🤰 Pregnancy week by week

4 Weeks Pregnant: Baby Size, Development & Symptoms

Your baby is about the size of a poppy seed.

By Cushies Editorial Team · 2 min read · Updated 10 September 2026

Baby's size	About the size of a poppy seed
Length	about 1 mm
Weight	under 1 g
Trimester	First trimester, month 1

Your baby this week

The fertilised egg has implanted in the uterus lining. The cells that will become the placenta and the embryo are separating.

Your body this week

Your period is due about now. A home pregnancy test may already show positive.

Tip of the week

Start or continue taking folic acid every day.

Quick answers

How big is my baby at 4 weeks?

About the size of a poppy seed: around 1 mm long and under 1 g.

How many months is 4 weeks pregnant?

4 weeks is in month 1 of pregnancy, in the first trimester.

This article is general information, not medical advice. If you are worried about your health or your baby's, please talk to your doctor.

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