325: Maternal age and uterine function: A biological basis for rising rates of cesarean delivery

Abstract

OF CESAREAN DELIVERY GORDON SMITH, YOLANDE CORDEAUX, IAN WHITE, D STEPHEN CHARNOCK-JONES, DHAMINTRA PASUPATHY, HANNAH MISSFELDER-LOBOS, JILL PELL, MICHAEL FLEMING, Cambridge University, Obstetrics & Gynaecology, Cambridge, United Kingdom, MRC Biostatistics Unit, Cambridge, United Kingdom, BHF Glasgow Cardiovascular Research Centre, University of Glasgow, Glasgow, United Kingdom, Common Services Agency, Information and Statistics Division, Edinburgh, United Kingdom OBJECTIVE: Older women are at increased risk of cesarean delivery. It is currently unclear whether this reflects a biological effect of age on the risk of emergency cesarean delivery. The direct contribution of delaying childbirth to increasing primary cesarean rates in the general population is also currently unclear. STUDY DESIGN: We examined the relationship between maternal age and the outcome of labor among 583,843 first births of women at term, in Scotland, between 1980 and 2005. We also characterized spontaneous contractile activity in 181 myometrial strips from 62 women in vitro in relation to the mother’s age. RESULTS: The mean duration of labor increased progressively from aged 16 upwards (co-efficient for 5 year increase in age 0.49 hours, 95% CI 0.46-0.51). The risk of cesarean delivery also rose progressively from aged 16 upwards (OR for 5 year increase in age 1.51, 95% CI 1.50-1.53). This was unaffected by adjusting for a range of maternal characteristics. Over the period of 1980-2005, the cesarean rate more than doubled. Over the same period of time, the proportion of women having their first birth aged 30-34 increased three fold, the proportion aged 35-39 increased seven-fold and the proportion aged 40 and above increased 10-fold. Over the period 1981-2005, there were 16,548 more cesarean deliveries than would have occurred had the rate stayed the same as it was in 1980. Logistic regression modeling estimated that if the age distribution had stayed the same as it was in 1980 across the period of study, 38% of the additional cesarean deliveries would have been avoided. When myometrial strips were studied in vitro, increasing maternal age was associated with reduced spontaneous activity (P 0.02) and increased coupling of spontaneous contractions (P 0.001). CONCLUSION: 1. Demographic trends to delay first childbirth have significantly contributed to rising rates of intrapartum primary cesarean delivery. 2. The association between increasing maternal age and cesarean risk is likely to have a biological basis.