Abstract
Background
We aimed to evaluate whether emergency contraception with levonorgestrel (LNG-EC)
administered after ovulation is equally effective to LNG-EC administered before ovulation.
Study design
We studied a cohort of women attending a family planning clinic for EC. From interview,
we recorded menstrual history, time of intercourse and of intake of LNG-EC. On the
day of intake of LNG-EC and during 5 days' follow-up, blood samples were taken for
examination of luteinizing hormone, estradiol and progesterone concentrations, and
vaginal ultrasound examinations were done for size of the leading follicle and/or
corpus luteum. Thereafter women were not contacted until next menses or pregnancy
occurred.
Results
Of 388 women attending for LNG-EC, 122 women had intercourse on fertile cycle days
according to ultrasound and endocrine findings. At the time of LNG-EC intake, 87 women
were in Days −5 to −1 and 35 women were in Day 0 (day of ovulation) or beyond. With
the use of the probability of clinical pregnancy reported by Wilcox et al. [N Engl J Med 333 (1995) 1517–1521], expected numbers of pregnancies among the 87 and 35 women
were 13 and 7, respectively, while 0 and 6 pregnancies, respectively, occurred.
Conclusion
We conclude that LNG-EC prevents pregnancy only when taken before fertilization of
the ovum has occurred.
Keywords
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Article Info
Publication History
Published online: January 28, 2010
Accepted:
December 16,
2009
Received in revised form:
December 10,
2009
Received:
November 9,
2009
Footnotes
☆This study has been supported by grants 1060252 and FB0807 from Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT) and by grant A 65559 from the World Health Organization, Department of Reproductive Health and Research (WHO/RHR) .
Identification
Copyright
© 2010 Elsevier Inc. Published by Elsevier Inc. All rights reserved.
