What does the Pill do?
There seems to sometimes be some confusion as to whether or not the combined Pill inhibits implantation, or "only" supresses ovulation. Here are several sites which indicate it does indeed inhibit a fertilized egg from implanting:
"Oral contraceptives typically contain estrogen and progestin. Combination pills suppress ovulation (the release of an egg) each month and therefore prevent pregnancy by denying sperm a chance to connect with an egg and fertilize it. The progestin in these pills also decreases the chance of pregnancy by altering the mucus in a woman's cervix, thus making it harder for sperm to move into contact with an egg. Continuous progestins in combination oral contraceptives also inhibit the growth of the endometrium, which is triggered by estrogen. They also alter uterine secretions to reduce the chance for implantation of the egg."
"Birth control pills fool the body into acting as if it's pregnant. Birth control pills, also called oral contraceptives (OCs), come in two forms: the combined OC, a combination of two synthetic hormones, estrogen and progestin; and, the minipill, which consists solely of progestin. Combined OCs are more commonly used, though both kinds are available through health care providers. The combination pill prevents ovulation by suppressing the natural hormones in the body that would stimulate the ovary to release an egg. By taking this estrogen throughout the month, you insure that no egg will be developed or released for that cycle. Progestin thickens the cervical mucus, hindering the movement of sperm. Progestin also prevents the uterus's lining from developing normally; so, if an egg were fertilized, implantation is unlikely.
The minipills, which contain no estrogen, inhibit the egg's ability to travel through the fallopian tubes, alter the cervical mucus to block sperm, partially suppress the sperm's ability to unite with an egg, and partially inhibit implantation in the uterine wall. For maximum effectiveness, you need to take the pills as prescribed."
Birth control pills, also known as "The Pill," are a type of contraception in the form of small tablets that you swallow each day. Most pills contain two type of synthetic (man-made) female hormones, progestin and estrogen, and are called the "combination oral contraceptive". The hormones estrogen and progesterone are normally produced by the ovaries. There are many different types of the combination oral contraceptives. The estrogen and progestin prevent pregnancy by suppressing your pituitary gland, which stops the development and release of the egg in the ovary, called ovulation. The progestin also helps to prevent the sperm from reaching the egg and changes the lining of the uterus.
One type of pill contains only one hormone, progestin, and is called either the "progestin-only pill," or the "mini-Pill." It works by suppressing ovulation and helping to prevent the male's sperm from reaching the egg.
"How It Works
Combination ( estrogen and progestin) hormonal methods—pills, skin patch, or vaginal ring—help to prevent pregnancy by preventing eggs from being released from the ovaries (ovulation). These methods also thicken cervical mucus to prevent sperm from entering the uterus and can prevent a fertilized egg from implanting in the uterus."
"Combined birth-control pills work by preventing ovulation (the release of a mature egg from a woman's ovary). The estrogen in the pill causes this. Without the release of the egg, pregnancy can't happen. Combined birth-control pills also work by making cervical secretions thicker, making it very difficult for sperm to get into the uterus; by causing changes in the fallopian tubes (the tubes that carry the egg from the ovaries to the uterus); and by making it hard for a fertilized egg to implant. These effects are caused by the progestogen in combination birth-control pills. The minipills do not usually prevent ovulation because they don't contain estrogen. The minipills are good for women who either have difficulty taking estrogen or who are at some risk in taking estrogen (for example, women who smoke)."