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Male newborn infant (Source : common.wikimedia.org).

Trial for Pre-Implantation Genetic Screening to be held in three public hospitals from 2017

The National University Hospital (NUH) will be leading the trial of Pre-Implantation Genetic Screening (PGS) to identify chromosomal abnormalities in embryos created through in-vitro fertilization (IVF) which will start next year.

This was stated by Senior Minister of State for Health Amy Khor during the Parliament last week that the Government has given its approval.

There will be three public hospitals which will offer the government-funded trial in the country, NUH, Singapore General Hospital and KK Women’s and Children’s Hospital, said NUH consultant Lim Min Yu, from its department of obstetrics and gynaecology.

NUH said that there are two criterias for women to join the in a clinical trial to genetically screen embryos before they are implanted. The first is that a woman must be 35 or older. The second is that the woman must have experienced at least two failed pregnancies or implants regardless the age of the woman.

The country did not allow the procedure since the published evidence on it was unclear. However, as new technology developed and that countries like the United States, Australia, Malaysia and Thailand already offer the screening, Singapore then starts to look into it as a possible tools to improve the chances of conceiving.

Currently, the chance of having a baby through IVF is one in five.

A member of NUH’s Division of Reproductive Endocrinology and Infertility, Dr Lim Min Yu, said that the biggest reason for failed pregnancies or implants is chromosomal abnormalities.

Dr Lim explained that the PGS is a technique where embryos created through IVF. They are tested for the correct number of chromosomes before they are transplanted into a woman’s uterus. The correct number of chromosomes in a human is 46 — made up of 22 pairs of chromosomes and the sex chromosomes, XX in females and XY in males.

He noted that the chances of success in an IVF cycle are about 20 per cent and chromosomal abnormalities are probably behind the largest proportion of unsuccessful cycles.

Dr Lim, who is also an investigator in the trial, said that the fears that parents will abuse the system to select certain characteristics for their baby, including its gender, will be eliminated, saying, “Preimplantation genetic screening does not screen for genetic diseases, in terms of looking for these faulty genes. It is designed to assess the number of chromosomes each embryo has, and only select embryos with the correct number (46) for transfer.”

A stringent study which was carried out in Beijing and Los Angeles, involving more than 100 women, found that women whose embryos had been checked for the correct number of chromosomes had a 65 per cent higher chance of getting pregnant. However, the study did not report on the number of live births.

Dr Lim stated that the purpose of the trial is to find out if such screenings can improve the outcome of an IVF cycle in our local population by increasing the live birth rate and reducing the risk of miscarriage and chromosomal abnormalities.

He also said that screening for the correct number of chromosomes is very different from checking for known hereditary diseases. This is called preimplantation genetic diagnosis and done here to check for disorders like thalassemia, haemophilia and muscular dystrophy.

Singapore does not allow screening for Down syndrome in embryos, which affects a child’s mental and physical development. However, the extent of impairment varies.

Embryos with Down syndrome will not be used under the trial, as they have an extra chromosome.

Dr Lim said that while, PGS was not allowed here, another procedure called pre-implantation genetic diagnosis (PGD) is permitted.

PGD is a test for couples who are known to be affected with a genetic disorder, or are carriers of a genetic disorder, which can be passed to their children.

There are some of genetic disorders, including muscular dystrophy, haemophilia, and alpha and beta thalassemia. PGD enables embryos that are unaffected by the “erroneous” genes to be transferred to the uterus.