The result that says nothing is not nothing
A no-call carries a higher chance of a chromosome problem and a lower chance of a live birth. It is not an administrative hiccup.
Sometimes the laboratory cannot produce a result and you are asked to come in for a second blood draw. It is usually explained as a technical problem. Often it is. But the group of women this happens to is not the same as the group it does not happen to.
In the large confirmed cohort, 602 of 17,851 (3.4%) had no usable result after the first draw. After second draws, 287 (1.61%) still had no result. Among those 287 women, the ones still without a result after a redraw, the rate of trisomy was 2.8%, against 0.7% among women who got a result the first time.
A companion analysis of the same cohort took the wider group, all 602 women whose first sample gave no usable result, and followed what happened next. That group includes the women whose second draw did produce a result, so it is a different set of women from the 287 above, and the figures below are not a second measurement of the same group.
| After a first non-reportable result (602 women) | Result obtained on the first draw | |
|---|---|---|
| Trisomy 13, 18 or 21 confirmed | 1.6% | 0.7% |
| Live birth | 94.9% | 98.8% |
Both pairs are absolute rates taken straight from the study, not calculated here. When a redraw was attempted, it failed again in 112 of 427 cases (26.2%). No usable result was more likely with higher body mass index, chronic high blood pressure, later gestational age and lower fetal fraction.
Patients with nonreportable cfDNA results should be offered genetic counseling, comprehensive ultrasound evaluation, and diagnostic testing because of the increased risk for fetal aneuploidy.It adds that whether to try the blood test again instead
may depend on several factors, including the presence of abnormal ultrasound findings and gestational age.
So the offer of a genetics appointment, a detailed scan and a diagnostic test is what current guidance says should happen. If all you are offered is another needle, ask about the rest.
"Should I be offered genetic counselling and a detailed scan now, rather than another blood test?"
"If we redraw and it fails again, what then?"