Related Experiment Video
Updated: Sep 3, 2026

Assessment of Child Anthropometry in a Large Epidemiologic Study
Published on: February 2, 2017
Body weight and risk of oral contraceptive failure
Victoria L Holt1, Kara L Cushing-Haugen, Janet R Daling
1Department of Epidemiology, School of Public Health and Community Medicine, University of Washington, Seattle, Washington, USA. vholt@u.washington.edu
Objective:
To examine the hypothesis that higher body weight increases the risk of oral contraceptive (OC) failure.
Methods:
We conducted a retrospective cohort analysis of data from 755 randomly selected female enrollees of Group Health Cooperative of Puget Sound who completed an in-person interview and dietary questionnaire between 1990 and 1994 as control subjects for a case-control study of ovarian cysts. Among the 618 women who were OC ever-users, we used Cox proportional hazards regression models to estimate the relative risk (RR) of pregnancy while using OCs associated with body weight quartile.
Results:
During 2822 person-years of OC use, 106 confirmed pregnancies occurred (3.8 per 100 person-years of exposure). After controlling for parity, women in the highest body weight quartile (70.5 kg or more) had a significantly increased risk of OC failure (RR 1.6, 95% confidence interval [CI] 1.1, 2.4) compared with women of lower weight. Higher elevations of risk associated with the highest weight quartile were seen among very low-dose OC users (RR 4.5, 95% CI 1.4, 14.4) and low-dose OC users (RR 2.6, 95% CI 1.2, 5.9), controlling for parity, race, religion, and menstrual cycle regularity.
Conclusion:
Our findings suggest that body habitus may affect metabolism sufficiently to compromise contraceptive effectiveness. Consideration of a woman's weight may be an important element of OC prescription.
Related Concept Videos
Obesity
Birth Control Methods
Types of Biopharmaceutical Studies: Controlled and Non-Controlled Approaches
Non-controlled studies, commonly employed for initial exploration, lack a control group, rendering them susceptible to biases and external influences. In contrast, controlled...
Drug Dosing: Obese Patients
Pharmacokinetics in Obese Patients: Drug Absorption and Distribution
Pharmacokinetics in Obese Patients: Drug Metabolism and Excretion

