How Messing with Your Birth Control Affects Your Body

"The more pills that you skip, then the less effective the birth control pill will be in preventing a pregnancy," says Dr. Andrew Rynne of Medical Advice for You. "The pill, if taken perfectly, gives a pregnancy rate of 0.1 percent. In other words, if taken perfectly, it is very effective in preventing pregnancy. However, if taken typically, that is, missing an odd pill here and there, it gives a pregnancy rate of 5 percent. That is a huge difference."

Your body is a fortress; the pill is your army, defending the fortress from the foreign sperm-shaped invaders. Missing several pills at a time to move your period up or down the calendar would leave one very impregnable.

To understand the risks of sporadic hormonal birth control, we must first understand how it works. Most birth control pills contain two hormones: estrogen and progestin. (Some pills, colloquially called minipills, only have progestin.) Both progestin and estrogen prevent follicular development in the ovary. While still inside the ovary, eggs are like little berries growing on a stem called the follicle. Every cycle, one or two follicles are chosen to develop into fully baby-producing ova. These ova travel down the fallopian tube, maybe meeting a sperm along the way, and implanting into the uterine lining. But the hormones in birth control prevent any one follicle from producing a viable ovum.

So imagine your reproductive system is a carnival game, maybe the one where you can toss a ping-pong ball into a goldfish bowl and win a new pet. Your dude can throw ping-pong balls all day, but all those goldfish are dead. Progestin also thickens the cervical mucus, which prevents sperm from even getting inside the uterus-fallopian zone, so, like, you've cling-wrapped the goldfish bowls too.

The pill has been fine-tuned since its creation. Originally, each pill contained far more estrogen, which caused more severe side effects, but also meant that skipping an occasional pill was less likely to result in pregnancy. Low-dose estrogen pills require a steady schedule to prevent pregnancy: one pill every 24 hours. If the dosage is off even a little bit, those follicles might start developing. "If you measure hormone levels for people that are on birth control, they're very low. They're very suppressed," says Dr. Jani Jensen of the Mayo Clinic. "After three days off birth control, there's a chance that you will ovulate."

Ironically, skipping your birth control to reschedule your period might result in exactly the opposite. "One of the most common reasons women discontinue birth control pills is breakthrough bleeding," says Dr. Jensen. Breakthrough bleeding is when you have some light bleeding in the middle of your cycle. According to Dr. Jensen, breakthrough bleeding diminishes significantly over the first year of birth control use. "The rates of breakthrough bleeding are much higher in the first pack than the 12th," she says. "If you keep starting and stopping birth control, you're probably never going to see that get better."

So what's Methy to do if she wants to go to the beach without attracting sharks? "The pill may be taken continuously to avoid a period," says Dr. Mamta Mamik, assistant professor of obstetrics, gynecology, and reproductive science at the Icahn School of Medicine at Mount Sinai.

Rather than moving your period up, delay it. "When you stop the pill, you get a 'withdrawal bleed,'" says Dr. Rynne. "If you continue the pill nonstop, you get no withdrawal bleed."

You may feel there's something disconcerting about going months without a period, but it's not a big deal. There is no medical benefit to having a period every month. "I think patients are worried the uterus is going to overgrow and maybe explode like a water balloon," says Dr. Jensen, "but that's not the case."

Birth control prevents the development of a uterine lining that would need to be sloughed off with a period. Dr. Jensen likens the uterus to a lawn: "The grass grows, the lining of the uterus thickens, then you mow the lawn. When you take birth control, you're basically mowing the lawn every day."

For those of you keeping score, the uterus has been compared to a fortress, a carnival game, a water balloon, and a lawn. But thanks to science, one thing your uterus does not have to be is a burden.

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