Although most couples are blissfully unacquainted with the statistics surrounding miscarriage, pregnancy loss is really quite common, with 10-25% of recognized pregnancies ending in miscarriage. If you have suffered a pregnancy loss or are in the process of experiencing a miscarriage, you might be wondering what caused losing 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 do chromosome testing help?
Causes of Miscarriage
There are many different reasons why miscarriage occurs, but the most typical cause for first trimester miscarriage is a chromosome abnormality. Chromosome abnormalities – extra or missing whole chromosomes, also known as “aneuploidy” – occur due to 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 necessary that it have the right level of chromosome material; missing or extra material during conception or within an embryo or fetus can cause a woman to either not become pregnant, miscarry, or have a child with a chromosome syndrome such as for example Down syndrome.
Over 50% of most first trimester miscarriages are due to 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 upsurge in women older than 35.
Pregnancy Loss – How Common could it be?
Miscarriage is a lot more common than most people think. Up to one in every four recognized pregnancies is lost in first trimester miscarriage. The opportunity of having a miscarriage also increases as a mother gets older.
Most women who experience a miscarriage continue to have a healthy pregnancy rather than 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’re having a miscarriage because home pregnancy tests have improved early pregnancy detection rates in the last decade, whereas in the past the miscarriage would have appeared to be just a unique period. Another reason could be that more women are conceiving at older ages.
Types of Genetic Testing Helpful for Miscarriages
Genetic testing actually identifies many types of testing that can be done on the DNA in a cell. For miscarriage tissue, also known as products of conception (POC), probably the most useful type of test to execute is a chromosome analysis. A chromosome analysis (also known as chromosome testing) can examine all 23 pairs of chromosomes for the presence of extra or missing chromosome material (aneuploidy). Because so many miscarriages are due to aneuploidy, chromosome analysis on the miscarriage tissue can often identify the reason behind the pregnancy loss.
The most common approach to chromosome analysis is called karyotyping. Newer methods include advanced technologies such as microarrays.
Karyotyping analyzes all 23 pairs of chromosome but requires cells from the miscarriage tissue to first be grown in the laboratory, a process called “cell culture”. For this reason requirement, tissue that is passed at home is often unable to be tested with this particular method. About 20% or more of miscarriage samples fail to grow and thus no results are available. Additionally, karyotyping struggles to tell the difference between cells from the mother (maternal cells) and cells from the fetus. In case a normal female result is found, it may be the correct result for the fetus or it might be maternal cell contamination (MCC) in which the result actually originates from testing the mother’s cells present in the pregnancy tissue rather than the fetal cells. MCC appears to occur in about 30% or even more of the samples tested by traditional karyotype. Results from karyotyping usually have a few weeks to months to come back from the laboratory.
Microarray testing is a new type of genetic testing done on miscarriage samples; both most common types of microarray testing are array CGH (comparative genomic hybridization) and chromosome SNP (single-nucleotide polymorphism) microarray. Microarray testing can be able to test all 23 pairs of chromosomes for aneuploidy, but does not require cell culture. Therefore, you’re more likely to receive results and the results are typically returned faster when microarray testing is used. Additionally, some laboratories are collecting a sample of the mother’s blood at the same time the miscarriage tissue is sent to enable immediate detection of maternal cell contamination (MCC).
Chromosome Testing – How can it help?
If a chromosome abnormality is identified, the kind of abnormality found could be assessed to help answer fully the question: “Will this happen to me again?”. Quite often, chromosome abnormalities in an embryo or fetus are not inherited and have a minimal chance to occur in future pregnancies. pregnancy loss Sometimes, a particular chromosome finding in a miscarriage alerts your doctor to do further studies to investigate the chance of an underlying genetic or chromosome problem in your family that predisposes one to have miscarriages.
Furthermore, in case a chromosome abnormality is identified it could prevent the need for other, sometimes quite costly, studies your physician might consider to investigate the cause of the miscarriage.
Lastly, knowing the explanation for a pregnancy loss might help a couple of start the emotional healing up process, moving past the question of “Why did this happen to me?”.
Chromosome testing could be especially important for patients with repeated miscarriages, as it could either give clues to an underlying chromosomal cause for the miscarriages or rule out chromosome errors as the reason behind the miscarriages and invite their doctor to pursue other styles of testing. For couples with multiple miscarriages determined to have a chromosomal cause, in vitro fertilization (IVF) with preimplantation genetic diagnosis (PGD) testing may be able to help increase their likelihood of having a successful healthy pregnancy.