Table I: Neonatal complications of very preterm (n=247) and moderate preterm infants (n=228)


Table II: The rate of administration of antenatal steroids and infant surfactant treatment, nasal CPAP, and advanced resuscitation were used  according to gestational age


Table III: The ferequncy of death according to infant age


Discussion
 
This study was conducted to assess risk factors for preterm birth and perinatal outcome in terms of perinatal mortality and morbidity for infants born at less than 34 weeks gestation. As known premature births are increasing in recent years and the highest rate of mortality and morbidity are seen in this age. Our results showed that preterm babies represented about one-fifth (23%) of all newborn births in our hospital; among these 40.08% were less than 34 weeks gestation. Significant obstetrical risk factors for preterm labor were preeclampsia (21%), premature rupture of membranes (20.3%), abruption of placenta (10%) and idiopathic cases (48.7%). These results were consistent with other studies' findings (3).
In another report conducted in Shiraz, the rate of preterm delivery was significantly higher as compared to the results obtained in this study. This may be due to the improvement of prenatal care services during the last decade in Iran (13).
The neonatal mortality rate in infants at less than 34 weeks was 9.05%. In infants with gestational age of 32-33 weeks and 6 days, the mortality rate was 2.6%. In our study, while no mortality was reported in infants with the same age by Bastek et al study (14). In our study, for infants with gestational age less than 32 weeks, the mortality rate was 15%, that is similar to Larroque et al (14%) and Torres et al report (16%) (15, 16). While in Stoelhorst et al study this rate was shown to be 11% (17). Higher infant mortality in the present study could have been arisen from a low percentage of pregnant mothers who received antenatal treatment with corticosteroid (36% versus 73%) (17).
Of course, the lower level of care in neonatal intensive care unit may also contribute to the higher incidence of our mortality. In the present study, the most common cause of death in infants less than 28 weeks is was sepsis (27.9%), RDS (23.3%) and pneumothorax (19.2%). In Stoelhorst et al study, RDS and cerebral complications have been the causes of 45% and 24% of deaths respectively (17). Our results demonstrated advanced resuscitation rates in the delivery room in infants with gestational age less than 28 weeks, 28-29 weeks and 6 days, 30-31 weeks and 6 days were 42.2%, and 18.5%, 18.9%, respectively. It can be a major contributing factor in increasing mortality.
In infants with gestational age less than 32 weeks, IVH rate was 9 % (7.5% grade I, II and 1.5% grade III, IV). Compared to Stoelhorst et al and Bastek et al findings, these differences may be related to high frequency of RDS in Stoelhorst et al study and high prevalence of chorioamnionitis in Bastek et al study (14, 17). Our results showed in babies with gestational age of 32-33 weeks and 6 days gestation IVH rate was 0.87%, while Escober and coworkers reported lower rate of IVH (0.6% in babies with 30-31.6 weeks and 0% in infants with 32-33.6 weeks gestation). This was perhaps due to higher steroid treatment of infants in Escober et al study (18).
In the current study, nearly 55% of infants with gestational age ranged 32-33 weeks and 6 days and 40% of babies with gestational age less than 32 weeks had a clinical or positive culture of sepsis. This is higher than incidence of sepsis in the Stoelhorst et al's study (28%). This could have resulted from different criteria that we used for the diagnosis of sepsis. In Stoelhorst et al. study the diagnosis of sepsis was based on positive blood culture, whereas in our study, the diagnostic criteria were clinical signs and (or) positive blood culture (17). The incidence of sepsis was 43.4% in infants with gestational age 32-33 weeks and 6 days in Bastek et al's report which demonstrates the need for extra care in our hospitals (14).
The occurrence of RDS was 35.4 % in infants with gestational age at less than 32 weeks in our study which was lower, compared to Stoelhorst et al. report (60%) and Torres et al. study (64%) (16,17). This is justified by a higher incidence of our mortality in the delivery room or in the first few hours of birth before developing symptoms of respiratory distress syndrome or more infants with small for gestational age or ethnicity differences. In our study, 30% of infants less than 32 weeks received surfactant treatment, which was lower than the Stoelhorst and coworkers study (42% of cases received surfactant) (17). Basteke et al. reported a 41% rate of RDS in infants with gestational age between 32 to 33 weeks of gestational age that was lower than our finding (48.24). This may be related to the high prevalence of chorioamnionitis in Bastek et al. (i.e. 37.7% versus 0% in our study) that accelerated maturation of the lungs. 17.5% of our infants between 32 and 33 weeks and 6 days have received surfactant, which was not much different compared to Basket et al. study (18%). 17.5% of our babies through 30 and 33 weeks and 6 days received surfactant treatment that was similar to Bastek et al report (18%) (14). But more than 24.6% of babies with the same gestational age received treatment in Scober et al. study (18).
