In your column on Is 40 Too Old?, you advise women over 35 to have "prenatal genetic testing." What exactly is this, and what does it involve? My husband and I are going to try to get pregnant next year when I will be nearly 40. I've never used the pill and have very regular, uneventful periods (we use the rhythm method and condoms for contraception). Is there anything else I should be aware of to ensure conception and a healthy pregnancy and baby at this age?

Pauline

At age 40, the most important tests are those that are carried out before you attempt conception. Testing for ovarian reserve may show that your eggs are in fine shape, or it may show that, for you, 40 is too old and you may need to consider donor eggs. This testing can help you avoid needless treatment, stress and expense. For details on the clomiphene challenge test and day 3 FSH testing, see my earlier column on Artificial Insemination at Age 40.

Prenatal genetic testing is performed once you conceive. Chorionic villus sampling (CVS) is carried out at 9-11 weeks. It involves placing a tiny catheter through the cervix into the uterus and withdrawing a few cells to test for chromosomal anomalies. An alternative test, amniocentesis, is performed later, at about 15-16 weeks, and involves using ultrasound to guide the placement of a needle through the abdomen into the gestational sac. Fluid is removed and tested for anomalies of the fetal nervous system and spine (neural tube defects). Fetal cells are tested for chromosomal abnormalities. If there is an anomaly, this information can be used to help you decide whether to terminate the pregnancy or to allow the medical team to better prepare for the baby's birth. If there is no anomaly, your pregnancy can proceed with much less stress.

Both CVS and amniocentesis have their own risks, including a very slight risk of miscarriage. At your age, this risk is less than that of an abnormal pregnancy. Still, you should discuss all the risks and benefits of these treatments with your doctor in plenty of time for you to make a decision about them.