The ponderal index in term newborn siblings

Rohrer's ponderal index in newborns (birth weight/heights x 100) has been used as an indicator of fetal growth status, especially to assess asymmetrical intrauterine growth retardation. Because low birth weight and intrauterine growth retardation tend to recur in sibships, we examined patterns of sibling correlation in the ponderal index in 795 live term (greater than or equal to 37 weeks) singleton sibling pairs without birth defects born between 1966 and 1986 and fathered by male US Army veterans participating in a nationwide health study. Data on birth weight, length, gestational age, and other maternal and infant health characteristics were abstracted from hospital-of-birth medical records. The correlation coefficient of ponderal index in sib pairs was 0.24 (p less than 0.001). Compared with 627 infants who had a prior sib with a ponderal index between the 10th and 90th percentiles, 92 infants who had a prior sib with ponderal index less than the 10th percentile had a lower mean ponderal index and a higher proportion with ponderal index less than the 10th percentile (13.0% vs. 8.5%). On the other hand, 76 infants who had a prior sib with ponderal index greater than the 90th percentile had a higher mean ponderal index and higher proportion with ponderal index greater than the 90th percentile (17.1% vs. 10.2%). The clustering of ponderal index in siblings persisted after controlling for factors such as race, gender, maternal age, gravidity, year of birth, gestational age, pregnancy complications, and prior maternal illnesses. The findings point to the presence of genetic and/or maternal factors affecting the growth status of term newborn infants. The significance of the ponderal index needs to be examined in future genetic and epidemiologic studies of intrauterine growth.