What is the foetal morphology scan for?
This morphology ultrasound is suggested at 18-20 weeks gestation to check for abnormalities in your baby. The word “morphology” means the “form, structure and configuration” of your baby.
Besides checking for abnormalities in your baby this morphology scan checks:
- Your baby’s heart is beating
- Multiple pregnancies
- Size of your baby
- Position of the placenta
- Volume of amniotic fluid around your baby
Why is the morphology scan done at 18 – 20 weeks?
At 18-20 weeks gestation there are usually good views of limbs as well as internal organs. It is sometimes called an “anomaly scan” because fetal abnormalities are looked for at this time.
Why do I need a full bladder for this scan?
Fluid in the bladder provides a clear “window” to the pregnancy. It also makes the uterus rise up from behind your pubic bone. Your bladder does not need to be uncomfortably full, so feel free to empty some if you need to.
Can I find out the sex of the baby at this scan?
While a morphology ultrasound examination is never 100% accurate at determining your baby’s sex, with extremely good ultrasound machines and highly trained sonographers the accuracy is very high. Scans are more accurate in diagnosing boys than girls. About 60% of pregnant women want to find out the sex of their baby at this scan.
What sorts of abnormalities can be detected?
Below is a list of different types of abnormality, and how likely scanning is to identify each problem.
- Spina Bifida (Open spinal cord): 90% chance of detection
- Anencephaly (Absence of the top head): 99% chance of detection
- Hydrocephalus (Excess fluid within the brain): 60% chance of detection
- Major congenital heart problems: 25% chance of detection
- Diaphragmatic hernia (A defect in the muscle which separates the chest and the abdomen): 60% chance of detection
- Exomphalos/gastroschisiss (Defect of the abdominal wall): 90% chance of detection
- Major kidney: Missing or abnormal kidney 85% chance of detection
- Major limb: Missing bones or very short limbs 90% chance of detection
- Down syndrome: May be associated with heart and bowel problems 40% chance of detection
Cerebral palsy, autism and spasticity are never diagnosed
What if a problem is found?
This will depend on the nature of the abnormality suspected. Usually further ultrasound scans are required particularly focusing on the concern.
- Some abnormalities resolve in the pregnancy or after birth
- Some abnormalities persist but are of no concern and don’t affect your baby’s well being or appearance
- Some abnormalities will have an impact on delivery – timing, type and even location of delivery
- Some abnormalities unfortunately will not be compatible with a good pregnancy outcome
I will discuss any abnormal finding in detail with you so you are fully informed and understand the diagnosis and implications and so good management planning can be made with you. Usually there an no abnormal finding and so usually discussion is more about the size of your baby and whether it is consistent with dates, the position of the placenta, etc.
How safe are morphology ultrasound scans?
Ultrasound scans use sound waves, not ionizing radiation like x-rays. There have been many long-term studies which have shown no adverse effect from an examination before birth. Follow-up has shown normal growth and development, normal eyesight and hearing and a normal range of school performance.