Taking long-term birth control pills will not cause pregnancy because the pills also contain estrogen and progestin, which inhibit the secretion of GnRH in the hypothalamus, thus inhibiting ovulation in women. The progestin component of the pill can make the cervical mucus sticky, which is not conducive to sperm penetration. Since progesterone and estrogen change the normal physiological changes of the endometrium, they can prevent the fertilized egg from being laid in the uterine cavity and cause the endometrium to develop out of sync with the embryo, thus acting as a contraceptive. In addition, it can also alter the function of the fallopian tubes, so that the operation of the fertilized egg is affected, thus interfering with the fertilized egg’s implantation in the uterine cavity.