Dr. Nanette Santoro proposes to test the specific question that obesity results in abnormal estradiol response at the level of the pituitary and hypothalamus. This will be shown in diminished pituitary sensitivity to gonadorelin releasing hormone with a reduced estradiol induced luteinizing hormone surge in obese women.

This is an open-label, single site study in pre-menopausal women aged 18-40 years old with a history of regular menstrual cycles (25-35 days long) of normal BMI or high BMI. The objective of the study is to determine the effects of an estradiol patch on luteinizing hormone rise in both cohorts. The study consists of 2 periods: a screening period of up to 3 weeks and a Treatment Period of 7-10 days. During the treatment period participants will wear estradiol patches for up to 7 days and have on blood draw on day 3 of wearing the patches. Participants will also collect daily morning urine for all the days they wear the patches. Participants will use a reliable barrier method of birth control or abstain from intercourse for the duration of the study.

Inclusion Criteria:

• Age 18-38
• Regular menstrual cycles every 25-35 days
• No use of reproductive hormones within the past 3 months
• No use of medications interacting with reproductive hormones
• Agreement to use reliable barrier contraception or to abstain from intercourse for the duration of the study
• Normal thyroid stimulating hormone, prolactin and lipid profiles
• No more than 4 hours of moderate to vigorous intensity exercise per week
• No history of chronic disease impacting reproductive hormones
• No contraindications to administration of estradiol
• No history of estrogen dependent cancer
• Negative pregnancy test

Exclusion Criteria:

• Has diabetes
• Is a smoker
• History of venous thromboembolism or known thrombophilia

Eligibility is limited to only female (assigned at birth) participants due to the requirement for menstruating females.