Variation of sex ratio within very large sibships

Juntunen et al. (1997) report some remarkable data on the variation of sex ratio (proportion male) at birth within sibships of 10 children (largely produced by devout Lutherans in northern Finland). They found that the sex ratio declined significantly with birth order, maternal age and paternal age. However, stepwise logistic regression suggested that, of these variables, maternal age was the only significant independent one, and these authors concluded that their high maternal age 'explains why grand grand multiparous women deliver more girls than boys'. I suggest that, in general, such women do not deliver more girls than boys, and that these authors were wrong to generalize from their data -which in turn need explaining.