Presence of prolactin hormone in the blood of lactating mothers suppresses the release of gonadotropins (FSH and LH) from the pituitary gland. Gonadotropins are required for ovulation to occur. Thus, in the absence of gonadotropins, ovum is not released and hence chances of fertilisation are nil upto 6 months following parturition (if the mother is regularly breast-feeding). Therefore, intensely lactating mothers do not generally conceive.