Chapter

Gametogenesis and Conception, Pregnancy Loss and Infertility

R. J. McKinlay Gardner, Grant R. Sutherland and Lisa G. Shaffer

in Chromosome Abnormalities and Genetic Counseling

Fourth edition

Published on behalf of Oxford University Press

Published in print November 2011 | ISBN: 9780195375336
Published online October 2012 | e-ISBN: 9780199975174 | DOI: http://dx.doi.org/10.1093/med/9780195375336.003.0023

Series: Oxford Monographs on Medical Genetics

Gametogenesis and Conception, Pregnancy Loss and Infertility

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HUMAN CONCEPTION and pregnancy is both a vulnerable and a robust process. Vulnerable, in that a large proportion of all conceptions are chromosomally abnormal, with the great majority of such pregnancies aborting. Robust, in that more than 99% of the time, a term pregnancy results in a chromosomally normal baby. Unbalanced chromosomal abnormalities are seen in less than 1% of newborns (see Table 1–3 in Chapter 1). But the economic cost of chromosomally abnormal conceptions is not horrendous; it is measured largely in terms of miscarriage, seen or unseen. The occasional chromosomally abnormal child is, relatively speaking, an exceptional outcome—the tip of an iceberg (Fig. 23–1).

Most of this chromosomal vulnerability lies in the process of producing eggs and sperm. Meiosis hangs, literally and figuratively, upon “tender filaments,” and often the meiotic chromosomes are incorrectly distributed to the daughter cells. Indeed, humans are more prone to produce aneuploid germ cells than any other species studied (McFadden and Friedman, 1997).1 The group who are particularly likely to produce abnormal gametes are carriers of balanced chromosome rearrangements, and much of this book is devoted to that fact.

Advances in reproductive technology now enable many otherwise infertile couples to have children. Translocation carriers may have recourse to preimplantation genetic diagnosis (PGD) as a means to improve their chances of achieving a successful pregnancy (Chapter 26). In the case of men with poor sperm production, intracytoplasmic sperm injection (ICSI) at in vitro fertilization (IVF) is a means to get a single sperm into an egg. Success with IVF is not necessarily easy to achieve, neither is it a certain outcome, and counselors dealing with infertile couples need a particular awareness of the psychological and practical difficulties they may face (Boivin et al., 2001). A “failed embryo transfer” following IVF may be considered as a form of pregnancy loss not unlike that of the natural miscarriage of a wanted pregnancy.

Chapter.  16208 words.  Illustrated.

Subjects: Clinical Genetics

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