Q&A: Why do I need to wait three months to TTC after a methotrexate injection?

Methotrexate (MTX) is a medication that interferes with the activation of folic acid (folate) and therefore blocks the synthesis of DNA, RNA, and protein. The result is severe damage to the viability of living growing cells. It works best on rapidly dividing cells such as the cells that make up the placenta in a pregnancy. This makes MTX an effective medication to treat problems such as ectopic pregnancies and non-viable intra-uterine pregnancies.

Methotrexate, if given during a pregnancy, can cause a miscarriage or birth defects. Because MTX may remain in the body for a period of time after it is administered, it has the potential to interfere with pregnancies that are conceived months after it is given. Unfortunately, it has not been conclusively determined how long after giving MTX it is safe to attempt conception again. Manufacturers of MTX recommend waiting between three and six months before attempting pregnancy based mostly on non-human animal studies. Some researchers have recommended waiting a year.

The most recent study looked at 125 pregnancies conceived after women were treated for ectopic pregnancy with MTX. Forty-five conceptions that occurred in less than six months were compared to those conceived after six months. There was no difference detected in the outcomes of pregnancy in the two groups.

Based on this type of data, most physicians feel comfortable in allowing their patients to attempt pregnancy again after three months.