Although the incidence of Down syndrome increased with advanced maternal age, considerable cases have been reported in young age group. Thus maternal age indication for prenatal genetic diagnosis tends to be somehow lowered.
This study was performed at Yonsei University College of Medicine, Severance Hospital from January 1970 to December 1986, in order to evaluate the change in maternal age as indication for prenatal chromosomal study by analysing the relationship between the maternal age and the incidence of Down syndrome, actual number of Down syndrome and the karyotyping in 202 cases, which included 27 cases confirmed by live birth among total number of 29,800 cases delivered during the study period and 175 cases confirmed by prenatal genetic counselling.
The results were as follows;
1. According to the maternal age group, the age between 25 to 29 showed the highest delivery rate of 58 % (17,296/29,800 cases). The mean maternal age for the normal delivery was 29 years and the majority of the cases (94.1 %) were delivered below 35 years. The incidence of normal deliveries over 35 years of maternal age decreased from 8 % in 1970 to 4 % in 1986.
2. The incidence of Down syndrome was observed in 27 among total 29,800 normal deliveries, 0.091 %. The incidence of Down syndrome according to age below and greater than 35 years old was noted 1/1,169 and 1/579, respectively. The significant increased incidence of Down syndrome was observed in age group greater than 35 years. d-O-
3. There were no significant difference between 27 cases of live born Down syndrome and 175 cases of Down syndrome diagnosed by prenatal genetic counselling according to maternal age greater than 35 years old were noted in 11.1 % and 11.4 %, respectively. The prevalence age group, 25 29 was also noted in 56 % and 62 %, respectively. The actual number of Down syndrome was noted in young maternal age group rather than old maternal age group.
4. According to karyotype analysis, trisomy 21 took account for 85.1 % (172 cases), mosaicism 9.0 % (18 cases) and 5.9 % for translocation (12 cases). The sex ratio of male to female was 8:5 (61.9 %, 38.1 %).
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