What Are the Chances of Another Baby With Classic CAH?

If you have a child with classic congenital adrenal hyperplasia (CAH) due to 21-hydroxylase deficiency, the chance of having another child with the condition is 25% (or 1 in 4) with each future pregnancy, assuming the pregnancy involves the same two biological parents ^[1][2]. This probability is independent for every pregnancy; having one child with CAH does not reduce or change the risk for the next ^[2].

Understanding Autosomal Recessive Inheritance

Classic CAH is almost always an autosomal recessive genetic condition caused by changes in the CYP21A2 gene ^[2][3]. Because humans have two copies of most genes, a child must inherit two disease-causing variants (one from each parent) to be born with classic CAH ^[1][4].

When both parents are carriers—meaning they each have one normal gene copy and one disease-causing variant, but usually do not have classic CAH themselves—the odds for each pregnancy are:

• 25% chance the baby will inherit two disease-causing variants and have classic CAH ^[1].
• 50% chance the baby will inherit one disease-causing variant and one normal copy, making them a carrier like their parents, but without classic CAH ^[1].
• 25% chance the baby will inherit two normal copies, meaning they will not have CAH and will not be a carrier ^[1].

Why Genetic Counseling is Recommended

Because CAH genetics can be complex, meeting with a genetic counselor or a medical geneticist is highly recommended before trying to conceive again ^[5][4].

A specialist should review the specific CYP21A2 genetic test results of your child with CAH and test both parents to confirm carrier status ^[4][6]. Identifying your family’s exact disease-causing variants is essential because the CYP21A2 gene region is technically difficult to analyze in a laboratory, often involving gene duplications or complex missing segments ^[7][8].

Family Planning and Testing Options

Once your family’s specific variants are known, a genetic counselor can help you explore your options. You can choose to conceive naturally or explore assisted reproduction, and testing can be done at different stages.

In-Vitro Fertilization (IVF) with PGT-M

Families may choose IVF combined with Preimplantation Genetic Testing for Monogenic disorders (PGT-M) ^[5]. This allows a reproductive endocrinologist to test embryos for your family’s specific CAH variants before transferring an embryo to the uterus ^[9]. While this reduces the chance of having a child with CAH, IVF does not guarantee a pregnancy, not all cycles produce testable or unaffected embryos, and confirmatory testing during pregnancy is still generally recommended ^[5].

Prenatal Diagnosis During Pregnancy

If you conceive naturally or without PGT-M, testing can be done during pregnancy by a maternal-fetal medicine specialist to see if the fetus has inherited the condition ^[4]. This requires targeting your family’s specific variants. Options include:

• Chorionic-Villus Sampling (CVS): A procedure typically performed between 10 to 13 weeks of pregnancy ^[4].
• Amniocentesis: A procedure typically performed at or after 15 weeks of pregnancy ^[4].

Both are invasive procedures with a small risk of complications, which should be discussed with your obstetric team ^[5].
(Note: You may read about prenatal dexamethasone treatment intended to reduce physical changes in affected female fetuses, but this is considered experimental, not routine care, and should only be discussed with specialists ^[10][11].)

Postnatal Plan and Newborn Safety

If you choose not to have prenatal testing, it is critical to have a postnatal care plan in place. A baby at risk for classic CAH—particularly the salt-wasting form—can become dangerously ill from an adrenal crisis in the first weeks of life.

Do not rely solely on standard newborn screening. Inform your obstetric and pediatric teams about your family history so they can arrange for targeted hormone testing and pediatric endocrinology monitoring immediately after birth. Seek emergency medical care if a newborn shows warning signs like poor feeding, repeated vomiting, unusual sleepiness, or dehydration.