['We evaluate the association between gestational weight gain and offspring birth weight in singleton term pregnancies of women with type 1 diabetes.', 'One hundred fifteen consecutive women referred at <14 weeks were retrospectively classified as underweight (prepregnancy BMI <18.5 kg/m(2); n = 1), normal weight (18.5-24.9; n = 65), overweight (25.0-29.9; n = 39), or obese (≥30.0; n = 10). Gestational weight gain was categorized as excessive, appropriate, or insufficient according to the Institute of Medicine recommendations for each BMI class. Women with nephropathy, preeclampsia, and/or preterm delivery were excluded because of restrictive impact on fetal growth and limited time for total weight gain.', 'HbA1c was comparable at ∼6.6% (49 mmol/mol) at 8 weeks and ∼6.0% (42 mmol/mol) at 36 weeks between women with excessive (n = 62), appropriate (n = 37), and insufficient (n = 16) gestational weight gain. Diabetes duration was comparable, and median prepregnancy BMI was 25.3 (range 18-41) vs. 23.5 (18-31) vs. 22.7 (20-30) kg/m(2) (P = 0.05) in the three weight gain groups. Offspring birth weight and birth weight SD score decreased across the groups (3,681 [2,374-4,500] vs. 3,395 [2,910-4,322] vs. 3,295 [2,766-4,340] g [P = 0.02] and 1.08 [-1.90 to 3.25] vs. 0.45 [-0.83 to 3.18] vs. -0.02 [-1.51 to 2.96] [P = 0.009], respectively). In a multiple linear regression analysis, gestational weight gain (kg) was positively associated with offspring birth weight (g) (β = 19; P = 0.02) and birth weight SD score (β = 0.06; P = 0.008) when adjusted for prepregnancy BMI, HbA1c at 36 weeks, smoking, parity, and ethnicity.'] Is higher gestational weight gain associated with increasing offspring birth weight independent of maternal glycemic control in women with type 1 diabetes?