Pregnancy Week by Week
From a poppy seed to a watermelon — explore your baby's development, your changing body, and what to expect in each of the 42 weeks of pregnancy.
Weeks are counted as gestational age — from the first day of your last period — the same convention your provider and your due date use. The first trimester (weeks 1–13) is when every major organ forms, the second (weeks 14–27) is when growth and movement take off, and the third (weeks 28–42) is when your baby gains most of its birth weight and gets ready to meet you.
Last updated: October 23, 2026
How to use this week-by-week guide
Each week page covers your baby's size, length, and weight, key developmental milestones, the symptoms you're most likely to feel, recommended medical tests, and practical nutrition and exercise tips. Start from the week matching your current gestational age — count from the first day of your last menstrual period.
Not sure how far along you are? Use our How Many Weeks Pregnant Am I calculator to find your exact week, then jump to the matching guide above.
If the early weeks feel anxious, it can help to see how quickly the odds improve: our Miscarriage Risk Calculator shows how the risk of loss falls week by week, based on published study data.
Sources and References
Weekly milestones in this guide follow standard obstetric development timelines. Last reviewed October 23, 2026.