The anomaly scan is a detailed ultrasound performed between 18 and 22 weeks that examines your baby's anatomy from head to toe - brain, face, heart, spine, lungs, abdomen, kidneys, bladder, limbs and placenta. It takes 30-45 minutes, requires no fasting and no full bladder, and is the single best opportunity in pregnancy to detect structural problems. It catches roughly 50-70% of major anomalies - a normal scan is reassuring but is never a guarantee of a perfectly healthy baby. By Indian law (PCPNDT Act), foetal sex is never disclosed.
On this page
Why this particular scan is special
The first trimester scans you have already had - the dating scan and possibly an NT scan around 11-13 weeks - confirm a viable pregnancy, measure gestational age, and screen for chromosomal disorders. They are short and largely about numbers.
The anomaly scan is different. It is about anatomy. Between 18 and 22 weeks, the foetus is large enough that every major organ system is visible on ultrasound, but still small enough to be examined from multiple angles in one sitting. This is the only point in pregnancy when a single scan can survey the entire baby, head to heel, in clinically actionable detail.
If a serious structural problem exists, this is the scan that is most likely to find it. That is also why it can feel emotionally heavier than the others. We say this to every patient: most anomaly scans are reassuringly normal. Reading about everything that could go wrong is not the same as discovering that something has.
Timing - and why 19-21 weeks is the sweet spot
Indian and international guidelines (FOGSI, ISUOG, the UK's NHS FASP programme) all converge on a window of 18 weeks 0 days to 22 weeks 6 days. Within that window:
- Before 18 weeks, the heart is too small to confidently visualise the four chambers and outflow tracts. Many anomalies of the brain are also still developing.
- After 22 weeks, the baby's bones cast acoustic shadows that obscure the heart and spine. Worse, if a serious abnormality is found late, the legal options for parents under Indian MTP law (now permitted up to 24 weeks for diagnosed foetal abnormalities) shrink quickly.
- 19-21 weeks is where image quality and time-for-decision overlap perfectly.
Your obstetrician will pick a date in this window. If the baby is in an unfavourable position - face-down, with a hand or foot blocking the heart - you may be asked to come back in a few days. This is normal and not a sign that anything is wrong.
The 20-item anatomy checklist
Your sonographer is working from a standardised checklist of structures that must be visualised. While the exact list varies slightly between organisations, the core 20 items are:
- Head: skull shape, ventricles of the brain, cavum septi pellucidi, cerebellum, posterior fossa.
- Face: eyes, nasal bone, upper lip (cleft check), profile.
- Spine: longitudinal and transverse views, ruling out spina bifida and other neural tube defects.
- Heart: four-chamber view, left and right outflow tracts, three-vessel view - the most demanding part of the scan.
- Lungs and diaphragm: symmetry, integrity.
- Abdomen: stomach bubble on the left, bowel pattern, abdominal wall (umbilical insertion).
- Kidneys and bladder: both kidneys present, no hydronephrosis, bladder filling.
- Limbs: all four, with three long bones in each (femur, tibia, fibula in legs; humerus, radius, ulna in arms), plus hands and feet.
- Placenta: location relative to the cervix, appearance, cord vessels.
- Amniotic fluid: volume - too little or too much both flag something to investigate.
- Cervix: length (a short cervix at this stage is a marker of preterm-labour risk).
- Biometry: measurements of the head (BPD, HC), abdomen (AC) and femur (FL) to confirm gestational age and check growth.
How to prepare on the day
You can be wonderfully low-key about this. There is nothing to fast for and no special prep. Specifically:
- Eat normally on the day. A baby with sugar in its system tends to move around more, which actually helps us get the views we need.
- Empty your bladder partially before the scan. A massively full bladder is uncomfortable for a 30-45 minute scan and is not needed at this gestation.
- Wear two-piece clothing - a kurti and pants, or a top and skirt. We will only need access to your abdomen.
- Bring your previous reports - the dating scan, NT scan, any blood tests from this pregnancy. We compare against them.
- Bring company if you wish. Your partner, your mother, your sister - whoever you find reassuring. At Optima Diagnostics, one companion is welcome in the scan room, and a female sonographer is available on request.
