Low birth-weight and pre-term delivery in South-East Asia. The who international collaborative study of hypertensive disorders of pregnancy

Population-based data from 10 centres in Burma, Thailand, China and Vietnam, have been analysed to assess those social and environmental factors which may be associated with pre-term delivery and low birth-weight. The philosophy behind the study was that if the same association was found in different countries, then the association may be causal; if associations differed in the various countries, then causality was unlikely. The major findings were as follows: a strong association between low birth-weight and pre-term delivery and the unmarried state (RR 1.64, 1.39), a consistent reduced risk of pre-term delivery when the father was in a managerial post (RR 0.77), an excess risk of pre-term delivery if the mother was a housewife (RR 1.16), lifting heavy objects at the time of quickening (RR 1.63) or frequently bending and stooping at the time of quickening (1.15). Strong associations were found with both paternal and maternal education levels but these were strongest for the mother's education level. The association was far stronger for pre-term delivery than for low birth-weight and it is assumed that the low birth-weight effect is secondary to pre-term delivery. The only variation with maternal age concerned an excess of low birth-weight among teenage mothers, but not of pre-term delivery, and an excess of low birth-weight but not pre-term delivery among mothers with small head circumferences or small arm circumferences. We conclude that the aetiology of growth retardation and pre-term delivery are probably different in South-east Asia, and point out the need to elucidate further the strong variation with education level.