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Menstrual Cycle Length Associated with Conception

Cycles shorter or longer than 30 to 31 days linked to lower fecundity, higher spontaneous abortion

TUESDAY, Dec. 27 (HealthDay News) -- Women are more likely to conceive after menstrual cycles of 30 to 31 days compared with shorter cycles, according to a study in the January issue of Epidemiology. In addition, pregnancies conceived after a shorter or longer cycle are more likely to end in spontaneous abortion compared with 30 to 31 day cycles.

Chanley M. Small, Ph.D., from Emory University in Atlanta, and colleagues prospectively studied 470 women who used inconsistent or no birth control. The women recorded daily information on menstrual cycle, intercourse, birth control use and other covariates for one year or until clinical pregnancy. Human chorionic gonadotropin levels in urine were monitored.

Menstrual cycles lasting 30 to 31 days, and those with a bleed length of five days, were the most likely to be followed by conception. Spontaneous abortion was three times more likely when cycle times were greater or less than 30 to 31 days, and when bleed times were less than five days.

"Specific menstrual characteristics appear to be associated with decreased fecundity and increased risk of spontaneous abortion, suggesting that menstrual cycle characteristics may be useful measures of underlying reproductive states," the authors conclude. "However, the imprecision of our estimates suggests that large sample sizes may be necessary to see these effects."

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