The growing interest about late preterm newborns in the medical literature encouraged us to conduct this study to evaluate the outcome and clinical complications that could be associated with LPT compared with FT newborns. Our study was conducted on 250 neonates born in Fayoum University Hospital and Beni-Suef General Hospital. Out of them, 70 were LPT and 180 were FT neonates.
We found no statistically significant association between the gender of neonates and LPT delivery. This was in agreement with Teoh et al. [18] However, several earlier studies [19,20,21,22] reported an increased risk of preterm delivery associated with male fetus. Wilms et al. [21] suggested an effect of maternal race on the association between gender and preterm delivery. The postulated explanations for this association included that placental or chorionic trophoblastic cells of the male fetus produce more pro-inflammatory TNFα and lesser anti-inflammatory IL-10 and granulocyte colony stimulating factor than cells from pregnancies with a female fetus, resulting in the generation of a more pro-inflammatory intrauterine environment. Also, differences in gene expressions between placentae of male and female fetuses have been proposed as an explanation for male gender predominance in preterm labor [20].
In the present study, mothers at the extremes of reproductive age have a higher risk of preterm labor. The incidence of late preterm labor was significantly the highest among mothers who were less than 17 years of age, where 80% of them gave birth before 37 weeks of gestation, and the prevalence was also high (50%) when the maternal age was more than 35 years old. In agreement to our results, Carter et al. [23] found that maternal age ≤ 17 and ≥ 35 was associated with increased risk of LPT birth. Kozuki et al. [24] conducted a meta-analysis to study the association of maternal age with preterm delivery and neonatal outcome, and they found that the nulliparous women with age < 18 had the highest risk of preterm birth followed by multiparous women aged ≥ 35 years.
In our study, we did not find any significant association of LPT birth with parity, which is in line with the data reported by a case-control study in 5 Italian Centers [25]. However, in a study conducted over 10 years to estimate outcomes of LPT deliveries, a significantly increased prevalence of late preterm birth in multiparous patient was reported [26].
Comparison between LPT births and FT births in the present study indicated that mothers of LPT neonates were more likely to have had a previous preterm birth, which agrees with results reported by McDonald and his colleagues [27].
Till today, there is a controversy regarding the association between previous abortions and the risk of LPT birth. A systematic review [28] defined that, out of 24 considered papers, 12 reported an increased risk of preterm birth among women with previous abortions. In the present study, there was a significant association between LPT birth and having more than 1 previous abortion.
Several maternal medical conditions, including hypertensive disorders of pregnancy, diabetes, and asthma, have been associated with an increased risk for indicated or spontaneous preterm birth. In the present study, we found an increased incidence of LPT birth with hypertension, while it was not statistically different for gestational diabetes, urinary tract infection, cardiac, or respiratory diseases. In partial agreement to our results, Carter et al. [23] found that comorbidities, particularly hypertension and gestational diabetes, have been associated with the risk of LPT birth.
The mode of delivery has been linked to the risk of LPT births. We found that LPT neonates were more likely to be delivered by cesarean section than FT neonates. The most frequent indications for cesarean sections in LPT neonates were breech presentation and previous cesarean section. None of the CS was elective or indicated for maternal comorbidities. Cesarean sections in preterm deliveries are known to pose increased risks of neonatal morbidity and mortality [29, 30].
We found that Apgar scores after 1 min and 5 min were significantly lower among LPT neonates. These findings were comparable to those reported by in an Indian tertiary care teaching hospital [31]. Also, LPT neonates had significantly lower birth weight and head circumference, which agrees with some earlier reports [12, 32]. Accordingly, the incidence of 11.4% of SGA was significantly higher in LPT neonates compared with the FT group; this was comparable to the results of Araújo et al. [33] as about one quarter of the LPT neonates in their study were SGA.
The outcome of the studied neonates has been evaluated in terms of the feeding pattern, the incidence of NICU admission, as well as neonatal and mortality. In the present study, the LPT neonates had a higher incidence of formula feeding compared with the FT group, which agrees with previous reports [34,35,36]. Some of the reasons postulated for poor breastfeeding included decreased alertness, poor latching on skills, decreased oro-motor tone, disorganized sucking patterns, and poor suck/swallow coordination. The immature suction pressures produced may reduce lactogenesis [34, 35]. All these factors may result in difficulty in establishing maternal-infant bonding and the initiation/maintenance of successful breastfeeding. Feeding issues are of paramount importance in such cases; poor feeding can lead to decreased caloric intake and dehydration, which further exacerbate neonatal complications such as hypoglycemia, hyperbilirubinemia, respiratory distress, and temperature instability [37].
