Previous Genetic Defect and Pregnant Again

If you’ve previously given birth to a child with a genetic defect, you will likely be concerned about your risk of giving birth to another child with a genetic anomaly. Once you’ve had a child with a genetic defect, the odds of having a second child with a genetic defect may increase, depending on the nature of the defect and how it occurred. As worrying as this is, it is important to know just what to expect with future pregnancies if you have had experience with genetic problems in the past.

Down Syndrome
One of the most common genetic birth defects is Down Syndrome, which occurs in one in every 800 live births. The risk of conceiving a child with down syndrome depends on the age of the carrier. The number of incidents in women who become pregnant at age 20 is 1/1600 (0.000625%) but by age 35, this risk has increased to 1/370 (0.0027%). After a couple has conceived one child with down syndrome, the risk for conceiving another DS child in the next pregnancy is 1/100, or 1%. As the age of the mother increases, the elevated risk will also increase.

Congenital Heart Defects
About 1% of all children born will have a congenital heart disease (CHD). But a child’s risk increases when either parent has CHD, or when another sibling is born with it. If you have had one child with congenital heart disease, the chance that another child will be born with CHD ranges from 1.5% to 5%, depending on the type of CHD in the first child. If there are already two children in the family with CHD, then that the risk jumps to 5% to 10%. These children will not necessarily have the same type of CHD, though.

Neural Tube Disorders
Couples who have already had one child with a neural tube disorder have a 2% to 5% risk for a second affected pregnancy, depending on the baseline population risk. While NTDs due to nutritional deficiencies are on the decline, NTDs caused by unalterable factors, such as teratogenic exposures, maternal health problems, genetic disorders or syndromes and chromosomal abnormalities are on the increase. In the past, unalterable factors were the cause of NTDs in only a minority of cases.

Muscular Dystrophy, Sickle Cell Anemia, Cystic Fibrosis and Fragile X Syndrome
These genetic disorders are all passed to children through autosomal recessive inheritance, which occurs when both parents carry a certain recessive gene. Once parents have had a child with a recessive trait or disease, there is a one in four, or 25% chance, that each subsequent pregnancy will result in another child with the same trait or disorder.

Common Genetic Defects and Chance of Recurrence

Prevention
In the case of neural tube disorders, if the cause is not genetic or resulting from factors that can not be changed, such as teratogenic exposures or chronic maternal health problems, making positive changes to the mother’s diet and lifestyle (such as taking folic acid supplements before and during pregnancy) can play a role in preventing a second occurrence of NTD. Unfortunately, there is no way to guard against other genetic disorders.

Genetic Screening
If you have had one pregnancy resulting in a child with a genetic defect, you may wish to have genetic screening done on yourself and your partner to determine if you are carriers of any genetic defects. You may also wish to have any subsequent pregnancies genetically screened to determine if the fetus has any genetic irregularities. If you are undergoing IVF, you may opt to have preimplantation genetic diagnosis performed in order to ensure that only those embryos free of genetic problems are implanted.

These tests are not mandatory and any decisions made as a result of the tests will be left in your hands. For more information, please see our article on genetic counseling.

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