Medical Questions » Pregnancy Questions » Question No. 803
| Question: | My last pregnancy ended as a miscarriage, and I am now ten weeks pregnant again, but I am 38 years old, and my doctor wants me to have an amniocentesis in a few weeks. What do you think about these tests? The obstetrician says there are some risks with it. |
| Answer: | There is no simple answer to this question, so you must understand as much as possible about the test to enable you to make up your own mind.
While a foetus is in the womb, it is surrounded by the amniotic sac which contains fluid that protects it from harm. Amniocentesis is a procedure in which a small amount of the amniotic fluid is drawn off, and the cells it contains are cultured and analysed under a microscope to give information about the health of the baby. It will also disclose the baby' s sex. The cells contain the baby' s chromosomes, which it has inherited from its parents. These chromosomes can be analysed to give information about nearly 100 different genetic disorders, such as Down' s syndrome.
There is a slightly increased possibility of miscarriage as a result of amniocentesis, and it will not usually be carried out unless thete is some risk of abnormality.
Risk factors include: —A woman who is over 37 years of age, especially if it is her first child. Older
mothers are significantly more at risk of giving birth to a Down' s syndrome
child and will usually be offered this test as a matter of routine at between
16 and 18 weeks of pregnancy.
— One or other parent with a known chromosomal abnormality. For example,
a woman may be a carrier of a genetic disorder such as haemophilia, which
does not affect her, but which her sons have a 50% chance of inheriting.
— Certain diseases that run in eithet parent' s family (eg. muscular dystrophy).
—The fact that the mother has had three or more miscarriages.
—An earlier abnormal child, or a close family member with an abnormal child.
Before the procedure, an ultrasound scan will be performed so that the position of the foetus and placenta can be pinpointed. The woman will then be given a local anaesthetic in the abdomen, following which a hollow needle will be inserted through the abdominal wall into the uterus. About 14 mL (roughly two dessertspoons) of fluid will be removed by a syringe attached to the needle.
Amniocentesis is performed not less than 14 weeks (and usually 16-18 weeks) after the last period, because until then there is not enough amniotic fluid or cells to analyse.
Amniocentesis results are 99% reliable. The risk of injury to the baby is practically nil. The risk of a miscarriage occurring is very slight—about one in 200. Complications such as infection and bleeding are also rare.
It is not, however, a procedure that should be undertaken lightly. There is a risk, albeit a slight one. You will need to think about what your reaction will be if the results should prove to be abnormal. If you would not consider having the pregnancy terminated under any circumstances, the test is probably pointless. There is a long wait for the results and this can be stressful. Terminating a pregnancy at the stage the results become known is distressing and may need to be the same as an induced labour.
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