Incidence of Small for Gestational Age (SGA) Newborns is Significantly Lower than Reported in the Literature

Background –SGA is traditionally defined by either a birth weight that is lower than 2 standard deviations from the mean weight or a weight that is lower than the 10th percentile. SGA babies are susceptible to higher morbidity and mortality rates and to decreased overall growth rate that eventually results in decreased final height when compared to the general population. 10% of SGA babies do not have the expected “catch-up growth” by the age of 3 end are eligible to growth hormone therapy which may increase their final height by an average of 7 cm. Based on statistics one would expect 230 SGA babies for every 10,000 births, of which 25 should receive growth hormone therapy. As our observed incidence of SGA babies with no catch-up growth was significantly lower we have re-evaluation of the incidence of SGA at birth and subsequent catch-up growth achievement.
Method – Birth weights data from the newborn registry at Hadassah hospitals between 2008-2011 were studied and filtered to create a list of newborns presenting SGA. The definition of SGA was based on the accepted 2005 Dolberg's table for Israeli newborns. Percentiles of actual birth weights at Hadassah were compared to the accepted percentile data in Israel.
Results- During 2008-2011, there were 43,417 live births at Hadassah. Only 573 (1.32%) were SGA births. This translates to 132 out of 10,000 births. This finding was repeated in every one of the four years examined. Birth weight percentile comparisons showed that 1st and 5th percentile weights were greater within the Hadassah births as compared to accepted data in Israel by an average of 20%. Infants born at a premature gestational age showed an even greater difference. On the other hand, a comparison of 95th and 99th percentiles showed that commonly accepted birth weight data was greater than the evaluated group by about 5%.
Discussion – This research shows for the first time that accepted data regarding birth weights is at significant variance from actual birth weights; the number of SGA newborns is nearly half of what would be expected. This finding should have an immense influence on morbidity and cost planning regarding SGA in general and growth hormone therapy in particular. Continuation of this research regarding the incidence of catch up growth is ongoing. In light of the heterogeneous population of Jerusalem in terms of origin and socio-economic status, we believe that this data reflects the general situation in Israel. Considering the great effect that this data has on morbidity and planning health economics, the data should be confirmed on a national scale.