In reply: Emergency contraception

In Reply: I thank Drs. Kahlenborn and Severs for their comments. Controversy surrounds emergency contraception; thus, it is important to use peer-reviewed, current medical literature to reference mechanism of action. The product label is an unreliable resource, as it was written before current studies that clarified how emergency contraception works. The Noé study concluded that “levonorgestrel emergency contraception does not prevent embryo implantation and therefore cannot be labeled as abortifacient.”¹ They monitored ovulation via ultrasonography and hormonal assays, so they knew in which women ovulation had occurred when emergency contraception was taken. Of those who took it before ovulation, 16 pregnancies were expected and none occurred. When it was taken the day of ovulation or after, 8.7 pregnancies were expected and 8 pregnancies occurred. Because emergency contraception was ineffective after ovulation, a postfertilization effect is unlikely.

Although Drs. Kahlenborn and Severs cited 2004 Croxatto data, they did not cite the 2007 study by Novikova et al,² which concluded that levonorgestrel emergency contraception “has little or no effect on post-ovulation events, but is highly effective when taken before ovulation.”² In this study, when levonorgestrel emergency contraception was taken pre-ovulation, 0 out of 4 expected pregnancies occurred. When it was taken post-ovulation, 3 out of the 3 to 4 expected pregnancies occurred.²

The Frequently Asked Question 114 that Drs. Kahlenborn and Severs cited from the American Congress of Obstetricians and Gynecologists was updated in August 2011 and no longer cites prevention of implantation as a potential mechanism of action. Instead, it reads, “Progestin-only pills are thought to prevent pregnancy mainly by preventing ovulation.” ³ Another ACOG committee opinion, from November 2012, states, “A common misconception is that emergency contraception causes an abortion. Inhibition or delay of ovulation is the principal mechanism of action. Review of evidence suggests that emergency contraception cannot prevent implantation of a fertilized egg. Emergency contraception is not effective after implantation; therefore, it is not an abortifacient.”⁴

The International Federation of Gynecology & Obstetrics and the International Consortium for Emergency Contraception have issued a joint statement on emergency contraception, including mechanism of action.⁵ This is a good resource for providers and patients. We owe our patients an honest discussion about the current science, from current references and guidelines, so they can make educated decisions based on their own comfort level with emergency contraception.

In Reply: I thank Drs. Kahlenborn and Severs for their comments. Controversy surrounds emergency contraception; thus, it is important to use peer-reviewed, current medical literature to reference mechanism of action. The product label is an unreliable resource, as it was written before current studies that clarified how emergency contraception works. The Noé study concluded that “levonorgestrel emergency contraception does not prevent embryo implantation and therefore cannot be labeled as abortifacient.”¹ They monitored ovulation via ultrasonography and hormonal assays, so they knew in which women ovulation had occurred when emergency contraception was taken. Of those who took it before ovulation, 16 pregnancies were expected and none occurred. When it was taken the day of ovulation or after, 8.7 pregnancies were expected and 8 pregnancies occurred. Because emergency contraception was ineffective after ovulation, a postfertilization effect is unlikely.

Although Drs. Kahlenborn and Severs cited 2004 Croxatto data, they did not cite the 2007 study by Novikova et al,² which concluded that levonorgestrel emergency contraception “has little or no effect on post-ovulation events, but is highly effective when taken before ovulation.”² In this study, when levonorgestrel emergency contraception was taken pre-ovulation, 0 out of 4 expected pregnancies occurred. When it was taken post-ovulation, 3 out of the 3 to 4 expected pregnancies occurred.²

The Frequently Asked Question 114 that Drs. Kahlenborn and Severs cited from the American Congress of Obstetricians and Gynecologists was updated in August 2011 and no longer cites prevention of implantation as a potential mechanism of action. Instead, it reads, “Progestin-only pills are thought to prevent pregnancy mainly by preventing ovulation.” ³ Another ACOG committee opinion, from November 2012, states, “A common misconception is that emergency contraception causes an abortion. Inhibition or delay of ovulation is the principal mechanism of action. Review of evidence suggests that emergency contraception cannot prevent implantation of a fertilized egg. Emergency contraception is not effective after implantation; therefore, it is not an abortifacient.”⁴

The International Federation of Gynecology & Obstetrics and the International Consortium for Emergency Contraception have issued a joint statement on emergency contraception, including mechanism of action.⁵ This is a good resource for providers and patients. We owe our patients an honest discussion about the current science, from current references and guidelines, so they can make educated decisions based on their own comfort level with emergency contraception.

In Reply: I thank Drs. Kahlenborn and Severs for their comments. Controversy surrounds emergency contraception; thus, it is important to use peer-reviewed, current medical literature to reference mechanism of action. The product label is an unreliable resource, as it was written before current studies that clarified how emergency contraception works. The Noé study concluded that “levonorgestrel emergency contraception does not prevent embryo implantation and therefore cannot be labeled as abortifacient.”¹ They monitored ovulation via ultrasonography and hormonal assays, so they knew in which women ovulation had occurred when emergency contraception was taken. Of those who took it before ovulation, 16 pregnancies were expected and none occurred. When it was taken the day of ovulation or after, 8.7 pregnancies were expected and 8 pregnancies occurred. Because emergency contraception was ineffective after ovulation, a postfertilization effect is unlikely.

Although Drs. Kahlenborn and Severs cited 2004 Croxatto data, they did not cite the 2007 study by Novikova et al,² which concluded that levonorgestrel emergency contraception “has little or no effect on post-ovulation events, but is highly effective when taken before ovulation.”² In this study, when levonorgestrel emergency contraception was taken pre-ovulation, 0 out of 4 expected pregnancies occurred. When it was taken post-ovulation, 3 out of the 3 to 4 expected pregnancies occurred.²

The Frequently Asked Question 114 that Drs. Kahlenborn and Severs cited from the American Congress of Obstetricians and Gynecologists was updated in August 2011 and no longer cites prevention of implantation as a potential mechanism of action. Instead, it reads, “Progestin-only pills are thought to prevent pregnancy mainly by preventing ovulation.” ³ Another ACOG committee opinion, from November 2012, states, “A common misconception is that emergency contraception causes an abortion. Inhibition or delay of ovulation is the principal mechanism of action. Review of evidence suggests that emergency contraception cannot prevent implantation of a fertilized egg. Emergency contraception is not effective after implantation; therefore, it is not an abortifacient.”⁴

The International Federation of Gynecology & Obstetrics and the International Consortium for Emergency Contraception have issued a joint statement on emergency contraception, including mechanism of action.⁵ This is a good resource for providers and patients. We owe our patients an honest discussion about the current science, from current references and guidelines, so they can make educated decisions based on their own comfort level with emergency contraception.