4 weeks pregnant

4 weeks is about 0.9 months of gestation, counted from the first day of your last period. You are in the first trimester.

Around 1 mm long and < 1 g, roughly the size of a poppy seed. These are averages; individual babies vary.

Trimester 1 · about 0 months · baby is about the size of a poppy seed.

Baby at 4 weeksa poppy seed1 mm · < 1 g

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Your baby this week

The blastocyst has implanted in the uterine lining and is splitting into the layers that will become the embryo and the placenta.

A missed period is often the first sign. Home tests detect hCG from around now.

Care this week: Start or continue folic acid (400 mcg a day).

How many months is 4 weeks pregnant?

4 weeks is about 0.9 months of gestation, counted from the first day of your last period. You are in the first trimester.

How big is a baby at 4 weeks?

Around 1 mm long and < 1 g, roughly the size of a poppy seed. These are averages; individual babies vary.

Not sure which week you're in? The pregnancy calculator works it out from your last period or due date.