Second-Trimester Anatomy Scan
Around the midpoint of pregnancy comes the examination that many call “the big ultrasound.” And rightly so: the second-trimester anatomy scan is the most comprehensive imaging assessment available during pregnancy.
It examines the fetus literally “from head to toe,” assessing the structure and development of every organ in a level of detail that is not possible at any other stage.
It is also the time when many couples, if they wish, learn their baby’s sex.
What is the second-trimester anatomy scan and what does it show?
The second-trimester anatomy scan is an extensive anatomical assessment of the fetus performed in the second trimester. Its purpose is to systematically evaluate fetal anatomy and identify any structural abnormalities that were not visible earlier.
During the scan, we examine in detail:
Head & Brain
We assess the structure of the brain—ventricles, cerebellum, corpus callosum—as well as the integrity of the skull. We look for abnormalities such as hydrocephalus, anencephaly, and other structural disorders.
Face
We examine the facial structures—lips, palate, eyes, ears, and nose—for abnormalities such as cleft lip or cleft palate.
Spine
We examine the spine vertebra by vertebra, looking for open defects such as spina bifida.
Heart
We assess the structure of the heart—atria, ventricles, valves, and great vessels. Cardiac assessment is one of the most critical parts of the scan, as congenital heart defects are among the most common structural abnormalities.
Lungs & Diaphragm
We evaluate lung development and the integrity of the diaphragm.
Abdomen & Organs
We examine the stomach, liver, kidneys, bladder, bowel, and abdominal wall, looking for abnormalities in their development or function.
Limbs
We measure and evaluate the bones of the upper and lower limbs—the femur, tibia, humerus, and ulna—and check for any deformities.
Placenta, Amniotic Fluid & Cervix
We assess the position and maturity of the placenta, the amount of amniotic fluid, and the length of the cervix as an early indicator of the risk of preterm birth.
When is the second-trimester anatomy scan performed?
The second-trimester anatomy scan is performed between the 20th and 23rd week of pregnancy. The ideal time is around 20–22 weeks.
Why during this time?
Because at this stage the fetus has developed enough for all the structures we are interested in to be visible, while still being small enough to fit within the ultrasound field of view without needing to be “scanned” in sections. If performed earlier, some structures may not yet be developed enough for reliable assessment.
How is the examination performed?
The second-trimester anatomy scan is performed transabdominally, with the ultrasound probe on the abdomen.
It is painless and safe for the fetus.
The examination usually lasts 30–45 minutes, sometimes longer, depending on the fetus’s position. The baby needs to be in a suitable position for us to evaluate all the structures—and sometimes a little patience or a short walk is needed to encourage movement.
If a structure is not visible because of an unfavorable position, the examination may need to be repeated in a few days (which is common and not related to any problem).
Will I learn my baby’s sex during the second-trimester anatomy scan?
Yes, the second-trimester anatomy scan is the most reliable time to determine fetal sex during pregnancy. At 20–22 weeks, the genital organs are fully differentiated and clearly visible on ultrasound, with accuracy approaching 100% when the fetus is in a suitable position.
Second-trimester anatomy scan — girl
In girls, the sonographer looks for the characteristic signs of the female genitalia—the labia—and the absence of testes. The typical image is described as three parallel lines, known as the “hamburger sign.”
Second-trimester anatomy scan — boy
In boys, the penis and testes are clearly visible at 20–22 weeks. Their appearance on ultrasound is usually quite clear, provided the fetus has not “closed” its legs!
“Good nuchal translucency, concerning second-trimester scan” — What does this mean?
This is a situation that causes significant concern for many couples, and it deserves an honest and calm explanation.
The nuchal translucency scan and the second-trimester anatomy scan assess different things.
The nuchal translucency scan estimates the risk of chromosomal abnormalities; the second-trimester anatomy scan evaluates the fetus’s structural anatomy.
A fetus may have a normal chromosomal profile and still have a structural abnormality, and vice versa.
If the second-trimester scan identifies something that needs further evaluation, this does not automatically mean a serious problem. Many findings are minor, temporary, or simply require closer follow-up.
The next steps are always assessed individually, with calm and scientific judgment.
Frequently Asked Questions (FAQ)
It is strongly recommended by all international obstetric societies. It is the only examination that can assess fetal anatomy in the second trimester with this level of detail.
It depends on the finding. Some findings simply require a repeat scan in a few weeks; others are referred for specialized assessment by a fetal cardiologist or fetal neurologist; and some rarer findings may require invasive investigation.
No ultrasound can guarantee 100% detection of all abnormalities. Some structural abnormalities appear or become visible later in pregnancy, while image quality is affected by factors such as fetal position and maternal body habitus. For this reason, the examination is always complemented by clinical assessment and follow-up. In addition, conditions such as intellectual disability, autism, congenital deafness, and several neurological disorders cannot be diagnosed with this examination.
In the private sector, a referral is not required. It is enough to book your appointment early, ideally from 18–19 weeks, to ensure an appointment within the appropriate time frame.
No, a light meal or a small sweet snack shortly before the examination may help the baby be more active, which makes imaging easier. The same applies to a glass of cold water or juice. A full bladder is not necessary either.
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