What would cause a 17 year old pregnant girl to have a convulsion?

17 pregnant girl. My first concern would be eclampsia a condition during pregnancy with high blood pressure and seizures- this is life threatening. Other concerns would be alcohol/drug use as well as seizures due to non pregnancy related issues. Important to consult with a physician about the particulars.
Seek help urgently. Colvulsions during pregnancy at any age can be caused by several things that can harm mom and/or baby. It can happen with pre-eclampsia, a dangerous problem with elevated blood pressures. Seizure disorder, drug withdrawal, very abnormal blood sugars, blood clots in lungs, air embolism, and a tumors in the brain can all cause convulsions. Get help immediately.