The Pill Prevents Pregnancy in 4 Ways and it Starts in the Brain

It takes a lot of coordination, complex interactions, and energy for your body to release an egg each month. Surprisingly, there are only about three fertile days in a woman’s menstrual cycle and even when actively trying to get pregnant or conceive, only 20% of couples conceive each month. So, why is it that one form of contraception or ‘The Pill’ requires a daily ritual? Put simply, the oral contraceptive pill (OCP) is made of very low levels of synthetic estrogen and progesterone.

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Let’s start with the menstrual cycle since it is the basis for how the pill exerts its contraceptive effects. Four body systems must be functional to produce a menstrual flow each month which can vary from 21 to 35 days. The first organ necessary is the uterus or womb. It has three layers, but only the superficial lining sheds each month. The second organs are near the uterus, on either side and are called the ovaries. The fallopian tubes are hollow, flexible structures that are attached to the uterus and have an opening near the ovaries. This opening is essential for picking up the egg and transporting it to the uterus.

Ovaries are like testicles. Ovaries produce hormones and eggs while the testicles produce hormones and sperm. The necessary hormones that make us female and fertile are estrogen and progesterone from the ovaries. The ovaries are triggered to release those hormones from two substances released by the brain called follicle stimulating hormone (FSH) and luteinizing hormone (LH). More on that later.

The Pill-Job Number One

The primary function of the pill is to stop ovulation or egg release. Low doses of hormones in the pill signal the hypothalamus and pituitary in the brain to stop releasing FSH and LH. Why is that important? These two hormones travel through the bloodstream to the ovary and trigger the ovary to make a small egg sac called a follicle. This egg sac (some people call them ovarian cysts) also makes estrogen, and eventually progesterone. Estrogen and progesterone help the lining of the uterus grow ripe for egg implantation if it gets fertilized by a sperm. So, by stopping the production of FSH and LH, the ovary does not produce an egg sac or release an egg. That’s the primary and most important function of the pill—to trick the brain into ‘thinking’ it is already pregnant because of the circulating levels of hormones from the pill. It only takes a tiny bit of these hormones to stop the brain from starting the egg-releasing process by the ovary. The overall effect is lower circulating hormones and no egg.  

The Pill-Job Number Two

Because the levels of estrogen and progesterone are low, the lining of the uterus does not grow and become soft or receptive to egg implantation. In fact, the lining is very thin and sometimes this is the reason that women have very light or absent periods. The uterine lining is unfavorable for egg implantation—in case one gets released by accident.

The Pill-Job Number Three

Cervical mucus is made by glands in the cervix—which is the opening to the uterus and the part of the body that is accessible through the vagina for the collection of cells known as the ‘pap smear’. Cervical mucous is important for sperm survival and transport. The pill acts by causing the mucus to thicken, trapping the sperm and preventing egg fertilization because they die within minutes.

The Pill-Job Number Four

Although less well understood, the fallopian tubes must transport the egg to the uterus through a process of peristalsis (rhythmic squeezing). Think of a caterpillar creeping across your path. This rhythmic motion of the fallopian tube picks up the egg from the ovary under normal circumstances. However, the hormones in the pill stop this movement of the tube. So even if an egg is accidentally released from the ovary, it can’t make it to the uterus and the sperm cannot reach the egg (to fertilize it) because it depends on normal fallopian tube movement.

The Outlook for the Sperm is Bleak

It takes four organs to make an egg. To recap, they are the hypothalamus, pituitary, ovary, and uterus. The pill shuts them all down in a stealth-like manner. The pill leaves nothing to chance. That’s why it works so well. A sperm has almost no chance to fertilize an egg.

What is your experience of the pill? Does it work well for you? Help other women to make better birth control decisions by sharing your experience.