Risk factors for spontaneous preterm birth among aboriginal and non-aboriginal women in Manitoba

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Heaman, Maureen Isabella
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In the province of Manitoba, the incidence of preterm birth (PTB) has been increasing and is about 17% higher among Aboriginal than non-Aboriginal women. The purpose of this study was to identify risk factors for spontaneous PTB in Manitoba women, and to compare risk factors among Aboriginal and non-Aboriginal women. A case-control study was conducted at two tertiary care hospitals in Winnipeg, Manitoba. Cases were women who delivered a live singleton infant at less than 37 weeks gestation following spontaneous labor, while controls delivered between 37 and 42 weeks gestation. A ratio of two controls per every case was used, and stratified sampling by race was employed. An interview was conducted with each subject on the postpartum unit and information was collected from the health record. Data were analyzed using SPSS and SAS. There were 226 cases (36% Aboriginal) and 458 controls (38% Aboriginal). Using stratified analyses, adjusted odds ratios (AOR) and 95% confidence intervals were calculated. Significant risk factors for PTB across both strata, after controlling for race, included: previous PTB, two or more previous spontaneous abortions, hospitalization during pregnancy, gestational hypertension, vaginal bleeding after 12 weeks gestation, smoking in the month prior to pregnancy, short stature, low total weight gain during pregnancy (less than 20 pounds), and inadequate prenatal care. Risk factors for non-Aboriginal women included abuse during pregnancy, low support from others, low self-esteem, rupture of membranes (ROM) before labor, and moving two or more times in the last year. Risk factors for Aboriginal women included ROM before labor, high perceived stress, and anemia, while age less than 19 years and single marital status were protective factors. After adjusting for other factors in a multiple logistic regression model, significant modifiable risk factors included smoking prior to pregnancy (AOR 1.69), low weight gain (AOR 3.41), and inadequate prenatal care (AOR 3.36). The population attributable risk was 24.5% for smoking prior to pregnancy, 22.3% for low weight gain, and 15.9% for inadequate prenatal care. This study identified some modifiable risk factors for PTB which can be targeted for public health inte ventions, and contributed to our understanding of differences in risk factors among Aboriginal and non-Aboriginal women.