Introduction

A clinical geneticist can have several roles in a fetal medicine unit: assisting with management of the family at high risk of a genetic condition, aiding the interpretation of complex chromosome rearrangements and facilitating the diagnosis of a fetus with structural anomalies but apparently normal chromosomes. With increasing routine use of prenatal sonography for the diagnosis of fetal anomalies and the technological improvements in ultrasound machines, more fetal abnormalities are being detected. Defining the prognosis for a fetus with structural abnormalities if the karotype is abnormal can be reasonably straightforward but cases with apparently normal chromosomes are more challenging. Accurate prenatal diagnosis of rare syndromes is becoming an increasing reality with the advances in ultrasonography and molecular technology. Such accuracy is not always possible prenatally, and postnatal confirmation is thus essential.

For the past two decades, increasing numbers of gene mutations have been identified that allow invasive prenatal diagnosis in subsequent pregnancies in early gestation, giving parents in many countries around the world choices in the management of affected pregnancies. This does, however, require a couple to have a family history of a disorder, with accurate confirmation of the diagnosis, usually before pregnancy. In the absence of a family history, an abnormality will only be identified by a screening test. Screening tests during pregnancy fall into two groups:

1. ■ those identified on blood tests, such as sickle cell trait, and first- and second-trimester biochemical screening for Down syndrome

2. ■ those identified on ultrasound.