[Spontaneous abortion and genetic natural selection].

Author reviews the recent researches related to the genetic causes of spontaneous abortions as well as the results of the cytogenetic examinations of gametes, early embryos and clinical miscarriages. In the background of more than half of first trimester spontaneous pregnancy losses severe chromosomal aberration of the fetus can be found. About 60% of abnormal karyotypes is formed by autosomal trisomies, the rest is divided among polyploidies, X-monosomy and different structural anomalies. The incidence of fetal trisomies correlates with maternal age, besides balanced translocations of parents and delayed fertilisation can also play a role in the etiology of fetal chromosomal abnormalities. Regarding that most of these abnormalities accidentally develop because of meiotic or mitotic error there is no great risk of recurrence. Women who have had one spontaneous abortion will soon get pregnant again and give birth to a healthy child. The abortion of fetuses with abnormal karyotype is the appearance of natural genetic selection.