A woman gets drunk and has sex. She becomes pregnant as a result. She goes to a doctor and says "I choose to not be involved in this pregnancy". The child dies and the woman goes free.
A women gets drunk and drives home. She is involved in an accident and, as a result, a child is put in ICU. She goes to the judge before the trial and says "I choose not to be involved in this trial". The child dies and she goes free.
That's a good one. It basically boils down to an equal protection argument, unless the law decrees that a fetus up to a certain age is not human - but then you can't legally prosecute someone for killing a similar fetus without a significant contradiction.