Abstract:

Objective This study aims to analyze the catch-up growth trajectory patterns of premature infants aged 0 - 18 months in the middle and late stages， and further explore the influencing factors of the observed growth trajectories. Methods A single-center retrospective cohort study was conducted on 201 mid-to-late preterm infants （32 - 36 weeks of gestation） admitted to hospital between January 2021 and September 2024. Birth characteristics and longitudinal follow-up data were collected， and periodic anthropometric measurements were performed in accordance with the Recommendations for Physical Growth Evaluation of Chinese Children. The weight-for-height Z-score （WHZ） was calculated based on the Growth Standards for Children Under 7 Years of Age （WS/T 423） issued by the National Health Commission of the People's Republic of China to assess participants' growth status. WHZ was adopted as the longitudinal observation indicator， and corrected age （0， 6， 12， and 18 months） was set as the time variable. The group-based trajectory model was constructed using StataMP 16 software to characterize the growth trajectories of mid-to-late preterm infants during the catch-up growth period from 0 to 18 months corrected age. Infants were categorized into three trajectory groups： slow catch-up， appropriate catch-up， and accelerated catch-up. Univariate analysis and multiple logistic regression analysis were performed to identify influencing factors associated with the distinct growth trajectories. Results Among the 201 included cases， 121 were boys （60.20%） and 80 were girls （39.80%）. The average birth weight was （2.5 ± 0.5） kg， and the average birth height （length） was （46.0 ± 3.4） cm. Using the group-based trajectory modeling， three distinct growth trajectory patterns were identified： the slow catch-up group （n = 22）， the appropriate catch-up group （n = 131）， and the rapid catch-up group （n = 48）. The birth weight of the rapid catch-up group was significantly higher than that of both the slow catch-up group and the appropriate catch-up group. The age at initiation of enteral feeding in the appropriate catch-up group was later than that in the slow catch-up group and the rapid catch-up group. The age at achievement of full enteral feeding in the slow catch-up group was later than that in the appropriate catch-up group. The proportion of exclusive breastfeeding within 6 months was lower in both the slow catch-up group and the rapid catch-up group than in the appropriate catch-up group. The incidence of extrauterine growth restriction （EUGR） was significantly higher in the slow catch-up group than in the appropriate catch-up group， and the difference was statistically significant （P < 0.05）. Results from multiple logistic regression analysis showed that exclusive breastfeeding within 6 months of age is a protective factor for slow postnatal catch-up growth in preterm infants during the mid-to-late period， while birth weight， age at achievement of full enteral feeding， and EUGR are risk factors. For rapid mid-to-late catch-up growth in preterm infants， exclusive breastfeeding within 6 months of age is a protective factor， and birth weight is a risk factor. Conclusions The group-based trajectory model identifies heterogeneous catch-up growth trajectory patterns of preterm infants during the mid-to-late postnatal period after adjusting for gestational age for the 0-18-month age range. The slow versus fast catch-up trajectory is significantly associated with birth weight， enteral nutrition， breastfeeding， and EUGR. It is therefore necessary to account for these influencing factors and implement targeted clinical regulation to facilitate the transition of preterm infants in the mid-to-late postnatal period to an optimal catch-up growth pattern.

Key words: preterm infant, moderate-late preterm, group-based trajectory model, catch-up growth trajectory, influencing factors