Pregnancy outcome distribution and prenatal diagnosis of autosomal abnormalities, Hawaii, 1986-1999.

Background: Approximately 10% of birth defects result from chromosomal abnormalities. This study investigated the pregnancy outcome distribution of autosomal abnormalities and impact of prenatal diagnosis on autosomal abnormalities.

Methods: Data were obtained from a population-based birth defects registry and included all autosomal abnormalities delivered in Hawaii during 1986-1999.

Results: There were 1,015 autosomal abnormality cases, consisting of 523 (52%) live births, 38 (4%) late fetal deaths, 187 (18%) early fetal deaths, 265 (26%) elective terminations, and 2 unknown pregnancy outcome. Live births comprised the majority of translocations (81%), inversions (93%), and deletions (84%) but a smaller proportion of trisomies (42%). Autosomal abnormalities were prenatally diagnosed in 489 (48%) of the cases, of which 243 (50%) were subsequently electively terminated. By type of autosomal abnormality, prenatal diagnosis rates were trisomy (44%), translocation (68%), inversion (91%), deletion (29%), and subsequent elective termination rates were trisomy (73%), translocation (11%), inversion (4%), deletion (50%). The prenatal diagnosis rate was higher for maternal age 35 years or greater than for maternal age less than 35 years (relative risk (RR) 1.8, 95% confidence interval (CI) 1.6-2.0), as was the elective termination rate (RR 1.3, 95% CI 1.1-1.6). The prenatal diagnosis rate was higher in 1993-1999 than in 1986-1992 (RR 1.2, 95% CI 1.1-1.4), although there was no statistically significant difference between the two time periods for subsequent elective termination rate (RR 0.9, 95% CI 0.8-1.1).

Conclusions: Pregnancy outcome distribution, prenatal diagnosis rates, and subsequent elective terminations rates vary by type of autosomal abnormality.