Commentary

The study by Nybo Andersen et al is undoubtedly generalisable. Because of its population based design, it provides the best estimates to date of the incidence of pregnancy loss and its association with maternal age and previous reproductive history.

The authors do not attempt to explain their findings. The cause of miscarriages in older women now seems to be well understood: chromosomal deletions and fatal trisomies resulting from non-disjunction during meiosis are probably the underlying biological mechanisms.¹ Whether these mechanisms also explain the increased likelihood of ectopic pregnancy in older women remains to be seen. The study by Nybo Andersen et al favours the hypothetical role of the fertilised egg itself in the pathogenesis of ectopic nidation. Accumulation of other risk factors with increasing age (ie, those impairing tubal function) might also explain the association.²

The relation between stillbirth and maternal age, straightforward as it may seem, is much more difficult to comprehend. Stillbirths may result from a wide variety of underlying causes, such as vascular compromise with ensuing placental insufficiency and congenital malformations. Stillbirths represent only those cases in which obstetric intervention came too late or was deliberately withheld. Consequently, the study shows only the tip of the iceberg with respect to the true effect of maternal age on obstetric problems. If perinatal mortality had been the focus of the study (ie, including intrapartum and neonatal deaths), the prospects for older women would have been even grimmer.^{3, 4}

The authors conclude that the current tendency to postpone pregnancy increases the overall incidence of fetal loss and possibly the costs of health care. Information about these findings should be part of counselling in decisions about reproduction. Apart from these messages, the paper contains reference data for all researchers in the field of human reproduction and is bound to become a touchstone study.