(1) Background: Pregnancy presents a challenge to maternal glucose homeostasis; suboptimal adaptations can lead to gestational diabetes mellitus (GDM). Human milk oligosaccharides (HMOs) circulate in maternal blood in pregnancy and are altered with GDM, suggesting influence of glucose homeostasis on HMOs. We thus assessed the HMO response to glucose load during an oral glucose tolerance test (OGTT) and investigated HMO associations with glucose tolerance/insulin sensitivity in healthy pregnant women. (2) Methods: Serum of 99 women, collected at 0 h, 1 h and 2 h during a 75 g OGTT at 24–28 gestational weeks was analyzed for HMOs (2′FL, 3′SLN, LDFT, 3′SL) by HPLC; plasma glucose, insulin and C-peptide were analyzed by standard biochemistry methods. (3) Results: Serum 3′SL concentrations significantly increased from fasting to 1 h after glucose load, while concentrations of the other HMOs were unaltered. Higher 3′SL at all OGTT time points was associated with a generally more diabetogenic profile, with higher hepatic insulin resistance (HOMA-IR), lower insulin sensitivity (Matsuda index) and higher insulin secretion (C-peptide index 1). (4) Conclusions: Rapid increase in serum 3′SL post-oral glucose load (fasted-fed transition) indicates utilization of plasma glucose, potentially for sialylation of lactose. Associations of sialylated HMOs with a more diabetogenic profile suggest sustained adaptations to impaired glucose homeostasis in pregnancy. Underlying mechanisms or potential consequences of observed HMO changes remain to be elucidated.

Endothelial colony forming cells (ECFCs) are circulating progenitor cells essential for angiogenesis and vascular remodelling in pregnancy. ECFC numbers and outgrowth are often reduced with metabolic diseases and conditions associated with disturbed endothelial function. However, how pregnancy, a period of metabolic stress, affects ECFCs remains unclear. We isolated ECFCs from non‐pregnant women (NP, N = 28) and from women in early (EP, N = 23) and late (LP, N = 39) pregnancy using density gradient centrifugation. ECFC outgrowth was analysed in relation to markers of lipid and glucose metabolism (cholesterol, triglycerides, high‐density lipoprotein‐cholesterol, low‐density lipoprotein‐cholesterol, fasting glucose), endothelial function (interleukin‐6, E‐selectin, P‐selectin, intracellular adhesion molecule 1, vascular cell adhesion molecule 1, asymmetric dimethylarginine) and body composition (body mass index, body fat). ECFC morphology was microscopically assessed and scored from cobblestone‐like to spindle‐shaped. We found that ECFC outgrowth rate was higher in LP (60.9%) compared to EP (40.4%) and NP (49.1%). ECFC colony number and expansion rate were higher in LP than in EP and NP. ECFCs from NP donors had a more elongated morphology than ECFCs from pregnant donors. In EP, ECFCs predominantly derived from pregnancies with female fetuses, whereas the opposite was observed in LP. Higher interleukin‐6 and E‐selectin plasma levels, indicative of an inflammatory state, were associated with faster outgrowth, along with increased lipid levels. Gestational diabetes was associated with increased ECFC colony number compared to healthy pregnancy. These findings suggest that pregnancy alters ECFC characteristics, with late pregnancy marked by enhanced ECFC outgrowth and expansion, potentially reflecting vascular adaptation to metabolic and inflammatory changes. Our results underscore the potential role of ECFCs in maternal vascular health in pregnancy. image Key points: Pregnancy requires extensive vascular remodelling. Circulating endothelial progenitor cells are crucial for angiogenesis and vascular adaptations. In this study, we investigated the outgrowth of circulating endothelial colony forming cells from peripheral blood of non‐pregnant women, and of women in early and late pregnancy. We further correlated the outgrowth parameters with blood markers of endothelial function and with metabolic state. Our findings indicate that the outgrowth capacity of these cells is highest in late pregnancy and depends on fetal sex. Pregnancy‐induced markers of endothelial activation such as interleukin‐6 and E‐selectin, as well as markers of metabolism such as cholesterol and triglycerides, affect the outgrowth of endothelial colony forming cells. This study highlights the dynamic changes in endothelial colony forming cell abundance and morphology across different stages of pregnancy and their association with maternal metabolism and inflammation.