Kahlenborn, C., Peck, R., & Severs, W. B. (2015). Mechanism of action of levonorgestrel emergency contraception. The Linacre Quarterly, 82(1), 18-33. https://doi.org/10.1179/2050854914Y.0000000026
Kahlenborn C, Peck R, Severs WB. Mechanism of action of levonorgestrel emergency contraception. Linacre Q. 2015;82(1):18-33. doi:10.1179/2050854914Y.0000000026
Kahlenborn, Chris, et al. "Mechanism of action of levonorgestrel emergency contraception." The Linacre Quarterly, vol. 82, no. 1, 2015, pp. 18-33.
The Polycarp Research Institute, Enola, PA, USA01mkye871
Penn State Milton S. Hershey Medical Center01h22ap11
Linked to ROR, the Research Organization Registry
RRM Academy Synopsis
Levonorgestrel pill before ovulation may work after fertilization
A 2015 review argues levonorgestrel emergency contraception taken before ovulation may work after fertilization. One Chilean study of 450 women supplies some of the key data. Of 103 women who had sex before ovulation and took the pill, none became clinically pregnant. A model predicted 16 of them would have become pregnant without the pill.
Key Findings
In the Chilean study, 103 of 450 women had sex within the five days before ovulation. None of the 103 became clinically pregnant, while a model predicted sixteen pregnancies.
Among 45 women whose sex fell on the day of ovulation or after, 8 became pregnant. The model predicted 8.7.
Ultrasound showed follicular rupture in 80 percent of women dosed five to one days before ovulation, and in 22 of 24 (92 percent) dosed on day -2.
Across three studies, 1,034 of 3,496 women (29.6%) bled within 7 days of taking the pill. The authors say bleeding appears most common when the pill comes before ovulation, citing one study.
The Chilean study estimated efficacy at 68 percent. A major professional society cites 85 percent, and the authors say even 68 percent is likely too high.
Interpretation
The paper argues one position from published data. The expected pregnancy counts came from a model built on women trying to conceive. They label a hormone or device an abortifacient if it artificially ends a life that began at fertilization, and the conclusion depends on that definition. Their wording is "significant potential" and "unless proven otherwise." The authors say how often fertilization occurs after the pill cannot yet be determined, and they propose testing early pregnancy factor to find out. The findings support larger studies measuring that rate directly.
RRM Context
The debate turns on timing within the ovulatory cycle. The authors note that many earlier studies dated ovulation from recalled period dates. They cite research showing that recall is inaccurate. Ultrasound plus hormone tests gave firmer timing. Restorative reproductive medicine centers the ovulatory event for a similar reason. Cycle timing can be measured, and fertile window questions depend on measuring it well.
Our editorial summary of this paper, not the article's abstract.
Abstract
There has been much debate regarding levonorgestrel emergency contraception's (LNG-EC's) method of action since 1999 when the Food and Drug Administration first approved its use. Proponents of LNG-EC have argued that they have moral certitude that LNG-EC works via a non-abortifacient mechanism of action, and claim that all the major scientific and medical data consistently support this hypothesis. However, newer medical data serve to undermine the consistency of the non-abortifacient hypothesis and instead support the hypothesis that preovulatory administration of LNG-EC has significant potential to work via abortion. The implications of the newer data have important ramifications for medical personnel, patients, and both Catholic and non-Catholic emergency room protocols. In the future, technology such as the use of early pregnancy factor may have the potential to quantify how frequently preovulatory LNG-EC works via abortion.
Lay Summary
How Plan B (levonorgestrel emergency contraception) works has been vigorously debated ever since the Food and Drug Administration approved it in 1999. Many doctors and researchers claim that it has either no-or at most-an extremely small chance of working via abortion. However, the latest scientific and medical evidence now demonstrates that levonorgestrel emergency contraception theoretically works via abortion quite often. The implications of the newer data have important ramifications for medical personnel, patients, and both Catholic and non-Catholic emergency room rape protocols.
