Obesity and Oral Contraceptive Failure

Contraceptive failure is the primary cause of unintended pregnancy in the United States.
With obesity rates at epidemic proportions, any association between obesity and strategies
that prevent undesired pregnancies constitutes a significant public health and economic
concern. Evidence from recent epidemiological studies and our preliminary data
(sub-therapeutic levels of steroid hormones due to drug clearance and half-life) suggest
that obesity reduces oral contraceptive efficacy. Furthermore, preliminary analysis
suggested that a sub-group of obese women, defined by their own birth weight, are at higher
risk of contraceptive failure. Further studies are necessary to investigate whether birth
weight, a surrogate marker of in utero growth restriction, is a useful diagnostic marker for
the identification of women prone to contraceptive failure. Such an understanding is
critical to finding a contraceptive strategy with better efficacy for these women.

The overall goal of this project is to test pharmacokinetics of oral contraceptive agents in
obese women with low birth weight and compare to obese women with normal birth weight. The
main hypothesis for this proposal is that an adverse in utero environment programs the
expression and function of enzymes and transporters that underlie pharmacokinetics of oral
contraceptives, and leads to contraceptive failure.

Reproductive-aged, ovulatory women of obese BMI >30 kg/m2 with normal birth weight (5.5-8
lbs; n=10) and low birth weight (<5.5 lbs; n=10), will be placed on oral contraceptives for
1 month. At several key time points, synthetic steroid pharmacokinetics, gonadotropins
(luteinizing hormone, follicle-stimulating hormone) and ovarian hormone levels (estradiol,
progesterone) will be monitored.