Assessing socioeconomic correlates of birthweight in peninsular Malaysia: ethnic differences and changes over time

This paper presents evidence from the Malaysian Family Life Survey that mothers' reports of their babies' birthweights, including reports of unweighed babies' approximate size at birth, can be used to examine many biological and socioeconomic correlates of birthweight. The study uses a sample of 5583 singleton births that occurred between 1945 and 1976. In these data, the frequency distribution of birthweights and their bivariate and multivariate relationships with the biological correlates of mother's age, baby's sex, first parity and infant mortality are consistent with those found in prospective studies. A new biological correlate, mother's age at menarche, is introduced as a proxy for the mother's nutrition during childhood. Late age at menarche is associated with lower birthweight. Other results show mothers younger than 20 years and older than 35 appear to be at greater risk of bearing small babies, but the former effect is no longer important when parity is controlled. Short interbirth intervals are associated with small babies. We attempt to distinguish whether this is due to prematurity or to maternal nutritional depletion; both effects appear to be operating. Higher income appears to mitigate the pernicious effect of short interbirth intervals. Indian babies weigh significantly less than those of other ethnic groups. Furthermore, birthweights have increased since the 1950s for Malays and Chinese, but not for Indians. The lower birthweights and lack of improvement over time for Indians appear to be due to close birthspacing, lack of access to medical care and falling incomes.