Fathers' Day (1990)

Original title: La Fête des pères

In this comedy, Thomas and Stephane are a couple of gay men who want to raise a baby. When their efforts to adopt one fall through, they hit on the scheme of having Carole, the (gorgeous) young woman they have saved from a bad relationship, bear a child for them. When she insists that only natural reproduction methods be used, they gamely play good sports by going to bed with her, and become the father(s) of twins.