Literally, the Hebrew refers to a pair of stones; the same word is used in Jeremiah 18:3 for a potter’s wheel. This puzzling description has been given several different interpretations:1
A birthstool or set of birth stones upon which the woman would sit as she delivered the baby
The genitals of the baby
The genitals of the mother
It is difficult to be certain about any one interpretation, especially because the word is used only twice in Scripture. However, the central point is clear. The midwives were to look carefully as the baby was delivered to see whether it was a boy or a girl.
16 “When you serve as midwife to the Hebrew women and see them on the birthstool, if it is a son, you shall kill him, but if it is a daughter, she shall live.”