For women of reproductive age, the overall postpartum weight retention (weight gain between pregnancies) plays a significant role in long-term obesity. With 20% of women retaining ≥ 5 kg at 12 months postpartum, the risk of developing conditions, such as gestational diabetes mellitus (GDM), metabolic syndrome (MS) and subsequently diabetes and cardiovascular diseases, is substantially increased. In post-GDM mothers (women who had GDM in their recent pregnancy), postpartum weight retention is also an essential predictor of future diabetes.

Recent studies have identified the impact of circadian rhythms (influencing sleep/wake cycles) and diurnal rhythm of eating (when and how often calories are consumed over a 24h period) on cardio-metabolic disorders. In women, one remarkable feature of the postpartum period is an 'externally imposed' circadian misalignment of both sleep and eating rhythms, because most babies take several weeks to months to establish their daily pattern of activity and feeding, which is particularly relevant for breastfeeding women, as the responsibility is generally on the mother.

The overarching goal of this project is to explore the interplay between the diurnal rhythm of eating, circadian and metabolic parameters in humans. The potential postpartum effects of circadian disruption will be unraveled in women who had GDM during their pregnancy and those with an uneventful pregnancy. These women are subject to a circadian misalignment due to their 'externally imposed' changes in sleep/wake cycles and eating times in the postpartum period.

With a comprehensive approach combining molecular characterization of in vivo and in vitro circadian clock parameters along with metabolic, endocrine, transcriptomic, and lipidomic studies, the investigators will assess if eating duration and/or circadian misalignment impact on circadian clock parameters of postpartum women in a prospective cohort of 6 months.

Inclusion Criteria:

• Age 18-40 years
• Breastfeeding mothers at 4-8 week postpartum
• With or without gestational diabetes mellitus diagnosed at 24-32 gestational weeks, according to the International Association of Diabetes and Pregnancy Study Groups (IADPSG) consensus criteria
• Confident use of a smartphone and able to take regular pictures of food/drinks

Exclusion Criteria:

• Pre-existing diabetes (prior to pregnancy)
• Major illness/fever over the 2 weeks (prior to the visits with blood tests)
• Shift work or work at irregular hours planned after maternity leave
• Active cancer and/or oncologic treatment over the previous 12 months
• Coagulation disorder, on regular anticoagulant drug, skin disorder affecting wound healing
• Enrolled in a clinical trial / intervention study
• Major known mental illness, unable to give informed consent
• Inability to follow the study procedures

Postpartum women followed at the Lausanne University Hospital (CHUV)