The ‘natural miracle’ of conception is a complex process that allows a mature woman’s body to reproduce successfully. While the term conception refers to the fertilization of a mature ovum (egg) by a male sperm, we need to understand what happens to a woman’s body to prepare it for conception, as well as the changes that occur in her body after conception. Reproduction itself would not be possible without the menstrual cycle, a carefully orchestrated series of changes in a woman’s body that is regulated by hormones. This monthly cycle begins with the day of her first menses (period) when the endometrium (inner lining) of the uterus is expelled from the body. At this point, the levels of estrogen and progesterone are at the lowest. Then they begin to rise, causing the growth of several ovarian follicles. These follicles mature in about 14 days, when a surge of hormones causes one ‘dominant’ follicle to rupture and release a mature ovum. In some cases, a woman may have two mature ova, leading to twins, or multiple ova, usually observed in women undergoing some fertility treatment. This is the moment of ovulation, when the mature egg is ready for fertilization. If a healthy male sperm mates with the mature egg, conception occurs. For most women, the best chance at conception occurs if sexual intercourse takes place in a period from 5 days before until 1–2 days after ovulation.
Conception then begins a whole range of changes in the woman’s body. First, the fertilized ovum moves into the uterus, where it is embedded into the protein-rich inner lining and begins to grow into an embryo. The next important step is the release of human chorionic gonadotropin (hCG), a hormone found only in pregnant women. This hormone acts to stop the next step of the normal menstrual cycle, which would normally cause the uterus to shed its lining, leading to the menses. This is also the reason why the first sign of successful conception is usually a missed period.
At the same time, the woman’s body begins to physically change. Perhaps the most prominent change is in her breasts, which begin to swell in the first few weeks. They may also experience heightened sensitivity and tenderness. The veins on the surface of her breasts become more prominent and her nipples begin to enlarge. The reason for these changes lies in the mammary glands. These glands will eventually produce milk for the newborn baby, some nine weeks after conception.