First Trimester Week by Week: Complete Guide
The first trimester covers weeks 4 to 13 of pregnancy — the period when your baby develops from a cluster of cells into a fully formed foetus with all major organs in place, while your body adjusts to a wave of new hormones. Here's what tends to happen week by week, though every pregnancy has its own pace.
Weeks 4–7: early signs and rising hormones
- Week 4 — usually the point a missed period prompts a positive test. Implantation is complete and hCG levels are rising fast.
- Week 5 — fatigue and breast tenderness often start as hormone levels climb steadily.
- Week 6 — morning sickness and nausea commonly begin, alongside more frequent urination as the womb grows and presses on the bladder.
- Week 7 — often the peak of exhaustion and nausea for many women, as hCG levels reach their highest point.
Weeks 8–10: booking in and rapid development
- Week 8 — a good time to book your first midwife appointment (the "booking appointment") if you haven't already; symptoms like bloating and heightened smell are common.
- Week 9 — your baby's essential organs have formed and continue maturing; symptoms are often still at their most intense.
- Week 10 — bones begin to harden and your baby starts looking more distinctly human on scans.
Weeks 11–13: easing symptoms and the first scan
- Week 11 — fingerprints are forming and many women start to notice symptoms softening slightly.
- Week 12 — the dating/12-week scan is usually offered around now, giving you your first proper look at your baby and a chance to discuss screening options.
- Week 13 — the end of the first trimester; for most women, nausea and fatigue begin to lift noticeably from here into the second trimester.
What's happening for you, not just your baby
Alongside your baby's development, your own body is doing significant work — building the placenta, increasing blood volume, and adjusting hormone levels dramatically. It's completely normal for symptoms to vary week to week, and for two pregnancies (even for the same woman) to feel quite different. Staying on top of the basics helps regardless of how symptomatic you feel: take 400 micrograms of folic acid daily until week 12, take 10 micrograms of vitamin D daily throughout pregnancy, avoid alcohol, and steer clear of the specific foods flagged as higher-risk in pregnancy.
Frequently Asked Questions
What happens each week in the first trimester?
Broadly, weeks 4–7 bring the earliest signs (missed period, fatigue, nausea) as hormone levels rise quickly. Weeks 8–10 are often the most symptomatic, alongside key developmental milestones like organ formation and bone hardening, and this is when you'll typically have your booking appointment. Weeks 11–13 usually bring some relief as symptoms ease and end with the 12-week scan, which marks the close of the first trimester.
How long is the first trimester and when does it end?
The first trimester runs from conception (around week 2, though it's dated from your last period) to the end of week 13, meaning weeks 4 through 13 are when you'll typically notice you're pregnant and experience the bulk of first-trimester symptoms. It's followed by the second trimester, weeks 14 to 27, when most women feel a noticeable improvement in energy and symptoms.
Is it normal for symptoms to vary a lot week to week?
Yes, this is very common — nausea, fatigue, and other symptoms often fluctuate rather than following a smooth, predictable pattern, and some women have barely any symptoms at all while others have severe ones. Variation alone isn't usually a cause for concern, but any sudden, severe change — especially pain or bleeding — is always worth discussing with your midwife or GP promptly.
This article is for informational purposes only and does not constitute medical advice.
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