pattern of movement.
400 micrograms of folic acid until week 12, and 10 micrograms of vitamin D throughout pregnancy.
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