The recommended first line of treatment for an underweight woman with amenorrhea is to

Amenorrhea is the absence of menstruation (one or more missed menstrual periods). Women who have missed at least three menstrual periods in a row and girls who haven't began menstruation have amenorrhea. Pregnancy is the most common cause of amenorrhea. The first line of treatment for an underweight woman with amenorrhea is to add weight (weight gain).