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Racial variation in incidence of trisomy 21: survey of 57,742 Chinese deliveries.

The objective of this study was to establish whether the influence of advanced maternal age on the incidence of trisomy 21 in the local Chinese population is similar to that seen among European patients by comparing the observed number of trisomy 21 cases against the expected number which was calculated from age-specific Caucasian data and adjusted for intrauterine lethality and rate of amniocentesis. The obstetric and neonatal data of 57,742 pregnancies in ethnic Chinese were reviewed, of which 10.5% were from mothers age 35 or over. A total of 74 cases of trisomy 21 was detected (overall incidence of 1.28 per 1,000 deliveries). The expected number of trisomy 21 cases in mothers younger than 35 was 45.6, which was similar to the observed number of 43. Among mothers age 35 or above, the expected and observed numbers of cases were 38.52 and 31, respectively, again a difference not statistically significant. Therefore we conclude that there is no significant racial variation in the incidence of trisomy 21, both in the younger and older age groups, when comparing Chinese to Caucasian populations.