As the night that the woman ritually traditionally immerses is about 12 days after menstruation started, it often coincides with a woman's ovulation, and thus improves the chances of successful conception if sexual relations occur on that night.
Having sex every day improves the quality of men's sperm and is recommended for couples trying to conceive, according to new research.
Until now doctors have debated whether or not men should refrain from sex for a few days before attempting to conceive with their partner to improve the chance of pregnancy.
But a new study by Dr David Greening of Sydney IVF, an Australian centre for infertility and in vitro fertilisation (IVF) treatment, suggests abstinence is not the right approach.
He studied 118 men with above-average spermand found the quality of their sperm increased significantly after they were told to ejaculate daily for seven days.
Of course, this scientific evidence does not do anything to change the halacha.