Trisomy 16

Definition - What does Trisomy 16 mean?

Trisomy 16 is a chromosomal disorder occurring when an extra copy of chromosome 16 is found after fertilization. There are several degrees of trisomy 16 based on whether a partial or full extra chromosome is present. Full trisomy 16 is not compatible with life and always results in a first trimester miscarriage. Trisomy 16 is one oft he most common chromosomal abnormalities and is responsible for well over 100,000 pregnancy losses a year, representing almost 10% of miscarriages in the US. Experiencing a pregnancy with trisomy 16 does not affect the likelihood of trisomy 16 in subsequent pregnancies.

FertilitySmarts explains Trisomy 16

After the sperm fertilizes the egg the resulting embryo should have 46 chromosomes in each cell. When a trisomy occurs there is an extra copy of one or more chromosomes. In Trisomy 16 the extra copy is found on chromosome 16. This extra chromosome can have a range of effects based on how many cells in the embryo are affected.

There are three types of trisomy 16: full, mosaic, and partial.

  • Full trisomy 16 means that all of the cells in the embryo contain the extra chromosome and is the most severe form of trisomy 16. Full trisomy 16 is incompatible with life and almost all pregnancies with full trisomy 16 miscarry within the first trimester.
  • Mosaic trisomy 16 means some of the embryo's cells are affected while others have the normal number of chromosomes. Mosaic trisomy 16 may cause some complications during pregnancy including intrauterine growth restriction and preeclampsia but it is possible to carry a mosaic trisomy 16 pregnancy to term. A mosaic trisomy 16 infant may have some congenital defects based on how many cells are effected by the trisomy. If few cells are affected the infant can develop normally. As more cells are affected the likelihood of defects increases. Defects can include heart defects, facial deformities, or respiratory abnormalities.
  • Partial trisomy 16 means the cells of the placenta are affected by the trisomy but the developing fetus is not. Because the fetus contains only normal cells it develops normally without any indication of trisomy 16. This is the rarest form of trisomy 16.

Trisomy 16 can be found during chorionic villus sampling or amniocentesis, although if full trisomy 16 is present the pregnancy may miscarry before these tests can be performed. Genetic testing may be performed on the fetal tissue after a miscarriage to determine if chromosomal abnormalities contributed to miscarriage.

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