The association between pre-gravid and first trimester maternal weight and its implications for clinical research studies

Abstract In clinical research, weight measurement in first trimester is often treated as a surrogate for pre-pregnancy weight. The validity of this critical assumption, however, is uncertain. Thus, we sought to prospectively evaluate the relationship between pre-gravid weight and first trimester weight. In this prospective preconception observational cohort study, 474 newly-married women in Liuyang, China, underwent pre-gravid evaluation at median 17.7 weeks before a singleton pregnancy, during which they had weight measurement in first trimester. The relationship between pre-gravid and first trimester weight was assessed by Bland–Altman analysis, Concordance Correlation Coefficient, and Pearson correlation. Mean pre-gravid weight was 49.8 ± 6.4 kg and mean weight in first trimester was 51.1 ± 7.0 kg. The Concordance Correlation Coefficient between pre-gravid and first trimester weight was 0.76 (95% limits of agreement: 0.72–0.80) and Pearson correlation was r = 0.78 (p