What is the cause of a chemical or ectopic pregnancy in ivf?

Uterus vs tube: A "chemical" pregnancy in most cases is a pregnancy that implanted in the uterus, but miscarried very early. Before any sign on ultrasound. An ectopic pregnancy, which is more common in ivf pregnanices, is a pregnancy that implants in the tube, and is usually determined based on symptoms, abnormally rising HCG levels and ultrasound.