From the Guidelines
An estradiol level below 5 pg/mL while taking a combined birth control pill is expected and normal. Combined birth control pills contain synthetic estrogen (typically ethinyl estradiol) and progestin, which work together to suppress the body's natural hormone production through negative feedback on the hypothalamic-pituitary-ovarian axis, as discussed in the 2014 study on contraception for adolescents 1. This suppression prevents ovulation and reduces the body's natural production of estradiol. The synthetic hormones in the pill effectively take over the role of your natural hormones, maintaining feminine characteristics and preventing pregnancy while keeping your natural estradiol production very low.
This low level doesn't indicate a problem as long as you're taking the pill correctly and not experiencing concerning symptoms. The synthetic estrogen in the pill is providing the estrogenic effects your body needs, despite the low measured natural estradiol. If you stopped taking the pill, your natural estradiol production would typically return to normal levels within a few months. It's also worth noting that the use of combined hormonal contraceptives, including pills, patches, and rings, has been extensively studied, and guidelines such as those provided by the U.S. Medical Eligibility Criteria for Contraceptive Use, 2010, offer classifications for their use based on various conditions 1.
Key points to consider include:
- The synthetic estrogen in combined birth control pills suppresses natural estradiol production.
- This suppression is a normal and expected effect of taking the pill.
- The pill's synthetic hormones maintain feminine characteristics and prevent pregnancy.
- Low natural estradiol levels while on the pill do not indicate a problem if the pill is taken correctly and no concerning symptoms are present.
- Natural estradiol production typically returns to normal after stopping the pill. Given the information from the studies 1, it's clear that the primary concern with combined birth control pills is not the level of natural estradiol but rather ensuring the pill is used correctly and monitoring for any adverse effects or interactions with other medications.
From the Research
Estradiol Levels and Combined Birth Control Pills
- Estradiol levels can be affected by the type of estrogen used in combined birth control pills, with 17β-estradiol (E2) being used in some newer formulations instead of ethinyl estradiol (EE) 2.
- The use of E2 in combined oral contraceptives has been shown to have similar efficacy and cycle control as EE-based COCs, but with potentially fewer health risks 3, 2.
- Studies have reported that systemic estradiol levels can vary depending on the dose and type of estrogen used, as well as the detection method used to measure estradiol levels 4, 2.
- A study found that mean basal estradiol levels in postmenopausal women were 3.1 to 4.9 pg/mL, which is similar to the level of < 5 pg/mL mentioned in the question 4.
Factors Affecting Estradiol Levels
- The dose and type of estrogen used in combined birth control pills can affect estradiol levels, with lower doses of estrogen potentially resulting in lower estradiol levels 4, 5.
- The formulation and positioning of vaginal estrogens can also influence estradiol absorption and levels 4.
- The use of different detection methods, such as liquid or gas chromatography/mass spectroscopy (LC or GC/MS/MS) versus radioimmunoassay, can also affect the measurement of estradiol levels 4.
Comparison of Estradiol and Ethinyl Estradiol
- Ethinyl estradiol (EE2) is a synthetic estrogen used in many birth control formulations, while estradiol (E2) is a naturally occurring estrogen 6.
- Studies have shown that EE2 and E2 can have different effects on cell signaling and proliferation, with EE2 potentially having more pronounced effects on certain signaling pathways 6.
- The use of EE2 in birth control formulations has raised concerns about its potential impact on the environment and human health, particularly in terms of its persistence in treated waste waters and its potential to act as an endocrine-disrupting contaminant 6.