There is a way to determine your baby's risk of chromosome number disorders such as Down syndrome (trisomy 21), trisomy 18 and 13 during pregnancy: prenatal screening tests. In this article, we explain in simple and up-to-date language what common tests (double scan, quadruple scan, fetal DNA / NIPT) do, when you should have them done, how the results are interpreted, and what to do if you encounter an abnormal result.
📌 Brief summary: Double screening (11–14 weeks), quadruple screening (15–22 weeks) and fetal DNA / NIPT test (starting from the 10th week) are the most commonly used prenatal screening tests in Türkiye. The triple screening test is no longer included in modern guidelines — the quadruple test or NIPT is preferred instead. NIPT is the most sensitive screening test, but when it is positive, it must be confirmed with a definitive diagnostic test (CVS or amniocentesis); alone is not sufficient to decide on termination of pregnancy.
There are two types of tests for chromosomal diseases in pregnancy:
This distinction is very important: A "high risk" result on a screening test does not mean that your baby is sick. Even at high risk, most of the time the baby is healthy; On the contrary, there is always a small possibility in low risk. Screening tests create a risk map, but do not make a definitive diagnosis.
The three tests you will encounter most in daily practice in Türkiye are:
Apart from these, tests such as triple screening, fully integrated test, serum integrated test, and sequential screening are also mentioned in the medical literature; We will briefly touch on each below. However, in Türkiye, these tests are either out of practice (triple test) or are rarely performed due to operational difficulties.
is the most frequently used prenatal screening test in Türkiye. It is performed between day 0 of the 11th week of pregnancy and day 6 of the 13th week of pregnancy (sometimes it can be extended until the 14th week). Two measurements come together:
These three measurements + mother's age + personal factors such as smoking, gestational age, weight, ART (in vitro fertilization) are combined with a computer program; As a result, a risk ratio (such as 1:5000 or 1:80) emerges for each chromosomal disease.
How accurate is combined first-trimester (double) screening?
The strength of combined screening is that it can be performed early: the result is known at 11–14 weeks, and if necessary, a diagnostic test such as CVS can be planned in the same period. An additional measurement is required for open neural tube defect (spina bifida); therefore, the later anomaly ultrasound at 18–22 weeks remains important.
It is a second trimester blood test performed between the 15th week day 0 and the 22nd week day 6 (usually between the 15th and 18th weeks) for pregnant women who missed the double screening or did not have the opportunity to do it. Four items are measured:
These four values + maternal age + other factors are combined to obtain the risk ratio.
How successful is quad scanning?
Although quadruple screening does not offer as high a detection rate as dual screening, it is still widely used in Türkiye — especially in cases where dual screening is delayed or cannot be performed. The results appear within 1 week.
⚠️ Triple Test is no longer recommended. The triple test (AFP + hCG + estriol — i.e. the older version of the quadruple without inhibin A) is no longer recommended in modern guidelines ( ACOG, NICE, UpToDate 2026 ). The detection rate for Down syndrome is approximately 69% — 10 points lower than the quadruple test. In some laboratories in Türkiye, requests can still be made under the name "triple test", but this is against current guidelines. If possible, quadruple testing or NIPT should be preferred.
NIPT is the most sensitive test in modern prenatal screening. Small DNA particles (fetal DNA) circulating in the maternal blood and mixing with the blood from the placenta are counted and thus chromosome ratios are determined. It can be done starting from the 10th week.
What can NIPT screen for?
How successful is NIPT?
Important — NIPT limits:
🔴 If NIPT is positive, a definitive diagnostic test is essential. NIPT is a screening test, NOT a definitive diagnostic test. A positive (high risk) test result does not mean that the baby is definitely sick. The positive predictive value (PPV) varies between 50% and 93% depending on the type of result and maternal age. In other words, even in a test with a PPV of 80%, 1 in every 5 positives is a false positive. Therefore, after a positive NIPT, karyotype confirmation by CVS or amniocentesis must be made before any decision is made — including pregnancy termination. This is the strongest common message of all major guidelines worldwide (ACOG, SMFM, ISPD, ACMG).
The following tests are mentioned in the medical literature but are rarely used in Türkiye for practical reasons. Let's get to know it briefly:
You often do not need to make a decision about these tests in practice — standard usage in Türkiye is first-trimester combined or quadruple screening + optional NIPT.
| Test | Week of pregnancy | Down syndrome capture | False positive | Use in Türkiye |
|---|---|---|---|---|
| Dual (1st trim) | 11+0 – 13+6 | ~85% | ~5% | Common |
| Quad (2nd trim) | 15+0 – 22+6 | ~75%–80 | ~5% | Common |
| NIPT (fetal DNA) | ≥10 weeks | ~99% | ~0.04% | Increasing (special payment) |
| Triple test | 15+0 – 22+6 | ~69% | ~5% | Not Recommended |
| Fully integrated | 1st + 2nd trim | ~85% | ~1% | Rare |
| Serum integrated | 1st + 2nd trim | ~85% | ~4% | Rare |
The screening test result usually comes as a ratio of 1:X format: for example, "Risk for Down syndrome is 1:250". This means "Down syndrome is expected in 1 in 250 pregnancies like yours." The lower the risk (1:1000, 1:5000), the more confident the result; the higher (1:30, 1:80) the more carefully it is treated.
