BMI-related metabolic composition of the follicular fluid of women undergoing assisted reproductive treatment and the consequences for oocyte and embryo quality

STUDY QUESTION Is the metabolic composition of the follicular fluid of women undergoing assisted reproductive treatment (ART) related to serum composition and BMI and is it associated with oocyte and embryo quality? SUMMARY ANSWER We showed that metabolic alterations in the serum are reflected in the follicular fluid and that some of these alterations may affect oocyte quality, irrespective of BMI. WHAT IS KNOWN ALREADY Many studies have focused on the effect of metabolic disorders, such as obesity and type 2 diabetes, on assisted reproduction outcomes. There are, however, only few studies focusing on the importance of the correlation between serum and follicular fluid compositions and the composition of the follicular fluid as the oocyte's micro-environment, affecting its development and subsequent embryo quality. DESIGN, PARTICIPANTS AND SETTING In this prospective cohort study, patient information, fertility treatment outcome data, follicular fluid and serum were obtained from women undergoing ART. Patients were categorized according to their BMI (kg/m2) as normal (n = 60), overweight (n = 26) or obese (n = 20). Serum and follicular fluid samples were analyzed for urea, total protein, albumin, cholesterol, high-density lipoprotein cholesterol, triglycerides, non-esterified fatty acids, apolipoprotein A1, apolipoprotein B, glucose, lactate, C-reactive protein, insulin-like growth factor -1 (IGF-1), IGF-binding protein 3 (only in follicular fluid), free carnitine and total carnitine. Metabolite concentrations in serum and follicular fluid samples were correlated and were associated with BMI and fertility treatment outcome. MAIN RESULTS Most serum metabolite differences between patients were reflected in the follicular fluid (P < 0.05). Follicular fluid apolipoprotein A1 and follicular fluid total protein concentrations negatively affected oocyte quality parameters (P < 0.05). However, overall BMI-related associations were poor. BIAS, CONFOUNDING AND OTHER REASONS FOR CAUTION In this study, we included every patient willing to participate. Within this cohort, women with a BMI transcending 35 kg/m2 were scarce (n = 2), because extremely overweight women are mostly advised to lose weight before starting ART. Furthermore, the number of patients in each BMI group was different, possibly masking associations between the metabolic composition of serum and follicular fluid and oocyte quality parameters. GENERALIZABILITY TO OTHER POPULATIONS There were significant