Dear Jo I know only one study about the passage in milk of methotrexate. The mother was taking 22,5 mg/day for a cancer. The maximum level in milk was 2,7 µg/l, with a ratio milk/plasma of 0,08. So, methotrexate passes very very few in breast mil. It is told here than when a mother takes methotrexate in little doses, she can breastfeed. Better to look at the baby (hematology), and give folic acid to the baby and to the mother (done systematically for the mother). Hope this help Françoise Railhet LLL France Medical Associates Program