"Knowing that a woman is fertile (generally speaking) only for about three to five days out of the month and that her fertility is naturally obstructed (e.g. by the sticky mucous produced by progesterone around the cervix) the other days of the month, I do not want to say that the mere fact of a woman's fertility being obstructed is intrinsically wrong. Otherwise God would be immoral for creating a cycle which includes infertile periods! What I want to say is that a woman's cycle, on a biological level, is ordered toward fertility, toward the procreation of life. For example, the purpose the follicle stimulating hormone is to cause the maturation of an inchoate egg which is to be released into the fallopian tubes after ovulation. As the egg is maturing, the follicle which contains it releases estrogen which builds up the endometrium to prepare a home for the possible child that is conceived when the egg is fertilized. Furthermore, about day fourteen in a normal cycle, the luteinizing hormone causes ovulation, the egg is released into the fallopian tubes, the follicle where the egg had been is transformed (also by the luteinizing hormone) into the corpus luteum which then secretes progesterone which further prepares the endometrium to receive the child and also causes a change in the mucous around the cervix . . . . . . the mucous becomes thick, sticky, infertile; it will not allow sperm to pass through the uterus into the fallopian tubes where fertilization of the egg occurs. If fertilization does not occur the corpus luteum dies and therefore no longer secretes progesterone, the endometrium is no longer sustained by the progesterone; it is sloughed off, menstruation occurs, and a new, fresh release of the follicle stimulating hormone begins the cycle all over again. However, if fertilization did occur then the zygote floats down the fallopian tube, implants itself in the blood-rich endometrium with hair like roots; these roots (villi) just so happen to produce human chorionic gonadotropin which just so happens to keep the corpus luteum alive which just so happens to continue to secrete progesterone for the three months necessary before the placenta develops to the state where it can secrete a hormone to keep the endometrium intact so that they baby can grow and flourish. My point is that a woman's biological cycle is ordered marvelously, wondrously toward life. Yet, this cycle is not merely a biological phenomena; it is part of who the woman is. The human person does not ‘have' a body. The human person "is an incarnate spirit: a soul which expresses itself in a body and a body informed by an immortal spirit""