Our results showed that LPT neonates were more frequently admitted to NICU compared with FT neonates; however, no significant difference was observed in NICU readmissions. Moreover, we found that the lower the gestational age, the rate of NICU admission is increased, as there were 43.3%, 50%, and 83.3% for infants born at 36, 35, and 34 weeks of gestation, respectively. Similar results were reported by Tsai and his colleagues [2], where 21%, 43%, and 74% of their cases were to in NICU or special care nursery when born at 36, 35, and 34 weeks of gestation, respectively. Also, they found that hospital readmission rate was not different between LPT and FT neonates.
The duration of NICU stay in LPT neonates in our study was significantly longer than in FT neonates; the mean length of stay in NICU was significantly higher in neonates born at 34 weeks and 35 weeks than in those born at 36 weeks of gestation. Similarly, Hibbard and his colleagues [38] reported a statistically significant increase in both the incidence of NICU admission and duration of stay with decreased gestational age.
From our study, the mortality rate among LPT neonates was significantly higher than among the FT group; stratification of neonates by their GA revealed that the highest rates were among those born at 34th week of gestation, though statistical significance was not reached. In accordance with our findings, Hibbard and his colleagues [38] and Steure et al. [39] reported a significantly increasing mortality rate with the lowering of the gestation age. The lack of statistical significance in comparisons of the preterm subcategories may be attributed to the relatively small size of each subgroup. Moreover, a large population-based cohort study [40] from the USA and Canada showed that preterm infants are at high relative risks for infant death.
In our study, neonatal complications were more frequent in LPT compared with FT infants. The most common complications in the LPT group were neonatal jaundice (34.3%) and respiratory diseases (32.9%). In this study, the frequency of neonatal jaundice was significantly higher in LPT neonates compared with the FTs (34.3% vs. 7.8%). Similarly, Darcy [41] and Premji et al. [42] found that hyperbilirubinemia is the most common reason for admission in the LPT population (41.4% vs. 12.9% and 38.4% vs. 7.2%, respectively).
The most common cause of respiratory distress in LPTs was RDS (72%). Our study results were analogous to those reported by Tsai and his colleagues [2], who reported more neonatal respiratory complication in the LPT than in FT neonates (33.4% vs. 14.2%). Also a study from Pakistan found that LPT newborns had an increased risk of RDS (16.5–18.2% in LPTs vs. 0.3–2% in FTs) [43]. The higher incidence of respiratory distress in LPT neonates could result from immaturity of their lungs [44].
Our results showed a higher need for ventilation in LPT compared with FT infants (56.5% vs. 20%), with significantly higher percentage requiring CPAP and head box in the LPT group. In a similar study, Hibbard and his colleagues [38] found that LPT neonates, particularly those delivered at 34 weeks, required more oxygen supplementation (8.3%), intubation (2.9%), and mechanical ventilation (0.2%) in the delivery room than neonates born at each successive week gestational age.
We compared the incidence of neonatal jaundice and RD among different gestational ages, and it showed that the rate of jaundice increased with lowering of gestational age (50% in the 34th, 35.7% in the 35th, and 26.7% in the 36th weeks of gestation). Also, RD showed a similar trend (75% in the 34th, 42.9% in the 35th, and 6.7% in the 36th weeks of gestation). Our results were comparable with those of Hibbard et al. [38] who found the rates of jaundice were 55%, 45.7%, and 16.1% and those of RD were 50%, 45.2%, and 22.5% in the 34th, 35th, and 36th weeks of gestation, respectively.
We found also that hypoglycemia was significantly higher in the LPT than the FT group, and it decreased with increased GA. Similarly, Marrocchella et al. [45] found a significantly higher incidence of hypoglycemia that decreased with the increase in GA in all LPT compared with FT neonates. This finding could be explained by the limited glycogen stores and rapid depletion of glucose stores from the metabolic demands of the newborn transition period. In addition, cold stress, poor suck/swallow ability, and respiratory complications contribute to the risk of developing hypoglycemia [41, 46]. Another probable explanation for the susceptibility to hypoglycemia in the LPT neonates is that most of those neonates were exposed to steroids during late pregnancy [47].
As regards late onset sepsis, our study revealed that the rate was higher, though non-significantly different, in the LPT compared with the FT group (8.6% vs. 4.4%); the rate followed an inverse relationship with the GA. In partial agreement to our results, Bailit et al. [48] reported a significantly higher rate of late onset sepsis in LPT infants (9.9% vs. 1%), with improvement in NICU admission and rate of cases for each week of gestation until 39 weeks.
In this study, convulsions were significantly higher in the LPT group compared with the FTs; the rate decreased with the increased GA. Comparable findings in neonates born from the 34th to the 39th weeks of gestation were reported by Glass et al. [49]. In addition, Tsai et al. [2] reported that a remarkable risk of neonatal neurological disorders, particularly seizure and periventricular leukomalacia, was noted in LPT neonates.
