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Results of the Recent Immigrant Pregnancy and Perinatal Long-term Evaluation Study (RIPPLES)

From the Departments of Medicine (Ray), Obstetrics and Gynecology (Ray, Shah), and Health Policy Management and Evaluation (Ray), St. Michael's Hospital and University of Toronto; the Institute for Clinical Evaluative Sciences, University of Toronto (Vermeulen, Schull, Redelmeier); the Division of Emergency Medicine (Schull), the Department of Medicine (Redelmeier) and the Department of Health Policy Management and Evaluation (Schull, Redelmeier), Sunnybrook Health Sciences Centre; and the Centre for Research on Inner City Health, St. Michael's Hospital (Singh), Toronto, Ont.

Correspondence to: Dr. Joel G. Ray, Department of Medicine, St. Michael's Hospital, 30 Bond St., Toronto ON M5B 1W8; fax 416 864-5485; rayj{at}smh.toronto.on.ca

Background: People who immigrate to Western nations may experience fewer chronic health problems than original residents of those countries, which raises concerns about long-term environmental or lifestyle factors in those countries. We tested whether the "healthy immigrant effect" extends to the risk of placental dysfunction during the short interval of pregnancy.

Methods: We conducted a population-based retrospective cohort study of data for 796 105 women who had a first documented obstetric delivery in Ontario between 1995 and 2005. Recency of immigration was determined for each woman as the time from her enrolment in universal health insurance to her date of delivery, classified as less than 3 months, 3–5 months, 6–11 months, 12–23 months, 24–35 months, 36–47 months, 48–59 months and 5 years or more (the referent). The primary composite outcome was maternal placental syndrome (defined as a diagnosis of pre-eclampsia or eclampsia, placental abruption or placental infarction).

Results: The mean age of the women was 28.8 years. Maternal placental syndrome occurred in 45 216 women (5.7%). The risk of this outcome was lowest among the women who had immigrated less than 3 months before delivery (3.8%) and highest among those living in Ontario at least 5 years (6.0%), for a crude odds ratio (OR) of 0.62 (95% confidence interval [CI] 0.54–0.71). After adjustment for maternal age, income status, pre-existing hypertension, diabetes mellitus, multiple gestation and receipt of prenatal ultrasonography, the risk of maternal placental syndrome was correlated with the number of months since immigration in a gradient manner (OR, 95% CI): less than 3 months (0.53, 0.47–0.61), 3–5 months (0.68, 0.61–0.76), 6–11 months (0.67, 0.63–0.71), 12–23 months (0.69, 0.66–0.73), 24–35 months (0.75, 0.70–0.79), 36–47 months (0.75, 0.70–0.80) and 48–59 months (0.82, 0.77–0.87).

Interpretation: There was a progressively lower risk of maternal placental syndromes associated with recency of immigration. The "healthy immigrant effect" may extend to common placental disorders, diminishes with the duration of residency and underscores the importance of nongenetic determinants of maternal health accrued over a brief period.

This article has been cited by other articles:

				B. Gushulak Healthier on arrival? Further insight into the "healthy immigrant effect" Can. Med. Assoc. J., May 8, 2007; 176(10): 1439 - 1440. [Full Text] [PDF]

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