Miscarriage Causes: Chromosome Abnormality

Primary miscarrier (no live births) - 7%
Secondary miscarrier (one or more live births) - 50%

Chromosomes carry the genetic information for each individual.

Everyone has 23 pairs of chromosomes, making 46 in all. All but one pair are identical in men and women.

The 23rd pair – the sex chromosomes – decide the individual’s gender and are therefore different. Men normally have one X and one Y chromosome and women have two X chromosomes.

A baby inherits half of its chromosomes from its mother and half from its father.

Between 3-5% of couples with recurrent miscarriage have a problem with a chromosomal abnormality called a balanced translocation. In this situation, part of the information from one chromosome is replaced by that of another chromosome. Although this doesn’t cause a problem to the affected parent, it can be passed on to the baby and cause an unbalanced translocation, where some genetic information is present twice and some is missing. This can lead to miscarriage.

Diagnosis of chromosome abnormality

Chromosomal analysis involves taking a blood test from both the man and the woman and sending the samples to a genetics laboratory. The results can take between four and six weeks to obtain.

There is no treatment which can alter the chromosomes in an individual if they are already abnormal. If the analysis shows that you or your partner carries an abnormality, then you will be offered specialist genetic counselling to give you more information and help you decide about future pregnancies.

Your clinic may offer to carry out chromosomal analysis of fetal tissue, although this can depend on the laboratory facilities available. It involves sending tissue from the miscarriage to the genetics laboratory where it undergoes the same process as for blood. Unfortunately a result is obtained only in approximately half of cases. It takes about six to eight weeks or more to obtain the results. If the result is abnormal, but both parents have a normal chromosome pattern, then the abnormality in the baby is unlikely to recur in a subsequent pregnancy.