Trimester

What does trimester mean?

Trimester: One of the three stages of pregnancy: weeks 1 to 12, 13 to 27, and 28 to birth.

How it is used in the Splash library

• It is split into three Trimesters.

  From “Pregnancy trimesters: a gentle overview”

• Tommy’s estimates that early miscarriage happens in 10 to 20 in every 100 pregnancies, and later (second trimester) loss in 3 to 4 in 100.

  From “Pregnancy loss: you are not alone”

• At your booking appointment, and again in the second trimester, your midwife checks your risk.

  From “Pre-eclampsia: signs, checks and when to call”

Trimester explained

A trimester is one of the three stages of pregnancy, each roughly three months long. Weeks of pregnancy are counted from the first day of your last period, so you are already about 2 weeks "pregnant" at conception.

What's typical

First trimester: up to the end of week 13. Most organs form, and tiredness, nausea and sore breasts are common. The dating scan is usually between 10 and 14 weeks.

Second trimester: weeks 14 to 27. Many people feel more energetic, notice their bump, and feel the first movements, usually between 16 and 24 weeks. The mid-pregnancy scan is between 18 and 20+6 weeks (NHS).

Third trimester: week 28 to birth. Antenatal checks become more frequent. A pregnancy is considered full term from 39 weeks under ACOG definitions, and "at term" from 37 weeks in the UK.

When to talk to a GP, nurse or pharmacist

• You have bleeding, strong tummy pain, or fluid leaking from your vagina at any stage.
• You have a bad headache, vision problems or sudden swelling, especially after 20 weeks.
• Your baby's movements slow down or change. Contact your maternity unit straight away.

In the UK you can call NHS 111 for advice at any time. In an emergency call 999 (UK) or 911 (US). This is general information, not medical advice.