Objective To assess the growth of monochorionic diamniotic (MCDA) twins discordant for birth weight during their first 24 months of life.Methods Clinical data and growth parameters from birth to 24 months of age of 31 pairs(62 cases) of birth weight-discordant MCDA twins (≥ 25％ difference in birth weight) who were born alive in the First Affiliated Hospital,Sun Yat-sen University between January 1,2010 and June 30,2016 were retrospectively analyzed.Each pair of twins was divided into the large birth weight group (31 cases) and the small birth weight group (31 cases).All datas were statistically analyzed with Chisquare test,paired t test,analysis of variance or LSD-t test.Results (1) The incidence of birth defects and hypoproteinemia in the small birth weight group were higher than that in the large birth weight group [29.0％ (9/31) vs 0.0％ (0/31),54.8％ (17/31) vs 25.8％ (8/31);x2=8.319 and 5.429;both P ＜ 0.05].(2) The standard deviation scores (SDS) of weight,length and head circumference at birth and 1,6,12,18 and 24 months of age of the small birth weight group were lower than those of the large birth weight group [birth:(-2.00 ± 0.66) vs (-0.04±0.60),(-1.83±1.13) vs (-0.37±0.83),(-1.42±1.03) vs (0.17±0.84),t=17.214,8.390 and 7.759;1 month:(-1.77±0.81) vs (-0.60±0.65),(-2.36±1.20) vs (-0.94±0.74),(-1.71±1.26) vs (-0.44± 1.09),t=9.424,9.059 and 7.197;6 months (-1.00±0.84) vs (-0.09±0.56),(-1.31 ± 1.22) vs (-0.04±0.80),(0.30±1.51) vs (1.11 ± 1.20),t=-7.578,7.988 and 6.091;12 months:(-0.34±1.06) vs (0.47±0.79),(-1.00±0.92) vs (-0.14±0.73),(-0.16±0.76) vs (0.49±0.58),t=5.747,7.155 and 5.664;18 months:(-0.06±0.95) vs (0.74±0.66),(-0.92± 1.07) vs (-0.24±0.92),(-0.32±0.72) vs (0.29±0.66),t=6.153,4.496 and 3.877;24 months:(0.20±0.79) vs (0.88±0.62),(-0.66±0.59) vs (0.01 ±0.67),(-0.37±0.60) vs (0.34±0.68),t=5.317,4.800 and 4.905;all P ＜ 0.001].However,the changes in SDS (△ SDS) of weight,length and head circumference from birth to 24 months of age and the incidence of △ SDS ＞ 0.67 were significantly higher in the small birth weight group than those in the large birth weight group [△SDS:(2.20± 1.10) vs (0.92±0.91),(1.17± 1.21) vs (0.37± 1.14),(1.05± 1.07) vs (0.16±0.89),t=8.422,3.918 and 3.547,all P ＜ 0.001;△SDS ＞ 0.67:93.5％ (29/31) vs 61.3％ (19/31),61.3％ (19/31) vs 35.5％ (11/31),61.3％ (19/31) vs 29.0％ (9/31),x2=9.226,4.133 and 6.53 1,all P ＜ 0.05].(3) The difference in SDS for weight,length and head circumference between the large and small birth weight twins at 24 months of age were significantly lower than those at birth [(0.68 ± 0.71) vs (1.95 ± 0.63),(0.67 ± 0.77) vs (1.46± 0.97),(0.71 ± 0.80) vs (1.60±1.15);all P ＜ 0.05].Conclusions Growth differences are found between birth weight-discordant MCDA twins all the way to 24 months of age from birth at a reduced trend.