Impaired contraction of the womb could be a contributor to the association between older maternal age and the increased rate of cesarean sections, according to a study released on June 30, 2008 in the open access journal PLoS Medicine.

A cesarean section, sometimes also called a c-section, is a method of childbirth in which the newborn is surgically removed from the uterus. C-sections are associated with higher mortality and morbidity rates than vaginal deliveries, and are thus often reserved for cases in which vaginal birth could put the mother's or baby's life at risk. The rate of cesarean section performance has increased considerably in the last 20 to 30 years in the developed world, which could have implications for not just the mother and baby but also healthcare providers and policy makers. According to the World Health Organization (WHO), acceptable cesarean rates are between 10-15% in any given developed countries. In light of this, they report the following rates: 20% in the United Kingdom in 2004, 22.5% in Canada in 2001 and 2002, 30.2% in the United States in 2005.

Earlier studies indicate that increased maternal age generally increases the rate of cesarean performance, and this trend has been shown in many different countries. However, the reason for this association is unclear, and it is unknown to what extent this association is true. These questions were tacked in a two part study run by Professor Gordon Smith and colleagues at Cambridge University in the United Kingdom.

In the first part of the study, a large set of data taken in Scotland, known as the Scottish Morbidity Record (SMR2) was used to examine the association between maternal age and the outcome of labor. The records, taken between 1980 and 2005, comprised half of a million records. Specifically, they examined what proportion of the increase in c-section rates could be directly associated with a change in maternal age distribution. It was found that the risk of a cesarean section increased linearly as the age of the expectant first time mother increased. Over time, additional trends were observed in the proportion of women in age group: the number of women between 30 and 34 years increased three-fold, between 35 and 39 years increased seven-fold, and over 40 doubled. IT was estimated that approximately 38% of these additional cesarean surgeries could have been vaginal births if the age distribution had remained constant after 1980. The team concluded from this that a sizable portion of the cesarean section rate increase could be due to delaying the first childbirth in a woman's life.

In the second part of the study, samples of muscle from the wall of the uterus itself, known as myometrium, that were taken during the routine surgery to examine the correlation between muscle contractility and maternal age. The team hypothesized that it was this loss of the ability of the muscle to contract, a biological effect of aging, was a cause of the increased need for cesarean sections. The biopsies were taken from 62 women, with a variety of number of previous births, who were undergoing routine elective cesarean delivery. They found that impaired uterine function was indeed associated with age as based on the type of contraction and the ability of the muscle tissue to contract.

In conjunction, the article states, these studies indicate that the trend of advanced maternal age is not just associated with increased cesarean sections, but that this substantial increase in cesareans could potentially be caused by a decreased ability of the uterus to function. Further work is necessary to determine if this causal relationship is indeed true, but if explained, could help health care professionals and policy makers make decisions that could reduce population cesarean rates with minimal negative effects on maternal and infant outcomes.

About PLoS Medicine

PLoS Medicine is an open access, freely available international medical journal. It publishes original research that enhances our understanding of human health and disease, together with commentary and analysis of important global health issues. For more information, visit plosmedicine.

About the Public Library of Science

The Public Library of Science (PLoS) is a non-profit organization of scientists and physicians committed to making the world's scientific and medical literature a freely available public resource. For more information, visit plos.

The effect of delaying childbirth on primary cesarean section rates.
Smith GCS, Cordeaux Y, White IR, Pasupathy D, Missfelder-Lobos H, et al.
PLoS Med 5(7): e144.
doi:10.1371/journal.pmed.0050144.
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Anna Sophia McKenney

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