If you're talking about Roaccutane then YABVU. From the NHS website:
This medicine is likely to harm a baby. It also increases the risk of miscarriage.
If you become pregnant during treatment with isotretinoin capsules, stop taking the capsules and tell your doctor as soon as possible.
It's very important that you do not get pregnant while you're taking isotretinoin capsules. You'll be asked by your doctor to follow strict rules to prevent pregnancy during treatment and for 1 month afterwards.
Before starting treatment with isotretinoin capsules, women who are able to become pregnant must agree to:
use at least 1, and ideally 2, reliable methods of contraception for 1 month before starting isotretinoin capsules, and for 1 month after treatment has stopped - the second contraceptive should be a barrier method of contraception (for example, a condom), but you shouldn't use barrier methods on their own
have a pregnancy test before, during, and 5 weeks after the end of treatment - some doctors may ask you to have monthly pregnancy tests
Your doctor will give you a patient reminder card for isotretinoin. Read this card and the information leaflet that comes with your medicine before you start taking the capsules.
Do not breastfeed while you're using isotretinoin capsules. This medicine can get into breast milk and harm your baby.