Trisomy accounted for 41% of miscarriages: chromosomal abnormalities linked to age seen in most miscarriages.(Obstetrics)

VANCOUVER, B.C. -- Chromosomal abnormalities accounted for more than half of 1,103 miscarriages karyotyped in a recent study, and the majority of abnormalities in women aged over 40 years were trisomic.

Overall, trisomy accounted for 41% of the miscarriages, which occurred between 1998 and 2001. Triploidy was involved in 9%. Seven percent of the miscarriages were monosomic, 1% were tetraploid, and 4% had structural abnormalities. The remaining 38% of miscarriages were considered chromosomally normal, but some likely also had genetic abnormalities that could not be detected by cytogenetic analysis, Wendy P. Robinson, Ph.D., said during the annual meeting of the Teratology Society.

"I would argue we're only seeing the really big genetic changes here," she said. "I'm certain there have got to be at least some other genetic defects--either smaller chromosomal changes or point mutations that contribute to some of these remaining normals," commented Dr. Robinson of the department of medical genetics at the University of British Columbia, Vancouver.

Whereas maternal age is considered the leading risk factor for trisomy, monosomy X is often the result of loss of a paternal chromosome, and such abnormalities are increased when the father is subfertile, said Dr. Robinson.

Trisomy 21 has been the subject of extensive research in its association with Down syndrome, however, little is known about the causes of trisomy in general.

"We're left with this fact that trisomy increases with maternal age, but we can't find a lot that's associated with it," said Dr. Robinson.

One popular theory is that increased rates of miscarriage in older age are the result of follicular depletion, in which the ...