<prompt> Most common cause of first trimester abortion is:Chromosomal abnormalitiesSyphilisRhesus isoimmunizationCervical incompetence  <response>: Ans. is a, i.e. Chromosomal abnormalitiesRef. Dutta Obs. 7e, p 159,160; COGDT 10e, p 259; Williams Obs. 23e, p 215Abortion is spontaneous termination of pregnancy before 22 weeks or weight of fetus less than 500 gm.Incidence: About 15 of all conceptions end up in spontaneous abortions. Out of these 80 occur before 12 weeks i.e. in 1st trimester and among these 50-75 are due to chromosomal anomalies Germplasm defect. 