In lactational amenorrhoea, ovulation does not occur during the period of intense lactation because of

In lactational amenorrhea, ovulation does not occur during the period of intense lactation because of the high level of prolactin. Prolactin is a hormone produced by the pituitary gland that stimulates milk production in the mammary glands. During lactation, the high levels of prolactin suppress the release of gonadotropin releasing
hormone (GnRH) from the hypothalamus. GnRH is responsible for triggering the release of follicle-stimulating
hormone (FSH) and luteinizing hormone (LH) from the pituitary gland, which are necessary for ovulation.

(1) Oestrogen is involved in the regulation of the menstrual cycle and the development of secondary sexual
characteristics. A surge of estrogen alone would not inhibit ovulation  during lactational amenorrhea. In fact,
oestrogen levels typically decrease during lactation due to the inhibitory effect of prolactin on oestrogen
production. 

(2) During lactational amenorrhea, the release of GnRH is suppressed due to the high levels of prolactin. This suppression prevents the normal pulsatile release of GnRH, leading to the inhibition of ovulation.

(4) High levels of prolactin during lactation inhibit the release of FSH and LH by suppressing GnRH. Without the normal pulsatile release of GnRH, FSH and LH levels remain low, preventing ovulation.