Title Travel patterns during pregnancy : comparison between Global Positioning System ( GPS ) tracking and questionnaire data Permalink

Background: Maternal exposures to traffic-related air pollution have been associated with adverse pregnancy outcomes. Exposures to traffic-related air pollutants are strongly influenced by time spent near traffic. However, little is known about women’s travel activities during pregnancy and whether questionnaire-based data can provide reliable information on travel patterns during pregnancy. Objectives: Examine women’s in-vehicle travel behavior during pregnancy and examine the difference in travel data collected by questionnaire and global positioning system (GPS) and their potential for exposure error. Methods: We measured work-related travel patterns in 56 pregnant women using a questionnaire and one-week GPS tracking three times during pregnancy (<20 weeks, 20–30 weeks, and >30 weeks of gestation). We compared self-reported activities with GPS-derived trip distance and duration, and examined potentially influential factors that may contribute to differences. We also described in-vehicle travel behavior by pregnancy periods and influences of demographic and personal factors on daily travel times. Finally, we estimated personal exposure to particle-bound polycyclic aromatic hydrocarbon (PB-PAH) and examined the magnitude of exposure misclassification using self-reported vs. GPS travel data. Results: Subjects overestimated both trip duration and trip distance compared to the GPS data. We observed moderately high correlations between self-reported and GPS-recorded travel distance (home to work trips: r = 0.88; work to home trips: r = 0.80). Better agreement was observed between the GPS and the self-reported travel time for home to work trips (r = 0.77) than work to home trips (r = 0.64). The subjects on average spent 69 and 93 minutes traveling in vehicles daily based on the GPS and self-reported data, respectively. Longer daily travel time was observed among participants in early pregnancy, and during certain pregnancy periods in women with higher education attainment, higher income, and no children. When comparing self-reported vs. GPS data, we found that estimated personal exposure to PB-PAH did not differ remarkably at the population level, but the difference was large at an individual level. Conclusion: Self-reported home-to-work data overestimated both trip duration and trip distance compared to GPS data. Significant differences in PAH exposure estimates were observed at individual level using self-reported vs. GPS data, which has important implications in air pollution epidemiological studies. * Correspondence: junwu@uci.edu Program in Public Health, College of Health Sciences, University of California, Irvine, CA, USA Department of Epidemiology, School of Medicine, University of California, Irvine, CA, USA Full list of author information is available at the end of the article © 2013 Wu et al.; licensee BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Wu et al. Environmental Health 2013, 12:86 Page 2 of 12 http://www.ehjournal. net/content/12/1/86 Background There is a growing concern about the health impact of traffic-related air pollution on pregnancy outcomes [1-4]. Living close to freeways or high-traffic density areas have been associated with spontaneous abortion, pregnancy hypertension, preterm birth, and term low birth weight [5-8]. Several recent studies further reported that maternal exposure to traffic-related air pollutants is associated with risk of preeclampsia, reduced fetal growth, preterm birth, small for gestational age, and term low birth weight [2,9-11]. Exposures to traffic-related pollutants are strongly influenced by time spent near traffic emission sources (e.g. in-vehicle travel and walking). Concentrations of ultrafine particles and volatile organic compounds can be up to ten times higher in vehicles than in ambient outdoor environments [12-16]. It has been estimated that around 33-45% of ultrafine particles and 30-55% of black carbon exposure for nonsmoking urbanites in Los Angeles comes from time in vehicles [15,17]. We conducted a personal exposure measurement study and reported that in-vehicle travel time explained approximately 40% of the variance in daily personal exposure to particle-bound polycyclic aromatic hydrocarbon [18]. However, only two studies in Southern California specifically examined exposure to traffic-related air pollutants from time in transit in relation to health outcomes [19,20]. Ritz and Yu (1999) found higher risk of term low birth weight for women who commuted more than 60 minutes to work using a census-based measure of commuting level (although no individual data were available and no dose–response relation was reported). McConnell et al. (2010) reported the risk of severe wheeze was associated with commuting time in asthmatic children; the association was stronger in analysis restricted to children with commuting times 5 minutes or longer. Because of the potentially high air pollutant exposures in transit environments, it is essential to understand pregnant women’s travel behaviors for more accurate exposure assessment. However, few time-activity studies have focused on pregnant women, and little is known about travel behavior during pregnancy. The National Human Activity Patterns Survey (NHAPS) (the largest time-activity study in the U.S.) collected over 9,300 time-activity surveys but did not address pregnancy status [21]. A number of other studies have examined exercise and physical activities of pregnant women [22-25], but with no focus on time in traffic. A Canadian study examined the change in location-based activity patterns during pregnancy, but it relied on a self-reported time-activity log and focused on time spent at home rather than in transit [26]. Conventional methods for time-location collections (e.g. self-reported paper diary and telephone interview) have several major limitations, including omission of short trips and inaccurate reporting of trip duration [27,28]. Global positioning system (GPS) techniques have been increasingly used to track people’s time-location or commuting patterns [29-34]. GPS tracking has the advantages of continuous recording, high temporal resolution, and minimum reporting burden for participants [35]. However, sometimes GPS tracking is not an option in many epidemiological studies due to concerns about the protection of confidentiality in human subjects, cost considerations, or the study design (e.g. retrospective studies and interest in long-term exposures). Under such conditions, epidemiological studies have to rely on questionnaires to obtain time-activity data. Little information is available in the literature on how questionnaire and GPS tracking compare with each other in data quality. In addition, few epidemiological studies have effectively used GPS data for time-activity pattern classification, likely due to issues including the quality of GPS data, the compliance of human subjects, and the lack of reliable methods to mine raw GPS data [36]. The objectives of this paper are to examine the invehicle work-related travel behavior of pregnant women at different stages of pregnancy (<20 weeks, 20–30 weeks, and >30 weeks of gestation), examine the difference in travel time collected by two instruments (i.e. questionnaire and GPS tracking), investigate influential factors contributing to the difference of travel time, and examine potential exposure error in estimating personal particle-bound polycyclic aromatic hydrocarbon (PB-PAH) using the two instruments collecting travel data. PAH has been linked to adverse health effects, including adverse birth outcomes [37] and allergy and asthma in children [38].