MAGIC (maternal glucose in pregnancy) understanding the glycemic profile of pregnancy, intensive CGM glucose profiling and its relationship to fetal growth: an observational study protocol.

Background: Continuous glucose monitoring (CGM) provides the most objective method of assessing glucose in daily life. Although there have been small, short-term physiologic studies of glucose metabolism in 'healthy' pregnant women a comprehensive, longitudinal description of changes in glucose over the course of pregnancy and how glucose dysregulation earlier in pregnancy relates to traditional third trimester screening for gestational diabetes, fetal growth and pregnancy outcomes is lacking. This study aims to characterise longitudinal changes in glycemia across gestation using CGM, in order to understand the evolution of dysglycemia and its relationship to fetal growth.

Method/design: A multi-centre, prospective, observational, cohort study of 500 healthy pregnant women, recruited in the first trimester of pregnancy. Masked CGM will be performed for a 14-day period on five occasions across pregnancy at ~ 10-12, 18-20, 26-28, 34-36 weeks gestation and postnatally. Routinely collected anthropometric and sociodemographic information will be recorded at each visit including: weight, height, blood pressure, current medication. Age, parity, ethnicity, smoking will be recorded. Blood samples will be taken at each visit for HbA1c and a sample stored. Details on fetal growth from ultrasound scans and the OGTT results will be recorded. Maternal and neonatal outcomes will be collected. CGM glucose profiling is the exposure of interest, and will be performed using standard summary statistics, functional data analysis and glucotyping. The primary maternal outcome is clinical diagnosis of GDM. The primary neonatal outcome is large for gestational age (LGA) (> 90th centile defined by customised birthweight centile). The relationship of glucose to key secondary maternal and neonatal outcomes will be explored.

Discussion: This study will ascertain the relationship of maternal dysglycemia to fetal growth and outcomes. It will explore whether CGM glucose profiling can detect GDM before the OGTT; or indeed whether CGM glucose profiling may be more useful than the OGTT at detecting LGA and other perinatal outcomes.

Trial Registration: ISRCTN 15,706,303 https://www.isrctn.com/ISRCTN15706303 Registration date: 13th March 2023.