<prompt> Mechanism of action of oral contraceptive containing a combination of oestrogen-progestin isInhibition of ovulationA change in the cervical mucusInhibition of motility of the uterine tubesInhibition of motility of sperms  <response>: The mechanism of action of the combined oral pill is mainly to prevent ovulation This is achieved by blocking the pituitary secretion of gonadotropins that is necessary for ovulation to occur Reference: Park;s textbook of preventive and social medicine, 23rd edition, Page no: 501 