Oxycodone while pregnant?

So my cousin in law said she went to the hospital at 40+4 due to contractions. She said the dr told her she wasn't dilated enough and gave her oxycodone for the pain and sent her home.

Two days later she had the baby. She just told me that the hospital called children and youth because they found oxycodone in the baby's system (said they tested her placenta). So I found it odd since "the hospital " gave her the oxycodone that children and youth were called. Since the would have a medical record of them giving her the meds. Does this make sense to any of you? Because it definitely doesn't sound right to me.