Study examines gestational diabetes in American Samoan women

In a study conducted by the Yale School of Public Health (YSPH), researchers are looking at gestational diabetes among pregnant women in American Samoa, which has unusually high risks for developing the condition. The study, Gestational Diabetes - Risk Factors and Outcomes among American Samoan Women (GROW), is the first long-term, population-specific investigation into why so many Pacific Islander women develop gestational diabetes, and why some progress rapidly to type 2 diabetes after giving birth. The protocol for the GROW study was recently published as a preprint in medRxiv.

“We are anticipating that the results of this study will be useful in a number of ways. We are expecting to find early biological and behavioral indicators of risk in this understudied population,” said Dr. Nicola Hawley, PhD, associate professor of epidemiology (chronic diseases), who is leading GROW. “A better understanding of who is at risk based on very early pregnancy data will help us direct preventative resources to those who need them most.”

Gestational diabetes mellitus (GDM) is a type of diabetes that has its onset in pregnancy. The condition increases the risk of complications during pregnancy, birth, and long term, with women with GDM having significantly heightened risk of developing type 2 diabetes later in life. During a normal pregnancy, women can expect an increase in blood sugar to support the growth of the baby. Usually, the body will compensate by producing more insulin, the hormone that controls blood sugar.

For some women, particularly those who already have some risk for type 2 diabetes, GDM happens when their bodies can't keep up with that growing demand for insulin and their blood sugar increases. General risk factors include age, family history, obesity, and high blood pressure. But some populations, including Pacific Islanders, have much higher risk. According to Hawley, evidence from some of her earlier work showed that the prevalence of GDM may be as high as 40% among women in American Samoa versus only around 9% among women in the U.S. in general.

Despite the high burden of disease, the underlying causes of GDM in Pacific Islanders remain poorly understood. GROW aims to change that. With investigators at the University of Pittsburgh, Emory University, and the Obesity, Lifestyle and Genetic Adaptations (OLaGA) Research Center in American Samoa, Hawley and her team are enrolling 350 Samoan women early in pregnancy and following them for 18 months postpartum. Using state-of-the-art tools, including continuous glucose monitoring, advanced oral glucose tolerance testing, and genetic analysis, the team will examine how women’s bodies manage glucose before, during, and after pregnancy.

A central focus is a variant in the CREBRF gene (rs373863828), carried by around 40% of Samoans. The variant is associated with higher body weight but surprisingly lower risk of type 2 diabetes. Early evidence suggests it may even protect against gestational diabetes. The GROW Study will be the first to investigate, in depth, how this unique gene variant influences insulin production, glucose levels, and diabetes risk during pregnancy—a period researchers are calling a “natural stress test” for the body’s metabolic system.

By pairing high-quality metabolic data with postpartum follow-up, the study will also examine who goes on to develop pre-diabetes or type 2 diabetes and why. Findings may guide new clinical guidelines, community-based diabetes prevention programs, and even precision-medicine approaches tailored to Pacific Islander populations. "We may also learn something about the best timing for screening in this population. Usually, screening happens in mid-pregnancy, between 24- and 28-weeks' gestation, and it may need to be earlier among this group,” Hawley said.

They are hopeful that their findings will lead to a better future for screening recommendations and treatment.

The use of novel methods in a low-resource setting hasn’t been without challenges. The warm and humid climes of American Samoa have caused early problems with continuous glucose monitoring, specifically the adhesives used to hold the monitors on the arm for the needed 10-day wear period. Solving the problem has led to a new partnership with Australian company Not Just a Patch, who are now supporting the study with waterproof patches that support the sensors.

“We were lucky to connect with the CEO of Not Just a Patch, who has a wealth of personal experience with type 1 diabetes,” Hawley said. “They have offered incredible guidance and in return—since these devices are very new to American Samoa—we hope we will be able to generate some good data for them as they expand their markets to similar places and climates.”