2012-05-19
Karyotype analysis using miscarriage material
Recurrent miscarriage is the problem in many families. Miscarriage in the first trimester is outcome of 15% of clinically diagnosed pregnancies. Miscarriages are classified as follows: spontaneous abortions in normal pregnancy; non-developing pregnancies (fetus usually stops to develop on 2nd – 9th week of pregnancy, however, miscarriage occurs on 10th – 14th week of pregnancy); anembrionic gestation, when only extraembryonic membranes develop.
There are many causes of miscarriage. It could be caused by chronic and acute diseases, hormone and metabolism disorders, anatomical defects of genital organs, inflammation, trauma, etc. However, as much as 60-70% of miscarriages occur not due to mother “fault”, but due to chromosomal abnormality of fetus.
What is chromosomal abnormality? All human genes are packed appropriately and form chromosomes. This order is very strict. Human possesses 46 chromosomes (22 pairs of autosomes and to two sex chromosomes, XX or XY). Every human somatic cell contains complete complement of chromosomes (46 chromosomes - 2n). Chromosome entity in the cell is called karyotype. Female karyotype is 46, XX, and male karyotype is 46, XY. When number of chromosomes or their structure changes, chromosomal disease occurs manifesting by various organ system defects and malformations. Most commonly changes in number of chromosomes occur; additional chromosome occurs in the chromosome pair (trisomy) or one chromosome could be absent (monosomy). Aliquot number of chromosomes (2n+n) could occur, so called polyploidy. These changes occur due to erroneous cell division during sex cell development in male or female body. When affected sex cells (gametes) take part in the conception, fetus with chromosomal abnormalities develops. Most of these mistakes are fatal, and nature itself “corrects” these mistakes by miscarriage in early terms of pregnancy.
Mother’s health, past history of miscarriages or number of deliveries does not affect miscarriages due to chromosomal abnormalities. However, mother’s age is one of the key factors determining frequency of chromosomal abnormalities. Cell division errors often occur in women of older age. Approximately 5% of miscarriages occur when one of the parents possess irregular complement of chromosomes.
Only karyotype analysis using miscarriage material may help to diagnose that miscarriage occurred due to chromosomal anomaly. Embryonic membranes for karyotype analysis are obtained during uterine curettage after spontaneous abortion (non-developing pregnancy). Cells of these tissues are grown in special media and then analyzed. Growth of cell culture is not always possible. Result could be negative in 5-42% of cases depending on the circumstances of miscarriage, e.g., if dead fetus remained in the uterus for some time. After curettage miscarriage material is usually sent for histological examination. However, histological changes in embryonic membrane are not associated with chromosomal abnormalities. Histological examination and karyotyping are two different tests.
Various trials showed that when miscarriage occurred due to changes of number of chromosomes in fetus, more than 2/3 of succeeding pregnancies are successful. If analysis shows that this is an exact cause of miscarriage, this is good news, and prognosis of next successful pregnancy could be made. When findings show normal karyotype, additional examination of woman is recommended. It has been shown that the more miscarriages occurred in same female, the lower probability of chromosomal abnormality is. Thus karyotype analysis using miscarriage material is globally acknowledged and performed as method of undoubted importance. In 2/3 of all cases it helps to answer key questions: why this occurred? What caused miscarriage? What should be done further? This is the modern way to explore the causes of miscarriage: was it caused by chromosome anomaly of fetus or in mother chromosomes?
What are the benefits of this? When there are no possibilities to perform karyotype analysis using miscarriage material, attempts to find causes of miscarriage in mother’s body are made, and various costly and long-lasting tests are performed causing mother a lot of discomfort. When cause is determined, long-term medication treatment is prescribed, and sometimes surgery should be performed. However, all these measures do not ensure success of treatment. Chromosomal abnormality of fetus causes two of three miscarriages and supposed mother’s diseases has no influence on thus.
In many cases fetal karyotype analysis allows to determine cause of miscarriage, and there is no need of any other tests or treatment, anxiety and uncertainty disappears, and there is no need for additional expenses. Term “chromosomal abnormality” is quite intimidating, but don’t be afraid! In this case this is good news – next pregnancy likely to be successful.
If you have questions concerning test and specimen collection, please refer directly to the SORPO Laboratory Department, and we will provide you all necessary information and appoint consultation of our laboratory physician; you can also contact your obstetrician- gynecologist.