What Are the Prenatal Genetic Testing Options for CDH?

When a baby is diagnosed with a congenital diaphragmatic hernia (CDH) during pregnancy, it is completely normal to feel overwhelmed and anxious about their future. To better understand your baby’s health and determine if the hernia is the only issue or part of a broader genetic condition, doctors often recommend genetic testing ^[1][2]. To perform these diagnostic tests, doctors first need to collect a small sample of your baby’s DNA using a procedure like amniocentesis or chorionic villus sampling (CVS) ^[1]. The DNA is then analyzed using advanced laboratory tests, such as Chromosomal Microarray (CMA) and Whole Exome Sequencing (WES), to give your care team a clearer picture of what your baby will need after birth ^[3][4].

Screening Blood Tests vs. Diagnostic Procedures

If you have already had a Non-Invasive Prenatal Test (NIPT) via a maternal blood draw, you might wonder why more testing is needed. NIPT is a screening test that checks for a few common genetic conditions ^[3]. It cannot diagnose the complex, underlying genetic variations that are frequently linked to CDH ^[3]. To get a complete, diagnostic picture, doctors must look directly at your baby’s DNA using cells collected from the pregnancy itself ^[2].

How Doctors Collect Your Baby’s DNA

To safely gather cells containing your baby’s DNA, doctors use specialized, ultrasound-guided procedures ^[1].

• Chorionic Villus Sampling (CVS): Usually performed between 10 and 13 weeks of pregnancy, CVS involves taking a tiny sample of tissue from the placenta, which shares the same genetic makeup as your baby ^[1]. A doctor will use ultrasound to guide a thin needle through your abdomen or a small tube through your cervix.
• Amniocentesis: Typically offered after 15 weeks of pregnancy, this procedure involves collecting a small amount of the amniotic fluid that surrounds your baby ^[1]. Using ultrasound, a doctor carefully inserts a thin needle through your abdomen to draw out fluid, which contains cells your baby naturally sheds.

Both procedures are considered safe, but because they are invasive, they carry a small risk of complications, such as miscarriage or infection ^[1]. Your maternal-fetal medicine specialist will discuss your specific risks so you can make an informed choice ^[5].

How the DNA is Tested and What to Expect

Once the laboratory has your baby’s DNA, they will run specific diagnostic tests. You might hear your doctor mention a standard karyotype, which is sometimes run quickly to check the overall structure of the chromosomes. But for CDH, doctors rely on more detailed tests:

• Chromosomal Microarray (CMA): This is the recommended first-tier genetic test for CDH ^[6][7]. Think of your baby’s DNA as an encyclopedic reference book; CMA checks to see if entire pages or chapters are missing or duplicated ^[6][3]. These are called copy number variations. CMA is generally the faster test, though results can still take days to a couple of weeks to return ^[8].
• Whole Exome Sequencing (WES): If the CMA results are normal, doctors often recommend WES as a second step ^[3][9]. If CMA looks for missing pages, WES reads the actual text to find tiny spelling errors (mutations) in individual genes that could cause medical problems ^[8][3]. WES is a complex process and typically takes longer, sometimes several weeks, though some labs offer rapid options ^[8].

Waiting for these results can be an agonizing time for parents. Ask your doctor for a clear timeline so you know exactly when to expect a phone call ^[5].

Isolated vs. Syndromic CDH: Why Testing Matters

The main goal of this genetic testing is to help your care team determine whether your baby’s CDH is isolated or syndromic ^[10].

• Isolated CDH: This means the diaphragmatic hernia is the only major medical problem, and there is no underlying genetic syndrome ^[10].
• Syndromic CDH (Non-isolated): This means the CDH is part of a larger genetic syndrome, such as Trisomy 18, Pallister-Killian syndrome, or 1p36 deletion syndrome ^[11][12][3]. These conditions often involve other challenges, like heart defects or neurological issues ^[10][13].

Doctors recommend testing even if the hernia appears isolated on an ultrasound, because some genetic features are invisible before birth ^[3]. Knowing if the CDH is syndromic is vital for your care team. It ensures that the exact right pediatric specialists—such as cardiologists or neurologists—are in the delivery room the moment your baby is born ^[3][14]. It also impacts whether your baby might be eligible for specialized in-utero treatments, like Fetoscopic Endoluminal Tracheal Occlusion (FETO), which is typically reserved for isolated CDH cases ^[15]. While syndromic CDH often involves a more complex medical journey and different expectations for long-term health, having this information early gives you and your medical team the best chance to prepare and provide the most supportive care possible ^[3][16].

What if I Delay Testing Until After Birth?

If you prefer to avoid the risks of an invasive procedure like CVS or amniocentesis during pregnancy, you can choose to delay genetic testing. In this case, your baby’s DNA can be safely collected via a blood or saliva sample after they are born. However, waiting does mean your medical team will have less information to guide their immediate surgical and medical decisions during delivery, and it may change your eligibility for certain prenatal interventions ^[15][3]. A genetic counselor can help you weigh these options and support your family through whichever path you choose ^[5].