20-Week Anatomy Scan: A Dad's Complete Guide

At around week 19, someone handed me an appointment letter for the "anomaly scan." That word — anomaly — sat in my brain for two weeks. Even though I'd read about this scan. Even though I knew it was routine. Even though every pregnancy book describes it as "exciting." Anomaly. The word doesn't help.

The 20-week anatomy scan is routine in the same way that a really detailed engineering inspection is routine. It's thorough. It covers a lot of ground. And occasionally it finds something that needs a closer look. Most of the time, everything is fine. But if you walk in without knowing what they're checking — or you walk out with a report full of clinical terms you don't understand — the experience can go from exciting to terrifying very quickly.

This is the guide I wanted before we went in. Everything they check, why they check it, what happens if they find something, and what you can actually do to be useful that day.

What the anatomy scan actually is

The anatomy scan — also called the anomaly scan, the mid-pregnancy scan, or the Level II ultrasound — is a detailed ultrasound done between 18 and 22 weeks, most commonly at around 19–20 weeks. It's not a quick heartbeat check. It's a systematic, head-to-toe examination of the baby's structures.

The sonographer is working through a checklist. They need to see specific views of specific structures. The baby has to be in the right position for each one, which is partly why the scan can take up to an hour. If the baby is curled up or facing the wrong way, they'll wait or ask your partner to move around a bit.

This scan is also when most hospitals will confirm the position of the placenta, check the amniotic fluid levels, and take growth measurements. And yes — if you want to know the sex, this is typically when that's visible, though not all hospitals tell you.

What they're checking, head to toe

Here's what the sonographer is actually looking at. Knowing this in advance makes the scan far less mysterious.

Head and brain. They measure the head circumference and check the brain's key structures — the ventricles (fluid-filled spaces), the cerebellum, and the skull shape. They're looking for signs of conditions like hydrocephalus (excess fluid) or neural tube issues at the top of the spine.

Face. They check the lip and palate for signs of cleft, the nose bone (nasal bone absence can be a soft marker for Down syndrome), and eye positioning. This is often where you get the clearest "face" view — the one that makes the baby feel suddenly, unambiguously real.

Heart. This is the most complex part of the scan. The heart at 20 weeks is roughly the size of a walnut and beating at 110–160 bpm. The sonographer checks the four-chamber view and the outflow tracts — the major vessels leaving the heart. The outflow tracts are technically difficult to image, and if they can't get a good view, they'll often schedule a follow-up cardiac scan. This is extremely common and does not mean anything is wrong with the heart.

Lungs and diaphragm. They check for any fluid in the chest and confirm the diaphragm is intact — ruling out diaphragmatic hernia, where abdominal organs can herniate into the chest cavity.

Abdomen. The stomach should be visible as a fluid-filled bubble — confirming the baby is swallowing. They check the kidneys and bladder are present and the right size, and look at the abdominal wall where the cord attaches.

Spine. This has to be checked at every single level — the vertebrae need to be seen closing properly around the spinal cord from neck to sacrum. This rules out spina bifida. The baby has to be positioned just right for this view.

Limbs. Arms, legs, hands, feet. They count fingers and toes on screen, check the bone lengths (femur length, humerus length), and look at the positioning of the feet.

Umbilical cord. A normal cord has three vessels — two arteries and one vein. A two-vessel cord (single umbilical artery) is found in about 1% of pregnancies and usually has no significance, but will be monitored.

Placenta and fluid. They note where the placenta sits — whether it's posterior, anterior, fundal, or low-lying. They also measure amniotic fluid volume. Both matter for understanding how the pregnancy will progress.

When they say they need a follow-up

Around 3–5% of anatomy scans flag something that needs further assessment. That sounds small, but it still means tens of thousands of couples every year are handed a letter asking them to come back. If that happens to you, here is what it almost certainly means: they couldn't get a clear view of a specific structure, or they saw a finding they want to look at again in 2–4 weeks.

The most common reason for a follow-up is not that something is wrong — it's that the baby was in a bad position and they couldn't complete the checklist. Particularly for the heart outflow tracts and the spine, the imaging angle has to be precise. If the baby doesn't cooperate, they'll ask you to come back. This happens all the time.

What soft markers actually mean

A soft marker is a finding that doesn't indicate a structural problem on its own, but that slightly raises the statistical probability of a chromosomal condition. The word "slightly" is doing a lot of work there — and it's important.

A choroid plexus cyst is a good example. The choroid plexus is a structure in the brain that produces cerebrospinal fluid. Small cysts can form there — they appear in roughly 1–2% of all fetuses and almost always resolve completely by week 28. On its own, a CPC has very low clinical significance. It's only meaningful in combination with other findings or in the context of other risk factors.

Other soft markers include a short femur, a bright spot on the heart (echogenic focus), mild kidney dilation, or a single umbilical artery. Each one, in isolation, is common in healthy pregnancies. In combination, or alongside elevated blood screening results, they carry more weight. Your doctor or midwife will explain the context — and if they don't explain it clearly enough, ask them again.

What to do on the day — practical dad stuff

Arrive hydrated. Not bladder-full — just well-hydrated. Amniotic fluid is partly made from the mother's hydration, and a well-hydrated abdomen transmits ultrasound better. Some hospitals ask for a partially full bladder for early scans, but at 20 weeks, full hydration is usually all they need.

Bring a notepad. Or open the notes app on your phone before you walk in. The sonographer will tell you things. They'll use terms. They'll mention measurements. You will not remember all of it. Write down everything — even if it doesn't seem important. The words will be in the report later, but the context the sonographer gives verbally disappears fast when you're emotionally in it.

Ask questions in the room. The sonographer can tell you what they're looking at as they go. They can't diagnose — that's the doctor's job — but they can explain what structure they're examining. Ask them to walk you through what they're seeing. Most sonographers are happy to narrate if you ask.

Getting the report — and actually understanding it

You'll usually get a written report either on the day or sent to your care provider. These reports are written for radiologists to communicate with doctors. They are not written for a dad sitting in the car park trying to understand what just happened.

Terms like "normal fetal biometry," "posterior placenta grade 1," "bilateral choroid plexus cysts," and "no gross structural abnormality identified" are completely standard phrases that mean very different things to a radiologist than they sound to anyone else. "No gross abnormality" doesn't mean "we had to look really hard." It means "no obvious structural problems." That's good.

If you're in this position — staring at a report full of words you can't parse — that's exactly what Dadly's scan report analysis is built for. Upload the report, and Dadly walks you through it in plain English: what each finding means, what's standard, and what questions to bring to your next appointment. No panic spiral. Just clarity.

If you want to understand more about navigating pregnancy information as a dad — especially when results come back with findings you don't understand — read how I used AI through nine months of pregnancy. And if you're coming up on the third trimester, the week 28 dad's guide covers what changes after the anatomy scan.