- 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 Second-Trimester Anatomy Scan is performed between the 20th and 24th week of pregnancy, ideally in the 21st to 22nd week. It is the most important test of the second trimester of pregnancy. Its purpose is to rule out major anatomical abnormalities and to assess a range of specific markers that are more frequently associated with chromosomal abnormalities in the fetus. Measurements are taken to estimate fetal weight and evaluate fetal growth, and the fetal anatomy is examined in detail to detect any congenital anomalies.
During the Second-Trimester Anatomy Scan, the following structures are thoroughly evaluated: the skull, brain, face, spine, chest, lungs, heart, abdomen, intestines, kidneys, bladder, and both upper and lower limbs. The position of the placenta is also determined, and the amount of amniotic fluid is assessed.
In addition, nine (9) specific markers for possible chromosomal abnormalities are examined. The findings are correlated with the final results from the nuchal translucency ultrasound.
Detecting a possible problem in fetal anatomy, examining minor abnormalities or markers of chromosomal abnormalities, and determining the risk of preterm birth, preeclampsia and fetal growth restriction
The diagnostic value of this examination for detecting major congenital abnormalities is approximately 75% worldwide. This means that a normal Second-Trimester Anatomy Scan — no matter how thorough and complete it may be — can significantly reassure the couple and the treating physician, but it cannot rule out all abnormalities, nor guarantee the birth of a completely healthy baby.
The results of the examination will be discussed with a Maternal–Fetal Medicine Specialist, who will clarify any questions you may have and provide further information and guidance for managing any potential issues.
It is the most important and detailed ultrasound examination in prenatal care, so the level II ultrasound is recommended for all pregnant women.
The fetal anatomy is assessed system-by-system, covering all vital organs. A detailed examination is performed of:
The normal bone density and shape of the skull, the brain hemispheres, the ventricles and cerebellum, the lenses of the eyes, the nose, the upper and lower jaw, the tongue, the pharynx, the lips and the facial profile, the curvature, shape and bone density of the spine and pelvic bones, the neck, the chest and lungs, the anatomy of the heart, the abdominal wall, the umbilical cord insertion site, the gastrointestinal tract, the shape and position of the stomach, the kidneys, the urinary bladder and the genital organs, the shape and bone density of the humerus, radius, ulna, femur, tibia and fibula, the palms, the fingers and the feet.
The examination may include advanced imaging techniques, used to improve the detection of potential anatomical defects. Thus, among others, MRI-like scanning of the fetal brain and multiplanar imaging of the heart and the major thoracic vessels are performed using three-dimensional imaging (3D-TUI). Nevertheless, it should be noted that a normal ultrasound scan cannot fully exclude the presence of anatomical abnormalities, but the more detailed the evaluation, the lower the probability of their existence. The examination is performed using specific standardized ultrasound planes, as defined by the respective protocols of the Fetal Medicine Foundation–FMF and ISUOG, which have been proven to demonstrate the highest sensitivity in detecting potential fetal abnormalities.
During the Second-Trimester Detailed Anatomy Scan, markers for chromosomal abnormalities are assessed.
The most important among them are:
The presence of one or more markers does not usually constitute a problem on its own, but it significantly increases the likelihood that the fetus may have a chromosomal abnormality. It is worth noting that the Second-Trimester Detailed Anatomy Scan has low sensitivity in detecting chromosomal abnormalities, as 40% of children with Down syndrome appear normal during this examination.
Chromosomal abnormalities are primarily detected during the 11–14 week scan (nuchal translucency) with a sensitivity of 93–95%. The various ultrasound markers of the second trimester are considered “soft markers” and, if present, are used to recalculate the probability of chromosomal abnormalities previously established in the first trimester. The cervix and blood flow in the uterine arteries are also evaluated. In this way, the individualized risk of preterm birth, preeclampsia, and fetal growth restriction is determined.
If structural abnormalities are identified during the detailed fetal anatomical evaluation, the significance of the findings will be discussed, and the prospective parents will have the opportunity to receive additional counseling and guidance. Further diagnostic tests such as the NIPD test and invasive procedures like amniocentesis may also be performed.
