Pregnancy Guide

1 Weeks Pregnant

Your baby is the size of a Sperm & Egg. Discover exactly what is happening to your body and your baby this week.

New pregnancy guide: Learn how weeks are counted, what each trimester means, and how to interpret your calculator results for better preparation and planning. Read the full guide

Week 1 in detail

Counted from your period — development has not started

Baby this week

Clinicians date pregnancy from the first day of your last period, not from conception. This week you are having a period. Follicles in the ovary are lining up so one egg can mature later in the cycle.

  • No embryo yet — this is cycle timing, not a baby
  • The uterine lining is shedding so a new lining can grow
  • Folic acid taken now protects a neural tube that will form weeks later

Your body this week

Estrogen is low. Cramps, bloating, and tiredness are period symptoms, not pregnancy symptoms. If you are trying to conceive, this is the week to treat like a reset: sleep, food, and supplements.

  • Record the first day of bleeding — that date drives every later week
  • Ask a clinician before stopping or starting prescription medicines
  • Alcohol and high-mercury fish are worth dropping now, not after a positive test

Get ready

Use the checklist above for vitamins and your LMP date. A daily prenatal with at least 400 mcg of folic acid is the highest-yield step this week. The pregnancy guide explains why weeks are counted this way.

A general guide, not medical advice. Scan timing and symptoms vary — ask your clinician.

Baby Growth Curve

This chart visualizes the average length of the baby from week 1 to 40. Values are based on standard clinical averages.

Week 2 →