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First of all plz tell me your wife's age. Age is very important factor in infertility
. If your wife is not having follicles after treatment with letrozole then she need be evaluated thoroughly. First investigation will be to know present quantity of follicles in ovary( Ovarian reserve
) by doing blood tests like FSH, Estrogen,day 2 antral follicle
count by ultrasound. Other reason could be resistance/failure to letrozole. In case of resistance she may require other drugs for ovulation induction
like clomiphene or gonadotropins. Consult an infertility specialist soon before its too late . All the best.