A moderately full bladder is sufficient for performing the transabdominal ultrasound, while it is advisable to have eaten something light before your scheduled appointment.
The Second-Trimester Anatomy Scan is recommended for ALL pregnancies, regardless of maternal age. Additional indications include a previous pregnancy with an anatomical or genetic abnormality, suspicion of a fetal anomaly in the current pregnancy, known fetal growth disorder, or any other potential complication that may affect the fetus (e.g., congenital infection). In such indications, the evaluation of the fetus may require further assessment of the fetal anatomy or heart, compared to the standard second-trimester fetal examination.
It should be clarified that the only way today to diagnose or confidently exclude chromosomal abnormalities is through invasive prenatal procedures (amniocentesis or chorionic villus sampling), which are performed under specific indications or at the request of the mother. Therefore, although a normal Second-Trimester Detailed Anatomy Scan is reassuring, it does not guarantee the birth of a healthy baby.
Congenital heart defects are the most common serious structural abnormalities in newborns and also among the hardest to detect before birth. That is why the heart is examined using a specific sequence of views:
Prenatal diagnosis of a serious heart defect allows delivery to take place at a center with a pediatric cardiologist and a cardiac surgeon, which improves the newborn's outcome. When there is an indication, such as a heart defect in a parent or a previous child, pre-existing diabetes or increased nuchal translucency, a separate fetal echocardiogram follows.
Being told about a “marker” on the level II ultrasound often causes a lot of worry. Its significance, however, depends mainly on the risk already calculated in the first trimester and on whether the marker is isolated.
Ask your doctor to explain how your numerical risk changes. A marker is not a diagnosis.
At the same appointment the length of the cervix can be measured, usually by transvaginal ultrasound, which gives the most accurate value. A short cervix, under 25 millimeters before week 24, is linked to a higher risk of preterm birth.
This finding is useful because an effective intervention exists. In women with a short cervix and no history of preterm birth, vaginal progesterone reduces the risk. In women with a previous preterm birth or a second trimester miscarriage, the doctor may discuss cervical cerclage. The measurement is painless and takes only a few minutes.
The quality of the scan does not depend only on the machine and the examiner. The baby and the conditions of the pregnancy also play a role.
In these cases it is better to complete the scan at a second appointment one to two weeks later than to call an exam with gaps complete. A repeat scan does not mean there is a problem. It means some structures were not seen with the required accuracy.
3D and 4D images of the baby's face are often the most moving moment of the scan. Medically, however, diagnosis relies almost entirely on standard two-dimensional views.
3D imaging has real diagnostic value for specific questions, such as assessing the extent of a cleft lip, skeletal dysplasias or imaging certain spinal abnormalities. It is also used for multiplanar analysis of the heart.
The principle followed internationally is that exposure time should be as low as needed for medical purposes. That is why “keepsake” images are taken for just a few minutes, if the baby's position allows it and after the medical examination is complete.
If the scan is normal, the next ultrasound is usually done at 30 to 34 weeks to assess growth, amniotic fluid and blood flow with Doppler. See the full schedule on the page about obstetric ultrasound in pregnancy.
If a finding is detected, you will be offered an individualized plan: a follow-up scan, fetal echocardiogram, genetic testing or a meeting with a pediatric specialist, so you know in advance what the finding means for the baby after birth. Keep the report and images in your pregnancy file and bring them to the maternity hospital.
The scan is best interpreted when the doctor has the full picture of the pregnancy in front of them.
Between weeks 20 and 24.
About 30 to 45 minutes, depending on the position of the fetus.
In most cases yes, if the baby's position allows it.
No. It detects most major structural abnormalities, but some appear later or cannot be seen on ultrasound.
No, you do not need a full bladder or to fast.
Yes, and it is still valuable. However, as the fetus grows, the bones of the skull and spine harden and some structures become harder to see. There is also less time left for further investigation, if needed.
Yes. Diagnostic ultrasound has been used in pregnancy for decades without any documented harm. The machine settings and exposure time are limited to what is needed for the medical information.
Usually yes, and many couples prefer it. Having your partner there also helps when discussing the results, especially if a decision about further tests needs to be made.
