Rashi in Vayigash says, “isha mazraas techila, yoledes zachar, ish mazria techila, yoledes nekeiva” (if a woman gives seed first, she gives birth to a boy, if the man gives seed first, she gives birth to a girl).
What does this mean? Specifically, what does it mean when it says, “if a woman gives seed first”? Does this mean ovulation?
There are books available, such as the Shettles Method to determine the sex of your baby which seem to be based on this Rashi, i.e. on timing.
Since peru u’revu is a mitzva, and in order for the man to fulfill this mitzva he needs to have (at least) one boy and one girl, can you provide any advice on how to determine the sex of your baby?