There are, understandably, a number of possible complications of pregnancy, especially in teenage pregnancies. Among others, these include certain infections, anemia, trimester bleeding, hyperemesis gravidarum (pernicious nausea and vomiting), eclampsia (coma and/or convulsive seizure), erythroblastosis fetalis (Rh factor incompatibility), ectopic pregnancy (implantation outside the uterine cavity), and spontaneous abortion (miscarriage).

By convention, abortion is defined as delivery or loss of the product of conception before the twentienth week of pregnancy. About 35 % of women bleed or have cramping sometime during the first 20 weeks of pregnancy; about 20% actually abort. Since in 90 % of spontaneous abortions the fetus is either absent or grossly malformed, and in an additional 5% it has chromosomal abnormalities, spontaneous abortion may be a natural, purposeful rejection. If a woman has three or more successive pregnancies that end in spontaneous abortion, she is said   to have habitual abortion.

Other forms of abortion are missed abortion and septic abortion. Missed abortion occurs when the fetus has died but has been retained in utero for a month or longer. After about 6 weeks the dead fetus syndrome may develop, characterized by possible massive bleeding when delivery finally occurs (usually between 12 and 20 weeks). Septic abortion develops whe the uterine contents become infected before, during, or after an abortion.

Blood poisoning and shock are possible, and the prognosis is commonly grave. Septic abortions are typically associated with induced abortions done by untrained persons. As a consequence of legalized induced abortion, the septic abortion rate in the United State has fallen dramatically.