OverviewThe first trimester of pregnancy is the first three months after conception. Signs of early pregnancy are missed menstrual periods, fatigue, breast enlargement, abdominal distention, and nausea. During this period of time all organ development takes place so the fetus is most susceptible to damage from toxins, drugs, and infections.
Review Date 5/10/2017
Updated by: Anita Sit, MD, Department of OB/GYN, Santa Clara Valley Medical Center, San Jose, CA (for identification purposes only). Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.