The association between maternal weight gain and the birthweight of twins

Maternal pregravid weight, weight-for-height² (body mass index, BMI), and gestational weight gain are acknowledged factors influencing the intrauterine growth and subsequent birthweight of singletons. The effect of these factors, singly and in combination, on the birthweight of twins is less clear. Using an historical prospective design, this study evaluated the association between maternal pregravid weight, weight gain (as early rate of gain, late rate of gain, and total weight gain), and the birthweight of twins. One hundred and sixty-three twin pregnancies of 28 weeks gestation or greater with both twins born alive were evaluated in this study. Mothers were categorized by their BMI as underweight, normal weight, or overweight. Weight gain was measured as early (before 24 weeks) rate of gain, late (after 24 weeks) rate of gain, and total gain. Based on weight gain to 24 weeks gestation, early rate of gain (before 24 weeks) and late rate of gain (after 24 weeks) was calculated. Discordancy was evaluated as the difference between the birthweights of each twin pair divided by the larger of the two and modelled as a continuous variable and as categories of ≥15% ≥20% and ≥25% Using a race and gender-specific singleton standard, a birthweight ratio (actual divided by singleton 50th%ile for gestational age) was calculated for each twin. In addition, the smaller of each twin pair was categorized as > or ≤10th%ile. Length of newborn stay (LOS) was determined for each twin pair by averaging the nursery stay from birth to discharge home. Length of gestation was categorized as preterm (<37 weeks) and term (≥37 weeks), as well as 28-32, 33-34, 35-36, 37-38, and 39-41 weeks. Two multiple regression models were formulated using the average of the twin birthweights and combined twin length of stay each as the dependent variable. In addition, comparisons were made of weight gain (total and early and late rates of gain), length of gestation, birthweight, birthweight ratio, discordancy, and LOS by selected maternal and newborn factors. Our findings suggest significant correlations between twin birthweight, pregravid weight, and early and late rates of gain. Higher late rate of gain (after 24 weeks) and total gain was associated with higher birthweight and birthweight ratios and shorter LOS among twin infants in our study. Our findings support the recommendation of 40-45 lb of total weight gain in twin pregnancies and suggest that an early rate of gain (before 24 weeks) of about 1.0 lb/week and a late rate of gain (after 24 weeks) of 1.5 lb/week may have therapeutic advantages.