Patterns of Chromosomal Translocations Identified by a Birth Defects Registry, Hawaii, 1986–2000

Nuchal translucency thickness in the prediction of unbalanced translocations

OBJECTIVE

The aim of this study was to assess the role of nuchal translucency (NT) in the prediction of unbalanced translocation in offspring of couples in which one of the parents is a balanced translocation carrier.

MATERIAL AND METHODS

From January 1996 to December 2012, fetal NT was measured before chorionic villus sampling in 86 pregnancies referred because of parental balanced translocation.

RESULTS

No significant differences in pregnancy characteristics and in NT expressed in millimetres or in multiples of the median (MoMs) were observed between the 41 fetuses with a normal karyotype [1.72 mm, 95% confidence interval (CI): 1.49-1.96; 1.14 MoM; 95% CI: 1.01-1.26], the 38 fetuses with balanced translocations (1.78 mm, 95% CI: 1.44-2.12; 1.22 MoM; 95% CI: 1.01-1.43) and the 7 fetuses with unbalanced translocations (2.21 mm, 95% CI: 1.33-3.09; 1.59 MoM; 95% CI: 0.72-2.45). The proportions of fetuses with NT above 95th centile in the three groups were 9.1% in fetuses with normal karyotype, 18.4% in balanced translocations and 28.6% in unbalanced translocations, not significantly different.

CONCLUSION

Although a trend to an increased NT was observed in fetuses with unbalanced translocation, no significant differences were reached. According to our results, a normal NT evaluation should not preclude the performance of CVS in pregnancies of balanced translocation parents.

Patterns of chromosomal deletions identified by a birth defects registry, Hawaii, 1986-2003

The aim of the investigation was to describe the chromosomal deletions identified by a birth defects registry with respect to the chromosomes involved, pregnancy outcome, method of diagnosis, inheritance, sex, and the diagnosis of major structural birth defects. Cases were derived from a population-based birth defects registry in Hawaii and comprised all infants and fetuses with chromosomal deletions delivered during 1986-2003. A total of 71 cases were identified through a statewide birth defects registry in Hawaii during 1986-2003. The chromosomes involved in the greatest proportion of deletions were chromosomes 22 (14.1%), 4 (11.3%), and 5 (11.3%). Live births accounted for 58 (81.7%) of the cases. Diagnosis was made by amniocentesis or chorionic villus sampling in 19 (26.8%) of the cases. Of the 18 cases with known inheritance, the deletion was inherited in 5 (27.8%) and de novo in 13 (72.2%). Males accounted for 28 (39.4%) and females for 43 (60.6%) of the cases. Major structural birth defects were identified in 51 (71.8%) of the cases. Chromosomal deletions do not appear to affect all chromosomes equally. Most of the chromosomal deletions that were detected occurred among live births and were de novo conditions. Infants and fetuses with chromosomal deletions are more likely to be females and to be associated with major structural birth defects.

Nuchal Translucency Thickness in Fetuses With Chromosomal Translocation at 11–12 Weeks of Gestation

OBJECTIVE

To investigate differences in nuchal translucency thickness among fetuses in which either parent is a balanced chromosome translocation carrier.

METHODS

A prospective observational study was conducted with 98 pregnant women in the first trimester. Each had been advised to undergo chorionic villous sampling for fetal karyotyping for the indication of parental balanced chromosomal translocation. Fetal nuchal translucency measurement was performed before chorionic villous sampling. Nuchal translucency thickness was compared among fetuses with 3 kinds of karyotypes: normal, balanced translocation, and unbalanced translocation.

RESULTS

There were no differences in maternal age, gestational age, parity, and number of previous miscarriages among pregnancies with normal karyotype, balanced chromosomal translocation, and unbalanced chromosomal translocation. A significantly greater nuchal translucency thickness was shown in the unbalanced chromosomal translocation group (2.9 +/- 1.2 mm) compared with both the balanced chromosomal translocation group (1.0 +/- 0.6 mm; P < .001) and the normal karyotype group (1.0 +/- 0.8 mm; P < .001). No statistically significant difference in nuchal translucency thickness was found between the balanced chromosomal translocation group and normal karyotype group (P = .991). Nuchal translucency thickness did not differ significantly between unbalanced chromosomal translocation dependent on paternal origin and that dependent on maternal origin (P = .611).

CONCLUSION

In fetuses with unbalanced chromosomal translocation, nuchal translucency thickness tends to be greater, and thus nuchal translucency measurement might be considered part of the investigation for pregnancies marked by a parental balanced chromosomal translocation.