Perinatal mortality by birth order.

The conclusion reached by Bakketeig and Hoffman in an article published in the September 22, 1979 issue of the British Medical Journal that when sibship size is fixed, perinatal mortality declines with increasing parity, is erroneous since it is based on a statistical artefact. The positive association between increased perinatal mortality and parity observed in cross-sectional surveys may reflect either that more high risk women were included in the higher parity pregnancy group or that the risk of perinatal mortality actually does increase with parity.