Case Study: Fetal Abnormality

Clinical question

What is the diagnostic value and effectiveness of the following screening methods in identifying serious structural abnormalities?

• ultrasound undertaken in first and second trimesters
• nuchal translucency measurement
• serum screening – alpha-fetoprotein (AFP).

Previous NICE guidance (for the updated recommendations see below)

Pregnant women should be offered an ultrasound scan to screen for structural anomalies, ideally between 18 to 20 weeks of gestation, by an appropriately trained sonographer and with equipment of an appropriate standard as outlined by the National Screening Committee. [A]

9.1.1. Introduction and background

Since routine ultrasonography has been introduced into antenatal care women have had the opportunity to visualise the fetus at an early stage of pregnancy. The ultrasound scan has been used by health professionals to assess gestational age more accurately, to diagnose multiple births and to detect fetal anomalies. Improvements in technology have enabled health professionals to identify fetal structures, both normal and abnormal, and also to identify minor anomalies of uncertain significance, known as ‘soft markers’.

Detection of fetal anomalies on antenatal ultrasound offers women and their partners information that may help them better prepare for the birth of their child, the option of delivery in a setting that will permit rapid access to specialist surgical or medical care, and the possibility of considering pregnancy termination or palliative care in the newborn period. Routine antenatal ultrasound has therefore presented women and their partners with difficult decisions and an abnormal result on ultrasound imaging has the potential to cause great anxiety throughout the remaining weeks of pregnancy. These are important considerations with regard to the timing of routine ultrasound screening and the potential for false positive results or detection of ‘soft markers’.

Since the introduction of ultrasound in the 1970s, ultrasound technology has greatly improved. Modern equipment is now far superior and obstetric ultrasound is firmly established in routine practice, allowing identification of fetal anomalies and fetal growth problems. With this technology it is essential that healthcare professionals and clinicians who perform the scans are trained correctly to perform the examination and also understand and interpret the findings of the ultrasound scan correctly.³⁰²

This section of the guideline highlights the areas in which ultrasound screening is thought to have a role in the prenatal diagnosis of fetal anomalies.