More and more women are delaying having children until their mid to late thirties. There are concerns that many women have when they wait until their mid thirties to begin raising a family and some of these concerns are well founded.
Chromosomal defects increase with increasing maternal age. Down's Syndrome is the most well known. The risk for Down's at 20 years of age is approximately is 1 in 1600. At 35, it is 1 in 365. This is just the risk for Down's Syndrome.
Amniocentesis is definitely recommended for those women who will be 35 when they deliver.
There is also an increased risk of chromosomal defects in fathers over 50 years of age. The more mature pregnant woman, 35 or older, may also exhibit underlying medical problems that may increase her risk of poor outcome such as high blood pressure and diabetes, to name two.
The risk to the pregnancy is from the underlying medical conditions, not from her being older and pregnant. A pregnant woman who is 35 years or older, and is in good health, should expect a normal, healthy pregnancy, all things being equal.
Good prenatal care, good nutrition, and mild exercise can help reduce certain risks. Ask questions of your doctor and follow his or her recommendations closely.