- Email: [email protected]
Do Higher Weight And BMI Increase The Risk Of Oral Contraceptive Failure?
icant. Brachial plexus stretch of both the anterior and posterior shoulders was lowest for the anterior Rubin’s maneuver followed by the posterior Rubin’s maneuver and McRoberts’ maneuver. The primary limitations of this study are that it was conducted in a laboratory rather than a clinical setting, and that the same physician completed all of the simulations. The advantage is that this research provides a novel approach to a condition that is not easily studied in a clinical setting. Conclusive recommendations based on this study are unwarranted, but midwives may want to consider adding Rubin’s maneuver to the strategies they use when confronted with shoulder dystocia. DO HIGHER WEIGHT AND BMI INCREASE THE RISK OF ORAL CONTRACEPTIVE FAILURE? Holt VL, Scholes D, Wicklund KG, Cushing-Haugen KL, Daling JR. Body mass index, weight, and oral contraceptive failure risk. Obstet Gynecol 2005;105:46 –52. Reviewed by: Francis Likis, CNM, MSN, FNP, WHCNP This case-control study examined the effect of body mass index (BMI) and weight on oral contraceptive (OC) failure. The 248 women who served as cases had filled an OC prescription in the 3 months preceding a positive pregnancy test. An additional 533 women who filled an OC prescription during the study period but did not have a positive pregnancy test served as controls. All of the women received care from a health maintenance organization (HMO) in Washington State. Participants were interviewed about their OC use, and this information was compared with pharmacy records. Participants were also asked about their body weight, and these self-reports were verified with medical records. The risk of OC failure was nearly 60% higher (OR 1.58; 95% CI 1.11–2.24) for women with a BMI greater than 27.3, compared with women with a BMI of or below 27.3 and increased by more than 70% (OR 1.72; 95% CI 1.04 –2.82) for women with a BMI greater than 32.2. These results persisted when the analysis was limited to consistent OC users, those who reported no missing pills in the reference month. Women with a BMI greater than 27.3 had a significantly higher incidence of OC failure (OR 2.17; 95% CI 1.38 –3.41) than the risk of OC failure in women with lower BMIs. There was also a change in risk related to weight. Consistent OC users who weighed more than 74.8 kg had a 70% increase in risk (OR 1.71; 95% CI 1.08 –2.71) and those who weighed more than 86.2 kg had nearly double the risk (OR 1.95; 95% CI 1.06 –3.67) of OC failure. The data collection through multiple tools, including interviews, pharmacy records, and medical chart reviews, is a strength of this study. Limitations include the small sample size and possible influence of different baseline characteristics in women who become pregnant while
Journal of Midwifery & Women’s Health • www.jmwh.org
taking OCs compared with the characteristics of women who do not become pregnant when taking OCs. After logistic regression to control for known influences beside BMI status (age, race, low income, marital status, education, and parity), only parity was found to influence the OC failure rate. Women with more pregnancies and more live births were more likely to have an OC failure independent of BMI, and there were more multiparous women in the group who experienced OC failure. There are a number of possible explanations for the apparent reduction in efficacy noted here. Higher body weight may increase metabolism and clearance of medications, causing lower serum levels of contraceptive hormones. In addition, because oral contraceptives are lipophilic, these hormones may be sequestered in the adipose tissue of overweight women, again, leading to reduced serum levels. Failure rates of OCs with “perfect use” (efficacy) are 0.5 or less per 100 woman-years. Failure rates with “typical use” (effectiveness) are as high as 7 per 100 woman-years. The findings of this study reflect a potential increase of 2 to 4 pregnancies per 100 woman-years among overweight women. Nonetheless, even these apparently higher rates are lower than those quoted for barrier contraceptive methods.1 The authors of this study recommend that women who are overweight consider an alternative to OC use or use of an additional method with OCs. These recommendations have practical limitations. Women may not want to