Baby by Week
Week 1

Your week 1 guide

Pregnancy is dated from the first day of your last menstrual period, so conception has not happened yet.
Trimester

1

Month

1

Weeks left

39

Size at a glance

Comparison
Not conceived yet
Length
Not applicable
Weight
Not applicable
Measurements are approximate. Healthy babies grow at different rates.

Baby development

Your body is beginning a new menstrual cycle.
The uterus will rebuild its lining in preparation for a possible fertilized egg.
This dating method gives clinicians a consistent 40-week timeline.

Your body

You are likely having your period and your usual menstrual symptoms.
There are no pregnancy symptoms from a baby yet.
Cycle length varies, so ovulation may not follow a textbook schedule.

This week's checklist

If you are trying to conceive, ask your clinician about a prenatal vitamin with folic acid.
Review medicines, supplements, smoking, and alcohol with a qualified professional.
Note the first day of your period for pregnancy dating.

Call your care team

Seek urgent help for unusually heavy bleeding, fainting, or severe pelvic or abdominal pain.
Contact a clinician if you need personalized preconception or medication advice.

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.