Genetic risk in natural and medically assisted procreation.

Current in vitro fertilization techniques (IVF) including intracytoplasmic sperm injection (ICSI), microepididymal sperm aspiration (MESA) or testicular sperm extraction (TESE) clearly prevent any spontaneous choice of ova or spermatozoa. According to the widely admitted concept of gamete selection, pregnancies following IVF, when compared to natural fertilization, could therefore present a higher risk of genetic anomalies. However, no increased fetal or newborn abnormalities are noticed with IVF, except perhaps for sex chromosome aneuploidies. Data from the literature support the view that the uterus is, indeed, the organ where selection mechanisms occur (when they do so), as suggested by Carr in 1971. This selection concerns mainly autosome imbalances; unbalanced conceptuses are aborted. Sex chromosome aneuploidies, apparently, are less prone to natural abortion, but their higher rate of occurrence, as reported in a few series of studies, does not seem to be associated with the IVF procedures.