The many screenings you undergo during pregnancy all have a purpose, and one reason your practitioner might recommend certain tests is to check for chromosomal conditions like trisomy 16. 

This rare but serious abnormality can have different outcomes depending on the type, but a diagnosis doesn't mean you won't have a healthy pregnancy and baby in the future. Here's what you should know about this condition. 

What is trisomy 16?

Trisomy 16 is a type of chromosomal condition that happens when a fetus has an extra copy of chromosome 16 — three copies instead of two. It occurs in around 1.5 percent of clinically recognized pregnancies (in other words, pregnancies where a woman knows she’s pregnant).

Trisomy 16 is a common cause of first-trimester miscarriage, which often happens when a fetus isn’t developing normally, but it doesn’t always result in pregnancy loss. Babies with certain types of this condition can survive, though they may have serious and potentially life-long effects. The types of trisomy 16 include:

Full trisomy 16

A fetus with full trisomy 16 has an extra copy of chromosome 16 in every cell of the body. Sadly, this abnormality usually results in a first-trimester miscarriage. 

Mosaic trisomy 16

Mosaic trisomy 16 is a rare variation that occurs when a fetus has an extra copy of the chromosome 16 in some cells of the body, but not every cell.

Babies with mosaic trisomy 16 often survive, and though they’re typically born early and with a low birth weight, many grow to a normal weight and height by toddlerhood. Some may be otherwise healthy, but others may have congenital problems, including heart defects as well as developmental delays. 

Partial trisomy 16

Variations of trisomy 16 — called 16p or 16q — can also occur when every cell in a fetus’s body has changes to part, but not all, of a chromosome. In some cases babies with trisomy 16p or 16q can survive, but they can have developmental delays, intellectual differences, behavioral problems and distorted facial features.  

What causes trisomy 16?

All chromosomal abnormalities, including trisomy 16, happen when an embryo’s cells divide incorrectly. These problems happen more often when a mother is older than 35, since older eggs more frequently contain genetic errors. Researchers also suspect that some environmental factors could play a role, but for now, there’s no definitive evidence.

What are the symptoms of trisomy 16?

Chromosomal abnormalities like trisomy 16 don’t typically cause symptoms during pregnancy. Instead, noninvasive prenatal testing (NIPT) that looks at chromosome 16 in placental DNA may detect an issue. Based on the results, a woman and her doctor might opt for additional diagnostic tests like chorionic villus sampling (CVS) or amniocentesis to learn more about what’s going on.

When trisomy 16 does result in pregnancy loss, common symptoms include bleeding and abdominal cramping.  

Can trisomy 16 be prevented?

Most birth defects can’t be prevented because their causes aren’t yet well understood, according to the American College of Obstetricians and Gynecologists (ACOG). That said, understanding your risk factors for having a baby with a chromosomal abnormality (like being over 35 or having a family history of chromosomal disorders) can help you and your doctor decide whether you should undergo genetic screening or other prenatal tests to detect potential problems.  

You can also take steps to improve the odds of a healthy pregnancy. Try to:

  • Go to all of your prenatal visits, including your preconception checkup.
  • Take your prenatal vitamin every day, and if possible, before becoming pregnant. 
  • Maintain a healthy weight.
  • Stay on top of any health conditions you might have.
  • Talk with your doctor before taking any medications.
  • Avoid drugs and alcohol.
  • Avoid exposure to toxic substances or radiation. 

Can trisomy 16 happen again?

Having a pregnancy or baby affected by trisomy 16 once doesn’t necessarily mean it will happen again. Certain risk factors can increase the chances for chromosomal abnormalities in general — including being over 35, having a history of previous miscarriages, having a family history of chromosomal disorders or having a baby with a birth defect. But trisomy 16 is rare, and why some babies are affected isn’t fully understood.

You can give your baby the best possible start by sticking with healthy pregnancy habits. And if you have concerns about chromosomal abnormalities, talk with your practitioner about genetic counseling or other prenatal tests.