Gestational Age - the Most Important Factor of Neonatal Ponderal Index

Ponderal index (fetal weight in grams X 100 / (fetal length in centimeters)3) (PI) is one of the anthropometric methods used to diagnose impaired fetal growth. Irrespective of the infant's position on the growth-weight-for-gestational age charts, PI is low in malnourished infants and high in obese ones. As fetal growth is affected by ethnicity, geographic location and socioeconomic status, we developed standards for neonatal PI, and assessed the effects of gestational age, sex and maternal parity. Data on 5798 newborns from singleton pregnancies born in the Department of Gynecology and Obstetrics, Split University Hospital, were retrospectively analyzed. Over a 15-month period in 2000/2001, 5596 newborns from 24 to 42 weeks of gestation were born. The other 202 newborns, born from 24 to 34 weeks of gestation in the ten year period, 1990-1999, were added because of the small number of preterm infants; ensuring a minimum of 30 to fill up at least infants in each gestational week. All mothers were of Caucasian origin. Stillbirths and fetuses with congenital malformations were excluded. The 10th, 50th and 90th percentiles, mean values with standard deviation of PI and the 10th, 50th, and 90th percentiles of birth weight and birth length are presented separately at weekly intervals. PI showed linear correlation with gestational age from 24 to 39 weeks, after witch the data plateaued. Sex and parity had no impact on PI in infants born between 24 and 37 weeks. Analysis of variance revealed PI to be significantly higher in female than in male newborns, and in multiparous than in nulliparous infants after 37 weeks of gestation. In conclusion, gestational age is the most important factor of neonatal PI. The effects of sex and parity on PI should only be considered in term neonates.