MATERNAL AGE AND INTELLECTUAL FUNCTIONING OF OFFSPRING

Abstract

The Johns Hopkins Collaborative Perinatal Study (Baltimore Maryland) provided an opportunity to investigate possible relationships between maternal age at delivery and subsequent intellectual functioning of the child. In this study extensive information is available for each mother-child pair from the time of registration for prenatal care through 8 years of postnatal life. The subjects were the children of women who registered in the Johns Hopkins Collaborative Perinatal Study. Of the 4558 registrants in the study after exclusion of prenatal cancellations there were 3263 cases with recorded maternal age birth weight and results of Stanford-Binet Intelligence test scores obtained between 3 years 9 months and 4 years 3 months. The remaining 1293 cases were eliminated from this analysis for a variety of reasons. The 3263 children for whom Binet intelligence quotient (IQ) scores were available included 1333 black males 1354 black females 299 white males and 277 white females. This population included a range in socioeconomic (SE) level from welfare recipients to professional workers but the mean SE Index for blacks was 4.1 and for whistes 4.4. The difference was not statistically significant. The mothers and children lived for the most part in East Baltimore and came from the lower middle and lower socioeconomic levels of society. Each of the 3263 subjects was individually tested on the revised form of the Stanford-Binet Intelligence Test in addition to other measurements which comprised the routine 4-year psychological battery according to the protocol devised for the National Collaborative Perinatal Study. The null hypothesis that maternal age at the time of delivery has no relationship to the later intellectual functioning of the mothers offspring was tested and found to be incorrect. For both blacks and whites both intellectual functioning and birth weight increased with maternal age. The youngest black mother produced children with mean IQ scores in the mid 80s; older black mothers produces children with mean scores in the mid 90s. Young white mothers on the average slightly older than blacks produced children with scores in the lower 90s. The observed increase in IQ scores with increasing maternal age was clearly seen even when the effect of birth weight was minimized by exclusion of babies weighing less than 2500 grams at birth. When birth weight and IQ scores were compared babies weighing less than 2000 grams were observed to have the lowest mean IQ scores. This effect was most marked in the black male population. The black-white differences in measured intelligence in this sample were much smaller than are reported in other studies. The similarity in the mean IQ scores in this population may reflect the fact that both groups of children came from the lower middle and lower socioeconomic levels of Baltimore City.