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 8/24/2011
Updated by: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; and Yi-Bin Chen, MD, Leukemia/Bone Marrow Transplant Program, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.