Ananth, C. V., & Vintzileos, A. M. (2006). American Journal of Obstetrics and Gynecology, 195, 1557-1563.

It is now recognized that preterm birth can be either spontaneous or medically indicated. Twenty percent to 35% of all preterm births are due to "medically indicated" interventions, but data regarding maternal-fetal conditions necessitating these births are rare. To address this gap, data were analyzed from 1989 to 1997 in the state of Missouri for all singleton live births at longer than 20 weeks' gestation (684,711 births). The purpose was to see to what extent ischemic placental disease contributed to medically indicated births of less than 35 weeks' gestation. Near-term/term births (35 weeks or longer) were also analyzed. Ischemic placental disease was hypothesized to be most associated with medically indicated prematurity. Pre-eclampsia, fetal distress, small for gestational age, and placental abruption were all conditions considered to be in the ischemic placental disease category.

Results indicated that the overall preterm birth rate at less than 35 weeks was 4.6%, of these births 23.5% were considered medically indicated. At least one of the ischemic placental conditions (pre-eclampsia, fetal distress, small for gestational age, and placental abruption) was present in more than half (53.2%) of all medically indicated preterm births versus only 17.7% of near-term/term births. These results support data from a previous study indicating that pre-eclampsia, fetal growth restriction, or distress and placental abruption contributed to 87% of medically indicated births at less than 37 weeks (Meis et al, 1995). This growing body of research suggests that ischemic placental conditions may serve as an important pathway to preterm birth and underscores the need for prevention strategies for these conditions.

There are some limitations to the study. Thirty-five weeks' gestation was used as the cutoff versus the more commonly used 37 weeks. The authors' rationale was that "obstetricians are seldom aggressive in prolonging pregnancies at 35 to 36 weeks gestation." A second limitation is that no discrimination was made between early and later gestation prematurity in examining medically indicated births. That contribution to the literature would have been helpful to see if ischemic placental conditions also were prevalent in earlier gestation prematurity. The contribution of the research is undeniable, however. It quantifies medical interventions and preterm birth rates and the maternal-fetal conditions leading to these interventions.

Linda Beth Tiedje

References