Methergine is to be used only after delivery a baby. Do not breastfeed within 12 hours after taking Methergine. Methylergonovine may pass into breast milk in small amounts and could affect a nursing baby.Click to see full answer. Herein, does Methergine decrease milk supply?Although results of several imperfect studies are somewhat mixed, it appears that methylergonovine can decrease serum prolactin and possibly the amount of milk production and duration of lactation, especially when used in the immediate postpartum period.Also Know, what happens if you take Methergine while pregnant? Category C: Animal reproductive studies have not been conducted with Methergine. It is also not known whether methylergonovine maleate can cause fetal harm or can affect reproductive capacity. Use of Methergine is contraindicated during pregnancy because of its uterotonic effects. (See INDICATIONS AND USAGE). Beside above, why is Methergine given after delivery? Methergine is used just after a baby is born, to help deliver the placenta (also called the “afterbirth”). It is also used to help control bleeding and to improve muscle tone in the uterus after childbirth. Methergine may also be used for purposes not listed in this medication guide.What are the side effects of Methergine? Methergine Side Effects increased blood pressure (severe headache, blurred vision, buzzing in your ears, anxiety, shortness of breath); chest pain, sweating, pounding heartbeats or fluttering in your chest; seizure (convulsions); numbness, tingling, or cold feeling in your fingers or toes; confusion, hallucinations, vision problems;