The First Trimester: A Guide to Early Pregnancy

By Stacey Feintuch
Reviewed by Alyssa Quimby, M.D. , Jessie Everts, Ph.D.
April 28, 2023
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Wow, you’re pregnant! The first trimester is the earliest phase of pregnancy; it runs from the first day of your last period to the end of your 13th week. While this time is exciting for some, it can be overwhelming for others (or full of mixed emotions). Here’s a guide to the first trimester of pregnancy.

Common First-Trimester Symptoms

Your body is changing in response to a rapid rise in hormones so it can carry a baby. Everyone experiences first-trimester symptoms in slightly different ways. These feelings can come and go, or they can last for weeks or months.

Breast Changes

Your breasts are already getting ready for breastfeeding thanks to a hike in the pregnancy hormones estrogen and progesterone. It’s common for breasts to be tender, swollen, or sensitive starting around week 7 or 8, says G. Thomas Ruiz, M.D., a board-certified ob-gyn and lead at MemorialCare Orange Coast Medical Center in Fountain Valley, California. Wearing a supportive bra can help. You’ll be more comfortable once your body adjusts to the hormonal shifts.