According to the March of Dimes, "about 9 percent of recognized pregnancies for women aged 20 to 24 ended in miscarriage. The risk rose to about 20 percent at age 35 to 39, and more than 50 percent by age 42". Birth defects, especially those involving chromosome number and arrangement, also increase with the age of the mother. According to the March of Dimes, "At age 25, your risk of having a baby with Down syndrome is 1 in 1,340. At age 30, your risk is 1 in 940. At age 35, your risk is 1 in 353. At age 40, your risk is 1 in 85. At age 45, your risk is 1 in 35."