Chromosome analysis in human oocytes remaining unfertilized after in-vitro insemination: effect of maternal age and fertilization rate

The incidence of chromosomal abnormalities was studied in 719 unfertilized human oocytes obtained from our in-vitro fertilization (IVF) programme, To make chromosome preparations, a gradual fixation/air-drying method was utilized, Of 388 oocytes successfully karyotyped, 70 (18.0 %) were abnormal, The abnormalities included 33 aneuploidies (8.5%) (14 hyperhaploidies and 19 hypohaploidies), 25 diploidies (6.4%) and 15 structural abnormalities (3.9%), three of them being accompanied by aneuploidy. Of the 33 aneuploidies, 16 (48.5%) showed the loss or gain of dyads (so-called non-disjunction), while 17 (51.5%) showed the loss or gain of monads (so-called predivision). There was no maternal age-dependent increase in the incidence of aneuploidy, Unfertilized oocytes from patients with a high fertilization rate (>25 %) had a significantly higher (11.4 %, P < 0.05) incidence of diploidy compared with the oocytes from the remaining patients (4.3 and 4.0%), suggesting that diploid oocytes might have a lower fertilizing ability.