This study has demonstrated that late-preterm infants suffer significant morbidity and mortality and hence, this population needs to increase observation and close monitoring during birth hospitalization. In our study, the major risks associated with the mortality of late-preterm neonates were need for resuscitation and mechanical ventilation, CNS involvement (seizure), congenital heart disease, surfactant administration, pneumonia, feeding problems, hypoglycemia and septicemia. The mean weight of infants in this study was 2804 gr. In a study conducted by Kitsommart (13), the mean weight of infants was reported to be 2576 gr, which is inconsistent with the present study. This difference can be attributed to ethnic differences between infants. Lotfalizadeh and colleagues (14) also reported that the mean birth weight of infants was 2743 grams, that is consistent with the present study.
About days of hospitalization, the results showed the minimum and maximum hospitalization days were 1 and 30, respectively, with a mean of 9.1 ± 4.7 days. The mean hospitalization days in a study conducted by Kitsommart (13) was equal to 8.2. These results are consistent with the findings of the present study. The overall duration of hospitalization amongst late-preterm infants was twice than term infants in the study by Savitha (15). These results show that late-preterm infants have a higher risk of mortality, and therefore the pediatric physician must monitor late-preterm infants immediately after birth.
In terms of the cause of hospitalization, the results showed that the most common cause of hospitalization was respiratory distress syndrome (RDS) and transient tachypnea of the newborn (TTN) (80.7%) and then cardiovascular diseases (11.3%). In addition, the least cause was a CNS involvement (seizure) (8%). Kitsommart (13) reported that the most common cause of hospitalization of late-preterm infants was related to the respiratory system, including respiratory distress (34%), respiratory distress syndrome (RDS) (11%), and TTN (14%). This is consistent with the findings of the present study. In a study carried out by Correia and co-workers on respiratory morbidity in late-preterm neonates, 8.8% had RDS or TTN (16).
Tsai et al. studied morbidities in late-preterm infants and reported that respiratory problems are the most common cause of morbidities, which is consistent with the results of the present study (17). Differences between this study with ours is due to we studied only hospitalized late-preterms but they evaluated all late-preterms who were born in their center.
Since late-preterm infants may lack a complete respiratory system, natural evolution, and the ability to adapt to the environment, they require mechanical ventilation. The results of this study showed that 32% of infants needed mechanical ventilation. In studies of Kitsommart (13) and Tsai (17), 25.3% and 26% of infants needed mechanical ventilation, respectively. The results show that the need for mechanical ventilation is higher in this study which requires more attention and care in managing these infants.
Hyperbilirubinemia tends to be more intense and longer in late-preterm infants (18). Because of immaturity and delay in the bilirubin liver conjugation, late-preterm infants are twice more vulnerable to unconjugated pathologic hyperbilirubinemia than term infants (13, 19). The results of this study indicated that 42% of infants had hyperbilirubinemia. This is consistent with the findings of Tsai et al. (17) and Haroon et al. (20) who reported that the rate of hyperbilirubinemia was equal to 33% and 37.9%, respectively. Scheuchenegger et al. also showed that the rate of hyperbilirubinemia was 29% (21).
The risk of hypoglycemia in late-preterm infants is three times higher than term infants. Hypoglycemia may occur at any age due to inappropriate and inadequate metabolic response to the discontinuation of glucose from the mother's blood (22). The results of this study showed that hypoglycemia is statistically significant )9%) in late-preterm infants. Hosagasi and colleagues demonstrated the highest risk for hypoglycemia in the early postnatal period was present especially in late-preterm infants group (23). Tsai et al. reported that the prevalence of hypoglycemia is equal to 7%, 3.3%, and 3% in infants aged 34 weeks, 35 weeks, and 36 weeks (17). Kitsommart et al. also showed that the prevalence of hypoglycemia among infants is equal to 32.5% (13). According to a study by Bulut in Turkey on short-term complications of late-preterm infants, they founded hypoglycemia and sepsis were significantly higher in these infants compared to term infants (24).
