['To assess pregnancy outcome in women with anaemia during pregnancy.', 'The study design involved a retrospective chart review of all women registering for prenatal care in the area of Kuopio University Hospital between 1990 and 2000. A haemoglobin concentration below 100g/l was used as a cutoff for anaemia and affected women (N=597) were stratified by the trimester at which anaemia was diagnosed. Multiple regression analysis was used to compare obstetric outcomes in the study groups and in non-anaemic women (N=22,202).', 'The frequency of anaemia was 2.6%, with 0.3% occurring in the first trimester. After controlling for confounding factors, anaemia detected in the first trimester was associated with low-birth-weight infants (OR=3.14, 95% CI: 1.35-7.28) whereas the mid- and third-trimester anaemia groups showed no significantly different outcomes when compared with the non-anaemic women. First trimester anaemia was not significantly associated with small birth weight for gestational age (OR=0.98, 95% CI: 0.41-2.17) or with premature delivery <37 weeks (OR=1.80, 95% CI: 0.72-4.49).'] Is anaemia in the first but not in the second or third trimester a risk factor for low birth weight?