Obesity during pregnancy has serious implications for maternal and infant health. Studies in non-pregnant obesity models suggest that disturbances in circadian rhythms may contribute to adverse outcomes in obese pregnancy. The circadian system regulates most metabolic processes and is inherently linked to thermoregulation; core body temperature (CBT) exhibits distinct daily rhythms, which are altered late in rat pregnancy, presumably as a maternal adaptive response to the metabolic demands of the growing fetus.

This study examined the impact of maternal obesity on circadian variation in maternal CBT. Rats were fed either chow alone (CON) or chow supplemented with a cafeteria diet (CAF) (i.e. novel, high-energy food provided daily) for six weeks. iButtons were then implanted (i.p.) to record CBT every 15 min for 2-3 oestrous cycles and throughout pregnancy. Daily CBT profiles were assessed by cosinor analysis to derive mesors and amplitudes. Obesity reduced mesor CBT in the cycle (0.18 C lower; P<0.05), and CBT varied with cycle stage (P<0.001; maximal at oestrus/proestrus). CBT amplitude was unaffected by obesity but fell at oestrus before rebounding at proestrus (P<0.01; both groups). In pregnancy, CBT was lower in the obese group (P<0.01), but there was a significant interaction (P<0.02) between diet and pregnancy stage. Specifically, the pre-partum decline in CBT commenced by day 16 in both groups, but was smaller in CAF such that CBT values in the two groups converged.

In conclusion, diet-induced obesity reduced CBT before and for most of rat pregnancy. The normal pre-partum decline in CBT was reduced in obese mothers such that values converged (with those in CON mothers) near term. While the circadian profile of CBT was influenced by cycle stage, it was unaffected by obesity or pregnancy. Reduced CBT in obesity likely exacerbates the impact of the CAF diet on adiposity due to lower energy expenditure.