The 20-week anomaly scan examines your baby’s brain, face, spine, heart, kidneys and limbs. Here is what each check involves and what it cannot show.
Around the 20th week, your obstetrician will probably ask you to book an anomaly scan. It is the longest and most detailed ultrasound of the pregnancy, and many parents go in knowing it matters without being sure what the sonographer is looking for. This article goes through the examination area by area, so the screen in front of you makes more sense.
The head is measured and the skull shape checked. The sonographer then looks inside at the fluid-filled ventricles, the structures along the midline and the cerebellum at the back. Some major brain differences can be seen at this stage, though not all of them.
The profile, both eyes and the upper lip are examined if the baby is facing the right way. A cleft lip is usually visible. A cleft involving only the palate sits inside the mouth and is much harder to see.
The spine is scanned lengthwise and in cross-section to confirm that the bones are in line and that skin covers the back. This is the check aimed at neural tube defects such as spina bifida.
The doctor looks at the heart's position, its four chambers and the two large vessels leaving it, along with the lungs and diaphragm. Parents often assume this is a full heart scan. It is not. A fetal echocardiogram studies the heart in far greater detail and is arranged separately when there is a reason for it.
The stomach should appear as a dark bubble on the baby's left, and the point where the cord enters the abdomen is checked for any defect in the abdominal wall. Both kidneys and the bladder need to be seen. A small amount of extra fluid in the kidney is a fairly common observation, and a repeat scan later in pregnancy is often all that is needed.
Each limb is followed from the long bones down to the hands and feet. Do not be surprised if the sonographer does not count fingers aloud. Tiny fists are usually clenched, and a full count is often not possible.
Alongside the baby, the scan records where the placenta lies. A low-lying placenta near the cervix may need a recheck later in pregnancy. The amount of amniotic fluid is assessed, the cord is checked for its three blood vessels, and measurements of the head, abdomen and thigh bone show whether growth is in step with the dates.
No. Under India's PCPNDT Act, scan centres cannot reveal the baby's sex, so please do not expect to be told.
Clear pictures depend on things nobody controls, such as how the baby is lying, where the placenta sits, the amount of fluid and the mother's build. When a view is poor, you may be asked to turn on your side, take a short walk, or come back another day. In most cases the reason is simply a poor image rather than a finding.
The anomaly scan is a study of structure. It does not look at chromosomes or genes, and it cannot judge every functional or developmental condition. That is where tests like NIPT or amniocentesis come in, and your doctor can say whether either is relevant to you.
A useful habit at the end of the appointment is to ask whether all the views were completed and whether anything needs a second look. If you are in Trichy and want fetal medicine input, Trichy Fetal Medicine and Fertility Centre can be reached through its official website.
To arrange this at our Trichy centre, see anomaly scan; if you are unsure whether you need it, our doctors can tell you after a review.
This guide is for general information and does not replace a consultation with a fetal medicine specialist.
In line with the PCPNDT Act, we do not perform or support sex determination.
Anomaly Scan
The detailed mid-pregnancy scan that examines your baby's organs, growth, and wellbeing.
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