Data on structural chromosome abnormalities identified during prenatal diagnosis were used to estimate the number of such abnormalities that would be detectable in an unselected series of newborns using moderate levels of banding (400 to 500 bands). These estimates were compared with the rates detected in nonbanded surveys of newborns.Between 1976 and 1990 prenatal diagnosis using banding techniques was carried out in our laboratory on 14677 women aged 35 and over. Among these, we detected 112 structural rearrangements, 32 unbalanced and 80 balanced. These figures were adjusted by two methods to give an estimate of the frequency of structural abnormalities in the newborn. Our data suggest that the use of moderate levels of banding increases the frequency of unbalanced structural abnormalities from 0-052 to 0-061% and of balanced structural abnormalities from 0-212 to 0-522%. Thus, the total number of chromosome abnormalities detectable in the newborn is increased from 0-60% in unbanded preparations to 0-92% in banded preparations.
This report describes the third case of a complete trisomy 9 in a liveborn infant. A tentative explanation for the origin of a "very large" h-segment which was not present in either parent of the proposita is put forward.
The uptake of amniocentesis in Wessex for the period 1986-1988 was 36 per cent (2873 of 8004 births), a proportion that has not altered significantly since 1984. There is a large difference in uptake between women in the lower risk age group, 35-36 years, and those in the higher risk group, 37+ years, and very considerable differences in uptake among different districts. The prenatal detection over the 3-year study period for women aged 35 or more, after correction for spontaneous loss of Down's syndrome fetuses between prenatal detection and birth, is 53 per cent, a figure that must be inflated due to our failure to ascertain all liveborn Down's syndrome patients.
Prenatal diagnosis of mosaicism involving an apparently unstable 13/14 Robertsonian translocation is reported. This illustrates the difficulties encountered in counselling when mosaicism is ascertained prenatally. Other reported examples of apparently unstable Robertsonian translocations are discussed.
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