Prenatal mortality and genetic wastage in man

Abstract

Human pregnancy wastage is probably of the order of 50 %. It is greatest in the earliest weeks of conception when there is a close correlation with defective embryogenesis, approximating to 100% in the first 3 weeks.Approximately 36 % of all clinically recognized abortuses have a chromosome anomaly. This figure does not represent the primary incidence of heteroploidy at conception, because it excludes pre-implantation and early implanted losses which are not recognized clinically.This heteroploidy is most common in early pregnancy at the time when pregnancy wastage is highest. It is not a homogeneous problem but involves a wider range of chromosome anomalies than those found in the adult, autosomal trisomies, XO monosomy and triploidy being the most common findings.It follows that errors in gametogenesis, fertilization and early cleavage divisions are a major cause of prenatal mortality. Biological factors which predispose to these faults include maternal ageing, pre-ovulatory and postovulatory ageing of the oocyte and ageing of the spermatozoon. Parental chromosome rearrangements are of minor importance as a cause of chromosome anomalies in abortuses, although they may be of greater significance in recurrent abortions.Unsuccessful pregnancies which terminate in abortion or stillbirth generate a good deal of emotion, and obstetricians spend a good deal of their time trying to understand the causes of these misfortunes. Not unnaturally, they have concentrated their attention on the loss of older foetuses which are potentially viable. These intra-uterine deaths in the third trimester, together with deaths in the first week after * Delivered during a Course on Advances in Reproductive Physiology, Cambridge, 21st August 1970. 223

Problems of sperm fertility: A reproductive biologist's view

“…Since the oocyte and spermatozoa with abnormal chromosomes/ genomic constitutions are not discriminated against during fertilization [Almeida and Bolton 1994;Meschede et al 1995;Engel et al 1966;Marchetti et al 1999], one-third or even half of naturally fertilized human eggs and early embryos could be chromosomally/genomically abnormal. High pregnancy loss even in fertile women has been known for many years [Hertig et al 1959;Carr 1971;Kerr 1971;Edwards 1986]. An interesting study using mutant mice was reported by Gropp et al [1983].…”