Can you ovulate on birth control?

can you ovulate on birth control, breakthrough ovulation, breakthrough ovulation on birth control, signs of ovulation on birth control, breakthrough ovulation symptoms

Ever wondered, ‘can you ovulate on birth control?’ Would you believe that anywhere from 10 to 85% of cycles could be ovulatory, depending on the type of birth control used? This does not mean that you are likely to get pregnant in all of those instances. But ovulating on birth control, also known as breakthrough ovulation, is more common and has greater implications than you might think. So how can you know if or when breakthrough ovulation happens to you while on birth control? Are there signs of ovulation while on birth control? I’ll cover the answer to that question and others here. 

What is breakthrough ovulation?

We all have that friend who got pregnant despite being on one, or maybe even two or three different forms of birth control. How is that possible? The truth is, that while the primary aim of the birth control pill is to stop a woman from ovulating (i.e., releasing an egg for possible fertilization), ovulation is still sometimes possible. This phenomenon is called “breakthrough ovulation.” When it happens, it is possible for you to get pregnant that cycle if you have sex around the time of ovulation. Yes, this is despite taking the Pill! 

How the Pill works

Conception can occur if you have sex around the time of breakthrough ovulation because of how the Pill itself works. The Pill has three basic ways or mechanisms of action for preventing pregnancy. The first line of ‘defense’ against pregnancy is to block the hypothalamic-pituitary-ovarian (HPO) feedback loop, which stops ovulation. The second mechanism of action is to thicken your cervical mucus. This prevents sperm from reaching the cervix. The third and final mechanism is to thin your endometrium, or uterine lining, to make implantation impossible.

If breakthrough ovulation happens, that means the first mechanism did not work. This may be due to ‘normal’ usage of the Pill (more on perfect vs normal use in a bit), or the expected effects of the estrogen-free Minipill. If you have sex during your fertile window and the secondary mechanism also fails to thicken your cervical mucus enough, your partner’s sperm can reach your egg. Fertilization is possible. 

That’s when the final mechanism, thinning of the endometrial lining, comes into play. This tertiary mechanism does not prevent conception. Its purpose is to block an already conceived embryo from implanting in your uterus.

What causes breakthrough ovulation?

Breakthrough ovulation occurs for a number of different reasons. Most are due to more ‘normal’ or typical use of the Pill rather than perfect use (think: you take your pill an hour later than normal, or accidentally skip a dose altogether). Up to 9 out of 100 Pill users will conceive every year with ‘normal’ rather than perfect usage of the Pill. 

Speaking of skipping a dose (or two), you may be especially likely to conceive if you miss at the beginning or end of your monthly course. This is not the only way that breakthrough ovulation can occur, however. Gastrointestinal issues that cause vomiting or diarrhea can also decrease the efficacy of the drug. So can obesity or use of other medications that interact with the Pill. 

How often might breakthrough ovulation on hormonal birth control occur?

Even for those women who take the Pill perfectly, ovulation can still happen in up to 10% of cycles, which means fertilization may still be possible. It’s true that in many cases, a woman who ovulates while on birth control will still not get pregnant. But breakthrough ovulation is a significant factor to consider when you decide to use any kind of birth control. 

Oral contraceptives’ secondary mechanisms or back-up actions (such as the thinning of the endometrial lining) occur after fertilization. This may make implantation less likely to occur, which would lead to the loss of a newly conceived embryo, rather than the mere prevention of its creation [2]. A woman on birth control might not even realize she has conceived and is experiencing a very early miscarriage. 

The Minipill and breakthrough ovulation

Chances of ovulating while on birth control can be even higher if you are taking the progestin-only Pill, also known as the Minipill. (We’ve previously discussed efforts to make the Minipill, or Opill, available over-the-counter without physician oversight, which the FDA officially approved for OTC use on July 13, 2023). While the typical birth control pill includes the combination of both estrogen and progestin, the Minipill only includes progestin. 

The Minipill thickens the cervical mucus and thins the endometrial lining, but does not always stop ovulation. In fact, up to half of women taking the Minipill will still ovulate—and that’s with perfect usage! Taking this medication perfectly also requires that you take your birth control at the same time every single day, as taking it even a few hours late can result in it being ineffective at preventing pregnancy. 

The main reason women choose the Minipill over the combination pill is because it doesn’t come with the side effects of synthetic estrogen in the combination pill. This is especially important for women who breastfeed, for whom estrogen is discouraged for a number of reasons. However, the progestin-only pill has its own issues. These include ovarian cysts, irregular bleeding, plus increased risks of depression, breast cancer, and cervical cancer [3][4]. 

What about intrauterine devices (IUDs)? 

