Fertility Associates works closely with Genetic Health Services NZ hubs in the provision of procedures to identify potential abnormalities, both in embryos (Pre-implantation Genetic Diagnosis - PGD) and fetuses (Pre-Natal Diagnosis - PND). Critical to all decisions to use these techniques is the provision of genetic counselling and high quality advice about the consequences of the knowledge that one might gain, and also the procedures that one might undergo and the potential risks associated with them.
The decision about whether to proceed with genetic testing of any sort remains that of the patient alone. In the end only the patient can make the decision.
For PGD, the embryos are biopsied in Auckland or Christchurch, and the cells are sent to CHL in Christchurch or Monash IVF in Melbourne for testing.
Pre-implantation Genetic Diagnosis (PGD)
To download a fact sheet on PGD click here.
What is Pre-Natal Diagnosis (PND) and what tests are available?
There are a number of tests available that may help determine whether your baby has any problems prior to birth. The problems that these tests can detect include:
- Chromosomal abnormalities: This usually means the wrong number of chromosomes (too many or too few), for example Down syndrome, which is caused by an extra number 21 chromosome. Abnormalities can also be caused by a structural defect where chromosomes become broken or rearranged. Chromosomal abnormalities usually happen during cell division in the maturing egg or in the early embryo and may lead to a variety of problems in the baby, including structural abnormalities, severe mental retardation and infertility. This can happen in any pregnancy but is more common with advancing maternal age (see table 3), following the previous birth of a baby with a chromosomal abnormality or where either parent is known to carry a chromosomal problem.
- Some inherited diseases: These are where a malfunctioning gene is passed on from parent to child. Examples of inherited diseases include Huntington’s disease, haemophila and cystic fibrosis, which are caused by a gene mutation on a specific chromosome. Where a family history is present, it may be important to identify these genetic problems as they can be passed onto your children.
- Anatomical defects: The most common are neural tube defects, which occur in three out of every 1,000 pregnancies and include problems such as spina bifida or anencephaly (where the baby’s brain does not develop properly). Folic acid supplements can significantly help to reduce this risk.
Amniocentesis is the most common procedure used for diagnosing genetic abnormalities. A small amount of fluid is removed from the amniotic sac surrounding the baby, through a fine needle that is inserted through the wall of the uterus, guided by ultrasound. This amniotic fluid contains cells and proteins from the baby. The cells can be used to identify chromosomal abnormalities and some inherited diseases. A particular protein, alpha-fetoprotein fluid, is analysed to detect spina bifida.
Amniocentesis cannot reliably be performed before 14–16 weeks of pregnancy and there is a risk of 0.5% of causing a miscarriage. Results may take two weeks to be available, although in some cases results may be ready within two or three days in some centres which exclude the most common abnormalities. It is important to weigh up all factors before having amniocentesis, as you may have to make the difficult decision of whether or not to have a termination.
Chorionic villus sampling (CVS)
This procedure also identifies chromosomal abnormalities and can be done earlier than amniocentesis, usually at 11–13 weeks of pregnancy. Again a fine needle is inserted through the abdominal wall and a small sample removed, in this case a biopsy of the developing placenta is taken. For this procedure, the risk of miscarriage is about 0.5 to 1% and, as with amniocentesis, initial results can be available within two or three days but the complete result takes two weeks.
This is a scanning procedure, which is done at around 18 weeks of pregnancy. Many women choose to have an ultrasound as this has been shown, with increasing accuracy, to determine whether the baby has any anatomical abnormalities. There is no evidence that ultrasound is harmful to mother or baby.
Nuchal fold ultrasound
Many ultrasound units are now offering nuchal fold ultrasound. This type of ultrasound scan measures the neck fold thickness of the baby at 12–14 weeks of pregnancy. Studies have found this to be an accurate but not absolute determinant of chromosomal problems, such as Down syndrome, where the measurements are greater than in an unaffected baby. While it carries no risk to the pregnancy, it only provides a risk estimate of likelihood of chromosomal abnormality, unlike amniocentesis and CVS, which provide certainty about outcome rather than an assessment of risk. Sometimes a nuchal fold assessment may be combined with a blood test from the mother to give a more accurate risk of chromosomal abnormality.
Researchers continue to improve techniques to separate out fetal cells that can be collected from the maternal blood and the mucus in the cervix. It may be possible that in the near future a blood test from the mother or a cervical smear could determine the exact chromosomal make-up of the baby, from which abnormalities can be identified.