Sex Ed: How Birth Control Works

Many times, when a woman or person with a uterus visits us at Arizona Center for Reproductive Endocrinology & Infertility after months of not getting pregnant, their fear is that the birth control they’ve used in the past has affected their fertility now. Sadly, there is a lot of lore and misconceptions out there that warn against using birth control precisely for this reason. The good news, however, is that is rarely ever the case. 

There are several different methods of birth control for uterus owners—IUD, shots, vaginal ring, patch, pills, condoms, even the rhythm method—but they all have the same end goal: to prevent conception and pregnancy (for the time being). These are considered ‘reversible’ birth control methods as they don’t involve surgical removal of reproductive organs. So, in theory, once you stop using one of these methods, your chances of getting pregnant go back to normal. 

Different forms of birth control work in different ways, so here’s a quick look at how birth control works and its true affect on your fertility.

Understanding Conception

To understand how birth control prevents conception, you first need to understand what it takes for conception to occur. There are three main events that have to happen:

  1. Ovulation: A healthy, developed egg needs to be released into the fallopian tubes so it can be fertilized; fertilization needs to occur 12-24 hours after its release.
  2. Fertilization: Once the egg is released, it needs to meet with a sperm. Sperm needs to make its way past the cervix and through the uterus to the fallopian tube and ovulated egg. If the sperm and egg meet, the sperm needs to get through the zona pellucida, or egg’s outer membrane, for fertilization to occur.
  3. Implantation: If fertilization does happen, the new embryo needs to successfully implant in the uterine lining, which supports the embryo’s development.


A snag in any of these steps can make conception difficult, or even impossible. Birth control works by creating these obstacles in the conception process. 

Preventing Conception

Now, let’s talk about those obstacles. Again, most birth control methods work to create one or more obstacles in the three major events of the conception process.

Preventing Ovulation

The majority of reversible hormonal birth control methods work by preventing ovulation. When the birth control hormones are released, they actually inhibit the production of FSH and LH, which then prevents follicular stimulation and development. (You can read more about the phases of the menstrual cycle here.) No egg is matured or released, so ovulation doesn’t occur. Combination pills, some IUDs, the ring, patch, and birth control shot usually prevent ovulation.

Thickening the Cervical Mucus

When you’re in your fertile window, your body produces a special type of cervical mucus that actually helps sperm get past the cervix and into the uterus and fallopian tube to find an egg. This thinner mucus is the result of high estradiol and low progesterone levels. Hormonal birth control reverses these levels (by raising progesterone or lowering estradiol) which thickens the cervical mucus and makes conception much more difficult and highly unlikely. Combination pills, minipills, IUDs, the ring, patch, and birth control shot are methods that cause this thickening of cervical mucus to happen.

Preventing Thickening of the Uterine Lining 

For a fertilized egg to develop and grow, implantation needs occur. In typical menstrual cycles (where birth control is not being used) progesterone and estradiol hormones thicken the uterine lining and make it more welcoming of a fertilized egg. Hormonal birth control methods work by limiting these hormone levels, which makes the uterine lining too thin for an embryo to successfully implant and thus, develop. Combination pills, minipills, IUDs, the ring, patch, and birth control shot are methods that prevent the thickening of the uterine lining.

Lasting Effects of Birth Control on Fertility

Numerous studies have shown that the long-term use of birth control does not negatively affect future fertility. You are as likely to conceive if you used birth control in the past as a woman who has never used hormonal contraceptives.

Once you discontinue the use of birth control, your cycle will typically return to normal within one to three months. (Or six months to one year if your birth control method was the shot.) It’s important to note that if your menstrual cycle was irregular before using birth control, it will likely still be irregular once you go off birth control; some uterus owners mistake an irregular cycle as a side effect of birth control. 

So, what happens if you’ve stopped birth control, your cycles have returned, but you’re not getting pregnant? Chances are, there’s an underlying issue—completely independent from your birth control use. If you’ve been off birth control and are currently struggling to get pregnant, it may be time to visit a specialist.
At AZCREI, we can answer your questions and help identify the reason behind your struggles. Make an appointment now by calling 520-326-0001 or visiting us online.

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