[AF] PDS: no disminuye los embarazos y tiene efecto postfecundación

[Eduardo Satue]

También coincido que en salud pública la regla de oro es que algo es dañino hasta que se demuestra que no lo es y no al revés. Para mi esto 
significa que es importante dar toda la información al profesional y a la usuaria:
- el profesional, una vez conocido que existe la posibilidad (a nivel teórico) de efectos postovulatorios, puede optar por la objeción de 
conciencia si cree que va en contra de su ética
- la usuaria, una vez conocida esa posibilidad, puede tomar la decisión que considere oportuna, pero al menos no como si se tomara una aspirina.

En cualquier caso, el efecto postovulatorio, de existir, parece pequeño y la disyuntiva que planteas va más encaminada a que si una mujer ya ha 
ovulado, la eficacia del LNG como anticonceptivo no debe ser muy alta, o con bastante seguridad, muy inferior a la media dada del LNG por lo que 
es cierto que puede existir una sensación de falsa seguridad una vez tomada la PDS. Para ilustrar el caso está este estudio que me parece muy 
interesante:



Contraception. <http://www.ncbi.nlm.nih.gov/pubmed/17241840#> 2007 Feb;75(2):112-8. Epub 2006 Oct 27.


  Effectiveness of levonorgestrel emergency contraception given before or after ovulation--a pilot study.

Novikova N <http://www.ncbi.nlm.nih.gov/pubmed?term=%22Novikova%20N%22%5BAuthor%5D>, Weisberg E 
<http://www.ncbi.nlm.nih.gov/pubmed?term=%22Weisberg%20E%22%5BAuthor%5D>, Stanczyk FZ 
<http://www.ncbi.nlm.nih.gov/pubmed?term=%22Stanczyk%20FZ%22%5BAuthor%5D>, Croxatto HB 
<http://www.ncbi.nlm.nih.gov/pubmed?term=%22Croxatto%20HB%22%5BAuthor%5D>, Fraser IS 
<http://www.ncbi.nlm.nih.gov/pubmed?term=%22Fraser%20IS%22%5BAuthor%5D>.


      Source

Department of Obstetrics and Gynaecology, University of Sydney, NSW, 2006, Australia.


      Abstract


        BACKGROUND:

Although widely used, the mechanisms of action of the levonorgestrel emergency contraceptive pill (LNG ECP) are still unclear. There are 
increasing data to indicate that LNG is particularly effective as an ECP by interrupting follicular development and ovulation. An important 
outstanding question is whether it has any effect on fertilization or implantation.


        METHOD:

Ninety-nine women participated; they were recruited at the time they presented with a request for emergency contraception. All women took LNG 
1.5 mg in a single dose during the clinic consultation. A blood sample was taken immediately prior to ingestion of the ECP for estimation of 
serum LH, estradiol and progesterone levels to calculate the day of ovulation. The specimens were analyzed in a single batch. Based on these 
endocrine data, we estimated the timing of ovulation to be within a +/-24-h period with an accuracy of around 80%. Women were followed up 4-6 
weeks later to ascertain pregnancy status. The effectiveness of ECP when taken before and after ovulation was determined.


        RESULTS:

Three women became pregnant despite taking the ECP (pregnancy rate, 3.0%). All three women who became pregnant had unprotected intercourse 
between Days -1 and 0 and took the ECP on Day +2, based on endocrine data. Day 0 was taken as ovulation day. Among 17 women who had intercourse 
in the fertile period of the cycle and took the ECP after ovulation occurred (on Days +1 to +2), we could have expected three or four 
pregnancies; three were observed. Among 34 women who had intercourse on Days -5 to -2 of the fertile period and took ECP before or on the day of 
ovulation, four pregnancies could have been expected, but none were observed. We found major discrepancies between women's self-report of stage 
of the cycle and the dating calculation based on endocrine data.


        CONCLUSION:

These data are supportive of the concept that the LNG ECP has little or no effect on postovulation events but is highly effective when taken 
before ovulation.