Table 1 Variables included in the propensity score generation model

maternal demographics

race/ethnicity, partner status, education, expected payment source, WIC eligibility, maternal age, pre-gravid BMI,

region of residence [New England, mid-Atlantic, Southeast, Midwest, Southwest, West], whether the mother was Amish

obstetric history

gravidity, parity, history of cesarean, history of vaginal birth, history of other cervical surgery, history of other uterine surgery

pre-gravid history of chronic diseases

asthma, genetic disorders, hypothyroidism, frequent urinary tract infections, sexually-transmitted infections

pre-gravid history of psychosocial complications

anxiety, depression, eating disorders, domestic violence, sexual abuse, substance abuse

prenatal care characteristics

credentials held by the attending midwife, actual place of birth (home or birth center), number of prenatal visits

pregnancy complications

anemia, asthma, cholestasis, congenital anomalies diagnosed antenatally, spontaneous abortion of a twin with continuing pregnancy, group B strep infection, heart disease, hepatitis B or C infection, hyperemesis, hyperthyroid, hypothyroid, intrauterine growth restriction, urinary tract infection, oligohydramnois, polyhydramnios, preterm labor or premature rupture of membranes, post-term pregnancy, unexpected preterm birth diagnosed by clinical exam of the newborn, placenta previa, placental abruption, puritic urticarcical papules and plaques of pregnancy, Rh sensitivity, sexually-transmitted infections, genital herpes, single umbilical artery

psychosocial complications during pregnancy

anxiety, depression, eating disorder, sexual abuse, substance abuse, domestic violence

intrapartum characteristics and complications

whether an induction was attempted, either pharmacologic or non-pharmacologic, cord prolapse, maternal dehydration, malposition/malpresentation, maternal exhaustion, maternal request for pharmacologic pain relief, maternal shock, light meconium, thick or particulate meconium, non-reassuring fetal heart tones, hypertension, pre-eclampsia, prolonged rupture of membranes with or without labor, urine retention, maternal pushing position, failure to progress in the first stage, failure to progress in the second stage, length of active labor, length of pushing, length of time membranes were ruptured

postpartum and birth outcomes

gestational age at birth, birthweight, hemorrhage > 1000 cc, severe perineal trauma (3^rd or 4^th degree), any congenital anomalies, transfer to a hospital in the first 6 h for a maternal indication, transfer to a hospital in the first 6 h for a neonatal indication, NICU admission in the first 6 weeks, other neonatal hospitalization in the first 6 weeks, maternal hospitalization in the first 6 weeks