We have come to the most important part of this article. If your screening test returned "high risk", here's the procedure:
High risk = does not mean your baby is sick. Screening is a probability test. The positive predictive value — that is, whether a positive test actually predicts disease — varies depending on the type of test and the mother's age. In double or quadruple screening, this rate is generally very low (often below 5%); In NIPT, it is between 50-93%. In any case, a high screening result is not a definitive diagnosis, it is just a situation that needs to be examined more closely.
After the high risk result:
These questions should be discussed in detail with your physician and, if possible, with a genetic counselor. In many centers, "perinatology" (risky pregnancy) consultation is recommended.
If the NIPT result is positive, it should never be used alone to decide on termination of pregnancy. Karyotype (the baby's actual chromosome map) must be confirmed by CVS or amniocentesis. This is the common and strongest recommendation of all major guidelines in the world.
Both are definitive diagnostic tests. A sample is taken with a needle and the baby's chromosome map is created.
📊 The risk of pregnancy loss is low in current data. It used to be said that "amniocentesis/CVS carries a 1% risk of miscarriage." Recent large meta-analyses (Salomon 2019, Ultrasound in Obstetrics & Gynecology) have updated this figure: in experienced hands, the additional risk of pregnancy loss is approximately 0.2–0.3%—that is, 1 in 300–500 procedures. The RCOG 2021 guideline similarly summarizes this risk as "below 0.5%." Thus, the procedure itself is largely safe. However, no invasive procedure carries zero risk; therefore, the decision is made through shared decision-making with an appropriate clinical indication.
If NIPT or diagnostic test is negative, the baby does not have the chromosomal condition being tested for. However, prenatal screening tests do not detect all types of anomalies—especially structural anomalies. A detailed anomaly ultrasound at 18–22 weeks should still be performed. Low risk doesn't mean everything is guaranteed; The risk is low only for the chromosomal diseases tested for.
If the definitive diagnosis is positive, the decision is up to the patient and the family. The physician and genetic counselor provide information about the natural course of the disease (how the baby lives with Down syndrome, how it develops, what medical needs it has), pregnancy options (continuation, termination, adoption), the legal framework in Türkiye and social support resources. In this process, an informed and shared decision process, not a hasty decision, is essential.
NIPT is much more sensitive than combined or quadruple screening. If NIPT is planned, combined/quadruple screening adds no further value for chromosomal disease screening. However, NT (nuchal translucency) measurement at 11–14 weeks provides separate information: some structural anomalies, including heart defects, are associated with increased NT and are not detected by NIPT. The practical approach in Türkiye is therefore NT measurement at 11–14 weeks plus optional NIPT (or combined screening), quadruple testing at 16–18 weeks if needed, and detailed anomaly ultrasound at 18–22 weeks.
Yes. NIPT is a screening test. The placental cells and the baby's cells may differ in 1–2% of the DNA passed from the placenta to the mother (confined placental mosaicism - CPM). Therefore, even if NIPT is positive, only CVS or amniocentesis shows the chromosome map of the real baby. Appearing “normal” imaging does not invalidate positivity; The decision must be made after a definitive diagnosis.
The triple test is more likely to be a false positive than the quadruple test. Rather than immediately worrying about the high result, it makes sense to talk to your physician and re-evaluate with either quadruple testing or NIPT. If possible, avoid places that still recommend triple testing — modern guidelines do not recommend this testing.
In Türkiye, double and quadruple screening tests are often performed within the scope of SSI or with a very low contribution fee. NIPT is generally not covered by SSI — in private laboratories, the patient pays out of pocket (approximately in the range of 3,000–6,000 TL by 2026). CVS and amniocentesis are covered by SSI if there is a risky pregnancy diagnosis.
The decision is made together with your physician. Factors include: maternal age, previous pregnancy history, first USG and medical history, insurance/financial circumstances, and patient preference. There is no one right answer — a plan is created specifically for each patient.
👨⚕️ Don't forget to ask your physician: "Which test do you recommend, and why? What steps will we follow if the result is unfavorable (abnormal)? Which center or genetic counselor do you recommend for me?" Bringing written questions makes the consultation much more productive.
👩⚕️ For physicians and healthcare professionals: For an in-depth clinical review of this topic (guideline side-by-side comparison, GRADE precision table, and 28 resources), visit our Prenatal Screening Tests — Clinical Review page.
Last updated: 1 November 2026 · Author / content owner: Cem Akaltun, MD, Obstetrician and Gynecologist. This article is for information only; consult your physician about medical decisions.