I learned that a pregnant woman should get for kaporos an extra hen for the baby. Why does an unborn baby need a kapora – surely it has no aveiros?
Two possible explanations are suggested:
1) The kaparos are brought for sins in previous incarnations.
2) Because children are sometimes punished for the sins of parents, it is proper to bring a kaparah even for an unborn infant.
These explanations remain a little strained, but the custom (of taking both an extra hen and a cock, unless the gender of the infant is known) remains the custom.