When one is on birth control pills, does the uterus still prepare for pregnancy even though an egg has not been released? Does menopause come about because the body no longer has anymore eggs to release? I heard that if one has taken birth control pills then its harder to get pregnant once she has stopped using them - is this true? What are the long-term effects of take the Pill?
1. The hormones in birth control pills prevent the uterus from building up its lining (endometrium) as thick as it would be under a normal fertile cycle. This effect is mainly from the progesterone in the pills. Progesterone's function in the body is to maintain the endometrium in stasis, so that it neither thickens nor sloughs off. This is great during pregnancy because it creates a stable environment in the uterus. When you're on birth control pills, the progesterone concentration is kept elevated in your body, suppressing proliferation of the endometrium. When you go on your placebo week, the level of progesterone in your body drops to a level where your endometrium can no longer be maintained. The endometrium then sheds away as menstrual blood.
Some birth control pills still allow ovulation to happen. These are called minipills and they are progesterone-only. This is in contrast to combination pills which use a combination of estrogen and progesterone. Estrogen level control ovulation. Combo pills manipulate estrogen levels so that your ovaries don't recognize the signal to ovulate. In short: you release eggs on the minipill, you don't release eggs on the combo pill.
2. That's sort of true. It's not as if your body knows, "Oops! This is the last bean in the bag!" Yes, menopause coincides with having very few eggs left. But it has more to do with other cells in the ovary that have control over hormonal signals that go to both the ovary as well as glands in the brain. Specifically, a special hormone called inhibin B stops follicle stimulating hormone (FSH) from stimulating ... follicles (i.e., no new eggs will be prepared for release). This also results in changes in estrogen production. Specifically, women lose a lot of estrogen when they enter menopause, and this accounts for pretty much all the physiological changes during menopause (the vaginal dryness, suppressed libido, decreased bone density, et al).
3. This used to be true because birth control pills were a lot more potent in the past. But with time and additional research, scientists have figured out how to prevent conception with as little hormone as possible. That means on our new birth control pills, we can wash them out of our bodies faster and with fewer side effects. The result? A quicker return to fertility. Studies have shown that women who have been on hormonal contraceptives for prolonged periods of time then quit usually take about two or three months to resume normal fertility cycles. Fortunately, these studies also pointed out that fertility is not permanently impaired (i.e., you'll get it back eventually).