[Post-discharge growth of extremely premature infants within corrected age of 24 months]

Objective: To demonstrate the post-discharge catch-up growth of extremely premature infants (EPI) within 24 months of corrected age. Methods: This study retrospectively collected the anthropomorphic measurements of 311 EPI who visited Shenzhen Maternity and Child Healthcare Hospital from August 2013 to April 2020. These infants were stratified according to gestational age at birth (GA): 23-24+6weeks, 25-26+6weeks, 27-27+6weeks; and birth weight:<750 g, 750-999 g, ≥1 000 g. The anthropomorphic measurements, including weight, length, and head circumference for age, were recorded timely from discharge to 24 months of corrected age. And the growth curve stratified by GA and birth weight were fitted in both chronological age and corrected age, which were then compared with the World Health Organization Child Growth Standards for term infant (2006 version), to investigate the catch-up growth pattern of EPI. And appropriate catch-up was defined as the measurements reached the 25th percentile of WHO growth curve. Results: In these 311 EPI, 184 were males and 127 females, with gestational age of 23-27+6 weeks and birth weight of 480-1 430 g. Regardless of the GA and birth weight, the growth curves fitted in corrected age failed to overlap with that in chronological age by 24 months of corrected age. The growth velocity of weight, length and head circumference in both corrected and chronological age were all positively correlated with GA and birth weight: the 27-27+6weeks group showed a preferable growth pattern than the 25-26+6weeks group, and the curve of the 23-24+6weeks group was most unfavorable; and the same pattern was observed between the subgroups of different birth weight. Furthermore, the GA had more significant impact on the catch-up growth pattern than birth weight did. When assessed with corrected age curve, the weight and length of both male and female EPIs achieved appropriate catch-up by 24 months, as well as the head circumference of girls; whereas, boys' head circumference reached appropriate catch-up at the corrected age of 9 months, but fell behind the 25th percentile after that. However, when assessed with chronological age curve, both boys and girls failed to achieve appropriate catch-up in weight, length and head circumference by age 24 months. And no matter in corrected or chronological age, all physical measurements of girls were lower than those of boys. Conclusions: The rapid catch-up growth of EPI happens within 6 months of corrected age. The lower the birth weight and gestational age, the lower the physical measurements at each corresponding month of age, and the longer it takes to achieve appropriate catch-up. Gestational age has a greater impact on the longitudinal catch-up growth than birth weight does. And girls generally grow slower than boys in either correct or actual age. Before 24 months of corrected age, the growth should be assessed with corrected age rather than chronological age.