MedlinePlus Medical Encyclopedia: First trimester of pregnancy

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First trimester of pregnancy

The 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: 4/14/2004

Updated by: Dominic Marchiano, M.D., Department of Obstetrics & Gynecology, Pennsylvania Hospital, Philadelphia, PA. Review provided by VeriMed Healthcare Network.

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