Sources often list "maternal age" as a risk factor or cause for miscarriage and stillbirth, and it is true that the statistical odds of pregnancy loss are higher in a mother older than 35 than in a mother in her twenties. But why is this? What changes with age?
One reason for the link is that eggs are more likely to be affected by chromosomal abnormalities. Women have their lifetime supply of eggs at birth, and researchers theorize that the most robust eggs are the first ones ovulated. Then, by the time a mother reaches her mid-thirties, the eggs begin to decline in "quality." This same mechanism also explains why older mothers are more likely to have babies affected by chromosomal conditions such as Down Syndrome (trisomy of chromosome 21) and why doctors often suggest that mothers in this age bracket have an amniocentesis in their second trimester.
Another reason could be that, as women age, they are more likely to develop health conditions such as high blood pressure and diabetes. These conditions aren't as highly associated with miscarriage as chromosomal problems, but they do increase risk of stillbirth and premature delivery.
Source:
March of Dimes, "Pregnancy After 35." Jan 2006. Accessed 29 Nov 2007.
