A new study of 68 women suggests there may be biological reasons that encourage intercourse when a woman is most fertile.
The study found the women were more likely to have intercourse during the days fertility was at its peak compared to the rest of their cycle.
Researchers say it may be that ovulation increases a woman's sex drive or that sex accelerates ovulation and say the findings suggest that there are biological forces that influence the timing of intercourse.
The study was conducted at the National Institute of Environmental Health Sciences in Durham, North Carolina, and is published in the European journal Human Reproduction.
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