This 20-week pregnancy scan is the most important prenatal screening test as it can both screen for abnormalities and, with detailed analysis from a specialist, offer diagnosis. For this reason it is called the Second Trimester Fetal Development Anomaly Scan. It can be carried out between 15-22 weeks of pregnancy.
The 20-week scan is used to:
- check a baby's anatomy
- measure a baby's growth, including head and brain, body and limbs
- check a baby's organs and limbs for abnormalities
- check and measure the placenta and amniotic fluid
- identify a baby's gender
- show images of a baby in 3D/4D
At the 20-week anatomy and anomaly scan you'll be able to see your baby's body, arms, legs, fingers, toes and facial features. Your ultrasound specialist will inspect your baby's anatomy and study the internal organs, and will talk you through the images on screen. If the genitals are not obscured and you wish to know, we can tell you the gender of your baby. We will give you printed and digital images of the scan at no extra cost.
The majority of pregnancies are healthy, and this scan typically provides reassurance. In the unlikely event that any variations from normal development are detected, this helps parents and clinicians to plan care during the rest of pregnancy and make any special arrangement for birth and postnatal treatment.
You can have a 20-week pregnancy scan between 18 and 24 weeks into your pregnancy. You can calculate these dates from the first day of your last period.
Structural abnormalities that may be identified on the 20-week scan
The 20-week scan can detect structural defects including spinal defects, cleft lip/palate, significant clubfeet, body wall abnormalities, major urinary abnormalities, and major heart defects, and a variety of subtle markers that may indicate Down syndrome.
Very occasionally this 20-week scan can pick up abnormalities related to chromosome disorders that were missed in an earlier scan. This is becoming less common as the accuracy of tests increases, and with the introduction of non-invasive prenatal testing.
What to expect
You'll meet either our specialist prenatal sonographer or our doctor who specialises in prenatal diagnosis. The actual scan will take around 30 minutes and during this time you'll be able to see the 3D images of your baby on screen.
Your sonographer will check your baby's anatomy, including organs and the placenta, and will take detailed measurements in order to calculate your baby's growth. We will check these measurements against a set of fetal growth charts, which we use to predict your baby's development. We'll keep a record of these measurements so we can compare them with your earlier and subsequent scans.