Late-preterm infants have a 3.2 times higher risk of sepsis compared to term infants (25). Due to the lack of evolution of the immune system, late-preterm infants are at increased risk of a variety of infections and need antibiotics. In the present study, 98% of infants had received antibiotics. According to our results, Drazdienė and co-workers demonstrated “during one respiratory syncytial virus (RSV) season, the incidence of lower respiratory tract infection (LRTI) hospitalizations among late-preterm infants were 6.5% and the incidence of RSV LRTI hospitalizations was 1.7%. The majority of hospitalized infants (94.7%) had a mild or moderate respiratory illness (26). Similarly, the frequency of need for antibiotics was reported to be 83.5% in the study conducted by Lotfalizadeh and colleagues (14). However, Kitsommart et al. reported that the need for antibiotics among infants was equal to 56.5% which is less than the present study (13). In addition, the prevalence of sepsis )including pneumonia) in this study was 9.4%. This figure was reported to be 13.6% by Savitha et al. (15), and 10.3% by Sahana et al. (27) which are consistent with the present study. Jakiel et al. also showed that the prevalence of sepsis is equal to 3.3%. He also found that the prevalence of sepsis in term infants is significantly lower than late-preterm infants (28). In another study which performed by Swiss researcher to evaluate the risk of bacterial infections in late-preterm neonates, Stocker and colleagues suggested that asymptomatic infants in the first 48 hours after birth should be closely monitored, also symptomatic infants immediately need an intravenous antibiotics administration (29). Considering the higher prevalence of sepsis in this study than other studies, there is a need for paying more attention to care and preventing the transmission of infectious agents through examination with contaminated hands and other means of transmission.
The results of this study showed that the risk of congenital heart diseases (CHD) is statistically significant in late-preterm infants. congenital anomalies were the direct cause of neonatal deaths in the study by Abdel Razeq et al (30).
The need for surfactant in the present study was 26% and this amount of surfactant requirement in late-preterm infants is statistically significant. This figure in the study of Kitsommart et al. was reported to be 6.5%, which is not consistent with the present study (13). The incidence of respiratory problems such as RDS, TTN, and ventilator requirements in late-preterm neonates is higher than terms (31). In line with our results, Olivier and colleagues showed that minimally invasive surfactant therapy for respiratory distress syndrome management in moderate and late-preterm infants was associated with a significant reduction of mechanical ventilation exposure and pneumothorax occurrence (32).
The late-preterm infants had higher rates of resuscitation in the delivery room such as chest compression and intubation than control group. In the studies by de Araújo et al. (18) and Afjeh et al. (33) there were a positive correlation between the need for resuscitation and preterm birth which are inconsistent with the present study. In the present study, 16.8% of infants needed resuscitation measures and there was a difference between sexes, as male infants needed these measures more than females. The need for resuscitation measures was reported to be 21% and 18% by Haroon et al. (20) and Kitsommart et al. (13), which are consistent with the findings of the present study.
In our study late-preterm infants had more feeding problems that required nutritional and supportive management. Similar results were found by Savitha et al. (15) and Wagh et al. (34). The best way to feed late-preterm infants is breastfeeding because it is to the benefit of both the mother and the infant. However, these infants need more care and support than term ones, because the sucking- swallowing coordination and ingestion is still immature in these infants and they have nutritional problems. In the present study, the feeding problem is statistically significant in late-preterm infants. Johnson and co-workers demonstrated Infants born late and moderately preterm; 32–36 weeks of gestation, are at increased risk of oral motor and picky eating problems at 2-year corrected age. However, these are mediated by other neurobehavioral sequelae in this population (35). The results of this study showed that 24.7% of infants had feeding problem. This is consistent with the findings of Lotfalizadeh et al. (14) where the prevalence of nutritional problems among infants was equal to 20%.
Late-preterm infants also are at greater risk of developing neurological problems than terms. Jia You and co-workers were observed that the late-preterm infants had impairments in social competence and social cognition before 3 years of age (36). Given the increased risk of death caused by the seizure and long-term complications of this condition, it is necessary to pay more attention to the risk factors of seizure at this age, such as hypoglycemia, hypothermia, and infections.
The rate of mortality in late-preterm infants is three times higher than other infants. In the US, 10% of all neonatal deaths are related to late-preterm infants (37). In the present study, the mortality rate of admitted late-preterm infants was equal to 7.3%. This figure in studies conducted by Kitsommart et al. (13) and Tsai et al. (17) were 0.7% and 3% respectively. The high mortality rate in our study may be due to the fact that our hospital is a tertiary care referral center and hence, we admit sicker late-preterm infants that they had serious morbidities like need to resuscitation at delivery room, respiratory distress and sepsis.