Mecanismos de acción de la anticoncepción hormonal de emergencia: efectos del levonorgestrel anteriores y posteriores a la fecundación / Mechanisms of action of emergency contraception

El mecanismo de acción del levonorgestrel (LNG) como anticonceptivo de emergencia (AE) es aún controvertido. Para quienes consideran que el embarazo inicia antes de la implantación, todo compuesto capaz de interferir con etapas posteriores a la fecundación y anteriores a la implantación se considera abortivo. Investigaciones previas sugieren que en seres humanos este método actúa también después de la fecundación. Sin embargo, en la actualidad existe sólida evidencia que demuestra que los efectos anteriores a la fecundación son en realidad los que explican la acción anticonceptiva del LNG. En este artículo se revisa la evidencia acumulada sobre los mecanismos de acción propuestos. Los consensos derivados de la información disponible establecen que los mecanismos prefecundación (inhibición o retardo de la ovulación) son los que explican la efectividad anticonceptiva de los AE de progestina sola.

There is still controversy regarding the mechanism of action of levonorgestrel (LNG) for emergency contraception (EC). For those who state that pregnancy starts prior to implantation, any compound able to interfere with post-fertilization and pre-implantation stages, should be considered as abortifacient. Previous research suggests that EC in humans acts predominantly after fertilization. Current evidence with LNG-only EC supports a pre-fertilization mechanisms to explain its action. There are many potential mechanisms of action, which could vary pending on the day during the fertilization window of the ovarian cycle at which the contraceptive is given. This paper reviews the evidence for each potential mechanism of action. According to the most recently statements, it is concluded that the primary and possible the only mechanism of action of LNG-only EC is preventing or delaying ovulation.

Cómo y cuándo el levonorgestrel previene el embarazo si se administra como anticonceptivo de emergencia / How and when levonorgestrel prevents pregnancy if it is administered as emergency contraceptive

En esta revisión se actualiza el mecanismo de acción del levonorgestrel (LNG) usado en anticoncepción de emergencia. El análisis crítico de la estimación de la eficacia anticonceptiva del LNG indica que su tasa de falla es más alta que la publicada. El LNG aumenta la viscosidad del moco cervical impidiendo que los espermatozoides del reservorio cervical vayan a renovar la población espermática en el sitio de fecundación. Diversos autores han documentado que LNG suprime el pico preovulatorio de gonadotrofinas e interfiere con el proceso ovulatorio en la mujer y en modelos animales. Administrado después de la ovulación en rata, en la mona Cebus apella y en la mujer, no interfiere con la implantación del embrión. Se concluye que LNG previene el embarazo solamente cuando se administra en un momento del ciclo menstrual en el cual puede impedir la fecundación y que el método falla cuando la administración es más tardía.

This review updates the mechanism of action of levonorgestrel (LNG) used for emergency contraception. A critical analysis of estimates of the contraceptive efficacy of LNG indicates that its failure rate is higher than previously reported. Under the effect of LNG, cervical mucus turns highly viscous and hinders the exit of sperm from the cervical reservoir needed to renew the sperm population at the site of fertilization. Several authors have documented that LNG suppresses the preovulatory surge of gonadotropins and interferes with the ovulatory process in women and in animal models. Administered after ovulation in the rat, in the Cebus apella monkey and women, LNG does not interfere with embryo implantation. In conclusion, LNG prevents pregnancy only when it is administered at a time of the menstrual cycle in which it can impede fertilization and the method fails when it is given at later stages of the cycle.

Introduction of emergency contraception in India.

Emergency contraception is a safe and effective method for preventing unwanted pregnancy following unprotected sexual exposure. The method had not been included in the National Family Programme of India. A Consortium on National Consensus for Emergency Contraception met in New Delhi in January 2001, to reach a consensus on strategies for introduction of emergency contraception in India. During the consortium experts from different walks of life deliberated on issues related to emergency contraception introduction and formulated national consensus statements and guidelines. This paper describes highlights of consortium activity which has led to introduction of emergency contraception in India.

Parivar Seva's experience with emergency contraceptive pills.

Parivar Seva, an NGO working in the area of reproductive health carried out an operation research project as a feasibility study on emergency contraception recently. The study was conducted among 1120 clients coming after unprotected sexual intercourse or improper use of any contraceptive method by using emergency contraception pills coming within 3 days and IUCD coming between 3 and 5 days of unprotected sexual intercourse. It was found that failure of emergency contraception was as low as 0.6%. The success rate in term of preventing pregnancy was 99.4% both with combined oral contraception pills and laevonorgesterol. There lies the scope for introducing emergency contraception in India wide and it can occupy a unique position in a range of contraceptive choices currently available to Indian women, as it can prevent unwanted pregnancies. A coalition of 30 like minded organisations including the Parivar Seva had formed a subcommittee on emergency contraception to evolve strategies to address promotion of emergency contraception.

Anticoncepción de emergencia

Muchas mujeres no saben que la anticoncepción después del coito es factible y está a su disposición

Post-coital contraceptive efficacy of the seeds of Nigella sativa in rats.

Hexane extract of the seeds of Nigella sativa L. prevented pregnancy in Sprague-Dawley rats treated orally at 2 g/kg daily dose on days 1-10 post-coitum. Significant antifertility activity was also observed in its column fractions and subfractions. At contraceptive dose, the active hexane extract exhibited only mild uterotrophic activity comparable almost to 0.002 mg/kg dose of 17 varies; is directly proportional to-Ethinylestradiol, but was devoid of any estrogenicity in the immature rat bioassay.

Post-coital antifertility activity of the marine plant, Achrostichum aureum L. in rat.

The ethanolic extract of A. aureum and its fractions were evaluated for postovulatory antifertility activity in female rats. The water soluble fraction of ethanolic (95%) extract prevented (100%) pregnancy when administered to female rats on days 1-7 postcoitum. This fraction was found devoid of both estrogenic and antiestrogenic activities.