There are many risk factors: Past obstetric history Prior preterm births (biggest risk factor) Prior multiple pregnancies Prior multiple therapeutic abortions and / or spontaneous miscarriages Current pregnancy-related factors Pregnancy achieved by in vitro fertilization Little or no prenatal care Poor nutrition during gestation (and perhaps before) Cigarette smoking Younger or older maternal age (eg, < 16 years, > 35 years) Untreated infections (eg, bacterial vaginosis, intra-amniotic infection [formerly chorioamnionitis]) Multiple gestation (eg, twins, triplets) Cervical insufficiency (formerly cervical incompetence) Preeclampsia Placental abruption Certain congenital defects (fetuses with structural congenital heart defects are nearly twice as likely to be delivered prematurely as fetuses without congenital heart defects) Multiple gestation is an important risk factor; 59% of twins and > 98% of higher-order multiples are delivered prematurely.