Smoking has an effect on pregnancy. For men, smoking may affect the quality of sperm, which may lead to infertility, or may cause fetal abnormalities, miscarriage or premature birth after pregnancy. For women, smoking may also cause fetal deformities, miscarriage or premature birth. Smoking affects the blood supply to the placenta and also affects the position of the placenta, such as placenta previa or placental abruption. Patients who smoke have a significantly higher incidence of preterm labor compared to non-smokers. The incidence of miscarriage or preterm labor is also significantly higher in smokers than in non-smokers, so it is recommended that both spouses quit smoking during the first trimester of pregnancy.