Whole exome sequencing, or WES, is an advanced genetic test that looks at the coding regions of DNA. These regions contain many known disease-causing changes, so WES may be considered when a baby has structural findings on ultrasound and standard tests do not provide an answer.
WES is not a routine test for every pregnancy. It is usually discussed in specialist fetal medicine and genetic counselling settings.
When may WES be considered?
It may be considered when ultrasound shows one or more fetal anomalies, karyotype or microarray is normal, and doctors suspect a single-gene condition. It may also be useful when there is a previous affected pregnancy or a strong family history.
How is the sample obtained?
During pregnancy, WES usually requires fetal DNA from amniocentesis or CVS. In many cases, parental blood samples are also tested so the lab can interpret whether a variant is inherited or new.
What can WES find?
WES may identify gene changes linked to a suspected fetal condition. This can help with prognosis, pregnancy planning, neonatal care, recurrence risk counselling, and future family planning.
What are the limitations?
WES may not find an answer. It may find a variant of uncertain significance. It may also identify information that is complex or unexpected. This is why pre-test counselling is essential before deciding.
How long do results take?
Timelines vary by lab and clinical urgency. In pregnancy, timing matters, so the care team will discuss whether WES can provide useful information within the decision window.
Whole exome sequencing can be powerful when used for the right clinical question. It should be guided by detailed ultrasound findings, genetic counselling, and a clear discussion of what the result may mean.