Baby by Week
Week 4

Your week 4 guide

The blastocyst is settling into the uterine lining and the earliest support structures are forming.
Trimester

1

Month

1

Weeks left

36

Size at a glance

Comparison
Poppy seed
Length
Too small to measure
Weight
Too small to measure
Measurements are approximate. Healthy babies grow at different rates.

Baby development

Implantation allows the developing pregnancy to connect with your blood supply.
The amniotic and yolk sacs begin to form.
Early cells are organizing for the brain, spinal cord, and other organs.

Your body

A missed period may be the first clear clue.
Bloating, breast tenderness, fatigue, mood changes, or light spotting can occur.
Some people still have no symptoms.

This week's checklist

Take a home pregnancy test after a missed period and repeat if needed.
Arrange prenatal care after a positive result.
Check all medicines and supplements with a clinician or pharmacist.

Call your care team

Report any pregnancy bleeding to your care team.
Seek urgent help for heavy bleeding, severe abdominal or shoulder pain, fainting, or weakness.

Medical information, not medical advice

Every pregnancy is different. Use this guide for general education and follow the advice of your own maternity care team. Do not delay urgent care because of something you read here.