RELATION BETWEEN MATERNAL HEMOGLOBIN CONCENTRATION AND BIRTH-WEIGHT IN DIFFERENT ETHNIC-GROUPS

Objective-To assess the relation of the lowest haemoglobin concentrati on in pregnancy with birth weight and the rates of low birth weight an d preterm delivery in different ethnic groups. Design-Retrospective an alysis of 153 602 pregnancies with ethnic group and birth weight recor ded on a regional pregnancy database during 1988-91. The haemoglobin m easurement used was the lowest recorded during pregnancy. Setting-Nort h West Thames region. Subjects-115 262 white women, 22 206 Indo-Pakist anis, 4570 Afro-Caribbeans, 2642 mediterraneans, 3905 black Africans, 2351 orientals, and 2666 others. Main outcome measures-Birth weight an d rates of low birth weight (<2500 g) and preterm delivery (<37 comple ted weeks). Results-Maximum mean birth weight in white women was achie ved with a lowest haemoglobin concentration in pregnancy of 85-95 g/l; the lowest incidence of low birth weight and preterm labour occurred with a lowest haemoglobin of 95-105 g/l. A similar pattern occurred in all ethnic groups. Conclusions-The magnitude of the fall in haemoglob in concentration in pregnancy is related to birth weight; failure of t he haemoglobin concentration to fall below 105 g/l indicates an increa sed risk of low birth weight and preterm delivery. This phenomenon is seen in all ethnic groups. Some ethnic groups have higher rates of low birth weight and preterm delivery than white women, and they also hav e higher rates of low haemoglobin concentrations. This increased rate of ''anaemia,'' however, does not account for their higher rates of lo w birth weight, which occurs at all haemoglobin concentrations.