Maternal weight gain rate in the second trimester are associated with birth weight and length of gestation.

Background: Low total weight gain during pregnancy has been widely accepted as a valid risk factor for small-for-gestational-age infants and pre-term births. However, it is not obvious in which trimester the weight gain rate most affects birth weight and length of gestation.

Method: Using logistic regression analysis and Pearson's correlation coefficient test, data from 472 women who had vaginally delivered an infant at term without any complications were analyzed retrospectively.

Results: Pre-pregnancy underweight and low total maternal weight gain were significant independent predictors of small-for-gestational-age infants and shortened gestations. Pre-pregnancy weight was significantly related to the birth weight and length of gestation (r = 0.18, p < 0.0001; r = 0.10, p = 0.04, respectively), and total weight gain was also significantly related to those (r = 0.17, p = 0.0003; r = 0.11, p = 0.03, respectively). Significant correlations between maternal weight gain rate in the second trimester and the birth weight and length of gestation were found (r = 0.32, p = 0.005; r = 0.40, p = 0.0003, respectively), while such correlations were not found in the first or third trimester.

Conclusion: The most sensitive period of maternal weight gain for the birth weight and length of gestation was the second trimester.