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.
Update Date 7/14/2015
Updated by: Emily Wax, RD, The Brooklyn Hospital Center, Brooklyn, NY. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.