Gestational Diabetes Among Immigrant Women

To the Editor: Gestational diabetes mellitus is more common among certain non-White ethnic groups1; however, classifying these women as “African American,” “Asian,” or “Hispanic”2 fails to appreciate the broader ethnic fabric of many countries. We compared the risk of gestational diabetes mellitus among diverse groups of women who had immigrated to Canada compared with Canadian-born women. Using the federal Landed Immigrant Data System database, we identified a population-based cohort of women who were new immigrants to Ontario between 1985 and 2000. This data source has records for every permanent legal immigrant to Canada who arrived after 1984. As described elsewhere,3 these data have been linked to the Canadian Institute for Health Information Discharge Abstracts Database, thereby capturing all subsequent delivery hospitalizations in Ontario between 1 April 2002 and 31 March 2009. A diagnosis of gestational diabetes mellitus was captured at the time of any live birth or stillbirth delivery, based on an ICD-10-CA code for gestational diabetes mellitus, while excluding those with an ICD-10-CA diagnosis of prepregnancy diabetes. The rate and odds ratio (OR) of gestational diabetes mellitus were determined according to maternal World region of birth (www.unicef.org/infobycountry/index.html). ORs were adjusted for variables listed in the footnote of the Table. A woman could contribute more than one delivery to the dataset. The study was approved by the Ethics Review Board of Sunnybrook and Women's College Health Sciences Centre.Table: Risk of Gestational Diabetes Mellitus in Association With Maternal Place of BirthAmong 792,314 delivery records, 21,439 (3%) had missing or invalid information, leaving a final sample of 770,875 consecutive deliveries, including 118,849 deliveries (15%) among immigrant women (eAppendix, https://links.lww.com/EDE/A515). The overall risk of gestational diabetes mellitus varied by a woman's region of birth (Table). The risk was more than double among women from the Caribbean and East Asia/Pacific regions, and almost quadrupled among those from South Asia (Table). Among women without a prior live birth, these effect sizes were either unchanged or higher (data not shown). Although our dataset represents nearly all women who immigrated to Ontario, the period of immigration was only up to year 2000, and those arriving thereafter are not included in this study. Although we could not determine the ethnicity of Canadian-born women, we could infer the ethnicity of immigrants using world region of birth as a proxy. Comparing immigrant groups better deals with the potentially difficult-to-measure interaction among the healthy immigrant effect, ethnicity, and risk of gestational diabetes mellitus. Although we adjusted for some relevant covariates, information on maternal weight, dietary history, and a prior history of gestational diabetes mellitus was not available. It is noteworthy that women from South Asia, East Asia, and the Pacific (who together represented 44% of all deliveries among immigrants), all have high, but different, risk of gestational diabetes mellitus. This underscores the inadequacy of the general term, “Asian”; more specific descriptors should be used. In addition, the healthy immigrant effect does not appear to be protective against gestational diabetes mellitus, compared with native-born women. Maternal region of origin may help identify those immigrant women at highest risk in early pregnancy for developing gestational diabetes mellitus.4 Initiation of dietary and activity modification in early pregnancy is now being studied among high-risk women to prevent the onset of this condition.5 Finally, our data might aid in optimizing postpartum screening for type 2 diabetes, because gestational diabetes mellitus is a recognized long-term risk factor for type 2 diabetes, but most women do not develop the condition for many years or at all.6 Marcelo Urquia Centre for Research on Inner City Health St. Michael's Hospital Institute for Clinical Evaluative Sciences Toronto, ON Richard H. Glazier Institute for Clinical Evaluative Sciences Centre for Research on Inner City Health Department of Family and Community Medicine St. Michael's Hospital, University of Toronto Toronto, ON, Canada Howard Berger Department of Obstetrics and Gynecology St. Michael's Hospital University of Toronto Toronto, ON, Canada Ivan Ying Department of Medicine Schulich School of Medicine and Dentistry London, ON, Canada Leanne De Souza Department of Obstetrics and Gynecology St. Michael's Hospital University of Toronto Toronto, ON, Canada Joel G. Ray Departments of Medicine and of Obstetrics and Gynecology St. Michael's Hospital Institute for Clinical Evaluative Sciences University of Toronto Toronto, ON, Canada [email protected]