TABLE 1—

Design Features That Have Facilitated Reproductive Epidemiological Research in the Nurses’ Health Studies

Design Feature	Methodological Advantages and Research Facilitated
Health professionals as study participants	High validity of self-reported outcomes, in some cases superior to women in the general population
	High commitment to contributing to health research without compensation and for extended periods of time
Repeated assessment of pregnancy and unsuccessful attempts to become pregnant	Allows the estimation of incidence rates of infertility
	Allows the identification of infertility cases among women who did not seek medical attention for evaluation or treatment of this condition
	Allows the prospective identification of lifestyle risk factors for infertility
Repeated assessment of pregnancy outcome and common complications	Allows the estimation of incidence and recurrence rates of multiple pregnancy complications
	Allows the use of the “pregnancies at risk” approach for studies of pregnancy complications
	Allows the identification of risk factors for incident pregnancy complications and other adverse pregnancy outcomes
Repeated assessment of benign gynecologic conditions	Allows estimation of incidence rates for gynecologic conditions on the basis of prospective data from women in the general population
	For endometriosis, NHS II estimates were the first incidence estimates based on this type of data
Long-term prospective follow-up from reproductive years through postmenopause	Allows the evaluation of risk factors for multiple reproductive disorders with different distributions of peak age of incidence ranging from conditions with highest incidence during early reproductive years to conditions peaking in incidence around and after menopause
	Allows the evaluation of reproductive events as risk factors for chronic noncommunicable diseases
Repeated assessment of diet and lifestyle	Allows novel research linking diet and lifestyle factors with infertility and gestational diabetes to an unprecedented extent and based on prospective data
	Makes available preconception diet and lifestyle data thus avoiding major methodological problems in epidemiological research of risk factors for pregnancy loss
Wide geographical distribution	Facilitates generalizability to geographically diverse populations
	Can take into account known regional patterns in exposures of interest (e.g., diet, obesity) and reproductive events (e.g., age at first birth, cesarean delivery rates)
	Makes possible the evaluation of geographically determined exposures, such as air pollution and the built environment, as risk factors for adverse reproductive outcomes
Multigenerational component	Allows the evaluation of hypotheses regarding developmental and transgenerational determinants of health and disease including up to 3 generations in a subset of the study (Mothers of NHS II participants, NHS II participants, and GUTS—offspring of NHS II participants)
	Facilitates using generational changes in confounding structure as an advantage to etiological research (e.g., changes in the association between smoking during pregnancy and socioeconomic factors over 2 generations to evaluate the long-term health impacts on offspring of maternal smoking)

Note. GUTS = Growing Up Today Study; NHS = Nurses’ Health Study.