Baby by Week
Week 3

Your week 3 guide

If fertilization occurs, a single cell begins dividing while traveling toward the uterus.
Trimester

1

Month

1

Weeks left

37

Size at a glance

Comparison
Grain of sand
Length
Too small to measure
Weight
Too small to measure
Measurements are approximate. Healthy babies grow at different rates.

Baby development

The fertilized egg carries a complete set of genetic instructions.
Rapid cell division creates a blastocyst.
The outer cells will help form the placenta while the inner cells develop into the embryo.

Your body

You may feel no different yet.
Mild bloating, fatigue, or light spotting can occur for many reasons.
A test may turn positive late this week, but a negative result can still be too early.

This week's checklist

Wait several days and retest if your period is late but the first test is negative.
Calculate an estimated due date from the first day of your last period.
Continue prenatal nutrition and avoid alcohol and smoking.

Call your care team

Seek urgent help for heavy bleeding, severe or one-sided pain, shoulder pain, weakness, or fainting.
Contact a clinician if pain or bleeding concerns you even before a positive test.

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.