How does hormonal birth control work?

It’s common to take the pill like any other medication or multivitamin and not fully understand how it works. So, let’s start there.

In a natural state, your reproductive cycle is governed by a symphony of hormones whose fluctuations operate on a feedback system. In the early half of your cycle, estrogen steadily rises to prepare your uterus for a potential pregnancy. When it reaches a peak, this triggers a spike in two hormones:

• LH (luteinizing hormone)
• FSH (follicle-stimulating hormone)

Both of these contribute to the maturation, and later, release of your egg (otherwise known as ovulation), which occurs around a day later.

Oral contraceptives are designed to prevent pregnancy by disbursing synthetic versions of estrogens and/or progestins long after they would normally dissipate. The continual disbursal of these hormones works to arrest your reproductive cycle and prevent ovulation. They can also prevent pregnancy by:

• Giving your cervical mucus a thicker consistency – This physically makes it more difficult for a sperm to swim towards your egg.

• Preventing your uterine lining from getting thicker – This makes it more difficult for an egg to latch onto your uterine wall and grow.

While these methods are highly effective, it’s essential to consider that no contraceptive method is foolproof. To explore this further, read about Can You Get Pregnant While on Birth Control, which discusses the rare but possible scenarios where birth control might not prevent pregnancy.

Types of Birth Control Pills

Within the category of oral contraceptives, preventative birth control pills fall into two types:

• Combination pill – The most widely-used kind of oral contraceptive. Current statistics show that only about 9 out of 100 people taking the combination birth control pill become pregnant.

• Progestin-only – Also known as the “minipill,” these strictly contain progestin and may be slightly less effective than the combination birth control pills; pregnancy can occur in roughly 13 out of every 100 women who use it. That said, the minipill is recommended for certain groups, including:
  • New parents who are breastfeeding
  • People with certain health conditions or histories (e.g. blood clots)

Apart from preventative birth control pills, the morning-after pill can also be used as an emergency contraceptive to halt unwanted pregnancy. However, these emergency contraception pills should only be taken in urgent situations where you are at high risk of unwanted pregnancy. Though they also work by lowering your chances of ovulation, they can’t stop a pregnancy if an egg has already been fertilized and embedded in your uterus.

Factors that Could Cause Birth Control Failure

As a general rule, all medicines are only as effective as your ability to take them as directed. This is known as medication compliance.

With perfect compliance, oral contraceptives will prevent ovulation. If you’ve ovulated while taking your birth control, it’s usually because:

• You don’t always take your pill at regular intervals – For best results, the pill should be taken every 24 hours—with very little margin of error. In other words, if you take your pill each day at 10am, even occasionally taking your pill at 11am could result in ovulation (and pregnancy, if you have unprotected sex).

• Other medications are interfering with your birth control – Some birth control pills are vulnerable to interference by other medications or supplements. Some of the most common medications that can suppress birth control efficacy include:
  • Some antibiotics, such as rifampin
  • Anti-epileptic drugs (AEDs), like carbamazepine, phenytoin, and topiramate
  • Drugs for treating HIV (ARVs, or antiretrovirals)
  • Some herbal supplements, such as St. John’s wort

All in all, ovulating on birth control is rare. But there are occasions—simply by means of human error or other unique circumstances—where it can happen. With that, it’s important to know what to do if you think it’s happened to you.

What to Do if You Think You’re Pregnant While on Birth Control

If a mishap happens, it’s normal to be concerned you’ve ovulated. Fortunately, it’s usually relatively easy to get back on your regular schedule and boost your birth control’s efficacy back to 99%. Just be sure to watch for early signs of pregnancy in the weeks following your hiccup.

A missed period is usually the first sign of early pregnancy, so if your birth control normally lightens your menstrual cycle, be sure to keep an eye out for whether it arrives. Other early pregnancy symptoms include:

• Frequent urination
• Persistent tiredness (fatigue)
• Nausea, especially in the morning
• Enlarged, tender, or swollen breasts
• Spotting, a sign of implantation bleeding

Being concerned that you’ve ovulated is one matter, but suspecting a pregnancy is another story.

If you think you might be pregnant, it’s important to exercise caution and take a few necessary steps to protect your health:

1. Keep taking your birth control as usual – Keep taking your birth control pill (including placebo pills) as you normally would. Abruptly discontinuing oral contraceptive use can result in unwanted side effects, like mood swings.
2. Take a pregnancy test – As soon as you can, order or pick up an OTC, at-home pregnancy test. Like the pill itself, OTC pregnancy tests are highly accurate. Ideally, try to take your test when you first wake up; this is when your urine is least diluted, enabling the test to pick up on the presence of hCG (human chorionic gonadotropin), which floods your system during pregnancy.
3. Reach out to a healthcare provider – If you discover you’re pregnant, your next step is to speak to your healthcare provider as soon as possible. They can counsel you on how to terminate your birth control, as well as what to do next for your pregnancy and well-being. They will also tell you some things to avoid in early pregnancy, to ensure optimal health for you and your baby.

Some health conditions can mimic the symptoms of early pregnancy, including certain STIs, cancers, and uterine fibroids or cysts. For this reason, it’s important to have your pregnancy confirmed (or ruled out) by a healthcare professional to ensure you’re treated properly.

Finding a Family Planning Method That Works for You

Many people use the terms “birth control” and “the pill” interchangeably—but it’s important to recognize that there are many different kinds of birth control. Each birth control method can impact your body and reproductive cycle differently and has its own level of effectiveness.

If you’re struggling to take your birth control pill consistently, it may help to consider other methods of family planning to find one that suits your lifestyle. Some options include:

• IUDs – IUDs are about as effective as birth control pills. They’re inserted into your vagina and sit close to your cervix, and must be changed every 3 to 10 years. IUDs fall into two camps:
  • Hormonal IUDs, which use a low dose of progestin to thin the walls of your uterus and thicken cervical mucus.
  • Copper IUDs, which use their material—copper—instead of hormones to repel sperm.

• Vaginal rings – Vaginal rings are also more than 99% effective at preventing pregnancy. Like combination birth control pills, they release estrogen and progestin to prevent unwanted pregnancy. Like IUDs, they’re inserted into your vagina and rest near the cervix and must be removed every 3 weeks.

• Patches – Like the pill, birth control patches are a hormonal contraceptive that releases both estrogen and progestin to prevent pregnancy, but they’re applied to your skin. If used properly, they’re 99% effective—but “used properly” is key here. Without perfect use, efficacy drops to about 91%. Patches must also be switched out every 3 weeks.

• Barrier methods – Barrier methods of birth control like dental dams and condoms can also lower your chances of getting pregnant. While they’re less effective at preventing pregnancy, they can provide helpful reinforcements if you’re already using hormonal birth control.

All in all, ovulating on the pill is unlikely. Even still, it’s not unusual for life’s inconsistencies to challenge the consistency oral contraceptives depend on. Whether you’re ready to grow your family or not, finding an effective family planning approach that works with and for you is key for total reproductive and sexual health.

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