What is the significance of progesterone-estrogen combination as a contraceptive measure?

The significance of progesterone-estrogen combination as a contraceptive measure is as follows:

i. Oral administration of small doses of either progestogens or progestogen-estrogen combinations is mostly used as a form of female contraception. These are called pills. Pills inhibit ovulation and implantation as well as alter the quality of cervical mucus to prevent/ retard entry of sperms. Pills are very effective with lesser side effects.

ii. Progestogens alone or in combination with estrogen can be injected or implanted under the skin. Their effective periods are much longer.

iii. Administration of progestogens or progestogen-estrogen combinations or IUDs within 72 hours of coitus has been found to be very effective as an emergency contraceptive as they can be used to avoid unwanted pregnancy.