use or may not be good candidates for highly effective methods with efficacy unrelated to weight, such as intrauterine devices or sterilization. The use of an additional contraceptive method, although it is reasonable advice to give a patient, may not be realistic. How does the clinician proceed when a woman who is overweight wants a hormonal method? There is concern that other hormonal methods may also have decreased effectiveness among women with higher weights and BMIs.2– 4 If this is correct, women who are overweight and want a hormonal method may benefit from choosing a contraceptive that requires less effort (e.g., patch, ring, or injection) than daily pill taking to minimize the potential of user failure. REFERENCES 1. O’Mara NB. Efficacy of oral contraceptives in overweight women. Pharmacist’s Newsletter/Prescriber’s Letter 2005;21(2):12. 2. Gu S, Sivin I, Du M, Zhang L, Ying L, Meng F, et al. Effectiveness of Norplant implants through seven years: A large-scale study in China. Contraception 1995;52:99 –103. 3. Grubb GS, Moore D, Anderson NG. Pre-introductory clinical trials of Norplant implants: A comparison of seventeen countries’ experience. Contraception 1995;52:287–96. 4. Zieman M, Guilleband J, Weisberg E, Shangold GA, Fisher AC, Creasy GW. Contraceptive efficacy and cycle control with the Ortho Evra/Evra transdermal system: The analysis of pooled data. Fertil Steril 2002;77(Suppl 2):S13–S18.
251
Journal of Midwifery & Women’s Health • www.jmwh.org
taking OCs compared with the characteristics of women who do not become pregnant when taking OCs. After logistic regression to control for known influences beside BMI status (age, race, low income, marital status, education, and parity), only parity was found to influence the OC failure rate. Women with more pregnancies and more live births were more likely to have an OC failure independent of BMI, and there were more multiparous women in the group who experienced OC failure. There are a number of possible explanations for the apparent reduction in efficacy noted here. Higher body weight may increase metabolism and clearance of medications, causing lower serum levels of contraceptive hormones. In addition, because oral contraceptives are lipophilic, these hormones may be sequestered in the adipose tissue of overweight women, again, leading to reduced serum levels. Failure rates of OCs with “perfect use” (efficacy) are 0.5 or less per 100 woman-years. Failure rates with “typical use” (effectiveness) are as high as 7 per 100 woman-years. The findings of this study reflect a potential increase of 2 to 4 pregnancies per 100 woman-years among overweight women. Nonetheless, even these apparently higher rates are lower than those quoted for barrier contraceptive methods.1 The authors of this study recommend that women who are overweight consider an alternative to OC use or use of an additional method with OCs. These recommendations have practical limitations. Women may not want to use or may not be good candidates for highly effective methods with efficacy unrelated to weight, such as intrauterine devices or sterilization. The use of an additional contraceptive method, although it is reasonable advice to give a patient, may not be realistic. How does the clinician proceed when a woman who is overweight wants a hormonal method? There is concern that other hormonal methods may also have decreased effectiveness among women with higher weights and BMIs.2– 4 If this is correct, women who are overweight and want a hormonal method may benefit from choosing a contraceptive that requires less effort (e.g., patch, ring, or injection) than daily pill taking to minimize the potential of user failure. REFERENCES 1. O’Mara NB. Efficacy of oral contraceptives in overweight women. Pharmacist’s Newsletter/Prescriber’s Letter 2005;21(2):12. 2. Gu S, Sivin I, Du M, Zhang L, Ying L, Meng F, et al. Effectiveness of Norplant implants through seven years: A large-scale study in China. Contraception 1995;52:99 –103. 3. Grubb GS, Moore D, Anderson NG. Pre-introductory clinical trials of Norplant implants: A comparison of seventeen countries’ experience. Contraception 1995;52:287–96. 4. Zieman M, Guilleband J, Weisberg E, Shangold GA, Fisher AC, Creasy GW. Contraceptive efficacy and cycle control with the Ortho Evra/Evra transdermal system: The analysis of pooled data. Fertil Steril 2002;77(Suppl 2):S13–S18.
251