# Pregnancy trimesters: a gentle overview

> What usually happens in each stage, and what care to expect

Category: Pregnancy & postpartum · 5 min read · Written by the Splash team · Sources checked October 2026
URL: https://splash.care/learn/pregnancy-postpartum/trimesters

## Quick answer

- Pregnancy is counted from the first day of your last period.
- Trimesters: up to 12 weeks, 13 to 27 weeks, 28 weeks to birth.
- Most people first feel movements between 16 and 24 weeks.
- Contact your maternity team quickly about bleeding, severe pain or reduced movements.

[Pregnancy](https://splash.care/learn/fertility-ttc/early-pregnancy-signs) is counted from the first day of your last period, not from the day the egg meets the sperm. So by the time you get a positive test you might already be “4 weeks pregnant”. Yes, it is confusing. Everyone thinks so.

It is split into three [Trimester](https://splash.care/learn/glossary/trimester)s. Every pregnancy is different, so think of this as a rough map, not a checklist. Your [due date](https://splash.care/tools/due-date-calculator) is an estimate, and plenty of healthy babies arrive before or after it.

## First trimester (up to week 12)

Huge changes happen quietly. Early signs usually start around 4 to 6 weeks: tiredness, feeling sick, [sore breasts](https://splash.care/learn/body-literacy/breast-changes) and needing to pee more. Your first midwife (booking) appointment is usually at 8 to 12 weeks, and the dating scan at 11 to 14 weeks. [Folic acid](https://splash.care/learn/glossary/folic-acid) is advised until week 12.

## Second trimester (weeks 13 to 27)

The NHS describes this as the stage when you are hopefully past the worst of early symptoms. Most people first feel their baby move somewhere between 16 and 24 weeks. The mid-pregnancy scan is at 18 to 21 weeks, and the whooping cough jab is offered from 16 weeks.

## Third trimester (week 28 to birth)

Your bump grows fast. Backache, heartburn, tiredness and poor [sleep](https://splash.care/learn/movement-sleep/sleep-cycle) are common. This is the time to plan for birth and feeding, and to learn the signs of labour. The RSV jab is offered from 28 weeks. In later pregnancy, avoid lying flat on your back for more than a few minutes, as it can make you dizzy.

**150 mins** of moderate activity a week is the NHS advice in pregnancy, the same as for any adult. Any amount is better than none.

> **Splash says:** switch the app to pregnancy mode so it can follow your weeks instead of your cycle.

**Quick quiz:** When does the second trimester start?

1. Week 8
2. Week 13
3. Week 20

Answer: Week 13. The NHS counts weeks 13 to 27 as the second trimester.

### When to see a doctor

Call your midwife or maternity unit straight away if you have vaginal bleeding, severe tummy pain, fluid leaking, a bad headache that painkillers do not fix, blurred vision, sudden swelling of your face or hands, or (from about 24 weeks) your baby moves less. If you cannot get through, call NHS 111. Call 999 for heavy bleeding, severe pain, or if you feel faint.

## Sources

1. [NHS Best Start in Life: Week-by-week guide to pregnancy](https://www.nhs.uk/best-start-in-life/pregnancy/week-by-week-guide-to-pregnancy/)
2. [NHS: Your antenatal care and appointments](https://www.nhs.uk/pregnancy/your-pregnancy-care/your-antenatal-care-and-appointments/)
3. [NHS: Exercise in pregnancy](https://www.nhs.uk/pregnancy/keeping-well/exercise/)
4. [NHS: Your pregnancy and baby guide](https://www.nhs.uk/pregnancy/)

This is general information, not medical advice. Splash can’t diagnose. If you’re worried, talk to a GP, pharmacist or sexual health clinic. In an emergency call 999 (UK) or 911 (US).