Pregnancies associated with perinatal morbidity or mortality are considered high risk. Identification of high-risk pregnancies is essential to the care of the infant because they may result in intrauterine fetal death, intrauterine growth restriction (IUGR), congenital anomalies, excessive fetal growth, birth asphyxia and trauma, prematurity (birth at <38 weeks) or postmaturity (birth at ≥42 weeks), neonatal disease, or longterm risks of cerebral palsy, mental retardation, and chronic sequelae of neonatal intensive care. Ten percent to 20% of women may be high risk at some time during their pregnancy. Although some obstetric complications are first seen during labor and delivery and cannot be predicted, more than 50% of perinatal mortality and morbidity results from problems identified before delivery as high risk. After a high-risk pregnancy is identified, measures can be instituted to prevent complications, provide intensive fetal surveillance, and initiate appropriate treatments of the mother and fetus.
A history of previous premature birth, intrauterine fetal death, multiple gestation, IUGR, congenital malformation, explained or unexplained neonatal death (e.g., group B streptococcal sepsis), birth trauma, preeclampsia, gestational diabetes, grand multipara status (five or more pregnancies), or cesarean section is associated with additional risk in subsequent pregnancies.
Pregnancy complications that increase the risk of a poor outcome can be secondary to maternal or fetal causes or both. Complications include placenta previa; abruptio placentae; preeclampsia; diabetes; oligohydramnios or polyhydramnios; multiple gestation; blood group sensitization; abnormal levels of unconjugated estriols, chorionic gonadotropin, or alpha-fetoprotein; abnormal fetal ultrasound; hydrops fetalis; maternal trauma or surgery; abnormal fetal presentation (breech); exposure to prescribed or illicit drugs; prolonged labor; cephalopelvic disproportion; prolapsed cord; fetal distress; prolonged or premature rupture of membranes; short cervical length (<25 mm) and the presence of fetal fibronectin in cervical secretions at less than 35 weeks’ gestation (a predictor of preterm labor); cervical infections and vaginosis; and congenital infections, including rubella, cytomegalovirus, herpes simplex, human immunodeficiency virus (HIV), toxoplasmosis, syphilis, and gonorrhea.
Maternal medical complications associated with increased risk of maternal and fetal morbidity and mortality include diabetes, chronic hypertension, congenital heart disease (especially with right-to-left shunting and Eisenmenger complex), glomerulonephritis, collagen vascular disease (especially systemic lupus erythematosus with or without antiphospholipid antibodies), lung disease (cystic fibrosis), severe anemia (sickle cell anemia), hyperthyroidism, myasthenia gravis, idiopathic thrombocytopenic purpura, inborn errors of metabolism (maternal phenylketonuria), and malignancy.