A microdeletion is a small, missing piece of a chromosome. Some microdeletions are known to cause specific genetic syndromes with major health impacts to the baby—including intellectual disabilities and other health implications which can include heart and breathing issues, immune system problems, trouble feeding, or other problems that may need immediate care upon birth.

Unlike Down syndrome, which occurs more frequently in mothers who are 35 and older, microdeletions occur in pregnancies at the same rate for mothers of any age. When considering age and pregnancy together, the likelihood of a woman under the age of 28 having a child with a microdeletion syndrome is higher than Down syndrome (trisomy 21).