First trimester: weeks 1 to 13
What changes, what gets checked, and what to watch for — week by week.
The first trimester runs from week 1 to week 13. Each week below has its own page with your baby's size, how you may feel, what is offered clinically, and the signs worth a call.
Pregnancies differ, and so do the dates a clinic works to. Treat the week numbers as the common pattern rather than a schedule you are behind on.
Every week of the first trimester
- 1 weeks pregnant — about the size of a poppy seed
- 2 weeks pregnant — about the size of a poppy seed
- 3 weeks pregnant — about the size of a poppy seed
- 4 weeks pregnant — about the size of a poppy seed
- 5 weeks pregnant — about the size of a poppy seed
- 6 weeks pregnant — about the size of a lentil
- 7 weeks pregnant — about the size of a lentil
- 8 weeks pregnant — about the size of a raspberry
- 9 weeks pregnant — about the size of a raspberry
- 10 weeks pregnant — about the size of a strawberry
- 11 weeks pregnant — about the size of a strawberry
- 12 weeks pregnant — about the size of a lime
- 13 weeks pregnant — about the size of a lime
What nutrition matters most now
The nutrients these weeks call out, each with what it does and how much you need.
Common questions
Which weeks are the first trimester?
Weeks 1 to 13. Clinics count from the first day of your last period, so the dates on your notes may differ slightly from how far along you feel.
What tests happen in the first trimester?
Blood group + Rh, Hb, infections screen; Booking / dating scan; Nuchal-translucency + combined first-trimester screen (weeks 11–14). What is offered varies by country and by your own history.
How might I feel in the first trimester?
Because dating starts from the last period, there is usually nothing to notice yet — this is a good time to start a folic-acid supplement if trying to conceive. Ovulation signs (such as changes in cervical mucus) may be noticeable; folic acid supplementation is recommended if trying to conceive. It's typically too early for pregnancy symptoms; hCG hormone has usually not yet risen enough to detect. A home pregnancy test may turn positive around now, typically near the time of a missed period.
Show the evidence
Sources: ACOG, WHO, NHS, UNSW Embryology.
This page gathers and links what the individual week and nutrient pages already publish — it introduces no figure they do not carry, and each one names its own source.
Educational reference, not medical advice. Pregnancies and the care offered around them differ; follow the team looking after you.