Home page
About the New Zealand HD Associations
Living with Huntington's Disease
Predictive testing
Revised presymptomatic testing protocol
Family planning and prenatal testing
Four case studies
Young people's pages
Publications, press releases, conference information
Selected articles from HDA newsletters
News, articles and links to items of interest in HD research
New Zealand contacts
Acknowledgement and Disclaimer

Pre-implantation Genetic Diagnosis (PGD) in New Zealand

by Alice Christian
Senior Genetic Associate, Central and Southern Regional Genetic Services

Updated: 15 May 2007
Prenatal Diagnostic Testing

Pre-implantation Genetic Diagnosis (PGD) is a technique whereby fertilized embryos can be tested for specific genetic conditions prior to being implanted within the mother's womb.

PGD involves using in-vitro fertilization (IVF), a process frequently used by infertile couples to improve their chances of conceiving a pregnancy. The prospective mother's egg is fertilized outside the body using sperm from the prospective father. Fertilized eggs hopefully become embryos. They are then cultured in the laboratory to the 8 cell stage (3 days). One (or more) of the cells from the embryo is then removed (embryo biopsy) and tested for the genetic condition in question. Only those embryos unaffected by the condition and which appear to be growing well are implanted back into the mother.

PGD is an additional option for couples where one or both partners carry a gene mutation for a serious genetic condition that may affect their children. PGD may allow them to have a family free of that particular condition. It has the advantage of allowing the couple to have their own biological children while potentially avoiding termination of an affected pregnancy.

In New Zealand ethical approval has been received for provision of PGD under specific circumstances. Couples where one partner carries an expanded HD gene mutation are eligible for PGD. Other conditions that are approved for PGD include cystic fibrosis, beta- thalassaemia and spinocerebellar ataxia and myotonic dystrophy. The government has announced limited funding for PGD which gives approximately 40 couples per year access to one cycle each. This funding covers couples at risk of all serious genetic conditions, not just HD.

Privately funded PGD is being performed in New Zealand. The cost is approximately $15 000 for a single cycle (attempt at pregnancy) and is accessed through private fertility clinics. At the time of writing only Fertility Associates in Auckland are providing embryo biopsy, although other clinics are likely to offer this in the future. Due to the limited availability of procedures a couple may need to travel to complete the PGD process.

For example a couple may have egg stimulation, blood tests and monitoring scans at home, then travel to Auckland where the embryos are allowed to grow for approximately 3 days. The embryos are then biopsied and cells sent to Australia (without their parents!) for genetic testing. Fertility Associates are then advised of the test results and the best choice of embryo is transferred into the mother approximately 2 days after the biopsy was performed, when the embryo at the 5-day stage. This is termed transport PGD.

There are a number of drawbacks to PGD, which include:
  • The medicalisation of a pregnancy (there is a lot of people helping you get pregnant - not that romantic).
  • The potential cost and inconvenience.
  • Genetic testing must have been performed for the parent/s and preliminary testing performed to confirm that genetic testing can be performed for a specific couple.
  • The technology is not guaranteed, and so some embryos may not return a result at all.
  • Couples are still recommended to have pregnancy testing (chorionic villous sample or amniocentesis) to confirm that the baby does not carry the expanded HD gene.
  • The technology appears to be safe, but potentially there may be long term effects on an individual born via PGD technology that have not been identified.
  • PGD pregnancies are subject to the same risks as all pregnancies - the conception may not result in a viable pregnancy, other genetic conditions may be present, and there is a background risk of miscarriage.

Despite this, PGD technology has been the preferred choice for many families who wish to avoid a genetic condition in their children.

For more information you may wish to view the "Guidelines for preimplantation Genetic Diagnosis" available from the NECAHR (National Ethics Committee on assisted Human Reproduction) website (www.newhealth.govt.nz). Sydney IVF has an excellent website outlining information about PGD.

If you want to get the ball rolling, you can ask your GP for a referral to your nearest genetic service, or fertility clinic.

Back to the top

Prenatal Diagnostic Testing

Prenatal diagnostic tests can give a definite answer about whether your baby has a particular problem. However, these are invasive and involve a risk of miscarriage.

Amniocentesis (From 14+ weeks)

1. Diagnostic test for: Chromosome problems

Some inherited disorders that are known to run in a family (these tests are arranged for specific conditions after discussion with genetic services).

Amniocentesis is available to couples with any of the following:
  1. Late maternal age (35 years or older)
  2. A “high risk” result from a prenatal screening test
  3. A family history of certain inherited disorders
  4. A previous pregnancy with a chromosome problem
  5. Foetal anomalies detected by prenatal ultrasound

This test involves a risk of miscarriage. Although there is a small chance of miscarriage in any pregnancy, women who have an amniocentesis have an increased risk (0.5%, or 1/200, above the general background rate).

Amniocentesis involves passing a thin needle through the mother’s tummy to take some fluid (amniotic fluid) from around the baby. Ultrasound is used during the procedure to make sure that the needle is inserted in a safe position, away from the baby.

The amniotic fluid contains some of the baby’s cells, which are naturally shed during development. These cells are grown in the lab, and then scientists look at the cells to see the baby’s chromosomes. Results take between 2–3 weeks.

This test can give a definite answer about chromosome problems (more than 99.5% accurate). Down syndrome can be detected, as well as some rarer chromosome problems that can be either more severe, or less severe than Down syndrome.

There are many problems that cannot be detected by amniocentesis, such as a tiny change on a chromosome, cleft lip, club foot, many forms of mental retardation, and most heart defects.

Chorionic Villus Sampling (CVS) (From 10+ weeks)

1. Diagnostic test for: Chromosome problems.

Some inherited disorders that are known to run in a family (these tests are arranged for specific conditions after discussion with genetic services).

CVS is only performed under specific circumstances. For example, it may be offered when a baby is at significant risk for a particular genetic condition, based on family history. The risk of miscarriage with CVS is 1% (or 1/100) above the general background rate. This procedure involves inserting a fine needle through a woman’s tummy (transabdominal CVS) or using small forceps through the cervix (transvaginal CVS) and removing a small amount of tissue (called chorionic villi) from the placenta for analysis. Ultrasound is used to guide the procedure. Results usually take between 2–3 weeks. The baby’s chromosomes are analysed from all CVS samples. However, CVS is not routinely offered as a chromosome test for late maternal age, since there is a higher risk of miscarriage and a higher chance of unclear results compared to an amniocentesis.

Centre for Genetic Education in Australia

Back to the top

Appreciation and thanks must go to Judy Lyon for compiling the wealth of information available
on this site, and to Graham Taylor for maintaining the original site for so long.

Home | About | Information | Resources | Newsletters | Research | Contacts | Disclaimer |
Original content © HD Associations of New Zealand