Biodemographic Models of Reproductive Aging
(BIMORA)

Our laboratory conducts population-level research on female reproduction, with a focus on reproductive aging. The National Institutes on Aging funded BIMORA project examines the transition to menopause.

The transition to menopause encompasses a wide-ranging set of changes for women, including increasingly variable menstrual cycle length, highly variable hormone patterns, reduced fecundity (ability to get pregnant), and a host of other biological changes.

To examine this transition we are collecting daily urine specimens from 130 U.S. women for six months per year for five years. The women collect and store their samples at home, and mail them to the lab once a month. The urine specimens are assayed for the principal steroid hormones (estrogen, progesterone) and gonadotropins (luteinizing hormone and follicle-stimulating hormone) involved in regulating ovarian (menstrual) cycles and signaling reproductive aging.

After measuring hormones in urine samples, we use statistical models to examine how hormonal patterns and menstrual cycles change across the transition to menopause. We also use the models to link these changes to the underlying process of follicular depletion. Follicles are the structures that hold and nurture a woman's eggs, and each egg has its own follicle. Follicular depletion is the steady loss of follicles (and eggs) that occurs in all women from before birth up until menopause, when the ovaries have completely depleted the original stock of follicles. We hypothesize that most of the wide-ranging set of reproductive aging changes for women are a result of the process of follicular depletion.

The BIMORA project will provide insight into the patterns and causes of variation in women's experience of the menopausal transition. The BIMORA women are also participating in the Tremin Trust Research Program and have been part of that research project for many years. Consequently, we will be able to link characteristics of the transition to menopause for the BIMORA women with the menstrual cycle and health data they have collected for many years for the Tremin Trust.

This is a unique research opportunity for women's reproductive health, thanks to the incredible dedication of the Tremin Trust/BIMORA participants.

Publications

O'Connor KA, Brindle E, Miller RC, Shofer JB, Ferrell RJ, Klein NA, Soules MR, Holman DJ, Mansfield PK, Wood JW. (2006) Ovulation detection methods for urinary hormones: Precision, daily and intermittent sampling, and a combined hierarchical method. Human Reproduction (advance on-line publication).
[ Abstract ] [ Full Text ]

Ferrell RJ, O'Connor KA, Holman DJ, Brindle E, Miller RC, Schechter DE, Gorrindo T, Korshalla L, Simon J, Voda A, Wood JW, Mansfield PK, Weinstein M. (2005) Monitoring the transition to menopause in a five year prospective study: aggregate and individual changes in steroid hormones and menstrual cycle lengths with age. Menopause 12(5):567-577. [ Full Text ]

Collaborators on the BIMORA project

Darryl J. Holman
Co-investigator
Department of Anthropology
University of Washington

Phyllis Kernoff Mansfield
Co-investigator
Women's Studies Program
The Pennsylvania State University

Kathleen A. O'Connor
Co-investigator
Department of Anthropology University of Washington

Steven M. Pincus
Mathematician

Germán Rodrîguez
Office of Population Research
Princeton University

James A. Simon
Clinical Professor
George Washington University

Burton Singer
Office of Population Research
Princeton University

Maxine Weinstein
Principal Investigator
Department of Demography
Georgetown University

James W. Wood
Principal Investigator
Department of Anthropology
The Pennsylvania State University

Ann M. Voda
College of Nursing
University of Utah