Can You Get Pregnant On The Pill?

Q: Can you get pregnant on the pill?

A: Yes. Being on a pill does not mean that you will not get pregnant. In fact, scientific literature has shown that even with perfect usage, 0.3% of women get pregnant within a 12-month period.

How Do Pills Work?

Birth control pills contain hormones. The most common type of pill contains two hormones, estrogen and progestin. This type is called a combination pill. The other type of pill contains progestin only and is also called the mini-pill. This is usually used for women who are breastfeeding or who become nauseated with estrogen.

The hormones work in the following ways:

They stop the production of follicle stimulating hormone (FSH) and luteinizing hormone (LH). This prevents the mature egg from being released by the ovary.
They change the cervical mucus so it is thicker and hence more difficult for sperms to go through.
They change the uterine lining so a fertilized egg cannot attach (implant) to the uterus.

How Effective Are The Pills?

When the pills are used according to instructions (perfect use), the pregnancy rate of women who are using pills is only 0.3% over a 12-month period. With typical use (i.e., occasional missed dose or taking pills at different times each day), the pregnancy rate of women who are on the pill is about 8% over a 12-month period.¹

Is There A Difference In Effectiveness Between Combination Pills And Progestin-Only Pills?

There is a perception that combination pills are more effective at protecting against pregnancy than progestin-only pills. However, there has not been published scientific research indicating this to be the case.² For now, therefore, the two types of pills should be viewed as equally effective.

Conclusion

It is possible to get pregnant while on the pill. With strict adherence to the correct protocol (taking the pill at around the same time everyday), though, the possibility of getting pregnant is greatly reduced.

References

[1] J. Trussell, K. A. Guthrie. Choosing a contraceptive: Efficacy, safety, and personal considerations. In RA Hatcher et al., eds., Contraceptive Technology, 20th ed., pp. 45–74. Atlanta: Ardent Media (2011).

[2] D. A. Grimes, L. M. Lopez, P. A. O'Brien, Progestin-only pills for contraception. Cochrane Database Syst Rev., 2013 Nov 13;11 [CD007541].

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