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|Title: ||Mechanism of action of emergency contraceptive pill|
|Authors: ||Novikova, Natalia|
|Keywords: ||contraception, emergency conraceptive pill, postinor, levonorgestrel, morning after pill, ovulation, conception|
|Issue Date: ||Feb-2007|
|Publisher: ||University of Sydney.|
Obsterics and Gynaecology
|Abstract: ||The number of unwanted pregnancies has not decreased in recent years and this should be addressed. Emergency contraception may be effective when used correctly having the advantage that it can be used after an episode of unprotected sexual intercourse (when regular contraception has failed or was not used).
In this research project I set out to explore some of the major reasons why there are still many unwanted pregnancies in Australia. I decided to focus on the use and non-use of emergency contraception, e.g. emergency contraception pill (ECP) “method failures” are not well understood because the actual mechanisms of action are still unclear. There is evidence ECP can effectively interfere with follicle growth and ovulation. It is much less clear is whether ECP is able to interfere with fertilization and implantation, in a way, which may make it acceptable to those who have strong religious beliefs in fertilization being the start of new life.
Emergency contraception has the potential to prevent many unwanted pregnancies when unprotected intercourse has occurred. It has relatively high efficacy in many studies, but true method failures are not well understood. By contrast, many unwanted pregnancies occur for “social reasons” where emergency contraception has not been used. I set out to study changes in knowledge and usage of emergency contraception in these groups of Australian women seeking termination of pregnancy:
1. Before a dedicated emergency contraception pill (ECP) pack (Postinor) became available in Australia
2. One year after dedicated ECP became available on prescription
3. One year after the ECP pack became available “over the counter” without prescription.
Ninety-nine women were recruited during their presentation with a request for ECP at the six Family Planning Clinics in Australia. All women took LNG 1.5mg 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, oestradiol and progesterone levels to calculate the day of the menstrual cycle. Based on these endocrine data we estimated the timing of ovulation to within a ±24-hour 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.
Three women in this study became pregnant despite taking the ECP (pregnancy rate 3%). All three women who became pregnant had unprotected intercourse between day -1 and 0 and took the ECP on day +2, based on endocrine data. Day zero was taken as ovulation day. Among seventeen women who had intercourse in the fertile period of the cycle and took the ECP after ovulation occurred (on day +1 to +2) we could have expected 3 or 4 pregnancies, based on Wilcox et al data. Three pregnancies were observed. Among 34 women who had intercourse on days –5 to –2 of the fertile period, and took ECP before or around ovulation, four pregnancies could have been expected, but none were observed. The major discrepancies between women’s self-report of stage of the cycle and the dating calculation based on endocrine data were observed in this study.
These data are supportive of the concept that the LNG ECP has little or no effect on post-ovulation events, but is highly effective before ovulation. Our interpretation of the data in terms of timing of treatment relative to ovulation may explain why EC with LNG works sometimes and fails at other times. A larger study is needed to prove this hypothesis.
To investigate other reasons for such a high rate of unwanted pregnancy, which probably has a larger impact we looked into womens knowledge of and attitude towards ECP.
Seven hundred and eighteen women participated in this study by answering a questionnaire consisting of 15 questions on their demographic and reproductive characteristics as well as the knowledge about the ECP, e.g. 208 women were enrolled before the ECP was marketed in Australia in 2001, 308 after it was marketed and 202 after it became available over the counter (Group 1, 2, and 3, respectively).
We found that the participants who have heard about ECP were significantly younger (p<0.005). The mean age of women who have never heard about of ECP was 29.8 years compared to 26.3 years in women who have heard about ECP. More women were aware about the ECP after it became available over the counter. Women in group 2 had higher educational level in comparison to women in group 2 and 3 (p<0.005). There was significant trend in increased use of ECP in women of higher educational level (p<0.005). The use of ECP did not increase significantly with improved availability and access to the ECP amongst women presenting for termination of pregnancy.
Wider availability of he ECP pack in Australia and an easier access to it has increased women’s awareness about the ECP. However, the use of ECP has not increased.
This study provides better understanding of mechanism of action of LNG ECP and an explanation to the method failure. It also reveals poor knowledge about ECP despite its wider availability and accessibility. Improving these is a worldwide challenge for family planners and all health professionals.|
|Description: ||Master of Medicine|
|Rights and Permissions: ||The author retains copyright of this thesis.|
|Type of Work: ||Masters Thesis|
|Appears in Collections:||Sydney Digital Theses (Open Access)|
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