Genetic Causes And Infertility

Recurrent miscarriage is often due to genetic causes

Fertile couples with repeated miscarriages should be evaluated for the presence of a chromosomal abnormality.

Up to seventy percent of miscarriages are caused by chromosomal errors, Chromosome abnormalities occur in 1 of 160 live births, the most common being extra chromosomes 21, 18 and 13.

Chromosomal abnormalities are more common in women who are over thirty-five. Women (and men) older than 35 have a greater tendency to produce eggs or sperm with chromosomal abnormalities.

One or both partners may have a balanced translocation or other silent chromosomal abnormality like  an aneuploid mosaic that gives the couple a statistically increased odds of miscarriage in each pregnancy.

The transmission of a chromosome abnormality to an embryo can result in a low implantation rate, miscarriage, or the birth of a baby with a genetic disorder.

Aneuploidy refers to an abnormal number of chromosomes. An extra or missing chromosome is a common cause of genetic birth defects. Aneuploidy occurs during cell division when the chromosomes do not separate properly between the two cells.

Is there help for recurrent miscarriage?

Preimplantation genetic diagnosis (PGD) is most frequently recommended for patients who are at risk for genetic disorders such as cystic fibrosis, Tay Sachs disease, or thalassemia.

PGD is also helpful for patients with unexplained infertility, a history of recurrent miscarriage, unsuccessful IVF cycles, advanced maternal age, or the birth of a child with a chromosome abnormality such as Down syndrome. or male factor infertility. In these cases, the most likely cause is a chromosome abnormality.

Male Factor Infertility

Approximately one-half of all infertility is caused by sperm abnormalities. Many sperm disorders are due to a chromosome abnormality such as aneuploidy or a structural chromosome abnormality.

Y chromosome deletions are found in approximately 5 to 20 percent of males with a very low sperm count. These deletions appear to impair normal sperm development. While these deletions do not appear to cause any genetic disease, they appear to decrease the chance of men with a low sperm count to successfully fertilize eggs in a normal condition .

Men who carry a balanced translocation chromosome are at risk of producing sperm with a structural chromosome abnormality. Studies have shown that approximately 3 to 8 percent of sperm from normal, fertile men are aneuploid and 27 to 74 percent of sperm from men with severe infertility are aneuploid.

Couples with infertility due to male factor should consider chromosome analysis of the male’s sperm prior to IVF.

Aneuploidy and Advanced Maternal Age

Women 35 and older are at a higher risk of producing aneuploid embryos, which results in implantation failure, Aneuploidy is believed to be a major reason for the decrease of fertility with age. Studies have shown that approximately 62 percent of embryos from women of advanced maternal age might be aneuploid.

Prior to attempting a pregnancy, women in this age group should talk with their physician or a medical geneticist about their chances of having a child with a genetic disease and if PGD should be considered.

Dr. Moujahed Hammami
Consultant Obs.& Gyne.
ARMADA MEDICAL CENTRE

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