Pregnancy disorders that lead to delivery before the 28th week of gestation: an epidemiologic approach to classification.

Epidemiologists have grouped the multiple disorders that lead to preterm delivery before the 28th week of gestation in a variety of ways. The authors sought to identify characteristics that would help guide how to classify disorders that lead to such preterm delivery. They enrolled 1,006 women who delivered a liveborn singleton infant of less than 28 weeks' gestation at 14 centers in the United States between 2002 and 2004. Each delivery was classified by presentation: preterm labor (40%), prelabor premature rupture of membranes (23%), preeclampsia (18%), placental abruption (11%), cervical incompetence (5%), and fetal indication/intrauterine growth restriction (3%). Using factor analysis (eigenvalue = 1.73) to compare characteristics identified by standardized interview, chart review, placental histology, and placental microbiology among the presentation groups, the authors found 2 broad patterns. One pattern, characterized by histologic chorioamnionitis and placental microbe recovery, was associated with preterm labor, prelabor premature rupture of membranes, placental abruption, and cervical insufficiency. The other, characterized by a paucity of organisms and inflammation but the presence of histologic features of dysfunctional placentation, was associated with preeclampsia and fetal indication/intrauterine growth restriction. Disorders leading to preterm delivery may be separated into two groups: those associated with intrauterine inflammation and those associated with aberrations of placentation.

Effects of chronic maternal anemia on systemic and uteroplacental oxygenation in near-term pregnant sheep.

OBJECTIVE: The hypothesis of our study was that both the systemic and uteroplacental circulations would adapt to chronic maternal anemia to ensure that oxygen supply to maternal tissues would be adequate. STUDY DESIGN: We measured cardiac output and uteroplacental blood flow and calculated systemic and uteroplacental oxygen delivery, extraction, and consumption in pregnant sheep that were anemic for 6 days (hematocrit 14%) and in normal sheep (hematocrit 28%). RESULTS: When compared with normal pregnant sheep, anemic pregnant sheep had increases in cardiac output and uteroplacental blood flow, neither of which was sufficient to prevent systemic or uteroplacental oxygen delivery from decreasing. In spite of decreases in oxygen delivery, systemic and uteroplacental oxygen consumptions were maintained at normal levels because of increases in oxygen extraction. CONCLUSION: Maternal systemic and uteroplacental circulations are capable of adapting well to chronic maternal anemia.

Pregnancy outcome following ultrasound diagnosis of macrosomia.

Both elective cesarean and early induction have been proposed for pregnancies in which the fetus is suspected to be macrosomic by ultrasound examination. We studied 242 nondiabetic women with estimated fetal weights (EFWs) by ultrasound of at least 4000 g or the 90th percentile for gestational age at 36 or more weeks' gestation. In 66 of 86 women (77%) delivering within 3 days of ultrasound examination, EFW exceeded birth weight. In only 41 of these 86 women (48%) were the EFWs within the corresponding 500-g category of birth weight. A trial of labor resulted in vaginal delivery in 76 of 106 women (72%). There were five cases of shoulder dystocia but no birth trauma. Estimated fetal weights and birth weights were not significantly different between the women who had a trial of labor and those who did not. Our results do not support cesarean delivery or early induction as a means of preventing infant morbidity when fetal macrosomia (weight of 4000 g or more or the 90th percentile for gestational age) is diagnosed by ultrasound.