There are many factors causing preterm delivery,[15–16] such as maternal age, primary diabetes, hypertension, and other diseases. The results of this survey revealed an association between the older age of the mother and the lower birth weight of the newborn, which is consistent with previous reports,[17] It has been shown that the use of antenatal corticosteroids can improve neonatal outcomes,[18] especially for preterm infants with gestational age less than 34 weeks. However, only 54.5% of the infants in this study received prenatal hormonal therapy, which was similar to that in other low-income and middle-income countries.[19] This suggests that the cooperation between neonatology and obstetrics needs to be strengthened, and prenatal hormones should be recommended to improve the survival rate and prognosis of preterm infants in China.
Previous studies have also suggested a protective effect of noninvasive ventilation in preterm infants. CPAP is recommended as the preferred noninvasive ventilation mode after birth.[20] Early CPAP can avoid alveolar collapse and can reduce the chance of invasive ventilation.[21] From the previous study on preterm infants at 24 to 28 weeks of gestation, the proportion of using CPAP in the delivery room was 81.1%,[21] and in this study, CPAP was the most frequently used ventilation mode for VELBWIs, accounting for 65.2%. Previous studies have shown that preterm infant with gestational age < 28 weeks have a 50% probability of failure at first extubation, which may lead to higher mortality and morbidity.[22] The application of CPAP for support after extubation helps to reduce the re-intubation caused by extubation failure. However, the proportion of preterm infants with birth weight less than 750g who needed invasive ventilation reached 50% in this study.
In addition to noninvasive ventilation, caffeine administration also played major roles on promotion of neonatal morbidity. Caffeine can help VELBWIs wean earlier, reduce the incidence of BPD, and improve the prognosis of neurodevelopment.[23–26] In this study, 71.8% of VELBWIs were treated with caffeine. PS also has an important role in the respiratory tract management of VELBWIs.[17] The results of our study showed that 51.4% of VELBWIs received PS; the smaller birth weight was associated with a higher probability of using PS. Recent studies have shown that early use of budesonide atomization can reduce the incidence of BPD in preterm infants.[20,27–29] And in this study, the proportion of VELBWIs atomization was only 19.4%. Most of the time, the atomization was administered after BPD occurred in preterm infants. Thus, we concluded that the smaller birth weight was associated with a higher proportion of atomization. In the future, the respiratory tract management of VELBWIs should be considered.
Adequate nutrition supply is the key for the survival of preterm infants. Proper vascular access is the key to parenteral nutrition but limited study focus on the vascular choices in the NICU. UVC and PICC are the most commonly used vascular accesses for VELBWIs. In this study, UVC and PICC were used in 75.2% and 39.3% infants, respectively. Meanwhile, smaller birth weight was associated with the longer indwelling time of UVC and PICC, which is consistent with previous study.[28] In this study, the duration of parenteral nutrition in VELBWIs was 27.0 ± 19.5 days, the indwelling time of the feeding tube was 36.2 ± 21.0 days; smaller birth weight was associated with a longer need for parenteral nutrition and indwelling gastric tube.
In terms of enteral nutrition, breast milk is the first choice for VELBWIs, and it is related to the prognosis and survival rate.[29,30] According to a survey in Jiangsu Province in 2018, the breast feeding rate of VELBWIs in the NICU of 29 hospitals was 37.2% .[31] In this study, the breast feeding rate of preterm infants with weight > 1250g was 78.3%. Moreover, 66.8% of the preterm infants used their own mother's milk, which was higher than that reported in other studies.[32,33] The potential reason was the multidisciplinary team of breast milk management, including doctors, nurses, nutritionists, international breast milk consultants, and family members with breast feeding experience, which ensured the safety and successful implementation of breast feeding in NICU.[34] The corrected gestational age for complete oral feeding was 35.3 ± 6.5 weeks, which was similar to the gestational age of complete oral feeding in other studies.[35] However, the gestational age and weight of the study population included in other studies were relatively small, which suggests that if the gestational age and weight were the same, the time to achieve full oral feeding would be longer. At the same time, our results also revealed that the smaller birth weight was associated with the greater the corrected gestational age when reaching full oral feeding. Because birth weight is an important factor affecting the oral feeding process of preterm infants.[36]
The management of body temperature is very important for preterm infants, in this study, hypothermia was observed in 19.3% of cases during hospitalization. We concluded that the smaller birth weight was associated with a higher incidence of hypothermia. Some researchers have suggested that bundles of golden hour temperature management could significantly reduce the incidence of hypothermia in VELBWIs.[37,38] What’s more, hyperthermia was observed in 34.7% of total infants, and preterm infants with a birth weight of 750-1250g had the highest probability of hyperthermia (42.2%). However, while we investigated whether hyperthermia occurred in the whole process of hospitalization, it is possible that there are numerous confounding factors.
EEG monitoring, brain or intestinal oxygen monitoring, and transcutaneous oxygen partial pressure monitoring are very important noninvasive monitoring methods in clinic. However, our results revealed that these monitoring methods were not frequently applied in VELBWIs, which also indicated that this kind of monitoring was not taken as routine monitoring in clinic. Infants with smaller birth weight and the more serious diseases were associated with the higher the proportion of such kind of monitoring.
The mortality rate of VELBWIs included in this study was 2.4%. Lower birth weight was associated with a higher mortality rate. Compared with other domestic studies,[1] the mortality in this study was relatively low. Because this study included only infants who died in hospital, and did not consider infants who died after discharge or due to withdrawal treatment. Apart from focus on the mortality of VELBWIs, it was necessary to pay attention to the incidence of various important short-term prognosis of the surviving infants. Compared with the domestic research results,[1] the incidence of BPD in this study was higher, but the incidence of sepsis was lower, which may be due to the role of collaborative quality improvement in the prevention of infection in preterm infants, but it also needs to be used in the prevention of other complications.