Karyotype Test
The karyotype (or chromosome analysis) checks the structure, number, arrangement of chromosomes and their DNA code. The chromosomes are separated, processed and photographed to see if there are any missing or extra. It can find structural changes that cause miscarriage or genes that cause illness. It’s very similar to “amniocentesis” or “chorionic villus sampling” (CVS) testing in pregnancy that checks a baby’s health or sex but uses a blood sample.
Karyotype testing can reveal defective chromosomes carried by parents that could cause problems for their baby’s development or growth. Even if both partners are healthy, one might have genes that risk severe defects. Some genes are “recessive” (they’re carried but not ‘expressed’ in that person), and when both parents carry the recessive gene, there’s a high chance their children will be affected.
Miscarriage
Around 50% of pregnancy losses in the first trimester are due to genetic problems. Genetics may play a part for couples who experience repeated miscarriages without a known cause or who have unexplained infertility, and the only way to know is by testing. Both partners must test to get a complete picture as some rare genetic matches can prevent pregnancy. This includes HLA DQα genotype compatibility, where there’s an unfortunate and crucial co-incidence of matching genes.
Abnormal numbers of chromosomes “trisomy” cause genetic conditions such as Down’s syndrome; they increase in the eggs and sperm as people get older and cause most of the higher miscarriage and lower pregnancy rates experienced by older couples. The karyotype test cannot detect DNA fragmentation, but there are tests available for sperm.
Couples need to discuss the pros and cons of having the tests (preferably with a specialist counsellor) before having them, as the results can be challenging and emotionally difficult.
