Elective cesarean section: its impact on neonatal respiratory outcome

Abstract

Physiologic events in the last few weeks of pregnancy coupled with the onset of spontaneous labor are accompanied by changes in the hormonal milieu of the fetus and its mother, resulting in preparation of the fetus for neonatal transition. Rapid clearance of fetal lung fluid is a key part of these changes, and is mediated in large part by transepithelial sodium reabsorption through amiloride-sensitive sodium channels in the alveolar epithelial cells, with only a limited contribution from mechanical factors and Starling forces. This article discusses the respiratory morbidity associated with elective cesarean section, the physiologic mechanisms underlying fetal lung fluid absorption, and potential strategies for facilitating neonatal transition when infants are delivered by elective cesarean section before the onset of spontaneous labor.

Fig 1

The Total cesarean, Primary cesarean and vaginal birth after cesarean rates in the United States from 1989 to 2006. Source: U.S. National Center for Health Statistics (Note: for comparability, 2004 and 2005 primary cesarean and VBAC rates are limited to 37 jurisdictions with unrevised birth certificates, encompassing 69% of 2005 births; 2006 total cesarean rate is preliminary).

Fig 2. Neonatal respiratory morbidity after elective caesarean section and intended vaginal delivery for 34 458 pregnancies at Aarhus University Hospital, Denmark, 1998–2006. Infants with meconium aspiration syndrome, sepsis, or pneumonia excluded

Adjusted for smoking, alcohol intake, parity, body mass index, marital status, maternal age, and years of schooling. Adapted from Hansen AK, Wisborg K, Uldbjerg N, et al: Risk of respiratory morbidity in term infants delivered by elective caesarean section: cohort study. Bmj 336:85, 2008, with permission

Figure 3

The mode of delivery of 14,603 infants ≥34 weeks who required ECMO in the US for respiratory failure between 1986 and 2006. Infants with congenital anomalies like congenital diaphragmatic hernia were excluded. A total of 2,145 infants were late preterm (defined as ≥34 and <37 weeks GA) and 12,458 term (≥37 weeks GA). Infants born by ECS constituted a large fraction of ECMO infants in both subgroups. In contrast, the ECS rates for the study period for the rest of the population were ~10%.

Figure 4. A schematic model for assembly and regulation of amiloride-sensitive sodium channels in the lung. Alveolar environment, particularly oxygen tension, steroid exposure, and alveolar distension, are likely to influence assembly of ENaC subunits. Signal transduction pathways mediated by several protein kinases including A, G, and C regulate each of these channel types in different ways. T1 and T2 cells with different channel types (and, therefore, different regulation) will have very different levels of sodium transport that will respond quite differently to hormonal and transmitter agents

From Jain L, Eaton DC: Physiology of fetal lung fluid clearance and the effect of labor. Semin Perinatol 30:37, 2006 with permission

Figure 5

Logistic regression model predicting the probability of admission to special care baby unit with respiratory distress by gestation, from a randomised trial of 998 mothers scheduled for ECS at term (≥37 weeks). Mothers in the treatment arm (n=508) received 2 doses of betamethasone 48 hours before delivery. Adapted from Stutchfield P, Whitaker R, Russell I: Antenatal betamethasone and incidence of neonatal respiratory distress after elective caesarean section: pragmatic randomised trial. Bmj 331:665,2005, with permission