Experience MedEx Seamless Care Delivery — 10% OFF on Your First Appointment - Use 'TRYMEDEX' Coupon Code on Checkout //////////////////////////////////// General Price List — Consultation: 750 THB | Home Lab Test Service Fee: 750 THB (FREE for Orders Over 5,000 THB)
MedEx is a one-stop destination when it comes to medical tourism and digital specialized health care services. MedEx serves as a connector between patients and trusted world-class health service providers.
Prenatal screening guide · 2026
A no-result report is not a failed pregnancy or a bad sign in itself. But repeated failure carries information worth taking seriously.
Fetal fraction is the proportion of cell-free DNA in maternal blood that originates from the placenta. Laboratories generally require a minimum — commonly around 4% — to report a reliable result. Below that, the report comes back as “no result”, “test failure” or “non-reportable”, and a repeat draw is usually offered one to two weeks later. The most common reasons are testing too early and higher maternal weight. A single failure is common and usually resolves. Repeated failure is associated with a modestly increased chance of aneuploidy and should prompt clinical review rather than a third attempt.
| Typical threshold | Around 4% fetal fraction, varying by laboratory and method |
|---|---|
| Rises with | Advancing gestational age |
| Falls with | Higher maternal weight; testing too early; some medications |
| First failure | Common; a repeat draw 1–2 weeks later usually succeeds |
| Repeated failure | Clinically relevant — review rather than repeat indefinitely |
| Counselling | Doctor consultation or specialist teleconsultation before and after testing |
Cell-free DNA in a pregnant woman’s blood is a mixture: mostly her own, with a minority fraction from the placenta. The test compares chromosome proportions in that mixture, so it needs the placental contribution to be large enough for a genuine difference to stand out from background noise.
Below the laboratory’s threshold, the honest answer is that the result cannot be called. Reporting one anyway would risk a false negative, so laboratories decline — which is the correct behaviour, even though it is frustrating to receive.
Fetal fraction is typically stated on the report. It is worth looking at, since it puts any subsequent result in context.
| Early gestation | The commonest cause. Fetal fraction rises with gestational age, which is why 10 weeks is the minimum. |
|---|---|
| Higher maternal weight | More maternal cell-free DNA dilutes the placental fraction. This is the second most common cause and is dose-related. |
| Certain medications | Low molecular weight heparin has been associated with lower fetal fraction in some reports. |
| Sample handling | Delay, incorrect tube or poor transport conditions can degrade the sample. |
| Placental factors | Some placental abnormalities and certain aneuploidies, particularly trisomy 13 and triploidy, are associated with lower fetal fraction. |
That last row is the reason repeated failure is not simply a technical inconvenience.
Planning a redraw or a first test? Confirm gestational age with a scan first.
Studies have consistently found that pregnancies with persistently low fetal fraction have a somewhat higher rate of chromosomal abnormality than pregnancies where the test succeeds first time. The association is modest but real, and it is thought to reflect placental function.
Professional guidance therefore advises that a persistent non-reportable result should not simply be repeated indefinitely. Instead it should prompt:
This is a conversation worth having with a specialist rather than a laboratory. Book a specialist teleconsultation or a doctor consultation.
None of these guarantees success, but together they remove most avoidable causes. Timing detail is in the NIPT timing guide.
It means the proportion of placental DNA in the blood sample was below the level the laboratory needs to report a reliable result. The report comes back as no result rather than as a wrong answer.
Most often because the test was taken too early or because higher maternal weight dilutes the placental fraction. Sample handling problems and some medications can also contribute.
A single failure is common and usually resolves on a repeat draw. Repeated failure is associated with a modestly increased chance of chromosomal abnormality and should prompt ultrasound assessment and a discussion about diagnostic testing.
Usually one to two weeks later, by which point fetal fraction has typically risen with advancing gestation.
Guidance advises against repeating indefinitely. A detailed ultrasound and a discussion of chorionic villus sampling or amniocentesis are the appropriate next steps, ideally with genetic counselling.
Yes, and the effect is dose-related. More maternal cell-free DNA dilutes the placental fraction, so waiting slightly longer in gestation improves the chance of a reportable result.
Failed twice? That warrants review, not a third attempt.
Medical disclaimer: This article is general health information and does not replace medical advice, diagnosis or treatment. Laboratory reference ranges differ between laboratories and results must be interpreted alongside your symptoms, medicines and medical history. Speak with a qualified clinician before starting, stopping or changing any treatment. Service details, inclusions and prices can change — confirm them with MedEx before booking.
When to draw estradiol, why the day of the cycle changes everything, what it adds in menopause assessment and how it is used in men.
Why NIPT starts at 10 weeks, how gestational age affects fetal fraction, and how to plan timing around the dating scan and confirmatory options.
Why Ureaplasma parvum, U. urealyticum and Mycoplasma hominis are usually normal flora, what a positive result means and when treatment is justified.
Find quality services, specialists, procedures and more from the comfort of your home. All you need to do is enter a keyword or phrase describing what you are looking for.
DOWNLOAD MEDEX ONE APP
MedEx is a one-stop digital care navigation concierge backed by physical infrastructure, owning the patient experience and decentralizing the care continuum across Asia—integrating provider aggregation, satellite clinics, telemedicine, and at-home care.
MedEx is a one-stop digital care navigation concierge backed by physical infrastructure, owning the patient experience and decentralizing the care continuum across Asia—integrating provider aggregation, satellite clinics, telemedicine, and at-home care.
© 2020-26 MedEx Ventures Co., Ltd.
