Impact of catch-up growth on bone age development in preterm infants from a cohort study

Objective To evaluate the catch-up growth features of preterm infants and to explore the influence of catch-up growth on bone age development. Methods The two-way cohort study was conducted.The preterm infants who visited the Child Health Department of Wuhan Children′s Hospital from January 1st to December 31th in 2015 were selected as the exposed group and the full term infants with age, gender and ethnicity matched with the exposed group ones were selected according to the ratio of 1∶1 for the non-exposed group who visited the same hospital at the same time non.Information of those childeren as the birth history, past birth and development history were collected in both groups were followed up till 3 years old and photographed on the left wrist X-ray film for bone age evaluation at 3 years old. Results At the time of enrollment, 392 subjects were selected in the exposed group and non-exposed group and 239 infants in the exposed group and 247 infants in non-exposed group were followed up till 3 years.During the follow-up period, there was a conspicuous catch-up growth trend of body length and weight in the exposed group, and weight Z score was the lowest at 2 months old, but the overall level of body length and weight were still lower than the non-exposed group.The start of catching up growth in body weight took precedence over the length, which was reflected in the time when the weight caught up to Z=-2 and Z=-1 as 3.78 months old and 16.18 months old, whereas the time of length catching up to Z=-2 and Z=-1 was 7.24 months old and 22.21 months old.The length catch-up growth was slower during the period of 5-10 months old and 12-21 months old.The age of bone age assessment in the 2 groups was between 2.80 and 3.20 years old(mean 3.03 years old). The bone age of boys in the exposed group was higher than that of the non-exposed ones[(3.13±0.61) years old vs.(2.75±0.51) years old], and there was statistical significance (t=-5.52, P 0.05). Body length Z-score at the age of 1 month, 2 months, 4 months, 5 months, 6 months, 12 months and weight Z-score at 2 months, 3 months, 4 months were the facilitating factors for skeletal development, whereas body length Z-score at 15 months, 18 months, 36 months and weight Z-score at 15 months were obstacles. Conclusions Premature infant have a catch-up trend before 3 years old.In order to delay the skeletal development, it is necessary to avoid rapid catch-up growth of weight and length in premature infants before 1 year old. Key words: Preterm infants; Catch-up growth; Bone age development; Cohort study