# IVF and Thermal Manipulation at the First Cleavage Stage Alter Offspring Circadian Phenotype, Sleep, and Brain Epigenetics

## TL;DR

This study shows that IVF and temperature changes during early embryo development affect offspring's sleep, circadian rhythms, and brain epigenetics.

## Contribution

The study identifies disrupted circadian rhythms and sleep as a novel mechanism for metabolic dysfunction in IVF offspring.

## Key findings

- IVF offspring showed disrupted circadian rhythms and sleep-wake patterns.
- Reduced culture temperature (35 °C) partially mitigated these effects.
- Altered histone modifications in the brain suggest an epigenetic basis for these changes.

## Abstract

In vitro fertilization (IVF) exposes embryos to environmental stressors that can disrupt early development and confer long-term health risks, though the mechanisms remain poorly understood. Here, we tested the hypothesis that reducing incubation temperature during the first zygotic cleavage would promote long-term developmental stability in IVF-conceived offspring. Using a mouse model, we compared the long-term effects of standard (37 °C) versus reduced (35 °C) IVF culture temperature on energy balance, circadian rhythms, sleep architecture, and brain histone modifications. Although offspring from both IVF groups exhibited increased body mass without notable effects on glucose metabolism, significant disruptions in circadian rhythms and sleep–wake patterns were detected. The 37 °C group exhibited altered amplitudes in oxygen consumption rhythms and respiratory exchange ratios, as well as pronounced alterations in sleep–wake patterns, including reduced sleep duration and increased nighttime activity. The 35 °C group displayed intermediate phenotypes, substantiating the importance of optimizing embryo incubation parameters. These metabolic and behavioral changes were paralleled by altered histone modifications in the cerebral cortex of IVF offspring, suggesting an epigenetic basis for circadian misalignment. Our results identify disrupted circadian rhythm and sleep architecture as a novel mechanism contributing to metabolic dysfunction in IVF-conceived offspring. The partial mitigation of these effects through reduced culture temperature underscores the importance of optimizing IVF protocols to minimize long-term epigenetic and metabolic risks.