What the anomaly scan cannot see
This is the part most blog posts gloss over, and we think they shouldn't. A normal anomaly scan is not a clean bill of health for the rest of pregnancy. Here is the honest list:
- Mild congenital heart defects - small ventricular septal defects (VSDs), some atrial septal defects, mild valve abnormalities - are commonly missed and often not visible until after birth.
- Chromosomal disorders like Down syndrome are not diagnosed by ultrasound. The anomaly scan may show soft markers that raise suspicion, but only NIPT (cell-free DNA) or invasive testing (amniocentesis) can give a real answer.
- Most genetic and metabolic conditions have no visible footprint on ultrasound - cystic fibrosis, thalassaemia, phenylketonuria, autism. These need targeted testing if at risk.
- Hearing and vision cannot be assessed on ultrasound.
- Late-developing problems - intrauterine growth restriction, late-onset placental issues - emerge after this scan, which is why third-trimester growth scans exist.
None of this should make you anxious. Knowing what a test cannot tell you is exactly what lets you read a normal result with appropriate confidence.
Reading your report calmly
A well-written anomaly report has three sections: a clean list of measurements (BPD, HC, AC, FL with percentiles), a systems-based findings section, and an impression. Look at the impression first. If it says "normal foetal anatomy survey for gestational age, no obvious foetal anomaly detected," the rest of the report is supporting evidence.
If a finding is reported - say, an echogenic intracardiac focus, a single umbilical artery, or borderline mild ventriculomegaly - your obstetrician will discuss what is and is not concerning. Many findings are soft markers: small variations that on their own are usually harmless, but in combination may warrant further testing.
One sentence to remember: a normal anomaly scan does not promise a perfect baby, and an abnormal finding does not always mean a serious problem. The report is the start of a conversation with your obstetrician - not a verdict.
PCPNDT Act and why we will not tell you the sex
India's Pre-Conception and Pre-Natal Diagnostic Techniques (PCPNDT) Act, 1994, prohibits the disclosure of foetal sex at any stage of pregnancy. The law exists for good reason - female foeticide is a documented public-health problem - and we honour both its letter and its spirit. Every Optima Diagnostics scan room carries a visible "sex of the foetus will not be revealed" notice, and our sonographers are trained never to volunteer or hint at this information, even to a determined parent. We appreciate your understanding.
Getting an anomaly scan in Silchar
The anomaly scan is a senior-level study and the operator's experience matters. At Optima Diagnostics, anomaly scans are performed on a high-resolution GE Voluson machine by consultant radiologists with sub-specialty training in obstetric ultrasound, with a female sonographer available on request. Reports are typically ready within a few hours, and we are happy to forward images directly to your obstetrician's WhatsApp on your authorisation. For further reading on what an obstetric ultrasound entails earlier and later in pregnancy, see our guide on the scope and limits of routine ultrasound.
Frequently asked questions
When should the anomaly scan be done?
Between 18 and 22 weeks of pregnancy. 19-21 weeks is the sweet spot - the baby is large enough to see organ detail but small enough to be examined from every angle.
Do I need a full bladder?
No. By the second trimester the pregnant uterus has risen out of the pelvis and the amniotic fluid provides its own acoustic window. A moderately empty bladder is more comfortable for the 30-45 minute scan.
How long does it take?
Usually 30 to 45 minutes, sometimes longer if the baby is in a difficult position. You may be asked to walk around, eat something sweet, or lie on your side to encourage movement before the scan is finished.
Does it detect every problem?
No. Even an expert anomaly scan picks up roughly 50-70% of major structural problems. Some conditions cannot be seen on ultrasound at all. A normal scan is reassuring, not a guarantee.
Is it safe for my baby?
Yes. Diagnostic ultrasound has been used in obstetrics for over 50 years with no evidence of harm to the baby at standard settings used by trained operators.
Can I learn my baby's gender?
Under the PCPNDT Act, disclosing foetal sex is illegal in India. Centres that comply with the law - including Optima Diagnostics - will not share this information under any circumstances.
This article is for general education. Investigations and any decisions about further testing must be made together with your obstetrician.
