European Journal of Clinical Pharmacy

Volume 17 - Issue 6, November-December 2015

SHORT REPORTS

POST-FERTILIZATION EFFECT OF POSTCOITAL LEVONORGESTREL

ALEGRE DEL REY EMILIO J, FÉNIX CABALLERO SILVIA, DÍAZ NAVARRO JORGE, RODRÍGUEZ MARTÍN ESTEBAN

Introduction: The possibility of a post-fertilization effect of Postcoital Levonorgestrel (PL) holds an ethical discussion. There are evidences of its anovulatory effect until one day before ovulation. But, when PL is administered, sometimes ovulation cannot be already stopped. In absence of a post-fertilization effect, the
reduction in pregnancy rate would be limited by this cause. A Bayesian model can estimate the minimum post-fertilization effect required to explain a given reduction in pregnancy rate. But this reduction in pregnancy rate with PL could not be quantified precisely until now, as there is a lack of comparative data.

Method: A pooled analysis which includes 6,794 women in four large WHO studies, referred a 1.01% pregnancy rate when PL was taken during the first four days after intercourse and 5.22% on the fifth day, near the estimated rate of pregnancy without contraception (6-8%). The fifth-day group pregnancy rate could
be used as a control, and assess the minimal effect of PL, with a conservative approach. By interpolation to the graphic Bayesian model, the post-fertilization effect associated required to explain the given reduction in pregnancy rate was assessed.

Results: The adjusted pregnancy reduction was 82.78% (95% CI: 67.94-90.75) if PL intake was 24h after intercourse, and 73.47% (95% CI: 46.47-86.85) 72h after intercourse. Not-anovulatory mechanisms could account for 51.2% (95%CI: 35.4-59.3) of the pregnancy reduction in the 24 h-delay group and 65.4% of the pregnancy reduction (95% CI: 38.7-78.8) in the 72 h-delay group.

Conclusions: This clinical-based results support a post-fertilization effect of PL,as a key point for ethical discussions regarding PL use.

POSTCOITAL CONTRAC EPTION – LEVONORGESTREL – PREGNANCY RATE

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