Parental contributions to early embryo development: influences of urinary phthalate and phthalate alternatives among couples undergoing IVF treatment

STUDY QUESTION Are preconception urinary concentrations of phthalates and phthalate alternatives associated with diminished early stage embryo quality in couples undergoing IVF? SUMMARY ANSWER Male, but not female, urinary concentrations of select metabolites of phthalates and phthalate alternatives are associated with diminished blastocyst quality. WHAT IS KNOWN ALREADY Although phthalates are endocrine disrupting compounds associated with adverse reproductive health, they are in widespread use across the world. Male and female preconception exposures to select phthalates have been previously associated with adverse reproductive outcomes in both the general population and in those undergoing IVF. STUDY DESIGN, SIZE, DURATION This prospective cohort included 50 subfertile couples undergoing IVF in western Massachusetts. PARTICIPANTS/MATERIALS, SETTING, METHODS This study includes the first 50 couples recruited from the Baystate Medical Center's Fertility Center in Springfield, MA, as part of the Sperm Environmental Epigenetics and Development Study (SEEDS). Relevant data from both partners, including embryo quality at the cleavage (Day 3) and blastocyst (Day 5) stages, were collected by clinic personnel during the normal course of an IVF cycle. A spot urine sample was collected from both male and female partners on the same day as semen sample procurement and oocyte retrieval. Concentrations of 17 urinary metabolite were quantified by liquid chromatography mass spectrometry and normalized via specific gravity. Generalized estimating equations were used to estimate odds ratios (OR) and 95% CI, with urinary phthalates and phthalate alternatives fitted as continuous variables and embryo quality as a binary variable. MAIN RESULTS AND THE ROLE OF CHANCE The 50 couples contributed 761 oocytes, of which 423 progressed to the cleavage stage, 261 were high-quality cleavage stage embryos, 137 were transferrable quality blastocysts and 47 were high-quality blastocysts. At the cleavage stage, male urinary monoethyl phthalate concentrations were positively associated with high-quality cleavage stage embryos (OR = 1.20, 95% CI 1.01-1.43, P = 0.04); no other significant associations were observed at this stage. At the blastocyst stage, male urinary concentrations of monobenzyl phthalate (OR = 0.55, 95% CI 0.36-0.84, P = 0.01), mono-3-hydroxybutyl phthalate (OR = 0.37, 95% CI 0.18-0.76, P = 0.01), mono-n-butyl phthalate (OR = 0.55, 95% CI 0.42-0.73, P < 0.01) and monomethyl phthalate (OR = 0.39, 95% CI 0.26-0.60, P < 0.01) were inversely associated with high-quality blastocysts. A borderline statistically significant relationship was observed for male concentrations of mono(2-ethylhexyl) phthalate (OR = 0.52, 95% CI 0.27-1.00, P = 0.05) and cyclohexane-1,2-dicarboxylic acid-monocarboxy isooctyl ester (OR = 0.21, 95% CI 0.04-1.03, P = 0.05) at the blastocyst stage. Similar inverse associations were observed between male urinary phthalate metabolite concentrations and likelihood of transferrable quality blastocysts. For female partners, select metabolites were positively associated with odds of high or transferrable blastocyst quality, but the observed associations were not consistent across blastocyst quality measures or between sex-specific and couples-level models. All models were adjusted for age of both partners, urinary metabolite concentrations of female partners and male infertility status, while models of blastocysts were additionally adjusted for embryo quality at cleavage stage. LIMITATIONS, REASONS FOR CAUTION Our modest sample included only 50 couples contributing one cycle each. In addition, non-differential misclassification of exposure remains a concern given the single-spot urine collection and the short half-life of phthalates. WIDER IMPLICATIONS OF THE FINDINGS Our results suggest an inverse association between male preconception concentrations of select phthalate metabolites and blastocyst quality, likely occurring after genomic activation. If corroborated with other studies, such findings will have public health and clinical significance for both the general population and those undergoing IVF. STUDY FUNDING/COMPETING INTERESTS This work was generously supported by grant K22-ES023085 from the National Institute of Environmental Health Sciences. The authors declare no competing interests. TRIAL REGISTRATION NUMBER N/A.