Pregnancy Termination: How can we tell that the fetus would have severe handicap?

Thirty years ago our ability to diagnose serious inherited disorders or anatomical abnormality (deformity) before birth was very limited. Technological advances, particularly the combination of blood screening tests and ultrasound now allow us to exclude many, but by no means all, of these problems. The question of screening for foetal abnormality is never an easy one. Some would find the thought of caring for a handicapped child intolerable whereas others believe the practice of pregnancy termination is unacceptable (Q19.15). It is only feasible to provide a brief account of the principles, benefits and risks here. Other sources of information are provided inQ19.16 and Q19.17 When screening indicates that the fetus has a serious defect, there are two options. Many couples elect to continue the pregnancy and the obstetrician in collaboration with the paediatrician can counsel on what is to be expected and the treatment options for the baby. Other couples decide that they do not wish the pregnancy to continue and termination can be arranged. Counselling may be offered to provide support for you to come to terms with a decision to discontinue a planned pregnancy. You will also need advice on the chance of recurrence in another pregnancy. Your gynaecologist may be able to supply you with this information or otherwise arrange for you to see a clinical geneticist.

Down syndrome (mongolism), which is associated with typical facial features and reduced mental ability, is due to an extra chromosome 21 (genes - chromosomes). This syndrome is more common with increasing maternal age. A definitive diagnosis can only be reached from genetic (laboratory gene) evaluation of foetal cells obtained either from the amniotic fluid (the fluid around the baby during pregnancy) or from placental type cells (chorionic villus sampling). We used to offer all mothers aged 37 years or more the option of amniocentesis; at the age of 37, the chance of having a Down’s baby is about 1 in 250 pregnancies. Amniotic fluid is obtained (amniocentesis) by introducing a fine needle through the abdominal wall and uterus, usually with local anaesthetic, under ultrasound control. There is an approximately 1% risk that this may cause miscarriage. The fetal cells are cultured in preparation for analysis of the chromosomes (genes). The culture may take two weeks or more. Recently molecular biological techniques such as “FISH” (fluorescence in situ hybridisation) have been introduced. These techniques involve a more direct analysis of genetic material and provisional results can be provided within hours rather than weeks.

As the majority of babies are born to women younger than 37, most babies with Down syndrome were missed by the age-related screening programme. Blood tests, including the triple or quadruple tests, could modify the risk for each pregnancy. Some women aged 37 years or more may find that the test shows that their risk is relatively low so that they would be happy to decline amniocentesis whereas for some younger women the test may show that their risk is greater than would have been indicated from their age and they may elect to have further investigation.

Ultrasound undertaken at around eleven weeks into the pregnancy with particular reference to the back of the baby’s neck (nuchal translucency) may provide a valuable guide to the risk of Down syndrome. It has been shown that ultrasound is more accurate than the blood test screening and it also has the advantage of screening five weeks before the quadruple test leading to earlier diagnosis or, hopefully, reassurance. Interest is now focusing on a combination of ultrasound and early blood test screening.

The spina bifida group of defects, and heart and limb defects may be demonstrated by ultrasound. Some families are prone to inherited disorders and many of these can be detected by specific screening techniques.

Screening tests are discussed inscreening tests

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