title: Chromosomal analysis in 894 induced abortuses from women of advanced maternal age in relation to gestational weeks and fetal sex ratio.
abstract: OBJECTIVE
  To clarify the prenatal sex ratio, and types and frequencies of chromosome anomalies in relation to gestational weeks in women of advanced maternal age.
  
  
  METHODS
  Chromosomal analysis was performed in 894 induced abortuses derived from elderly pregnant women 35 or more years of age.
  
  
  RESULTS
  The embryonic sex ratio in the chromosomally normal (abnormal) gave a preponderance of females over males in lower gestational weeks [366/458 (63/73); 79.9 to 100 (86.3 to 100) in 4-10 weeks]; the reversal of dominancy in those from females to males occurred in the 11th gestational week [41/29(5/4); 141.4 to 100 (125.0 to 100) in 11-20 weeks]. The frequency of trisomy in females at 10 weeks of gestation was significantly high (7/28; 25%).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Obstetrics and Gynecology, Hokkaido University School of Medicine, Sapporo, Japan.
authors.forename: N
authors.initials: N
authors.lastname: Hoshi
authors.forename: K
authors.initials: K
authors.lastname: Hanatani
authors.forename: T
authors.initials: T
authors.lastname: Kishida
authors.forename: T
authors.initials: T
authors.lastname: Sagawa
authors.forename: S
authors.initials: S
authors.lastname: Fujimoto
mesh_terms: D000028:Abortion, Induced / Q000706:statistics & numerical data*; D000328:Adult; D002869:Chromosome Aberrations / Q000175:diagnosis / Q000453:epidemiology*; D025063:Chromosome Disorders; D005260:Female; D005865:Gestational Age; D006801:Humans; D015994:Incidence; D007621:Karyotyping; D008297:Male; D008423:Maternal Age; D008875:Middle Aged; D010053:Ovary / Q000502:physiology; D011247:Pregnancy; D018566:Pregnancy, High-Risk; D012744:Sex Ratio; D014314:Trisomy