The rising rates of cesarean sections have been a concern for over two decades. An acceptable rate of cesarean sections is between 10% and 15% for countries in the developed world, according to the World Health Organization (WHO).
However, the estimated rate in the United Kingdom was 20% in 2004. In Canada, it was estimated at 22.5% in 2001â€“2002. And in the United States, the rate was 30.2% in 2005 (rising 46% since 1996).
This increase may have implications for the mother, baby, healthcare providers, and policy makers.
Though it is difficult to directly compare risks between vaginal and cesarean deliveries, higher mortality and morbidity rates are associated with the latter.
Risks encountered during the operation may include anesthetic complications and difficulty in stopping bleeding. Later risks include infections, wound healing problems, and increased risk of problems in subsequent pregnancies including malpresentation, placenta previa, and uterine rupture.
The trend of increased rates of cesarean sections with maternal age appears to be consistent in different countries and has previously been reported by several epidemiological studies.
However, it remains unclear why the risk of having cesarean section is associated with advancing maternal age. Could the association reflect a biological effect of advanced age, or is it a consequence of physician and maternal preference?
Researchers in the United KingdomÂ aimed to:
(1) Characterize the association between maternal age and the outcome of labor.
(2) Determine the proportion of the increase in primary cesarean rates that could be attributed to changes in maternal age distribution.
(3) Determine whether the contractility of uterine smooth muscle (myometrium) varied with maternal age.
To address aims (1) and (2), the researchers analyzed data collected over the period 1980 to 2005 by the Scottish Morbidity Record (SMR2), which has been demonstrated to be 99% complete since the late 1970s and free from substantial errors in more than 98% of the records in most of the specific fields used for their analysis.
Their analysis showed a linear association between the risk of having a cesarean section and advancing maternal age in first pregnancies.
The cesarean rate also more than doubled over the study period. They estimated that 38% of the additional procedures would have been avoided if maternal age distribution had remained the same as in 1980.
Therefore they conclude that a substantial part of the increase may be associated with the trend of delaying of first childbirth.
They then hypothesized that this trend is a result of a biological effect of aging on the contractility of the uterus. This hypothesis was further evaluated with aim (3) of the study, where they biopsied the uteri of 62 women (of mixed parity) undergoing routine elective cesarean delivery to test their contractility.
They found that advancing age was associated with impaired uterine function as evidenced by a reduced degree of spontaneous contraction and the type of spontaneous contraction.
What Do These Findings Mean?
This study adds to the evidence that advancing maternal age is associated with higher rates of cesarean sections.
It also suggests a possible mechanism for this association, i.e., impaired uterine function. Though it was not studied here, the researchers hypothesize that impaired uterine contractility may be a consequence of prolonged stimulation of the uterus by estrogen and progesterone, resulting from a prolonged interval between menarche and first birth.
Further research is needed to understand the determinants and management of dysfunctional labor in older women to help design strategies for reducing population cesarean delivery rates without adversely affecting maternal and infant outcomes.
Smith GCS, Cordeaux Y, White IR, Pasupathy D, Missfelder-Lobos H, et al. (2008) The Effect of Delaying Childbirth on Primary Cesarean Section Rates. PLoS Med 5(7): e144 doi:10.1371/journal.pmed.0050144. Copyright: Â© 2008 Smith et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License.
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