Question

I've been trying to figure out through online sources (I don't own any medical textbooks) what the exact mechanism behind the birth control pill (henceforth the pill) is, and I am often finding contradicting information. This surprises me, since so many women take hormonal birth control that what it does should be known and accessible to everyone.

The following is gathered from PBS and Harvard. As I understand it, the female menstrual cycle is controlled by several organs working in feedback loops: after menstruation, there is a low concentration of estrogen and progesterone in the bloodstream, impelling the hypothalamus-hypofysis to secrete FSH and LH. This stimulates the maturation of a single follicle in the ovaries. This follicle secretes estrogen, signalling to the hypothalamus-hypofysis duo to stop producing FSH and LH. With enough estrogen, a sudden burst of FSH and LH is secreted, causing ovulation. The rest of the cycle is high in progesterone, and by lack of implantation, progesterone production slows and we are back at menstruation.

The goal of the pill is to prevent ovulation (rather than prevent implantation) by playing into these feedback loops.

Answer 1

Birth control pills prevent pregnancy primarily by inhibiting ovulation through maintaining constant levels of estrogen and progesterone, which provide negative feedback to the hypothalamus and pituitary gland, suppressing FSH and LH release.

Step-by-step explanation:

How Birth Control Pills Prevent Pregnancy

The birth control pill is a hormonal method of contraception widely used to prevent pregnancy. The pill typically contains synthetic forms of estrogen and progesterone, which exert their effects by tapping into the body's hormonal regulation system of the menstrual cycle. Taking the pill results in a constant level of these hormones in the bloodstream, providing negative feedback to the hypothalamus and pituitary gland. This feedback inhibits the secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH), which are crucial for follicle development and the LH surge leading to ovulation, respectively. Without a rise in FSH and LH, no follicle matures and ovulation is prevented, making pregnancy unlikely.

In addition to preventing ovulation, the pill also leads to changes in the endometrial wall and cervical mucus. The wall does not thicken as much as in a normal cycle, reducing the likelihood of implantation, while the mucus gets thicker, making it more difficult for sperm to reach any egg that might have been released. It's important for users to take the pill consistently at the same time every day to ensure effective prevention of pregnancy. Skipping doses or being late in taking the pill may disrupt the hormonal balance, potentially leading to ovulation and increasing the risk of pregnancy.