Human embryos from overweight and obese women display phenotypic and metabolic abnormalities

Study question: Is the developmental timing and metabolic regulation disrupted in embryos from overweight or obese women?

Summary answer: Oocytes from overweight or obese women are smaller than those from women of healthy weight, yet post-fertilization they reach the morula stage faster and, as blastocysts, show reduced glucose consumption and elevated endogenous triglyceride levels.

What is known already: Female overweight and obesity is associated with infertility. Moreover, being overweight or obese around conception may have significant consequences for the unborn child, since there are widely acknowledged links between events occurring during early development and the incidence of a number of adult disorders.

Study design, size, duration: We have performed a retrospective, observational analysis of oocyte size and the subsequent developmental kinetics of 218 oocytes from 29 consecutive women attending for ICSI treatment and have related time to reach key developmental stages to maternal bodyweight. In addition, we have measured non-invasively the metabolic activity of 150 IVF/ICSI embryos from a further 29 consecutive women who donated their surplus embryos to research, and have related the data retrospectively to their body mass index (BMI).

Participants/materials, setting, methods: In a clinical IVF setting, we compared oocyte morphology and developmental kinetics of supernumerary embryos collected from overweight and obese women, with a BMI in excess of 25 kg/m(2) to those from women of healthy weight. A Primovision Time-Lapse system was used to measure developmental kinetics and the non-invasive COnsumption/RElese of glucose, pyruvate, amino acids and lactate were measured on spent droplets of culture medium. Total triglyceride levels within individual embryos were also determined.

Main results and the role of chance: Human oocytes from women presenting for fertility treatment with a BMI exceeding 25 kg/m(2) are smaller (R(2) = -0.45; P = 0.001) and therefore less likely to complete development post-fertilization (P < 0.001). Those embryos that do develop reach the morula stage faster than embryos from women of a BMI < 25 kg/m(2) (<0.001) and the resulting blastocysts contain fewer cells notably in the trophectoderm (P = 0.01). The resulting blastocysts also have reduced glucose consumption (R(2) = -0.61; P = 0.001), modified amino acid metabolism and increased levels of endogenous triglyceride (t = 4.11, P < 0.001). Our data further indicate that these differences are independent of male BMI.

Limitations, reasons for caution: Although statistical power has been achieved, this is a retrospective study and relatively small due to the scarcity of human embryos available for research. Consequently, subanalysis of overweight and obese was not possible based on the sample size. The analysis has been performed on supernumerary embryos, originating from a single IVF unit and not selected for use in treatment. Thus, it was not possible to speculate how representative the findings would be of the better quality embryos transferred or frozen for each patient.

Wider implications of the findings: The data indicate that a high BMI of women at conception is associated with distinct phenotypic changes in the embryo during the preimplantation period, highlighting the importance of prepregnancy body weight in optimizing the chances of fertility and safeguarding maternal and offspring health. These changes to the metabolic fingerprint of human embryos which are most likely a legacy of the ovarian conditions under which the oocyte has matured may reduce the chances of conception for overweight women and provide good evidence that the metabolic profile of the early embryo is set by sub-optimal conditions around the time of conception. The observed changes could indicate long-term implications for the health of the offspring of overweight and obese women.

Study funding/competing interests: This study was funded by the Hull IVF Unit Charitable Trust and the Hull York Medical School. There are no conflict of interests.