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The answer depends entirely on the cause. This is one of the most important reasons to find the exact genetic cause before planning another pregnancy.
Chance of it happening again, by type of cause
New (de novo) change. When the change appeared for the first time in the child and neither parent carries it, the chance of it happening again is usually low, around 1%. It is not zero. Rarely, a parent carries the change in some of their egg or sperm cells but not in their blood.
Recessive condition. When both parents are healthy carriers of a change in the same gene, each pregnancy has a 1 in 4 (25%) chance of being affected. This pattern is more common when parents are related by blood, as in cousin marriages seen in some Indian communities.
X-linked condition, with the mother as a carrier. Each son has a 1 in 2 (50%) chance of being affected. Each daughter has a 1 in 2 chance of being a carrier.
Fragile X syndrome. The risk depends on the size of the mother’s repeat in the FMR1 gene. A mother may carry a “premutation”, a medium-sized repeat, without knowing it. Her sisters and other female relatives on her side may benefit from testing too.
Chromosome condition. Conditions such as Down syndrome are usually not inherited. If a parent carries a rearranged chromosome, called a balanced translocation, the risk is higher.
Cause not found. The risk is higher than in the general population but difficult to estimate. Your genetic counselor will discuss it based on your family history.Options once the exact cause is known
Preimplantation genetic testing with in vitro fertilisation. Embryos are tested before transfer to the womb, and only unaffected embryos are transferred.
Prenatal diagnosis during pregnancy. The baby’s DNA is tested through chorionic villus sampling or amniocentesis. Genetidoc arranges these through partner centres, because it does not currently perform invasive prenatal procedures.
Natural conception without testing, with full information about the risk.
Every family’s decision is personal. The role of genetic counseling is to inform, not to direct.
What a routine pregnancy blood test cannot do
Non-Invasive Prenatal Testing screens the baby’s chromosomes using a blood sample from the mother. It cannot test for most single-gene causes of intellectual disability, and it does not look for the specific change found in your family.
When the affected child has passed away
Some families reach us only after losing a child. If a stored blood or tissue sample is available, it may still be tested. If not, the parents can sometimes be tested to see whether they are carriers, especially when they are related by blood.
Plan before the next pregnancy
Genetic testing and analysis can take weeks to months. Decisions are easier without the pressure of an ongoing pregnancy. If you are thinking about having another child, the best time to speak with a clinical geneticist is before you conceive.
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