Genetic heterogeneity of prematurity and intrauterine growth retardation: clues from the Old Order Amish.

We studied differences in the role of genetic factors in prematurity and intrauterine growth retardation with the use of data on 312 Amish singleton live children ascertained from Amish records in Lancaster county, Pennsylvania, between 1969 and 1980. Birth and death certificates were obtained on all children, and inbreeding coefficients of child, mother, and father were computed by use of the path method of tracing common ancestors in a unique genealogic registry of Amish ancestors dating back to the 1700s. Multivariate analysis with linear and log linear models showed that a lower mean gestational age and a higher risk of prematurity (less than 37 weeks) and borderline maturity (37 to 38 weeks) were significantly associated with increased maternal inbreeding but not child or paternal inbreeding. On the other hand, a higher risk of intrauterine growth retardation (less than the tenth percentile in birth weight for gestational age) and mild intrauterine growth delay (tenth to twenty-fifth percentile) were associated with increased child inbreeding but not maternal or paternal inbreeding. The analysis suggests the presence of genetic heterogeneity in the etiology of prematurity and intrauterine growth retardation; while prematurity is mostly related to the maternal genotype, intrauterine growth retardation is related to the fetal genotype. The study reemphasizes the need for separating low birth weight into prematurity and intrauterine growth retardation in genetic and epidemiologic studies.