In the present study, the incidence of patent ductus arteriosus in infants with less than 32 weeks was 24.3% that was slightly higher compared with other study (26%) (17). It may be due to ethnicity differences or prophylactic use of indomethacine in our center.
In addition, in this study the retinopathy of prematurity rate was 6.1%, 0.87%, and 2.1% among infants with less than 32, 32-33 and 6 days and 30-33 weeks and 6 days of gestation, respectively, that was greater than that of Escober and coworkers' study in age groups of 30-33 weeks and 6 days (0%) (18). A systematic approach should start from the delivery room in order to reduce the rate of this morbidity. In our study, the frequency of broncho pulmonary dysplasia was 1.6% among infants at less than 32 weeks of gestation. In the Stoelhorst et al. report the prevalence of this diagnosis was 19% and the frequency of this morbidity was reported 6.7%. Escober and coworkers reported this finding with a frequency of 1% among infants 30-31 weeks and 6 days and 32-33 weeks and 6 days of gestation (17, 18). This discrepancy may be due to greater use of nasal CPAP in our center. In our study, nasal CPAP was used in 43.7% and 56.5% of infants through 30-31weeks and 6 days and 32-33 weeks and 6 days, respectively, while in Escober et als study this rate was 19% among infants. Only 18.9% of our infants received mechanical ventilation versus 45.7% in Escober et al study. This discrepancy is acceptable due to the high rate use of nasal CPAP (18).
The prevalence of necrotizing enterocolitis was 2.02% among infants born with gestational age less than 32 weeks and 1.3% among babies born at 32 to 33 weeks and 6 days respectively. Stoelhorst and coworkers reported the necrotizing entrocolitis rates 9% among infants born with gestational age less than 32 weeks. Whereas these frequencies were published 1.2% and 0.7% for infants born through 30-31 weeks and 6 days and 32-33 weeks and 6 days, respectively in Escober et al. study and the prevalence of this morbidity was reported 8.2% for infants born through 32 -33 weeks gestation in Basket et al. study. This significant difference is acceptable due to better care of infants in Escober et al. study and a high percentage of their mother who received treatment with betamethasone. While in comparison with Bastek et al. report, it may be justified by high prevalence of chorioamnionitis (37.7%) in Bastek et al. study. The high rate of infants mortality before admission in the hospital may be a possible explanation for the difference seen with Stoelhorst et al study (14, 17, 18).
regarding the result of this study mortality and sepsis rates of infants at less than 32 weeks is greater than similar studies and rate of RDS, IVH, BPD and necrotizing enterocolitis are less than the other studies. In our study, with increasing gestational age from 28 to 34 weeks, the mortality rate is clearly reduced, but it is not true about incidence of sepsis and respiratory distress. This may be due to pregnancy with premature rupture of membrane expectantly managed until 34 weeks gestational age. This reason is required to be examined in future studies.
This study found that in order to achieve significant reductions in adverse outcomes of preterm infants the following step should be taken. First, the clinicians must focus their efforts on prevention of preterm birth by implementation of effective strategies for identifying the high risk group of preterm delivery in asymptomatic women by sonographic measurement of cervical length at 18 weeks gestational age during anomaly scan and special attention should be placed  in the uterine artery PI for prediction of preeclampsia at 12 weeks gestational age during first trimester screening. Second, it is necessary to pay more attention to improve our mothers’ knowledge about the warning signs of pregnancy since a high proportion of high risk mothers, admitted just at the time of delivery, make management of these groups difficult. Third, appropriately increased resources should be considered to meet the needs for care of this high risk babies and greater attention needs to be paid for conducting formal evaluations of the therapies and to follow-up strategies employed in caring of preterm infants. This study has several limitations. First, this is a retrospective study, which may encompass some missing data. Second, the data were collected just from one hospital files which may not be too representative of all maternity hospitals in Iran. Also, the sample size should be increased in further studies.
 
Acknowledgments
 
This work was funded by a grant from Vice Chancellar in Research Affairs of Shahid Beheshti University of Medical Sciences, Tehan, Iran.
 
Conflict of interest
 
The authors declare no conflict of interest.