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Briefly, participants ranged from ages 16 to 39 years with 72% below age 25 years. Fifty- six percent of the sample had not completed high school at enrollment while 50% were employed or in school at some point during pregnancy. With respect to acculturation factors, 45% were born outside the Continental U.S., 33% were bilingual (Spanish and English) or preferred to speak only Spanish, and 85% were of Puerto Rican descent. Regarding medical factors, 60% were multiparous, 60% had a family history of type II diabetes mellitus, 5% had been diagnosed with GDM in a previous pregnancy, and >40% were overweight or obese in pre-pregnancy.

Patterns of sedentary behaviors differed from pre-pregnancy to the early and mid

pregnancy time periods. For example, 25% of participants reported watching 4 or more hours of TV per day in the year before pregnancy, whereas this percentage increased to 35% in early pregnancy and 29% in mid-pregnancy (Table 2.10). Similarly, the frequency of sitting at work increased from pre pregnancy through mid pregnancy (Table 2.11). The percentage of women who often or always sat at work increased from 30% in pre-pregnancy to 48% in early and 42% in mid pregnancy. In addition, the number of employed women decreased from 75% in the year prior to pregnancy to 50% and 42%, in early and mid pregnancy, respectively.

Quartile median values of sports/exercisescorewere greater for pre-pregnancy indicating a wider distribution and higher values (4.0, 2.8, 1.5, 1.3) as compared to both early and mid pregnancy (2.5, 1.5, 1.3, 1.0) (Table 2.12).

We created two composite sedentary behavior variables: Composite I, a composite of TV watching and sports/exercise (reversed scored), and Composite II, a total sedentary behavior

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score which was a composite of total sitting (TV watching and sitting at work) and sports/exercise reverse scored (Table 2.13). For Composite II, the median values for the sedentary score in each tertile were lower for pre-pregnancy (1, 2, and 3, respectively) as compared to early and mid pregnancy (1, 3, and 4, respectively) (Table 2.13).

Of the total sample screened (N=1,009), 11% (N=119) of women were classified as having AGT and 3% (N=33) were diagnosed with GDM (Table 2.14). With regard to maternal characteristics, increasing age, educational attainment, income, parity, and pre-pregnancy BMI were associated with an increase in the risk of AGT, whereas cigarette smoking in pregnancy was associated with a decrease in risk of AGT (Table 2.15). Having a family history of type II

diabetes mellitus, personal history of GDM, and a history of adverse pregnancy outcome were statistically significantly associated with an increased risk of AGT (p<0.05). Associations were similar in terms of risk of GDM, with the exception of parity and cigarette smoking, which were not significantly associated with GDM risk (Table 2.15).

We then evaluated participant characteristics in relation to sedentary behaviors and observed several consistent associations (Tables 2.16-2.18). Maternal age, employment,

education, pre-pregnancy BMI, history of GDM, illicit drug use and total physical activity were negatively associated with time spent TV watching in pregnancy, whereas history of GDM was positively associated with time spent TV watching (Table 2.16). These same factors, with the exception of age, BMI and drug use, were positively associated with frequency of sitting at work (Table 2.17). In addition, income and cigarette use were positively associated with sitting at work, whereas Spanish/bilingual language preference (vs. English only) and total physical activity were negatively associated with sitting at work. Finally, a similar grouping of

characteristics (i.e., employment, income, parity and total physical activity) was negatively associated with low participation in sports/exercise in pregnancy.

In unadjusted analyses, time spent TV watching and frequency of sitting at work were not significantly associated with risk of AGT in pre, early or mid pregnancy (Table 2.19). Low participation in sports/exercise in mid pregnancy was associated with increased risk of AGT, with those in the lowest quartile having a 2-fold increased risk for AGT compared to those in the highest quartile (OR=2.06, 95% CI 1.06-4.01) with a significant linear trend (Ptrend=0.03).

Regarding the composite sedentary behavior variables, Composite I was not associated with increased risk for AGT in any pregnancy period. However, Composite II was associated with significantly increased risk of AGT in mid pregnancy with significant linear trend (Ptrend=0.005). Odds ratios for the top two tertiles of Composite II were 4.9 (95% CI 1.10-21.88) and 8.0 (95% CI 1.7-37.54), respectively as compared to the lowest tertile although confidence intervals were wide and the referent category had only 2 AGT cases in mid pregnancy (Table 2.19).

Similar to the unadjusted analyses, after adjustment for maternal age, smoking, pre- pregnancy BMI and history of GDM, time spent TV watching and frequency of sitting at work were not statistically significantly associated with risk of AGT and the direction or magnitude of results remained comparable (Table 2.20). After adjusting for maternal age, education, cigarette smoking, parity, and pre-pregnancy BMI, the relative risk for low participation in sports/exercise in mid pregnancy remained similar at 2.01 (95% CI 1.01-4.02). Again, sports/exercise in pre or early pregnancy was not associated with AGT risk. Similar to the unadjusted results, Composite I was not associated with AGT risk; however, increase in total sedentary behavior as assessed by

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Composite II in mid pregnancy was associated with significantly elevated AGT risk after adjustment for multiple confounders, although again confidence intervals were wide.

We evaluated several dietary components, total caloric intake, dietary fiber, and dietary fat, as potential confounders in a sub-sample for which dietary information was available. We ran each model including these variables singly in addition to the other final model covariates. The estimates were virtually unchanged after adjustment.

With regard to the secondary aim of evaluating sedentary behaviors as risk factors for GDM, time spent TV watching and frequency of sitting at work in pre, early and mid pregnancy were not associated with risk of GDM in unadjusted analyses (Table 2.21). However this analysis was limited by sparse numbers of GDM cases within strata and wide confidence intervals. As observed for AGT, low participation in sports/exercise in mid pregnancy was associated with a significantly elevated risk of GDM (Ptrend=0.05). Due to the small total number of GDM cases (N=33) in our cohort, we limited adjustment in multivariable analyses to maternal age and pre- pregnancy BMI, the two strongest risk factors for GDM in our population. Similar to unadjusted results, lower mid pregnancy sports/exercise (Ptrend = 0.04) and higher Composite II score (Ptrend = 0.05) were positively associated with GDM risk (Table 2.22).

We also evaluated sedentary behaviors as predictors of glucose values on the non-fasting 1-hour 50-gram OGTT (Table 2.23). Time spent TV watching, sitting at work, and

sports/exercise in pre, early and mid pregnancy were not associated with glucose values. However, higher total sedentary behavior as assessed by Composite II score in mid pregnancy was significantly associated with elevated glucose values (highest vs. lowest tertile: β=0.081, p- value=0.04), though the linear trend was not statistically significant.

Finally, we evaluated several factors as effect modifiers of the association between sedentary behaviors and risk of AGT. Family history of diabetes, parity (parous vs. nulliparous), BMI (<25 and ≥25 kg/m2), total caloric intake (<50th percentile and ≥50th percentile) and

pregnancy weight gain at GDM screen (at/or below vs. above weight gain recommendations) were not statistically significant effect modifiers (data not shown).