Pregnancy Loss and Miscarriage Testing
Although most couples are unaware of the statistics surrounding miscarriage, pregnancy loss is actually quite common, with 10-25% of recognized pregnancies ending in miscarriage. If you have suffered a pregnancy loss or are currently in the process of having a miscarriage, you may be wondering what caused the loss and worry about whether it will happen again. This article aims to answer the following questions:
What causes miscarriage?
How common is pregnancy loss?
What type of genetic testing is available for miscarriage tissue?
How can chromosome testing help?
Causes of Miscarriage
There are many different reasons why miscarriage occurs, but the most common cause for first trimester miscarriage is a chromosome abnormality. Chromosome abnormalities – extra or missing whole chromosomes, also called “aneuploidy” – occur because of a mis-division of the chromosomes in the egg or sperm involved in a conception. Typically, humans have 46 chromosomes that come in 23 pairs (22 pairs numbered from 1 to 22 and then the sex chromosomes, X and Y). For a baby to develop normally it is essential that it have exactly the right amount of chromosome material; missing or extra material at the time of conception or in an embryo or fetus can cause a woman to either not become pregnant, miscarry, or have a baby with a chromosome syndrome such as Down syndrome.
Over 50% of all first trimester miscarriages are caused by chromosome abnormalities. This number may be closer to 75% or higher for women aged 35 years and over who have experienced recurrent pregnancy loss. Overall, the rate of chromosome abnormalities and the rate of miscarriage both increase with maternal age, with a steep increase in women older than 35.
Pregnancy Loss – How Common is it?
Miscarriage is far more common than most people think. Up to one in every four recognized pregnancies is lost in first trimester miscarriage. The chance of having a miscarriage also increases as a mother gets older.
Most women who experience a miscarriage go on to have a healthy pregnancy and never miscarry again. However, some women seem to be more prone to miscarriage than others. About five percent of fertile couples will experience two or more miscarriages.
Of note, the rate of miscarriage seems to be increasing. One reason for this may be awareness – more women know they are having a miscarriage because home pregnancy tests have improved early pregnancy detection rates over the past decade, whereas in the past the miscarriage would have appeared to be just an unusual period. Another reason may be that more women are conceiving at older ages.
Types of Genetic Testing Helpful for Miscarriages
Genetic testing actually refers to many different types of testing that can be done on the DNA in a cell. For miscarriage tissue, also called products of conception (POC), the most useful type of test to perform is a chromosome analysis. A chromosome analysis (also called chromosome testing) can examine all 23 pairs of chromosomes for the presence of extra or missing chromosome material (aneuploidy). Because so many miscarriages are caused by aneuploidy, chromosome analysis on the miscarriage tissue can often identify the reason for the pregnancy loss.