Gestational diabetes mellitus (GDM) is a common pregnancy complication characterized by impaired glucose metabolism and increased insulin resistance. GDM is associated with adverse pregnancy outcomes and an increased long-term risk of metabolic and cardiovascular disease for both mother and offspring.

This prospective observational cohort study aims to establish a longitudinal pregnancy and birth cohort of women diagnosed with GDM. Pregnant women with a positive 75 g oral glucose tolerance test (OGTT) between gestational weeks 24 and 28 will be recruited after diagnosis and followed through late pregnancy, delivery, and early postpartum.

Participants will undergo two study visits during pregnancy, sample collection at delivery, and one postpartum visit 8-12 weeks after birth. Clinical data, physical measurements, questionnaire-based information, and biological samples will be collected from mothers and infants to enable comprehensive phenotyping of GDM pregnancies.

Data and biosamples from this cohort will be used for descriptive and hypothesis-driven analyses and may be compared with data from an existing longitudinal cohort of healthy pregnancies to support interpretation of GDM-related changes.

Gestational diabetes mellitus (GDM) develops when physiological insulin resistance during pregnancy exceeds adaptive capacity, resulting in impaired glucose regulation. GDM is associated with increased perinatal morbidity and elevated long-term risk for metabolic and cardiovascular disease in both mothers and offspring. Despite its clinical relevance, the biological mechanisms underlying GDM and its long-term consequences are incompletely understood.

This prospective, monocentric observational cohort study is designed to establish a well-characterized longitudinal pregnancy and birth cohort of women diagnosed with GDM. The primary objective is to collect clinical data and biological samples across pregnancy, delivery, and early postpartum to support detailed phenotyping of GDM pregnancies and early-life outcomes.

Approximately 100 pregnant women with a confirmed diagnosis of GDM will be recruited per year at the Department of Obstetrics and Gynecology. Eligible participants are women aged 18 years or older with an ongoing pregnancy prior to gestational week 32 and a positive 75 g OGTT performed as part of routine clinical care. Women with major fetal anomalies are excluded.

Study participation includes four time points: 1.) a visit following GDM diagnosis (approximately gestational weeks 26-30), 2.) a late pregnancy visit (approximately weeks 34-37), 3.) sample and clinical data collection at delivery, and 4) a postpartum follow-up visit 8-12 weeks after birth.

At each study visit, standardized clinical assessments, physical measurements, and questionnaire-based information will be collected. Maternal assessments include anthropometry, body composition, blood pressure, and selected non-invasive cardiovascular and metabolic measurements. Fetal growth is assessed by routine obstetric ultrasound. At delivery, perinatal samples such as placenta, umbilical cord, and cord blood are collected. Postnatal assessments include maternal and infant anthropometry and selected cardiovascular measurements where applicable.

Biological samples collected longitudinally may include blood, urine, saliva, vaginal swabs, breast milk, placental tissue, umbilical cord tissue, and umbilical cord blood. Samples are processed and stored in a biobank for future analyses following separate ethical approvals. Clinical metadata include pregnancy outcomes, GDM treatment, delivery characteristics, and neonatal outcomes.

Lifestyle and behavioral factors, including nutrition and physical activity, are assessed using standardized questionnaires. Data are pseudonymized and handled in accordance with applicable data protection regulations.

This study is designed as a cohort and sample collection platform.

For contextual comparison, data and biosamples from an existing longitudinal cohort of healthy pregnancies will be used where appropriate. Alignment of visit timing and data collection procedures allows comparative analyses between GDM and normoglycemic pregnancies.

Inclusion Criteria:

• ongoing pregnancy prior to the 32nd gestational week and a positive GDM screening

Exclusion Criteria:

• gestational age 32nd gestational week
• fetal genetic anomalies /malformation

The study population consists of pregnant women diagnosed with gestational diabetes mellitus (GDM) based on a positive 75 g oral glucose tolerance test performed as part of routine clinical care between gestational weeks 24 and 28. Participants are recruited after diagnosis at a tertiary care obstetric center and followed through late pregnancy, delivery, and early postpartum.

Eligible participants are adults aged 18 years or older with an ongoing singleton pregnancy prior to gestational week 32. Women with major fetal anomalies are excluded. In addition, a non-pregnant reference cohort of healthy adult males and non-pregnant females may be recruited for selected analyses to provide pregnancy- and sex-independent reference data.