Two women, 4.5 month ~> 1 baby?

I heard this from an ex-colleague while working for a Japanese MNC in Australia. His team was running badly behind schedule and he was relating to some of us how some managers where trying to solve the problem by throwing resources at it. Sometime certain task just cannot be rushed and he explained that very succinctly in the following manner.

1 woman, 9 months => 1 baby
2 women, 4.5 months => 2 "half" babies