Participants were part of a longitudinal cohort, the Glowing Study (clinicaltrials.gov # NCT01131117), which is examining the effects of maternal body composition on infant birth weight, growth, body composition, and risk of overweight at 2 years old. Participants were recruited from 2011 to 2014 in a small southern city. Women were eligible if they had a single previous pregnancy, had a BMI between 18.5 and 35 kg/m2, and were 21 years of age or older. Exclusion criteria included having preexisting medical conditions (e.g., diabetes mellitus, hypertension), taking medications known to influence fetal growth (e.g., glucocorticoids, insulin, thyroid hormones), and planning to smoke or drink alcohol during the pregnancy. A total of 287 participants met the inclusion/exclusion criteria and were enrolled in the study. Participants were enrolled in the primary study if they were planning a pregnancy or were less than 10 weeks gestation. Of those women, 51 women completed a preconception visit and of those, 43 women had measured weight at 4–10 weeks and 12 weeks; we will focus on this subsample of 43 participants for these secondary analyses.
At the preconception visit, participants were advised to remain weight stable during the first trimester, consistent with the IOM guidelines [2 ]. All participants received information on the IOM’s GWG guidelines [2 ] tailored to their BMI category at the 4–10 weeks gestation visit as well as the rationale for GWG guidelines during pregnancy (i.e., maternal and child health). Research staff also introduced and explained a GWG graph (tailored to BMI category) that would be used to track the participant’s GWG throughout her pregnancy. During pregnancy, all participants received six behavioral intervention sessions (i.e., at 4–10, 12, 18, 24, 30, and 36 weeks gestation) designed to promote healthy GWG, with intensified intervention offered in the presence of excessive GWG. The intervention has been described in detail elsewhere [7 ].
Weight was measured in a hospital gown with no shoes to the nearest 0.1 kg using a calibrated tarred standing digital scale at all study visits under fasted conditions. Height was measured to the nearest 0.1 cm using a wall-mounted stadiometer at preconception only. All measures were obtained in duplicate, with a third assessment if there is discrepancy between the first two. BMI was calculated from these measures [weight(kg)/height(m)2], and women were classified as normal weight (n = 22) or overweight/obese (n = 21) at the preconception visit [8 ]. Of those participants in the overweight/obese category at the preconception visit, 17 participants were overweight and 4 were obese. Informed consent was obtained from participants, and all study procedures were approved by the Institutional Review Board of the University of Arkansas for Medical Sciences.
Descriptive statistics were calculated to describe weight change over each interval, time interval to conception, and the proportion of women correctly classified using the first trimester weights. Cohen’s kappa (κ) statistic [9 (link)] was used to assess the agreement between preconception BMI classification (i.e., normal, obese, overweight) and BMI classification at 4–10 weeks and 12 weeks of pregnancy. Bland-Altman plots [10 (link)] were used to examine the agreement between preconception BMI and the later BMIs. Both mean bias and 95% limits of agreement were computed. Because a non-significant linear trend between the difference of paired BMI values and their average was observed, Bland-Altman’s limits of agreement were not adjusted for trend. Additionally, agreement between preconception BMI and the later BMI measurements was evaluated by computing and testing Lin’s concordance correlation coefficient [11 (link)]. Lin’s concordance correlation coefficient (CCC) provides an estimate of the degree to which repeated measurements deviate from the 45° line of perfect concordance. The concordance correlation coefficient combines measures of both precision and accuracy. Weight change from preconception was compared to first trimester weights by BMI category and based on whether BMI category changed using Wilcoxon’s rank-sum (Mann–Whitney) tests. Statistical analysis was performed using Stata 14.0 statistical package (Stata Corporation, College Station, TX, USA).
At the preconception visit, participants were advised to remain weight stable during the first trimester, consistent with the IOM guidelines [2 ]. All participants received information on the IOM’s GWG guidelines [2 ] tailored to their BMI category at the 4–10 weeks gestation visit as well as the rationale for GWG guidelines during pregnancy (i.e., maternal and child health). Research staff also introduced and explained a GWG graph (tailored to BMI category) that would be used to track the participant’s GWG throughout her pregnancy. During pregnancy, all participants received six behavioral intervention sessions (i.e., at 4–10, 12, 18, 24, 30, and 36 weeks gestation) designed to promote healthy GWG, with intensified intervention offered in the presence of excessive GWG. The intervention has been described in detail elsewhere [7 ].
Weight was measured in a hospital gown with no shoes to the nearest 0.1 kg using a calibrated tarred standing digital scale at all study visits under fasted conditions. Height was measured to the nearest 0.1 cm using a wall-mounted stadiometer at preconception only. All measures were obtained in duplicate, with a third assessment if there is discrepancy between the first two. BMI was calculated from these measures [weight(kg)/height(m)2], and women were classified as normal weight (n = 22) or overweight/obese (n = 21) at the preconception visit [8 ]. Of those participants in the overweight/obese category at the preconception visit, 17 participants were overweight and 4 were obese. Informed consent was obtained from participants, and all study procedures were approved by the Institutional Review Board of the University of Arkansas for Medical Sciences.
Descriptive statistics were calculated to describe weight change over each interval, time interval to conception, and the proportion of women correctly classified using the first trimester weights. Cohen’s kappa (κ) statistic [9 (link)] was used to assess the agreement between preconception BMI classification (i.e., normal, obese, overweight) and BMI classification at 4–10 weeks and 12 weeks of pregnancy. Bland-Altman plots [10 (link)] were used to examine the agreement between preconception BMI and the later BMIs. Both mean bias and 95% limits of agreement were computed. Because a non-significant linear trend between the difference of paired BMI values and their average was observed, Bland-Altman’s limits of agreement were not adjusted for trend. Additionally, agreement between preconception BMI and the later BMI measurements was evaluated by computing and testing Lin’s concordance correlation coefficient [11 (link)]. Lin’s concordance correlation coefficient (CCC) provides an estimate of the degree to which repeated measurements deviate from the 45° line of perfect concordance. The concordance correlation coefficient combines measures of both precision and accuracy. Weight change from preconception was compared to first trimester weights by BMI category and based on whether BMI category changed using Wilcoxon’s rank-sum (Mann–Whitney) tests. Statistical analysis was performed using Stata 14.0 statistical package (Stata Corporation, College Station, TX, USA).
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