There are currently two main types of IUDs used in the United States. One is the hormonal IUD (such as Mirena). The other is the non-hormonal copper IUD (Paragard). Hormonal IUDs like Mirena primarily thicken the cervical mucus to decrease sperm mobility [5]. Ovulation prevention is not the primary goal. In fact, according to Mirena’s product label, once patients reach their fourth year of use, the majority of cycles are ovulatory. 

The copper IUD, or Paragard, also does not stop ovulation. Like the Mirena, Paragard also works to prevent fertilization by creating a ‘toxic’ environment for sperm. It secondarily works by preventing the implantation of a newly-conceived embryo.

Although there are differences between hormonal and copper IUDs, one study found that the average chance of ovulation within a cycle with both IUDs is the same—about 85% [6]! The ovulation here isn’t necessarily “breakthrough” because the primary mechanism of action in either IUD is not to stop ovulation. Regardless, the bottom line for all types of birth control is the same: when ovulation occurs, there is a chance that fertilization and conception will not be prevented if one has sex around the time of ovulation. 

Why haven’t you heard any of this before? 

Keep in mind that prior to the 1960s, the medical definition of “pregnancy” was synonymous with fertilization, i.e., when sperm meets egg. Beginning with the advent of the birth control pill, major medical organizations sought to change the definition of “pregnancy” to begin at implantation, rather than at fertilization. By this newer definition, which was officially endorsed by ACOG in 1972, birth control does not technically end a pregnancy when it fails to prevent ovulation, and instead functions to prevent pregnancy by its endometrial-thinning mechanism if conception still occurs.

However, the science of embryology is clear that at the moment of conception, a unique, distinct, human life is created, regardless of whether or not it is able to implant within the womb. Therefore, by this tertiary mechanism, birth control undoubtedly facilitates the death of a newly created embryonic life. Despite the change in the definition of pregnancy, women still deserve this important information about how their birth control works, in order to make a truly informed decision about their family planning choices.

Women who are concerned about the implications of breakthrough ovulation and possible unintended pregnancy loss have other family planning options

Unfortunately, it is extremely difficult to tell whether you’ve experienced breakthrough ovulation. Even though you can monitor fertile symptoms such as temperature and cervical mucus while on the Pill (or while using an IUD), there is no way to know if those signs of fertility are real or just effects of the birth control. Plus, the bleeding you experience on hormonal birth control is not a true period. Because of this, it’s not really possible to completely prevent the conception and loss of a fertilized embryo if you are sexually active around the time of breakthrough ovulation. This is because there aren’t really any true symptoms of breakthrough ovulation. 

How fertility awareness can help

This doesn’t mean it’s impossible to know what’s going on with your body and when you ovulate. Countless women have made the switch from birth control to Fertility Awareness Methods, or FAM. When you stop birth control and instead learn your true signs of fertility, you are able to understand when ovulation occurs. You can use that knowledge to prevent or achieve pregnancy accordingly. 

There are also numerous health benefits of charting your cycle. They go far beyond simply avoiding the negative risks and side effects of birth control. When you utilize fertility awareness, you gain concrete information about what is going on in your body, including the confirmation of ovulation. 

References:

[1] Fraser, I S, and R P Jansen. “Why do inadvertent pregnancies occur in oral contraceptive users? Effectiveness of oral contraceptive regimens and interfering factors.” Contraception vol. 27,6 (1983): 531-51. doi:10.1016/0010-7824(83)90019-7

[2] Larimore, W L, and J B Stanford. “Postfertilization effects of oral contraceptives and their relationship to informed consent.” Archives of family medicine vol. 9,2 (2000): 126-33. doi:10.1001/archfami.9.2.126

[3] Mørch, Lina S et al. “Contemporary Hormonal Contraception and the Risk of Breast Cancer.” The New England journal of medicine vol. 377,23 (2017): 2228-2239. doi:10.1056/NEJMoa1700732

[4] Roura, Esther et al. “The Influence of Hormonal Factors on the Risk of Developing Cervical Cancer and Pre-Cancer: Results from the EPIC Cohort.” PloS one vol. 11,1 e0147029. 25 Jan. 2016, doi:10.1371/journal.pone.0147029

[5] Dinehart E, Lathi RB, Aghajanova L. Levonorgestrel IUD: is there a long-lasting effect on return to fertility? J Assist Reprod Genet. 2020 Jan;37(1):45-52. doi: 10.1007/s10815-019-01624-5. Epub 2019 Nov 11. PMID: 31709489; PMCID: PMC7000571.

[6] Apter, Dan et al. “Pharmacokinetics of two low-dose levonorgestrel-releasing intrauterine systems and effects on ovulation rate and cervical function: pooled analyses of phase II and III studies.” Fertility and sterility vol. 101,6 (2014): 1656-62.e1-4. doi:10.1016/j.fertnstert.2014.03.004

Additional Reading:

How the IUD, implant, pill, and other birth control methods work

How my awful experience with the copper IUD led me to truly natural birth control 

Birth control may soon be over-the-counter

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