Contraceptive efficacy of emergency contraception with levonorgestrel given before or after ovulation

Gabriela Noé, Horacio B. Croxatto, Ana María Salvatierra, Verónica Reyes, Claudio Villarroel, Carla Muñoz, Gabriela Morales, Anita Retamales

Resultado de la investigación: Contribución a una revistaArtículo

41 Citas (Scopus)

Resumen

Background: The contraceptive efficacy of emergency contraceptive pills containing levonorgestrel (LNG-EC) has been estimated in most previous studies by judging the day of ovulation from presumptive menstrual cycle data, thus providing poorly reliable estimates. Methods: In the present study, the efficacy of LNG-EC was determined in 393 cycles by dating ovulation on the basis of reliable hormonal and ovarian parameters validated by a database constructed in a separate study. In addition, the efficacy was determined separately for cycles in which LNG-EC was given before or after ovulation. Results: For the 148 women who had sexual intercourse during the fertile days, the overall accumulated probability of pregnancy was 24.7, while altogether 8 pregnancies were observed. Thus, the overall contraceptive efficacy of LNG-EC was 68%. Among the 103 women who took LNG-EC before ovulation (days -5 to -1), 16 pregnancies were expected and no pregnancy occurred (p<.0001). Among the 45 women who took LNG-EC on the day of ovulation (day 0) or thereafter, 8 pregnancies occurred and 8.7 were expected (p=1.00). These findings are incompatible with the inhibition of implantation by LNG-EC in women. The same cases were also analyzed using the presumptive menstrual cycle data, and important discrepancies were detected between the two methods. Conclusion: The efficacy of LNG-EC has been overestimated in studies using presumptive menstrual cycle data. Our results confirm previous similar studies and demonstrate that LNG-EC does not prevent embryo implantation and therefore cannot be labeled as abortifacient.

Idioma originalInglés
Páginas (desde-hasta)486-492
Número de páginas7
PublicaciónContraception
Volumen84
N.º5
DOI
EstadoPublicada - 1 nov 2011

Áreas temáticas de ASJC Scopus

  • Medicina reproductiva
  • Ginecología y obstetricia

Huella Profundice en los temas de investigación de 'Contraceptive efficacy of emergency contraception with levonorgestrel given before or after ovulation'. En conjunto forman una huella única.

  • Citar esto

    Noé, G., Croxatto, H. B., Salvatierra, A. M., Reyes, V., Villarroel, C., Muñoz, C., Morales, G., & Retamales, A. (2011). Contraceptive efficacy of emergency contraception with levonorgestrel given before or after ovulation. Contraception, 84(5), 486-492. https://doi.org/10.1016/j.contraception.2011.03.006