mother's age<unk>  is the most common chromosomal abnormality in humans. Globally, ,<unk>  occurs in about 1 per 1,000 births and results in about 17,000 deaths. More children are born with<unk>  in countries where abortion is not allowed and in countries where pregnancy more commonly occurs at a later age. About 1.4 per 1,000 live births in the United States and 1.1 per 1,000 live births in Norway are affected. In the 1950s, in the United States, it occurred in 2 per 1000 live births with the decrease since then due to prenatal screening and abortions. The number of pregnancies with<unk>  is more than two times greater with many spontaneously aborting. It is the cause of 8% of all congenital disorders. Maternal age affects the chances of having a pregnancy with<unk> . At age 20, the chance is 1 in 1,441; at age 30, it is 1 in 959; at age 40, it is 1 in 84; and at age 50 it is 1 in 44. Although the probability increases with maternal age, 70% of children with<unk>  are born to women 35 years of age and younger, because younger people have more children. The father's older age is also a risk factor in women older than 35, but not in women younger than 35, and may partly explain the increase in risk as women age.
Down syndrome
Alzheimer's disease
Baboon syndrome
Apert syndrome
Ring chromosome 14 syndrome
Ring chromosome 20 syndrome
TORCH syndrome
Williams syndrome