Variability of essential and non-essential 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 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 than blood or urine, however previous studies report follicle-to-follicle variability in FF constituents that may contribute to exposure misclassification. Our objectives were to investigate sources of trace element variability, to estimate FF biomarker reliability among women undergoing IVF (n = 34), and to determine the minimum number of follicles required to estimate subject-specific mean concentrations. We measured As, Hg, Cd, Pb, Cu, Mn, Se, and Zn in FF samples using inductively coupled plasma tandem mass spectrometry. Inter-subject (between-women) variability contributed most of the variability in FF element concentrations, with ovarian, follicular, and analytical as smaller sources of variability. The proportion of variability attributable to sources between-follicles differed by age, body mass index (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. Four to five individual follicles were sufficient to estimate subject-specific mean Cu, Se, and Zn concentrations, while >14 were necessary for As, Hg, Cd, Pb, and Mn. Overall, our results suggest that FF is a suitable source of biomarkers of As and Hg exposure in ovarian follicles. Although limited in size, our study offers the most comprehensive exploration of biological variation in FF trace elements to date and may provide guidance for future studies of ovarian trace element exposures.

Keywords: Biologic variability; Biomarkers; Follicular fluid; In vitro fertilization; Reliability; Trace elements.

Fig. 1.

Sampling strategy for follicular fluid (FF) trace elements for 212 determinations collected from contralateral follicles of in vitro fertilization (IVF) patients, (data from 34 women with replicate FF). Note: Each woman contributed up to four follicles with up to six determinations (repeat runs). Counts displayed are based on maximum number of repeat measures which were for mercury. Other totals were as follows: 211 for arsenic, 117 for cadmium, 104 for lead, 212 for copper, 202 for manganese, 211 for selenium, and 209 for zinc. Numbers in parentheses represent total samples with that specified number of determinations.

Fig. 2.

Intraclass correlation coefficients with 95% confidence intervals (CI) for follicular fluid trace elements (μg/L) measured in n = 34 in vitro fertilization (IVF) patients, describing the correlations between repeat measures from follicles within the same woman. As- arsenic, Hg- mercury, Cd- cadmium, Pblead, Cu- copper, Mn- manganese, Se- selenium, and Zn- zinc measured in FF specimens collected from contralateral follicles; Cd in ng/ L.