Maternal ageing and aneuploid embryos--evidence from the mouse that biological and not chronological age is the important influence.

Maternal ageing remains the overwhelming factor in the aetiology of human aneuploidy. Whether aberrant meiotic chromosome segregation in the oocyte relates causally to ovarian physiological ageing or to some factor dependent on the passage of chronological time, remains to be determined. The present experimental studies in the mouse indicate the former. An earlier cessation of reproductive life, brought on by unilateral ovariectomy in CBA females, resulted in the earlier onset of irregular cyclicity and an earlier rise in aneuploidy. The results could not be explained on the basis of the "production line" hypothesis. The clinical implications are that the probability of conceiving a Down foetus will be determined by distance in time from the approaching menopause, rather than by the chronological age of the woman per se.