Why is chemo used for ectopic?

Kills cells: Chemotherapy drugs are designed to kill or slow down the growth of rapidly dividing cells. Cancer cells are often rapidly growing. Similarly a growing embryo during pregnancy has rapidly growing cells. That is why a chemotherapy drug such as Methotrexate is effective.

Methotrexate: Methotrexate stops rapidly dividing cells by preventing utilization of folic acid. Is has been a known abortofascient drugas for years and will usually negate an ectopic pregancy. Woem who take mtx must wait 2 & 1/2 mo to rid their bodies of traces before retrying to get pregnant.