Variability of essential and toxic trace elements in the follicular fluid of women undergoing in vitro fertilization (IVF)

Abstract

Both essential and non-essential elements have been associated with female reproductive function in epidemiologic investigations, including those among IVF populations. To date, most investigators have used blood or urine to assess biomarkers of exposure, with few employing ovarian follicular fluid (FF). FF may offer a more direct 'snapshot' of the oocyte microenvironment, however previous studies report follicle-to-follicle variability in FF constituents which may contribute to exposure misclassification. Our objectives were to: investigate sources of trace element variability in FF among women undergoing IVF (n=34, ≤4 FF collections each; estimate biomarker reliability; and determine the minimum number of follicles to estimate mean concentrations at a 10% confidence level (m10%). We measured As, Cd, Hg, Pb, Cu, Mn, Se, and Zn in FF samples using ICP-MS/MS and employed linear mixed models using restricted maximum likelihood to generate variability components. Sources of variability between women contributed the greatest proportion of total variance for FF As (97.2%), Hg (97.8%), Cd (52.1%), Cu (60.4%), Se (48.1%), and Zn (56.8%), compared to sources between ovaries, between follicles, and analytical variation. The proportion of variability attributable to sources between follicles differed significantly (p<0.05) by age, BMI, race, and cigarette smoking for Cu, Se, and Zn, by BMI and cigarette smoking for As, by primary infertility diagnosis for Hg, Cu, Se, and Zn, and by ovarian stimulation protocol for Mn and Se. To estimate m10% for Cu, Se, and Zn 4 to 5 individual follicles were sufficient, while >14 were necessary for As, Cd, Hg, Pb, and Mn. Our results suggest that while FF As and Hg are suitable biomarkers, these elements and Cd, Pb, and Mn have comparatively higher between-follicle variability than the other analytes. Our findings may help elucidate the impact of trace element exposures on IVF outcomes and inform the design of future studies.