The results showed that only 14 of the 309 preterm infants (4.5%) were underweight at 12 months of actual age. The incidence was lower than those of Sharma’s [14] and Mukhopadhyay’s [15] studies, which may be due to the higher proportion of extremely low-birth-weight premature infants (30 and 15%, respectively) in their studies; in contrast, only 4 infants (1.3%) in this study were considered to have extremely low birth weight. Second, the incidence was also lower than that found in the results of Deng Ying’s survey in China [16]. It may be that only the very-low-birth-weight infants were included in that survey, but very-low-birth-weight infants comprised only 10.7% of the sample in this study. However, the study found that 52 infants (17.4%) did not meet the criteria for catch-up growth at 12 months of actual age. It can be seen that the incidence of catch-up growth in preterm infants was still not high. Current studies have shown that catch-up growth affects physical [17], nerve and motor development. Therefore, it is still necessary to pay more attention to catch-up growth in preterm infants after discharge and to help them achieve satisfactory catch-up growth to improve their long-term quality of life.
The logistic regression analysis showed that gestational age, regular health care, caregivers’ educational background, mothers’ daily contact with the baby, monthly average family income, the addition of breast milk supplement and daily milk volume were factors that affected the catch-up growth of preterm infants after discharge.
First, our study found that a smaller gestational age increased the risk of catch-up growth. Gestational age is closely related to the incidence of complications in premature infants. With the increase in gestational age, the incidence of various complications in preterm infants will gradually be lower, thus facilitating a more successful feeding process and the completion of catch-up growth. Bjelanovic V et al. [18] found that the smaller the gestational age was, the more complications preterm infants had. According to Clark’s [3] research, with decreases in gestational age and birth weight, the incidence of EUGR for each parameter of premature weight, body length and head circumference will increase. Therefore, preterm infants of small gestational ages merit much more monitoring after discharge.
We found that preterm infants receiving health care services on a regular basis were 4.687 times more likely to achieve catch-up growth than were preterm infants receiving health care services on an irregular basis. It is possible that among preterm infants receiving regular health care, medical personnel could find deviations in the growth of premature infants in a timely manner and could give caregivers more feeding guidance and control measures; in this way, the premature catch-up growth situation was relatively good. Therefore, it is recommended that preterm infants receive health care regularly.
In addition, we found that caregivers’ educational background, mothers’ daily contact with the baby and monthly average family income were also factors affecting catch-up growth; this finding may have arisen because the higher the caregivers’ educational background is, the longer the time of contact between the mother and the baby. Additionally, a higher monthly average family income would facilitate access to more comprehensive care for preterm infants and provide more material comfort for them, such as breast milk supplements and preterm infant formula; thus, the catch-up growth was also better.
Furthermore, the results showed that the addition of breast milk supplementation and daily milk volume were factors that affected the catch-up growth of preterm infants after discharge. Breastfeeding has many benefits, but its exclusive use in certain situations can lead to nutrient deficiencies and bone demineralization [19, 20], especially for very and extremely low-birth-weight infants. It has been recognized internationally that fortified breast milk is the best choice of nutrition for preterm infants at present, to meet the baby’s protein, energy and vitamin needs for their catch-up growth [9, 21]. However, there is some controversy about the results of studies on the effect of breastfeeding on premature infants. Some studies showed that the weight, body length and head circumference in the fortified breastfeeding group were superior to those of the breastfeeding group at 3 months of corrected age, but there was no statistically significant difference in the long-term neural development assessment and the growth index between the two groups [22,23,24]. Furthermore, the current research sample size of breast milk supplements was small; in the future, the sample size should be increased with multicenter research. In addition, we found clinically that preterm infants with more milk per day received more nutrition and more readily experienced catch-up growth. Premature babies are generally recommended to consume 110~130 kcal/kg every day. This study was a retrospective study, which could not accurately define the standard of daily milk grading. The standard should be improved in future studies.