Date Published: July 1, 2008
Publisher: Public Library of Science
Author(s): Gordon C. S Smith, Yolande Cordeaux, Ian R White, Dharmintra Pasupathy, Hannah Missfelder-Lobos, Jill P Pell, D. Stephen Charnock-Jones, Michael Fleming, Nicholas Fisk
Abstract: BackgroundThe relationship between population trends in delaying childbirth and rising rates of primary cesarean delivery is unclear. The aims of the present study were (1) to characterize the association between maternal age and the outcome of labor, (2) to determine the proportion of the increase in primary cesarean rates that could be attributed to changes in maternal age distribution, and (3) to determine whether the contractility of uterine smooth muscle (myometrium) varied with maternal age.Methods and FindingsWe utilized nationally collected data from Scotland, from 1980 to 2005, and modeled the risk of emergency cesarean section among women delivering a liveborn infant in a cephalic presentation at term. We also studied isolated myometrial strips obtained from 62 women attending for planned cesarean delivery in Cambridge, England, from 2005 to 2007. Among 583,843 eligible nulliparous women, there was a linear increase in the log odds of cesarean delivery with advancing maternal age from 16 y upwards, and this increase was unaffected by adjustment for a range of maternal characteristics (adjusted odds ratio for a 5-y increase 1.49, 95% confidence interval [CI] 1.48–1.51). Increasing maternal age was also associated with a longer duration of labor (0.49 h longer for a 5-y increase in age, 95% CI 0.46–0.51) and an increased risk of operative vaginal birth (adjusted odds ratio for a 5-y increase 1.49, 95% CI 1.48–1.50). Over the period from 1980 to 2005, the cesarean delivery rate among nulliparous women more than doubled and the proportion of women aged 30–34 y increased 3-fold, the proportion aged 35–39 y increased 7-fold, and the proportion aged ≥40 y increased 10-fold. Modeling indicated that if the age distribution had stayed the same over the period of study, 38% of the additional cesarean deliveries would have been avoided. Similar associations were observed in multiparous women. When studied in vitro, increasing maternal age was associated with reduced spontaneous activity and increased likelihood of multiphasic spontaneous myometrial contractions.ConclusionsDelaying childbirth has significantly contributed to rising rates of intrapartum primary cesarean delivery. The association between increasing maternal age and the risk of intrapartum cesarean delivery is likely to have a biological basis.
Partial Text: Rising rates of cesarean delivery are a major public health concern. In recent years, the proportion of women attempting vaginal birth after cesarean (VBAC) has declined . Hence, rates of primary cesarean delivery will become an increasingly important determinant of overall cesarean rates. Many studies have demonstrated that rates of primary cesarean delivery have risen throughout the developed world in recent years [2–4], and the reasons for this are unclear. Some of the increase can be explained by changes in obstetric practice, such as the trend toward elective cesarean delivery when the infant presents by the breech . However, the rise in primary cesarean rates has coincided with a trend of increasing average maternal age at the time of first birth. Previous studies have demonstrated that the risk of cesarean delivery increases with advancing maternal age. However, it is currently unclear whether the association reflects a biological effect of advanced age [6,7] or is a consequence of physician and maternal preference [8,9]. The contribution of delaying childbirth to recent rises in cesarean delivery rates is also unclear [3,10–12]. The aims of the present study were (1) to characterize the association between maternal age and the outcome of labor, (2) to determine the proportion of the increase in primary cesarean rates that could be attributed to changes in maternal age distribution, and (3) to determine whether the contractility of uterine smooth muscle (myometrium) varied with maternal age.
We show that the risk of intrapartum cesarean delivery among women having their first birth at term increased with advancing maternal age from 16 y old upwards. The association was linear and was not explained by a range of other maternal characteristics. Over the period 1980 to 2005, the proportion of women in Scotland having their first birth aged 30–34 y increased approximately 3-fold, the proportion aged 35–39 y increased approximately 7-fold, and the proportion aged ≥40 y increased approximately 10-fold (Figure 3B). The cesarean rate more than doubled over the same period. This increase represented approximately 16,500 more procedures than would have occurred had the cesarean rate stayed at the level observed in 1980. Using these nationally collected data, we estimated that approximately 38% of these additional procedures would have been avoided had the maternal age distribution stayed the same as in 1980. Hence, we show that a substantial proportion of the increase in rate of emergency primary cesarean delivery in recent years may be attributed to the trend of delaying of first childbirth. The current observations cannot be explained by the offer of planned cesarean delivery to older women.