In purely statistical terms, the risk of a miscarriage, or an alteration in the chromosome number (e.g. trisomy 21), increases in tandem with the age of the pregnant woman. It is slightly increased in women over 30 and more significantly in those over 40. However, the majority of older women give birth to perfectly healthy children.
Factors indicating high-risk pregnancy:
- The mother is older than 35 and/or the father is older than 45
- Hereditary diseases in the mother's and/or father's family
- Positive results during initial examinations
- Two or more previous miscarriages
- Mother contracts rubella infection or toxoplasmosis during the pregnancy
- Taking of certain medications during pregnancy
- X-ray exposure during pregnancy
In some cases, special examinations are conducted to determine whether the foetus has any genetic diseases. It is essential however that parents carefully consider the benefits and risks involved in such procedures.
Like chorionic sampling, amniocentesis is used to examine the unborn child for chromosome deformities which could be the cause of genetic disease.
The risk of having a child affected with chromosomal disorders is higher with pregnant women over the age of 35 and in those who have a familial disposition for genetic illnesses. The test is usually carried out between the 14th and 18th week of pregnancy.
During the examination, amniotic fluid is extracted through the abdominal wall. The foetal cells contained in the amniotic fluid are examined over a two week period in order to observe the number and structure of the chromosomes. The risk of miscarrying due to amniocentesis is approximately 1%.
Chorionic Villus Sampling (CVS)
CVS, also known as chorion sampling or placental biopsy, is a prenatal test that can detect genetic and chromosomal abnormalities by testing cells removed from the placenta, which has the same genetic makeup as the foetus.
The test can be done between 9 - 12 weeks of pregnancy, offering an earlier alternative to amniocentesis, which is done at 15 - 20 weeks.
It is recommended to women who may be at risk of carrying a foetus with a birth defect, having one or more of the following risk factors:
- Aged 35 and over (risk for a child with Downs Syndrome increases with maternal age)
- A history of miscarriages or children born with birth defects
- A family history of genetic disease
The test is done by putting a small tube or catheter through the vagina and into the uterus to remove some cells from the placenta. It can also be done by putting a needle through the mother's abdomen into her uterus and then into the placenta.
The risk of miscarriages due to CVS is 1%. It remains unclear, however, whether miscarriages recorded at this early stage of the pregnancy might not have happened anyway.