PGD may reduce miscarriages by 50%

Miscarriages after infertility treatment are common. Numerous studies have shown that most of miscarriages are due to abnormalities in the number of chromosomes in the embryo. This is called aneuploidy. Normally, an embryo should have 46 chromosomes or, more precisely – 23 pairs of chromosomes. In two-thirds to three fourths of all miscarriages, the embryo has something other than 46 chromosomes.

 

In addition, it seems that certain chromosomes are present in abnormal numbers more frequently. a recent study found that eight chromosomes (X, Y, 13, 15, 16, 18, 21, and 22) accounted for 83% of the abnormalities found in miscarriage specimens.

 

 

This is of particular interest since many chromosome abnormalities can be detected during IVF cycles using the technology known as PGD . Current PGD technology allows for the testing of 5 to 10 different chromosomes.

Data have shown increased incidence of aneuploidy in the embryos of patients with recurrent miscarriage compared with those from patients who underwent PGD for the prevention of sex-linked diseases.

A study published in the February 2008 issue of the medical journal Fertility and Sterility looked at chromosome analyses on miscarriage specimens with the intent of trying to determine whether pgd would have any impact in the reducing the number of miscarriages  that occur after IVF cycles.

The study authors reviewed 273 cases from which chromosome analyses were performed on miscarriage specimens. Two hundred patients were being seen for either infertility  and 50 patients were seen for  infertility and repeated miscarriage with a history of two or more spontaneous pregnancy losses. The overall abnormality rate was 64.8%.

Using a standard PGD panel which detects 5 chromosomes, 54 of the 177 abnormal embryos would have been detected. Using a PGD panel that looks at 9 chromosomes, 140 of the 177 abnormalities. This represented a significant increase. There was no significant difference in detection rate if PGD was performed using a 10 or 12 chromosome panel.

The type of abnormalities found in the miscarriage specimens included

• A single extra chromosome (trisomy) — 69% (Chromosome 16 was the most commonly found abnormality)
• A single missing sex chromosome (monosomy X) 5%
• Structural abnormality in the chromosomes 8/177
• An entire extra set of chromosomes (triploidy) 10/177
• Two extra sets of chromosomes (tetraploidy) 6/177

When the number of detectable abnormalities is compared with the total number of miscarriages analyzed, including those with normal karyotypes, the study authors found that approximately half of all miscarriages could have been detected and avoided if preimplantation genetic diagnosis had been performed as part of the in vitro fertilization cycle.

some studies have suggested that if PGD is used, the chances for a pregnancy during in vitro fertilization may be higher due to the ability to select normal embryos for transfer. However, if there are no extra embryos, it may not improve the overall live birth rate, but may prevent transfer of embryos that have a high chance of miscarriage. In some patients, the avoidance of an embryo transfer is preferable to a miscarriage because the time taken to diagnose, treat, and recover from a miscarriage can delay future treatments. It also avoids the emotional distress that accompanies a miscarriage.