- ATHENS OFFICE MED4WOMAN ATHENS
- VOLOS OFFICE MED4WOMAN VOLOS
Obstetrician-Gynecologist
PhD, University of Athens Medical School
Obstetrician-gynecologist Panagiotis Polyzos practices at the Institute of Life, the IVF Unit of IASO Maternity Hospital.
The nuchal translucency scan is recommended for all pregnant women, as it is the core prenatal care test during the 1st trimester of pregnancy.
As maternal age increases, so does the likelihood of the baby being born with one of the most common chromosomal abnormalities, such as Trisomy 21 (Down syndrome). If the final calculated risk for a chromosomal abnormality is high, and after counseling the couple, more specialized tests may be performed, such as chorionic villus sampling or amniocentesis.
Among other things, the nuchal translucency scan can:
The nuchal translucency ultrasound is a painless examination and carries no risk for the pregnant woman or the baby. It is usually performed transabdominally, and in certain cases, a transvaginal approach may be required.
The nuchal translucency scan detects:
For the estimation of the risk of chromosomal abnormalities, four ultrasound markers are evaluated:
At a later stage (usually the next day), the final risk calculation is completed. This includes a combination of the ultrasound findings and biochemical markers — hormones present in the mother’s blood (PAPP–A, free b-hCG and PlGF).
Before your scheduled appointment, think about any questions you may have regarding the ultrasound or your pregnancy and write them down so you can discuss them with your doctor or midwife during your visit.
A good breakfast, a light snack, and/or juice are ideally recommended before your appointment. At the same time, it is advised to drink enough water so that the bladder fills, allowing for better visualization of the uterus and cervix.
Upon your arrival at the clinic, you will be asked to complete the required medical history form, as well as provide any tests you have already undergone for evaluation of the results. For your own convenience, it is helpful to organize these tests in a folder by date and type of examination.
It is important to understand that this examination is a screening test and not a diagnostic method. Its sensitivity reaches 95%, with approximately 3% false-positive results. The screening assesses for Trisomy 21 (Down syndrome) as well as Trisomy 18 (Edwards syndrome) and Trisomy 13 (Patau syndrome).
The results of the ultrasound and biochemical tests will indicate a low risk for the above syndromes (i.e., a probability lower than 1:300) in most women.
In every case, you will receive full information regarding the significance of this risk and the various options for possible further testing, such as invasive testing (chorionic villus sampling — amniocentesis) or non-invasive testing (cell-free DNA test).
Nuchal translucency is a small collection of fluid under the skin at the back of the neck. It is present in all fetuses at this age and is temporary. After week 14 the lymphatic system matures, the fluid is absorbed and the measurement loses its value.
The window is defined by the fetus's crown-rump length (CRL), which must be 45 to 84 millimeters. Before 11 weeks the fetus is too small for a reliable measurement and for a meaningful assessment of the anatomy. After 13+6 weeks the reference curves used to calculate the risk no longer apply.
In practice, the best time for most women is week 12. The fetus is large enough for key organs to be visible, and there is still time for further testing if needed. Book your appointment early, as soon as the pregnancy is confirmed, so the window is not missed.
The difference between 2.5 and 3.5 millimeters changes the calculation significantly, which is why the measurement technique is strictly standardized by the Fetal Medicine Foundation (FMF):
Examiners who issue results with the FMF software must be certified and submit their measurements to an annual quality audit. It is reasonable to ask whether your scan is done within this framework.
The result is not “positive” or “negative”. It is a probability. A risk of 1:1,000 means that out of 1,000 women with exactly the same findings, one will have a fetus with that trisomy and 999 will not. The larger the second number, the lower the risk.
Ask to see the report with the numbers and not just the label “low risk”. The exact value is needed if another test is discussed later.
An increased nuchal translucency, usually 3.5 millimeters or more, is not only about chromosomes. Even when invasive testing is normal, the finding is linked to a higher likelihood of:
That is why the next step is usually a molecular karyotype (array) instead of a conventional one, an early anatomy scan around week 16 and a fetal echocardiogram. This is followed as usual by the level II ultrasound in the second trimester.
The reassuring side: when genetic testing and the follow-up scans are normal, the vast majority of these babies are born healthy. The higher the initial value, the closer the monitoring, but a number on its own does not determine the outcome.
The 11 to 13 week scan is the best time to determine whether the fetuses have separate placentas or share one, which changes the entire monitoring plan. Nuchal translucency is measured separately for each fetus. Blood hormones, however, come from both placentas, so the combined calculation is less accurate than in a singleton pregnancy.
Gestational age is calculated precisely in pregnancies conceived through in vitro fertilization by counting from the date of the embryo transfer. If donor eggs were used, the risk is calculated based on the donor's age at the time of egg retrieval, not your own. Also tell your doctor about any “vanishing” twin in the early weeks, because it may affect hormone levels.
The 12-week scan is not limited to trisomies. It provides information that can change your care early on:
Keep the scan report in your pregnancy file. First trimester measurements are used as a reference point in all later checks.
Sometimes a pregnancy is confirmed late or the appointment is not booked in time. Screening for trisomies is not lost, it is simply done with other tools. Noninvasive DNA testing from the mother's blood can be done at any time after week 10. There is also second trimester biochemical screening, although it is less accurate than combined screening. Assessment of the anatomy continues as usual with the 20 to 24 week scan. Discuss with your doctor which option suits the stage of pregnancy you are at.
From 11 weeks to 13 weeks and 6 days.
Usually below 3.5 millimeters, always in relation to the size of the fetus. The result is evaluated together with the mother's age and the hormones PAPP-A and beta-hCG.
A higher likelihood, not a diagnosis. A discussion follows about further testing with NIPT, chorionic villus sampling or amniocentesis, and a fetal echocardiogram.
No. The scan is usually done through the abdomen, with no preparation.
No. The scan also checks the fetal anatomy and the risk of preeclampsia, which NIPT does not do.
This happens often. The doctor may ask you to cough, turn onto your side or walk around a little, and repeat the measurement after a few minutes. Less often, a transvaginal approach or a new appointment a few days later, within the same window, is needed.
It can be done on the same day or a few days earlier, from week 9 onward. Having the blood drawn beforehand has the advantage that the final risk can be discussed right after the scan.
It usually falls in the intermediate zone. It does not mean the baby has a problem, but it justifies a discussion about noninvasive DNA testing from your blood, which can clarify the picture without any risk to the pregnancy.
At 12 to 13 weeks the doctor can sometimes make an estimate from the angle of the external genitalia. However, this estimate is not certain. DNA testing or the second trimester scan gives a more reliable answer.
