Suboptimal fetal growth resulting in an SGA infant or FGR is an important issue which is linked to increased morbidity and mortality rates, decreased lifespan as well as increased cost of care. Approximately five decades ago, it was reported that SGA infants born at term gestation had 6-fold increased risk for neonatal mortality and 3-fold increased risk for neonatal morbidities compared with the term appropriate for gestational age (AGA) infants . Previous studies have shown that asymmetric SGA infants (infants with PI < 10th percentile) have higher neonatal morbidity than symmetric SGA infants (infants with PI > 10th percentile) in terms of acute neonatal consequences including metabolic and hematological disturbances plus disrupted thermoregulation [1, 4]. In this study, we showed that term SGA infants with low PI had higher risk of hypoglycemia, jaundice requiring treatment and hospitalization rate than SGA infants with appropriate or high PI. None of the infants died or had a life threating complication due to growth restriction.
SGA infants face with many different medical problems after birth. The infants who are severely affected, deprived of oxygen and nutrients, may have difficult cardiopulmonary transition and develop perinatal asphyxia, meconium aspiration or persistent pulmonary hypertension. Due to respiratory distress, gastrointestinal problems, metabolic and hematologic disturbances, the hospitalization rates are higher in SGA infants than AGA infants [1, 12, 21]. Among our subjects, only one developed perinatal asphyxia but none developed persistent pulmonary hypertension. Although nine infants had meconium-stained amniotic fluid, only one of them with an appropriate PI developed meconium aspiration syndrome. However, in our study, hospitalization rates of SGA infants with low PI (15.6%) were higher than the infants with appropriate and high PI (5.9 and 5.1%, respectively) (p = 0.04).
Hypothermia is another common complication that can be observed in these infants due to inadequate measures of temperature control. Relatively large body surface area, low body and subcutaneous tissue fat, impaired thermoregulation and catecholamine consumption plus simultaneous occurrence of hypoglycemia and hypoxia are the main causes of hypothermia [12, 21, 22]. In this study hypothermia was only observed in five infants, all of whom had appropriate PI (group 2) which was not statistically significant.
In the first days of life, as a consequence of delay in postnatal metabolic adaptation, hypoglycemia becomes a major concern for SGA infants. It can be observed due to low glycogen stores, decreased gluconeogenesis, increased sensitivity to insulin, low fat and decreased ability to oxidize free fatty acids and triglycerides. In addition, perinatal asphyxia, polycythemia and hypothermia can exacerbate hypoglycemia [12, 21, 23]. The results of many reports recommend screening of SGA infants in the first 24 hours of life. There is no single set blood glucose concentration below which hypoglycemia is linked to neurologic deficit. According to AAP, the target plasma glucose concentration should be 45 mg/dL or higher for all infants . Doctor et al.  compared 372 SGA infants with the same number of AGA infants and demonstrated that SGA infants had significantly higher rates of hypoglycemia (5%) than AGA infants (1%). Deorari et al.  noticed that, of the 144 SGA infants, 24 (17%) of them developed hypoglycemia. Moreover, the ones whose BW was < 3th percentile (n = 12) had higher risk (25.5%) than the ones whose BW was between 3th -10th percentile. Nili et al.  conducted a study with 361 term SGA infants and reported that hypoglycemia was higher in the term SGA infants with low PI group than the infants with appropriate and high PI which was statistically significant. In the present study, the incidence of hypoglycemia was the highest in infants with low PI; 45% of these infants had hypoglycemia in this group and hypoglycemia was the lowest in infants with PI over 90th percentile (18.9%), which was statistically significant (p = 0.01). This result is rational; hence PI of babies increase as the BW increases, thus providing more glycogen stores to the babies.
Jaundice (indirect hyperbilirubinemia) is known to be associated with growth restriction in term infants which may be due to decrease in liver size and immaturity of liver function [25, 26]. In this study, we demonstrated that the rate of jaundice requiring phototherapy was 17.8% in low PI SGA infants which was higher than the other two groups (5.9 and 2.6% in infants with appropriate and high PI, respectively) and was statistically significant (p = 0.006).
We only included term babies in our study and therefore found no correlation between the GA and PI, though PI values increase as GA of the infants increase, they remain constant after the 37th week of gestation .
The present study has some limitations. First, the measurements were performed by several newborn nurses and the study is retrospective which may explain the discrepancy among the groups. Secondly, maternal socio-cultural and socio-economic levels were higher that may not reflect normal population. In addition, the data on maternal characteristics and the records of maternal weight gain during pregnancy were not available which would determine an association between poor maternal weight gain and low PI.
In conclusion, in the present study we demonstrated that SGA infants with PI levels less than 10th percentile have higher short-term complications including hypoglycemia, jaundice requiring treatment and hospitalization rate than other SGA infants. However, independent of PI, all SGA infants should be considered as a high-risk neonate and should be monitored closely for early identification of any short-term complication during the neonatal period. In this study, there is no data about the long-term outcomes of these infants. It is also recommended to follow-up all SGA infants including low PI infants in terms of neurologic, cognitive and metabolic outcomes in the long term and evaluate these babies according to their long term outcomes also.