3,681. Two Wives Who Haven't Given Birth Before

Hilchos Bikkurim 11:22

Let’s say that a man has two wives who have not previously given birth. They give birth to a boy and a girl, or to two boys and a girl (and we don’t know which mother gave birth to which baby, nor the order in which the babies were born). In such a case, the father must give five sela to a kohein. This is because, no matter how you slice it, at least one of these babies is a male firstborn.

Hilchos Bikkurim 11:23

Let’s say that the two wives give birth to two girls and a boy, or to two boys and two girls, and we don’t know who was born first. In such a case, the father need not pay a kohein anything. This is because it’s possible that each wife gave birth to the girl before the boy.