Prenatal assessment

Recent advances in ultrasound technique, equipment, and
training together with rapid advances in molecular biology have
increased the range of antenatal diagnoses. Some methods are
available only at specialised centres. This chapter will give a
background to successful techniques. An anomaly may be
detected during routine examination of the fetus which is
carried out by ultrasound between 18 and 24 weeks of gestation.
Maternal serum screening for Down’s syndrome is performed as
a double, triple or two stage integrated test (see below).
After the birth of an abnormal baby or the detection of
genetic disease in an older child, a paediatrician or geneticist may
recommend a specific test at a particular week in the subsequent
pregnancy. Some tests are at an early stage in development and
the false positive and negative rates have not been assessed. Some
genetic tests are not yet sufficiently precise to enable an accurate
prognosis to be given to every family with that disease.
At the first antenatal visit it is still important to carry out a
full blood count and haemoglobin electrophoresis, blood
grouping, rhesus antibody titre, tests for rubella and
hepatitis B, human immunodeficiency virus (HIV), and syphilis.
The haemoglobin electrophoresis may show that the mother
has
-thalassaemia trait or sickle cell trait and the father’s red
cell investigations may suggest that further studies of the fetus
are needed.