Interpretation
Immigrant women born in Ethiopia had an increased incidence of placental
abruption compared with non-immigrants. Ethiopia is a large country with
several regions and different ethnic communities, and the incidence of
abruption is known to vary by region (21). The region an Ethiopian woman
comes from is not registered upon arrival in Norway and it is possible
that they are more likely to come from regions with a higher background
incidence of placental abruption. A higher abruption incidence may also
be attributed to nutritional factors. Immigrant women from Ethiopia
appears to have a higher prevalence of vitamin D deficiency (22) as well
as a lower prevalence of folic acid supplement use than other immigrants
(23). Both these factors have previously been linked to placental
vascular pathology (24-26).
Immigrant women from sub-Saharan Africa have been reported to receive
suboptimal healthcare during pregnancy compared with non-immigrants in
Norway (27). They also have a higher risk of several adverse outcomes in
pregnancy, including stillbirth (28), hypertension (29), pre-eclampsia
(29) and gestational diabetes (30). Chronic hypertension and
pre-eclampsia are well-known risk factors for placental abruption, and
an increased association also for placental abruption in immigrant women
from sub-Saharan Africa might therefore not be unexpected. Somewhat
surprisingly though, the OR was only moderately increased for this
group. Our finding is in contrast to previous studies from the United
States suggesting that black women have a substantially higher OR for
placental abruption compared to white women (12, 31). The discrepancy
between findings may however be due to methodological differences where
aggregation of women into even larger categories (black and white) may
result in different outcomes. Furthermore, our study focused on
1st generation immigrant women and not on race, which
further complicates comparison of study results. In addition, the
different composition of the immigrant population in Norway compared to
the United States and dissimilarity in various risk factors associated
with abruption may further explain the difference in ORs between
studies.
We found a slightly higher incidence of placental abruption in refugees.
Refugees comprise a vulnerable group, often with poor health and low
socioeconomic status (11) and are known to have an increased risk of
preterm pre-eclampsia (9) and preterm birth (32). When addressing the
different needs of immigrants we must recognize the complexity of
immigration (2). For some immigrants, strong health made migration
possible in the first place, yet others have been forced to flee from
war or natural disasters and may be of poorer health and with history of
trauma. The process of refuge may be stressful, and refugees are exposed
to various health risks and are generally in more vulnerable situations
(10). Maternal stress during pregnancy is a potential risk factor for
abruption (33) and the challenges faced by refugee women likely add
significant stress in the whole process of immigration. In addition,
refugees may face structural barriers with difficulties accessing
information and advice during pregnancy in the receiving country,
reducing the understanding of signs, symptoms and responses to pathology
(10).
Several risk factors for placental abruption seems to increase with
length of residence in the receiving country (34). For instance, a
previous Norwegian study found an increased incidence of pre-eclampsia
with increasing length of residence in immigrant women, particularly in
women arriving for family reunion or establishment (9). Moreover, a
Canadian study found that the risk of pre-eclampsia/eclampsia, placental
abruption and placental infarction was significantly reduced in
immigrant women with less than three months in Canada compared to those
with more than 5 years of residence (13), possibly due to an adoption of
a less healthy lifestyle after migration (13). These findings were not
confirmed in our study where we found only a weak association for
abruption in immigrants with 1-4 years of residence in Norway. These
difference in findings could be due to methodological differences as the
Canadian study presented only crude estimates with no adjustment for
covariates.
There has been a temporal decline in placental abruption for both
non-immigrants and immigrants over the last decades. In our study the
incidence of abruption was 0.47%, which is lower than in the USA and
Canada (1) but consistent with other Nordic countries (1, 35). In the
United States the abruption incidence has plateaued; (1) however, the
significant decline in abruptions in our study is also seen across many
European countries over the last decade (1, 35). The reason for this
decline may be attributable to a change in specific risk factors for
abruption, like smoking. Compared to the host population, immigrants are
less likely to smoke and in Norway smoking habits have declined
significantly in recent times in both non-immigrants and immigrants
(36). In Sweden and the United States a change in smoking habits was
associated with a decline in abruption risk (1), and this may also
partly explain the decrease in abruptions in Norway.