Genetic Testing After Miscarriage: Which Test Do I Need?

Route A: the pregnancy is still in the womb

While pregnancy tissue is still in place, the placenta sheds fragments of its DNA into your blood. Using the same principle as NIPT, a blood sample can be analysed for extra or missing chromosomes in that DNA, without anyone needing to collect tissue.

Timing is the catch. In a large Danish study, these DNA levels fell once the tissue had passed and dropped significantly after about 12 hours: more than 1 in 4 samples taken 12 to 24 hours after passing gave no result, against about 1 in 11 while tissue was still in place. So the sample belongs before the miscarriage passes or is treated.

A scan shortly beforehand confirms tissue is still in the womb, and can show a twin or vanished twin that might confuse the result. The main studies did not include pregnancies of unknown location or molar pregnancies.

Pooled across eight studies, the test found about 78 in 100 of the chromosome changes later seen in tissue; in the largest single study it was 85 in 100, and about 1 in 9 samples gave no clear result. It can also occasionally report a change the tissue does not show. Most methods cannot detect triploidy (three full sets of chromosomes), and any finding is a screening result, not a diagnosis.

It is not standard NHS care. To explore it, book genetic counselling before your treatment date; testing before treatment explains the timing.

Route B: the pregnancy has passed and tissue was kept

Testing the tissue reads the pregnancy's own chromosomes, so a good sample gives the most direct answer. NHS laboratories usually pair a rapid test for the commonest changes with a chromosomal microarray, which reads DNA instead of growing cells. In one series of more than 8,000 samples, microarray gave a result in about 9 in 10.

The tissue should be fresh, in a sterile container, dry or with a little sterile saline, and never in formalin, the preservative used for routine pathology. Even then, the laboratory may end up testing your own tissue (maternal cell contamination), which can look like a normal female result; a SNP-based microarray or a sample of your blood helps check for this.

If the result shows an unbalanced rearrangement, route D applies as well. Our pregnancy tissue testing page has more on samples and methods.

Route C: the pregnancy has passed and nothing was tested

This is very common and not a failing on your part: in a large Copenhagen study, roughly a third of women either could not collect the pregnancy tissue or collected only tissue likely to be their own. Once the pregnancy has passed with nothing kept, it usually cannot be tested, so what comes next depends on your history.

• After one or two miscarriages, parental tests are not usually recommended; the useful step is a plan, so testing can happen in time if there is another loss
• If earlier losses were tested, ask for copies of those reports, because they can shape what is worth doing next
• After three or more miscarriages with no successful tissue result, both partners may be offered a karyotype, although NHS criteria are narrower than RCOG guidance
• A rearranged chromosome in the family, or a previous baby with a chromosome condition, may justify parental testing sooner, after a specialist risk assessment

Route D: recurrent miscarriage or an unbalanced result

A karyotype checks the parents' chromosomes for a balanced rearrangement, where nothing is missing but a piece sits in a different place. Carriers are healthy, but some of their pregnancies can inherit an unbalanced version and miscarry. When tissue shows an unbalanced rearrangement, RCOG guidance is to offer both partners a karyotype; in one hospital series, about 1 in 3 such rearrangements came from a parent carrying a balanced form.

Recurrent miscarriage alone does not automatically mean a karyotype. UK guidance (RCOG) defines it as three or more first-trimester miscarriages, with tests sometimes starting after two; ESHRE uses two or more losses. Around 3 to 6 in 100 affected couples have a parental rearrangement, so RCOG guidance offers karyotyping after an unbalanced tissue result or when no tissue result exists, and ESHRE only after an individual risk assessment.

If a rearrangement is found, the outlook is still good: in a Dutch study of couples with two or more miscarriages, 83 in 100 carrier couples went on to have a healthy child, against 84 in 100 non-carriers, although carriers were more likely to miscarry again along the way.

Tests for antiphospholipid syndrome (APS), thyroid function and antibodies, and the shape of the womb belong in recurrent miscarriage care too. Read more on parental karyotype after miscarriage.