Maternal Age - Prenatal Genetics

The risk for having a pregnancy with a chromosomal abnormality increases as maternal age increases. Eggs which are present at birth age with the individual, and once a woman is 35 years old at the time of delivery, she is considered to be of advanced maternal age. 

Chromosomes are the inherited structures in the cells of the body. Normally, there are 46 chromosomes in each cell, arranged into 23 pairs. Chromosomal abnormalities involving an entire missing or extra chromosome are not inherited and are not caused by an exposure during pregnancy. Instead, they are caused by random mistakes in cell division at the time of conception and can occur in anyone's pregnancy. The chance for such an event to occur does increase with advancing maternal age. 

The most common chromosomal abnormality seen in liveborns is trisomy 21 (Down syndrome). Babies with Down syndrome have mild to moderate intellectual disability and a higher incidence of birth defects. Two other chromosomal abnormalities which are more likely to occur with advanced maternal age are trisomy 18 and trisomy 13, resulting from three copies of chromosomes #18 or #13, respectively. Babies with these chromosomal abnormalities have severe intellectual disability and serious birth defects. Although more severe than Down syndrome, they are also far less common. Other chromosomal abnormalities seen in liveborns occur with the sex chromosomes, the X and the Y. An extra or missing X or Y chromosome may cause mild physical differences, learning disabilities, behavioral and sometimes fertility issues.