Pre-pregnancy genetic tests

Genetic screening tests are recommended before or at the beginning of pregnancy. These tests are tailored to the couple's specific needs and are typically done in consultation with a genetic counselor. No appointment is necessary for these tests and they are available to the general population, even where there is no family history of genetic disease. The Ministry of Health provides a list of recommended tests on its website, along with additional information.

The purpose of screening tests is to identify carrier couples who are at risk of having children with relatively common but severe genetic diseases for which no treatment currently exists. 

Most of the diseases included in the screening are inherited in an autosomal recessive manner. This means that a child can only be affected if he/she inherits two copies of the defective gene, one from each carrier parent. Carriers, who have one copy of the mutated gene, are typically healthy. However, if two carriers have a child together, there is a 25% chance of the child being affected by the disease - and this risk is repeated with each pregnancy.

The prevalence of carriers for the diseases included in the screening is high, ranging from 1 in 25 to 1 in 100 individuals. This means that even couples without a family history of these diseases have a chance of being carriers and being at risk of having a child with the disease.

Both spouses are encouraged to undergo screening, but it is possible to proceed even if only one spouse is available for testing (preferably the mother). 

Couples that have a family history of a disease or that are known carriers of a disease will be referred for individual genetic counseling as soon as possible. It is important to bring relevant medical documents for scheduling an appointment with the prenatal clinic.

In addition to genetic screening tests, there are also advanced methods available for prenatal genetic diagnosis, such as preimplantation genetic diagnosis (PGD). This involves examining embryos created through in vitro fertilization and selecting only those without the identified genetic mutations or abnormalities for implantation in the uterus.

Another technique, known as preimplantation genetic screening (PGS), allows for the examination of the number of chromosomes in the embryo. This method is particularly useful for women over the age of 36 and women experiencing difficulty conceiving, repeated miscarriages, or failures in the in vitro fertilization process. By selecting embryos with a normal number of chromosomes, the chances of a successful pregnancy can be significantly increased.

It's important to note that PGS is not effective in detecting minor defects or additions of chromosomes that may indicate syndromes such as DiGeorge Syndrome, Cri Du Chat Syndrome, Prader-Willi Syndrome, and Angelman Syndrome. To address this issue, the Institute for Preimplantation Genetic Diagnosis at Shaare Zedek has developed a method using Next Generation Sequencing (NGS) for detecting small deficiencies and additions in the PGS test. This new technique offers high-resolution diagnosis, fast results (within 24 hours), high efficiency for a large number of tests, and cost-effectiveness compared to older methods.

Apart from invasive prenatal diagnostic tests such as amniocentesis and chorionic villus sampling, non-invasive prenatal testing (NIPT) has also been developed. This test analyzes fetal DNA present in the mother's bloodstream and can detect chromosomal changes in the fetus. NIPT can be performed routinely from the 10th week of pregnancy and is especially effective in detecting changes related to the number of chromosomes, such as Down Syndrome. 

Shaare Zedek has also developed a method for detecting changes related to recessive genes in fetal DNA during pregnancy. This method has been successfully tested on couples at different stages of pregnancy, with results validated by standard prenatal tests and post-birth examinations of the children, showing a 100% match between the methods. This fast and cost-effective method can be applied during prenatal testing to various autosomal recessive diseases that exist in diverse populations worldwide.