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World region specific birth-weight curves better than Canadian curves for assessing risk of adverse events in newborns of immigrant mothers

Clinicians working with immigrant mothers and their babies may find that using birth-weight curves for specific regions based on the mother’s birth country rather than Canadian curves are a more accurate predictor of risk of adverse events after birth, according to a large study published in CMAJ (Canadian Medical Association Journal).

“Potentially misclassifying the physiologically small, but healthy, newborn as small for gestational age may lead to unnecessary interventions and undue parental stress,” states lead author Dr. Marcelo Urquia, Centre for Research on Inner City Health, Li Ka Shing Knowledge Institute, St. Michael’s Hospital, and the Institute for Clinical Evaluative Sciences, Toronto, Ontario.

The birth weight of babies born to immigrant mothers, especially East and South Asian mothers, is often lower than that of babies whose mothers were born in Canada. This lower birth weight, however, does not necessarily translate into adverse outcomes.

The large study included 1 089 647 singleton births over 10 years in Ontario between April 2002 and March 2012. About one-third of babies (328 387) were born to immigrant mothers, of whom more than half (53.6%) were of East and South Asian birth. The remaining 761 260 infants were born to nonimmigrant mothers. About 10% (33 780) of infants born to immigrant mothers were classified as small for gestational age on both scales. These babies were more likely to die or suffer adverse events than heavier infants.

About 6% additional infants born to immigrant mothers were classified as small for gestational age on the Canadian birth-weight curve but not on the curve for the mother’s country of origin.

Compared with newborns of Canadian-born mothers, newborns of immigrant mothers classified as small for gestational age on the Canadian curve had lower odds of adverse events such as a lengthy hospital stay or death, but babies classified as small on the world-region specific curves were more likely to die or suffer adverse events.

Approximately 5% of babies to immigrant mothers were deemed large for gestational age on both curves, and about 4% were classified as large on only the world-region specific curves. The deliveries of babies missed by the Canadian curve also had complications associated with large babies, such as perineal tears, shoulder dystocia and postpartum hemorrhage.

“World region-specific birth-weight curves seemed to be more appropriate than a single Canadian population-based curve for assessing the risk of adverse neonatal and obstetric outcomes among small- and large-for-gestational-age infants born to immigrant women. This was especially evident among infants whose mothers were from world regions where the birth-weight distribution differed markedly from that of the Canadian-born population, such as East and South Asian immigrants, who accounted for more than half of the births of immigrants in the study,” write the authors.

“Estimating the number of newborns who may be spared unnecessary prolonged stay in hospital, special care, or referral for specialized pediatric or nutritional interventions, and the cost savings therein, is a worthwhile step in evaluating the impact of applying world region-specific curves in certain immigrant populations.”


Risk of adverse outcomes among infants of immigrant women according to birth-weight curves tailored to maternal world region of origin, Marcelo L. Urquia PhD MSc , Howard Berger MD, Joel G. Ray MD MSc; for the Canadian Curves Consortium, CMAJ, DOI:10.1503 /cmaj.140748, published 10 November 2014.