Nishmat's Women’s Health and HalachaIn memory of Chaya Mirel bat R' Avraham

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Determining gender of baby

20 August, 2004


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?


This Rashi and the gemara he is quoting may refer to ovulation, but are often understood as referring to orgasm.  There is a theory that female-producing sperm endure longer, while male-producing sperm move faster.  In that case, it would be advantageous to have relations at ovulation with deep penetration for a boy, and before ovulation with shallow penetration for a girl.  However, this method remains unproved and modern medicine has yet to develop a reliable technique for sex determination in natural conception.

An in-depth discussion of the topic of gender selection can be found in the Spring, 2007, issue of Tradition.

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