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In this prospective cohort of pregnant Latina women, we found that time spent TV watching and frequency of sitting at work were not associated with risk of AGT and GDM. We also found that low levels of sports and exercise and a composite measure of high levels of total sedentary behavior in mid pregnancy were associated with abnormal glucose tolerance, but this finding was based on small numbers of AGT cases and must be interpreted with caution. Despite these limitations, this is the first study to investigate sedentary behaviors at multiple time points in relation to risk of AGT and GDM in a pregnant Latina population, an ethnic group at higher risk for glucose abnormalities both during and outside of pregnancy as compared to non-Latina white women.

2.7.1 Comparison with Prior Literature

Only two prior studies have examined perinatal sedentary behaviors in relation to risk of AGT or GDM. In the first study by Oken et al., the authors investigated both time spent TV

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watching and physical activity independently in relation to risk of AGT and GDM among 1600 predominantly white (80%) women (63). The authors found that TV watching in pregnancy (2+ hrs/day vs. <2 hrs/day) was not associated with AGT (OR=1.0, 95% CI 0.6-1.8) or GDM (OR=1.0, 95% CI 0.8-1.4). Similarly, we found no association between TV watching before or during pregnancy and risk of AGT (early pregnancy: OR= 0.9, 95% CI 0.5, 1.7) or GDM

(OR=1.25, 95% CI 0.4-3.9). Oken et al. also observed a reduced risk of GDM (OR=0.6, 95% CI 0.3-0.9) and AGT (OR=0.8, 95% CI 0.6-1.0) associated with any vigorous activity before pregnancy, though the association was weaker during pregnancy (GDM: OR= 0.9, 95% CI 0.5- 1.7; AGT: OR=0.7, 95% CI 0.5-1.0). Similarly, we observed an increased risk of AGT for those in the lowest quartile of sports and exercise as compared to those in the highest quartile in mid pregnancy (OR=2.0, 95% CI 1.0-4.0),but not in pre (OR= 1.0, 95% CI 0.5, 2.0) or early pregnancy (OR= 1.2, 95% CI 0.6-2.2) and in mid pregnancy for GDM (OR= 5.8, 95% CI 1.1- 30.8).

In the second prospective cohort study examining pre-pregnancy sedentary behaviors and risk of GDM among 21,765 predominantly white nurses, Zhang et al. found an increased risk for GDM associated with high levels of TV watching during the year prior to pregnancy (≥20 hrs/week vs. <1 hr/week: RR= 1.7, 95% CI 1.3-2.3) (89). Although we did not find an

independent effect of TV watching on GDM or AGT in pre, early or mid pregnancy, we did find that low sports/exercise and high total sedentary behavior in mid pregnancy was associated with AGT and GDM. As in the current study, Zhang et al. analyzed the joint effect of time spent TV watching and in physical activity on GDM risk. They observed a further increased risk (RR= 2.3, 95% CI 1.1-5.0) for those who watched ≥20 hrs/week of TV and did not perform vigorous

physical activity as compared to those who watched <2 hrs/week of TV and were in the highest quintile of physical activity. Similarly, we found that women in the highest tertile for total sedentary score (Composite II) compared to the lowest tertile in mid pregnancy had an increased OR for AGT (OR=11.8, 95% CI 2.25-61.86, Ptrend = 0.002) and GDM (Ptrend = 0.048). However, we had limited statistical power to detect a similar association using GDM as the outcome.

Differences in findings for the relation between TV watching and risk of AGT/GDM between the current study and those of the prior literature may be due to a number of different factors. The participants in the current study reported TV watching with less overall variability than in previous studies, thus limiting the contrast between comparison groups. For example, the majority (60%) of women in our sample reported watching 2+ hours of TV per day in early pregnancy suggesting that our population may be overall more sedentary than those of others. Though the distribution of TV watching was not reported by Zhang et al., Oken et al. reported that 34% of their pregnant population watched 2+ hours of TV/day. Moreover, the nurses in the study by Zhang et al. may be more physically active than our population, as Latina women tend to be less active than non-Latina white women (131, 132). Furthermore, the nurses were not pregnant during physical activity assessment, and their total activity score assessed a broader range of activities (a total of 9 aerobic activities) providing a higher range of total activity scores (89). Furthermore, 6.5% of women in the nurses’ cohort and 5% in Oken et al. developed GDM, compared to 3.3% in the current study, thus limiting statistical power in our sample. Finally, substantial differences in population characteristics exist between the current study and that of Zhang et al., such as ethnicity (100% Latina vs. 92% white), education (70% less than High

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School vs. 100% professional nursing degree), and age (mean age =24 years vs. mean age=30 years) that may have contributed to differences in findings.

Several studies have found an increased risk for abnormal glucose metabolism and type II diabetes associated with high levels of TV watching in non-pregnant populations (96-98, 127, 133). These studies have consistently found relative risks of 2 to 3-fold for those watching TV for >40 hrs/week as compared to <1 hr/week for type II diabetes (96, 98) and 1.5-fold for those watching >14 hrs/week of TV compared to <7 hrs/week for abnormal glucose metabolism (97). Our highest category of TV watching was 4+ hours/day as compared to <1 hour/day.

Furthermore, Healy et al. demonstrated that time spent TV watching disrupts normal glucose metabolism in a linear fashion even among those who are meeting Centers for Disease Control’s physical activity recommendations (133).