What Is a Trimester?
The word trimester means "3 months." This can be confusing, because a normal pregnancy is 40 weeks, a bit longer than 9 months. Yet, health care providers and pregnant women often use trimesters to give pregnancy a beginning, middle, and end. In fact, most providers talk about pregnancy in weeks, rather than months or trimesters.
The first trimester takes place from conception through week 14. The second trimester is from week 14 through week 28. And the third trimester is from week 28 through labor and delivery. Of course, delivery varies a lot, but it averages at week 40.
Review Date: 7/4/2019
Reviewed By: John D. Jacobson, MD, Professor of Obstetrics and Gynecology, Loma Linda University School of Medicine, Loma Linda Center for Fertility, Loma Linda, CA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. © 1997- A.D.A.M., a business unit of Ebix, Inc. Any duplication or distribution of the information contained herein is strictly prohibited.
A.D.A.M. content is best viewed in IE9 or above, Firefox and Google Chrome browser.