She was using birth control, she had an IUD.
An IUD is an "intra-uterine device", a small device that sits just inside the uterus and interferes with fertilization. This doctor was certainly a quack to not know (or care) she had one.
I didn't know women still used a shield. That means her boyfriend isn't using condoms exposing her to diseases.
Actually, the thing is designed to cause abortion by disallowing the fertilized egg to attach to the uterine wall.