First trimester · Week 4 of pregnancy
4 weeks pregnant: body, feeding, and care
Implantation usually completes this week. The embryo is about the size of a poppy seed, and a home pregnancy test may first turn positive.
Body and care — week 4
Implantation usually completes this week. The embryo is about the size of a poppy seed, and a home pregnancy test may first turn positive. Development notes on this page are general education summarized from ACOG patient-education material; they describe typical development, not your pregnancy specifically. Anatomy and growth are confirmed by your own provider and ultrasounds.
This week's checklist
- Note one body question — sleep, appetite, movement, comfort — and bring it to your next prenatal visit rather than searching it at 3 AM.
- Keep prenatal appointments on the schedule your provider sets; bring your questions list.
- Anything that worries you — bleeding, pain, reduced movement later in pregnancy — goes to your provider or urgent care first, never to a website.
Week 4 questions
What is happening at 4 weeks pregnant?
Implantation usually completes this week. The embryo is about the size of a poppy seed, and a home pregnancy test may first turn positive.
Which trimester is week 4?
Week 4 falls in the first trimester (weeks 1–13). See the first trimester hub.
How is a due date calculated?
A due date is typically estimated as 280 days (40 weeks) from the first day of the last menstrual period. It is an estimate — try the client-side due-date calculator; your provider's dating outranks it.
Educational information only — not medical advice. Every pregnancy and every baby develops on their own timeline. If you have any concern, talk to your obstetric provider or your baby's pediatrician.