Residential Mobility During Pregnancy in the North of England

Abstract

Background: Many epidemiological studies assign exposure to an individual's residence at a single time point, such as birth or death. This approach makes no allowance for migration and may result in exposure error, leading to reduced study power and biased risk estimates. Pregnancy outcomes are less susceptible to this bias, however data from North American populations indicate that pregnant women are a highly mobile group. We assessed mobility in pregnant women in the north of England using data from the Northern Congenital Abnormality Survey (NorCAS).

Effects of Ambient Air Pollution on Birth Outcomes: An Overview

“…Chen et al (2010) in New York demonstrated that the poor mobility is not able to cause misclassification. Similar results were obtained by other authors in Texas, Northern England, and Georgia (Hodgson et al, 2009;Lupo et al, 2010;Miller et al, 2009). Different conclusions were reached in another study carried out in Texas (Canfield et al, 2006) hypothesizing an important role of the residential mobility in the misclassification of the pregnant women.…”

“…As far as concerns this last issue, it is enough to say that the reviewed data derive from very different countries such as the Czech Republic (Bobak, 2000;Bobak and Leon, 1999;Dejmek et al, 2000), Poland (Edwards et al, 2010), England (Dolk et al, 2010;Lee et al, 2008;Rankin et al, 2009), Spain Llop et al, 2010), Sweden (Landgren, 1996), Norway (Madsen et al, 2010), Holland , China (Jiang et al, 2007;Wang et al, 1997), the United States (Bell et al, 2007;Gray et al, 2009;Maisonet et al, 2001;Morello-Frosch et al, 2010;Parker et al, 2005;Rogers and Dunlop, 2006;Salam et al, 2005;Wilhelm and Ritz, 2005;Xu et al, 2010), South Korea (Ha et al, 2001;Lee et al, 2003;Seo et al, 2010), Taiwan (Lin et al, 2004;Yang et al, 2003), Canada Dugandzic et al, 2006;Liu et al, 2003), Brazil (Gouveia et al, 2004;Nascimento and Moreira, 2009;Pereira et al, 1998), and Australia (Hansen et al, 2009;Hansen et al, 2007;Mannes et al, 2005). In addition, other sources of bias can be represented by the residential mobility of the pregnant women (Canfield et al, 2006), although some studies minimize or even exclude this issue (Hodgson et al, 2009;Lupo et al, 2010;…”

Exposure misclassification due to residential mobility during pregnancy

“…In addition, women who moved were younger, more often nullparious and of non-western ethnicity, had lower education, and their offspring had on average 47.5 g lower mean birth weight compared to those women who did not move during pregnancy (Madsen et al, 2010) suggesting the possibility of differential exposure error. In the NorCAS cohort, women who moved during pregnancy also tended to be younger and live in more socio-economically deprived areas (Hodgson et al, 2009) in keeping with findings from other populations (Bell and Belanger, 2012), and, as shown here, movers also tend to live near a higher density of roads and in areas with higher levels of air pollution. These women tend to have lower exposure at delivery than at conception.…”

“…While our previous study showed that movers in this cohort tended to be younger and to live in more deprived areas (Hodgson et al, 2009), independent sample t-tests show that, at conception, movers tend to live in more deprived, urban areas, near to a greater density of roads, and with lower air quality (as measured by PM10 and NO 2 ) (Table 3).…”

“…The relatively short period between exposure and disease manifestation should mean that studies on congenital anomalies are less prone to migration bias, as there is less time in which the population can migrate. However, there is now a significant body of literature showing that pregnant women are a highly mobile group, with 10-30% of women moving residence during pregnancy (Bell and Belanger, 2012;Canfield et al, 2006;Fell et al, 2004;Hodgson et al, 2009;Khoury et al, 1988;Shaw and Malcoe, 1992;Zender et al, 2001).…”