No abstract

The aims of the present study were to determine recent trends in the prevalence of Down syndrome (DS) in Japan, and to determine whether recent changes in demographic and social habits and access to prenatal diagnosis have influenced the livebirth rates of DS. Livebirth statistics indicate that the birth rate in Japan has decreased for women in their 20s and has increased for those in their 30s and 40s. During an 18-year period between 1980 and 1997, 1,299 consecutive DS infants were born among a total of 2,232,694 births, a rate corresponding to approximately 10% of all births in Japan over the same period. The increasing risk of DS with advancing maternal age was confirmed. The overall prevalence was 5.82 DS births per 10,000 livebirths (8.3-9.7 per 10,000 after correction according to the estimated ascertainment ratio: 60-70%). The prevalence rate by year of child birth represents a statistically significant increase (P = 0.001). In conclusion, recent trends in the prevalence of DS in Japan from 1980 to 1997 failed to show a consistent tendency to decrease, probably because of the concomitant increase in pregnancy in advanced maternal age.

The use of a TCBC with 180-250 mL of saline increases the risk of cord presentation.

Cytogenetic amniocentesis (CA) has been performed as a reliable prenatal diagnostic method for decades. The aims of the present study were to reveal the frequency of fetal chromosome abnormalities according to medical indications of CA, and to assess the risks of specific abnormal ultrasound findings. Data on chromosome karyotypes of fetuses from 5043 Japanese mothers were collected. Group I comprised 4626 fetuses whose mothers underwent CA due to a variety of parental reasons. Group II comprised 417 fetuses whose mothers underwent CA due to fetal abnormality, abnormality of amniotic fluid volume and fetal growth restriction. The frequency of chromosome abnormalities in Group II (17.7%) was significantly higher than in Group I (1.8%). The frequencies of chromosome abnormalities in Group II singleton fetuses with fetal abnormality, polyhydramnios and fetal growth restriction were 21.5, 22.9 and 19.6%, respectively. By multivariate analyses, we found that cystic hygroma (odds ratio 5.6, 95% CI 2.7-11.6), abnormal extremity (5.0, 1.7-14.4) and cardiovascular abnormality (3.3, 1.1-10.1) were significant variants associated with fetal chromosomal abnormalities. Information revealed in the present study constitutes a beneficial reference for genetic counseling.

This study showed that the existence of a difference of and a reversal of the sex ratio in gestational weeks. It was considered that there might be a lower viability of genetically handicapped males as compared to such females. However, the reversal of the sex ratio, such as that observed between 9th and 10th gestational weeks, might reflect events occurring after implantation.