What Are Trisomy 13 and Trisomy 18?

Human cells carry 23 pairs of chromosomes, 46 in total. When a cell ends up with three copies of one chromosome instead of two, the result is called a trisomy.

Trisomy 18 (Edwards syndrome) means three copies of chromosome 18. It is the second most common trisomy after Down syndrome, occurring in roughly 1 in 5,000 live births.

Trisomy 13 (Patau syndrome) means three copies of chromosome 13. It shows up less often, in about 1 in 10,000 to 16,000 live births.

No parent choice or lifestyle factor causes either condition. They arise from a random error in cell division. Maternal age does nudge the risk upward slightly, but that is as far as the explanation goes.

How They Are Detected

Screening

NIPT (cell-free DNA screening) can flag elevated risk for both Trisomy 13 and Trisomy 18 using a simple maternal blood draw, available from 10 weeks onward. First-trimester combined screening, which pairs blood work with a nuchal translucency measurement, can also point toward elevated risk.

A positive screening result is not a diagnosis. NIPT carries a higher false-positive rate for Trisomy 13 and 18 than it does for Trisomy 21. Any positive screen should be followed by diagnostic testing.

Diagnostic Confirmation

CVS (performed at 10 to 13 weeks) or amniocentesis (15 to 20 weeks) gives a definitive chromosomal readout. Only diagnostic testing can confirm whether the finding is a full trisomy, a partial trisomy, or mosaicism, where some cells carry the extra chromosome and others do not. That distinction matters because mosaic forms can carry different outcomes.

Ultrasound Findings

Both conditions often show structural differences on ultrasound: heart defects, brain abnormalities, limb differences, growth restriction. Ultrasound findings alongside diagnostic testing give the fullest clinical picture.

Medical Realities

Honesty about these conditions means acknowledging both the severity and the real variation in outcomes.

Trisomy 18

Full Trisomy 18 brings significant medical challenges. Nearly all affected babies have congenital heart defects. Kidney malformations, esophageal or intestinal abnormalities, and growth restriction are also common.

About 50% of babies with Trisomy 18 are stillborn. Of those born alive, roughly 40% survive to one month, and 5% to 10% reach one year. A small number, particularly those with mosaic Trisomy 18, live longer, sometimes into their teens or beyond. These longer-term outcomes are becoming more visible as medical care and family advocacy continue to evolve.

Trisomy 13

Full Trisomy 13 presents similarly serious challenges. Heart defects, brain malformations (especially holoprosencephaly), cleft lip or palate, and eye abnormalities are common findings.

Survival statistics mirror those for Trisomy 18. Most affected infants do not survive beyond the first weeks or months. Mosaic forms again may carry different outcomes.

These numbers are hard to sit with. They also do not capture the love, connection, and meaning families experience with their children, no matter how much time they share.

Care Options: A Spectrum of Choices

Families receiving a Trisomy 13 or Trisomy 18 diagnosis face deeply personal decisions. There is no single right path. The options include:

Continuing the Pregnancy With Full Medical Intervention

Some families pursue all available medical treatments, cardiac surgery among them, to extend their child's life as far as possible. A growing number of medical centers are offering more interventional approaches for these conditions, and outcomes data continues to shift.

Continuing the Pregnancy With Comfort-Focused Care

Perinatal palliative care focuses on comfort and quality of life rather than curative treatment. A palliative care team works with you to build a birth plan centered on your values, so your baby is comfortable and your time together is meaningful.

Perinatal palliative care can include:

  • Birth planning that reflects your wishes (skin-to-skin, photos, family time)
  • Pain management for your baby
  • Emotional and spiritual support for your family
  • Memory-making support (handprints, professional photography, naming ceremonies)
  • Bereavement care and follow-up

Ending the Pregnancy

Some families choose to end the pregnancy after a Trisomy 13 or 18 diagnosis. That decision is never made lightly, and it deserves the same compassion and respect as any other path. Access varies by state, and your care team or a genetic counselor can provide information specific to your situation.

Support for Families

Whatever path you choose, you do not have to walk it alone.

  • Genetic counselors can help you understand the diagnosis, your options, and what to expect
  • Social workers at your hospital or clinic can connect you with practical and emotional support
  • Organizations like SOFT (Support Organization for Trisomy 18, 13, and Related Disorders) offer community, resources, and connection with other families
  • Perinatal loss support groups provide a space to grieve if your journey includes loss

Your care team should inform and support you without judgment. If you ever feel pressured in any direction, you have every right to seek providers who honor your autonomy.

Finding Compassionate Care on BAABY

If you are facing a Trisomy 13 or Trisomy 18 diagnosis, the providers around you matter deeply. BAABY's provider directory can help you search for OB-GYNs and maternal-fetal medicine specialists in your area who can guide you through this experience with both expertise and compassion.