A study just out in PLoS Medicine suggests that an increasing trend of delaying childbirth is associated wiht a rising rate of the use of cesarean delivery. The explanation appears to be impared uterine function.From the editor’s summary:

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.

In the presumably more “natural” setting of a non-westernized, non-industrialized world, say among traditional horticultural populations, pastoralists or foragers, a woman rarely menstruates.A woman may experience 15 or so cycles prior to her first pregnancy. She does not cycle during pregnancy. She does not cycle during the post-partum period of lactational amenorrhea. Then she cylces a few times (say five) and is pregnant again. This may happen, say, four times prior to menopause, possibly with a post-last childbirth period of anothe 20 cycles (generously estimated).This adds up to about 55 cycles in total, or feer than five years of cycling.A woman who has her first child at the age of 30 and begins menstruating at the age of 15 cycles for 15 years.In other words, a woman living in a more traditional setting would be very unlikely to cycle more than 55 times, probably much less, and a woman in an industrial setting may cycle about 200 times. That could be a big difference.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 Received: December 14, 2007The original article should be HERE.

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