Chromosomal basis of recurrent fetal losses

Chromosome abnormalities constitute the single most etiological factor in spontaneous abortions and other fetal losses and include sporadic chromosome abnormalities such as monosomy, trisomy, triploidy, tetraploidy and chromosomal mosaicism. These errors either originate during gametogenesis or after fertilization during the early zygotic divisions. Based upon the information now available it is apparent that if a couple has had two fetal losses, the karyotypes of the abortuses are most likely to be concordant either both being normal or both being abnormal. Fetal losses may also be due to a chromosome abnormality carried by a parent in a clinically silent form such as a balanced translocation. A compilation of cytogenetic data from 17,112 parents (8,743 females and 8,369 males) revealed 517 instances of chromosome abnormalities, an incidence of 3 per cent (6% of couples). Approximately 50 per cent of all chromosome abnormalities detected were balanced reciprocal translocations, followed by balanced Robertsonian translocations (23%) and sex chromosome mosaicism in females (14%). Parental chromosome abnormalities are known to be factors in abnormal gametogenesis and zygote formation, and, therefore, prenatal diagnosis should be considered in future pregnancies. Further, even when parental karyotypes are normal, prenatal diagnosis should be offered to couples who have had two or more fetal losses due to their increased risk of having a fetus with a chromosome abnormality.