Private anomaly scan vs the NHS 20-week scan

The anomaly scan — sometimes called the mid-pregnancy or 20-week scan — is a detailed ultrasound examination of your baby's anatomy from head to toe. Our specialists work through a comprehensive checklist of the organs and structures, paying particular attention to the brain and heart, where subtle differences can be hardest to see. You can read more on our main anomaly scan page.

During the scan we assess your baby's growth, the position of the placenta, and the amount of amniotic fluid around your baby. We also examine the developing anatomy for a wide range of physical conditions. Not every difference can be seen on ultrasound, and some conditions develop later in pregnancy, which is why a scan is best thought of as reassurance rather than a guarantee. You can learn more about the fetal anomalies that ultrasound can and cannot detect.

Because some important brain structures are not fully formed until around 22 weeks, we are happy to schedule your private scan a little later in the 20–25 week window, which can give a clearer view than an earlier appointment sometimes allows.

The NHS offers one routine mid-pregnancy ultrasound, often called the 20-week screening scan, usually carried out between 18 and 21 weeks of pregnancy. It is part of the NHS Fetal Anomaly Screening Programme and looks for 11 rare but serious physical conditions, examining your baby's anatomy in a set, standardised way.

It is a valuable, free part of your maternity care and we always recommend attending it. You can read what it involves in our FASP guide, and our guide to what the 20-week anomaly scan checks walks through the 11 conditions and what happens on the day.

The NHS scan is thorough, but it is delivered as a screening test within a busy service. Appointments are time-limited, you usually attend once, and the number of people who can come with you may be restricted. If your baby is lying in an awkward position and the sonographer cannot see everything, you may be asked to return for a second appointment, and waiting times for that repeat scan can vary between hospitals.

A private anomaly scan does not replace any of this. Instead, it adds time and flexibility: a longer appointment, the option to be seen when it suits you, and a chance to ask questions without the pressure of a tight schedule. It sits alongside your NHS pathway as extra reassurance, not a substitute for it.

The large majority of anomaly scans are reassuring. If we do notice something that needs a closer look, our specialists will explain what they have seen in clear, calm terms and talk you through the options — you will never be left to interpret a report alone.

Where appropriate, we provide a referral letter so you can be seen quickly within the NHS or by a fetal-medicine specialist for further assessment. Continuity with your NHS team matters, and we make sure any findings are shared so your ongoing care and delivery planning are not disrupted.

Some conditions cannot be seen on ultrasound at all, and some develop later in pregnancy. For that reason we often suggest a follow-up 3rd trimester anomaly scan at 26–29 weeks and, where relevant, a detailed early echocardiography study of the heart. Chromosomal conditions such as Down's syndrome are not diagnosed by the anomaly scan and are better screened for with NIPT.