Problems of the Embryo
At least 60-90% of spontaneous miscarriages occur because of chromosomal abnormalities. This means that the oocyte or the sperm had a genetic (chromosomal) abnormality. This type of miscarriages represents nature’s ‘defense mechanism’, which does not allow babies with severe health problems to be born. Such chromosomal abnormalities in the oocytes or the sperm are rare, so such miscarriages usually are one-off incidents (they are not repeated).
The genetic cause of such recurrent miscarriage is diagnosed with a ‘karyotype’ analysis of the miscarried fetus (analysis of the chromosomes). This test explains the cause of the miscarriage in many cases.
In about 1-5% of couples, the cause of recurrent miscarriage is the chromosomal abnormality of one of the parents. This can be checked with a blood test. The most usual abnormality concerns structural problems of the chromosomes. In some cases a chromosome has lost a part, a phenomenon called ‘deletion’. In other cases, a ‘translocation’ is detected. This means that a part of a chromosome is located elsewhere.
If the karyotype is normal, the miscarriage is not due to a chromosomal abnormality. In that case, other possible causes need to be considered: uterine abnormalities, hormonal profile, sperm, immune system etc. If these factors are excluded, the couple is reassured that the miscarriage was a one-off incident and they can start trying again for a pregnancy.
If the karyotype is not normal, the risk of miscarriage is higher. In that case, each couple must be treated individually according to the type of chromosomal abnormality. Genetic advice from a geneticist is also required.
Low ovarian reserve
Age is a critical factor when it comes to the risk of miscarriage. At the age of 28, the risk of miscarriage is 10%, while at the age of 40 it rises to 33% (1 in 3 pregnancies).
Many women with recurrent miscarriage have low ovarian reserve. The cause of such miscarriages is poor quality of the oocytes, which have genetic abnormalities. Therefore the embryos also have genetic abnormalities and the pregnancy is discontinued.
These women might not have any fertility problems other than the fact that their oocytes are ‘old’ and of ‘poor quality’. These oocytes might look perfect but it has been proven that the embryos have more chromosomal abnormalities (due to the chromosomal abnormalities of the eggs).
Please read more on this subject:
‘Preimplantation genetic screening in women of advanced maternal age caused a decrease in clinical pregnancy rate: a randomized controlled trial’ Human Reproduction Vol.23, No.12 pp. 2806–2812, 2008
Problems of the sperm
Another factor believed to cause recurrent miscarriage is poor sperm quality. When sperm is abnormal, the embryo will be abnormal, too.
In at least 30% of male infertility cases, the actual cause of the problem is unknown. The only method available to evaluate male fertility was sperm analysis which measures 3 factors: sperm count, motility and morphology. In many studies, it has been suggested that sperm effect on embryo quality is not related to chromosomal abnormalities. Damaged sperm DNA could affect embryo development. Clinically, this manifests as a miscarriage. Recent studies suggest that DNA fragmentation in sperm is a key factor in male infertility. It can be measured with a DFI test (DNA fragmentation index).
Research shows that sperm with high DFI have a smaller chance of producing a healthy pregnancy. A statistical analysis of hundreds of sperm samples showed that men with DFI higher than 30% have compromised fertility (fewer pregnancies, twice as many miscarriages). In the past, sperm analysis was the ‘golden standard’ for evaluating male infertility. Today we know that some sperm samples that look normal might have extended DNA fragmentation.
Continue reading on this subject:
‘Sperm DNA integrity assessment in prediction of assisted reproduction technology outcome’ Human Reproduction Vol.22, No.1 pp. 174–179, 2007
In any case, studies on DFI are still preliminary. The clinical value of DFI test remains to be validated.
Read more on DFI test.