Birth Control Pills: What Roles Do Estrogen and Progestin Play Within Them?

During my time shadowing CNP Kelli Miller at Northwest OBGYN, I have learned a lot about the female body and ways that medicine can help manage reproductive health. One major topic that is often brought up by patients during appointments is birth control and the various options available. Each and every person reacts differently to all forms of birth control, so what works for some may not work for others!  Birth control comes in many forms, but today I will be talking about the pills and the different roles estrogen and progestin play within them.

*Birth control pills can be either combined (containing synthetic hormones: estrogen and progestin), or made up of progestin only.

What Is Estrogen and Progestin? 

Estrogen and progesterone are both female sex hormones and play an important role in reproductive health. Estrogen is related to secondary sex characteristics like menstruation, pregnancy, and menopause, as well as the development of characteristics like breasts and hips. Estrogen levels peak in the days before ovulation, resulting in a woman’s most fertile period. Some may ask, “Why take a pill containing estrogen for birth control if it is linked to a woman’s most fertile period?” The answer is quite fascinating: the synthetic hormones in the pill trick the body by mimicking its hormonal state as if it were to be pregnant. It suppresses the body's follicle stimulating hormone (FST), which in turn stops ovulation.  Estrogen is found only in combination oral contraceptives (pills that contain both estrogen and progestin).

Progestin, the synthetic form of progesterone, averts pregnancy by preventing ovulation and thickening the cervical mucus. This makes it more difficult for sperm to reach an egg. Some birth control pills contain progestin only. People may take progestin only pills due to risks and side effects they experience that are associated with estrogen. Progestin only pills are often referred to as “mini pills”. 

Why is There No “Estrogen Only” Birth Control Pill?

There is currently no approved estrogen-only birth control pill due to the risks associated with taking it. If too much estrogen is taken by itself, It can cause the lining inside of the uterus to become too thick, which increases the risk for endometrial (uterine) cancer. Also, estrogen by itself cannot completely prevent pregnancy. It works mainly to prevent FSH (follicle stimulating hormone), and LH (luteinizing hormone) from being produced by the pituitary gland by releasing artificial estrogen into the body. Typically, the brain would send a signal to the ovaries causing them to produce their own FSH (which then causes the ovaries to produce estrogen), but due to the negative feedback loop caused by the artificial estrogen, the production of FSH is suppressed, thus hindering ovulation as well. However, it does not thicken cervical mucus like progestin does. This is why the two hormones are paired, as the combination of estrogen with progestin makes for a safe and effective contraceptive. 

Hopefully you learned something new or are now better informed about oral contraceptives by reading this blog today!