Results
The characteristics of the study samples are outlined in Table S1. Among
the immigrants, women from Central Europe, Eastern Europe and Central
Asia, comprised the largest group (n = 56,466), while those from
Latin America and Caribbean (n = 6,451) represented the smallest
group. Mean maternal age across groups ranged from 28.5 to 31.2 years.
Immigrant women born in sub-Saharan Africa had higher parity and, lower
education levels, but were less likely to be smokers. In contrast, women
from high income countries had the highest level of education.
Non-immigrant women were more likely to be smokers during pregnancy,
compared to all other groups.
The mean length of residence among immigrants ranged from 5.0 to 8.6
years. Close to 50% of the sub-Saharan immigrants were registered as
refugees, which is by far the highest among all the regions of birth.
More than 50% of the immigrant women born in countries defined ashigh-income were Nordic immigrants .
The overall incidence of placental abruption was 0.47%
for both immigrants and
non-immigrants. There was a significant decrease in placental abruption
for both groups over the study period. The decrease in immigrants was
from 0.68% to 0.44% while the decrease in non-immigrants was from
0.80% in 1990 to 0.34% in 2016, (Fig. S1).
Immigrant women born in the sub-Saharan African region had the highest
incidence of placental abruption (0.62%), while the lowest incidence
(0:39%) was found in immigrants from Central Europe, Eastern Europe or
Central Asia (Fig. 2; Table 1). When compared to non-immigrants, the
adjusted OR for placental abruption was 1.35 [95% CI: 1.15-1.58]
for women from sub-Saharan Africa and 1.05 [0.92-1.21] for women
from Central Europe, Eastern Europe or Central Asia (Table 1).
The adjusted ORs for placental abruption by maternal country of birth
relative to non-immigrant women is presented in Fig. 3. A strong
association was found for immigrant women born in Ethiopia (2.39
[1.67-3.41]). A higher OR was also found for Brazilian women (1.58
[0.95-2.63]), but the
confidence interval was wide.
Compared with non-immigrants, we found a weak association between length
of residence and placental abruption for immigrants with 1-4 years of
residence in Norway (1.13 [1.03-1.24]). There was also a slightly
higher OR for abruption for refugees (1.15 [0.99-1.33]).