• At age 25, a woman has about a 1-in-1,250 chance of having a baby with Down syndrome.
• At age 30, a 1-in-1,000 chance.
• At age 35, a 1-in-400 chance.
• At age 40, a 1-in-100 chance.
• At 45, a 1-in-30 chance.
• At 49, a 1-in-10 chance (1, 4).

The American College of Obstetricians and Gynecologists (ACOG) recommends that women who will be 35 or older at the time of delivery be offered prenatal testing to diagnose, or far more likely, rule out Down syndrome and other chromosomal problems (4). Prenatal tests include amniocentesis and chorionic villus sampling (CVS). Most women who have these tests learn that their baby does not have a chromosomal problem.

Both amniocentesis and CVS pose a very small risk of miscarriage (pregnancy loss before 20 weeks of pregnancy). Some women choose to have a first- or second-trimester screening test (a blood test, sometimes with a special ultrasound exam) to get more information on their risk of having a baby with Down syndrome before deciding on amniocentesis or CVS. Women who learn they are at low risk may choose not to have amniocentesis or CVS, whereas women at increased risk may decide to have CVS or amniocentesis. A screening test, however, cannot definitively diagnose or rule out Down syndrome and other chromosomal problems as amniocentesis and CVS can.

Does the risk of miscarriage increase as a woman gets older?
Most miscarriages occur in the first trimester for women of all ages. The risk of miscarriage increases with age. Studies suggest that about 10 percent of recognized pregnancies for women in their 20s end in miscarriage (5). The risk rises to about 20 percent at ages 35 to 39, and about 50 percent by ages 40 to 44 (5). The age-related increased risk of miscarriage is caused, at least in part, by increases in chromosomal abnormalities.

Can preexisting health conditions affect pregnancy?
Women over age 35 are more likely than younger women to have a health condition that began before pregnancy. Some health conditions, such as high blood pressure, diabetes and kidney and heart problems, can affect pregnancy. For example, poorly controlled diabetes can contribute to birth defects and miscarriage, and poorly controlled high blood pressure can slow fetal growth.

At any age, a woman should see her health care provider before trying to conceive. A preconception visit helps ensure that she is in the best possible health before conception. A preconception visit is especially important if a woman has a chronic health condition. Her provider can treat the condition and make any necessary changes in her medications to help assure that she has a healthy pregnancy. The provider also can recommend that a woman planning pregnancy take a daily multivitamin containing 400 micrograms of folic acid to help prevent certain serious birth defects of the brain and spinal cord (neural tube defects).

Are women over age 35 more likely to have pregnancy complications?
Women in their late 30s and 40s are very likely to have a healthy baby. However, they may face more complications along the way than younger women.

Some complications that are more common in women over 35 include:

• Gestational diabetes. This form of diabetes develops for the first time during pregnancy. According to a 2005 government study conducted at many medical centers, women over age 35 are about twice as likely as younger women to develop gestational diabetes (6). Women with gestational diabetes are more likely to have a very large baby who is at risk of injuries during delivery.
• Placental problems. The most common placental problem is placenta previa,  in which the placenta covers part or all of the uterine opening (cervix). A 2005 government study found that women in their late 30s were almost twice as likely, and women in their 40s nearly three times as likely, as younger women to have this complication (6). Placenta previa can cause severe bleeding during delivery, which can endanger mother and baby. A cesarean delivery often can prevent serious complications.
• Premature delivery. A 2005 government study found that women over age 40 were 40 percent more likely than younger women to deliver prematurely (before 37 weeks of pregnancy) (6). Premature babies are at increased risk of health problems in the newborn period and of lasting disabilities. Other studies have found that women between 35 and 39 also have an increased risk of premature delivery, though their risk may be lower than that of women over age 40 (7). Some studies also suggest that women in their 40s may be at increased risk of having a low-birthweight baby (less than 5˝ pounds) (4, 5, 6).
• Stillbirth. Stillbirth is the death of the fetus after 20 weeks of pregnancy. A number of studies have found that women over age 40 are about twice as likely as women in their 20s to have a stillborn baby (4, 5, 7). The reasons for these tragic losses in the over-40 age group are poorly understood.

As with diabetes, high blood pressure can develop for the first time during pregnancy. This may be referred to as pregnancy-induced hypertension (high blood pressure) or, in its most severe form, preeclampsia. Some studies have found that pregnancy-induced high blood pressure is more common in women over age 35 (6, 7).

Are women over 35 more likely than younger women to have a cesarean delivery?
The chances of a cesarean delivery rise with age. First-time mothers over age 40 appear to be more than twice as likely as first-time mothers under age 30 to have a cesarean delivery (9). In 2003, according to the Centers for Disease Control and Prevention (CDC), about 47 percent of first-time mothers over age 40, 33 percent between ages 30 and 39, and 21 percent under age 30 had a cesarean delivery (9).

How can a pregnant woman reduce her risks?
Today, most women in their late 30s and 40s can look forward to healthy pregnancies. Women of all ages can improve their chances of having a healthy pregnancy if they:

• Have a preconception checkup with a health care provider.
• Get early and regular prenatal care.
• Take a multivitamin containing 400 micrograms of folic acid daily, starting before pregnancy and in early pregnancy, to help prevent certain serious birth defects of the brain and spinal cord (neural tube defects).
• Begin pregnancy at a healthy weight (not too heavy or too thin).
• Don't drink alcohol.
• Don't smoke and avoid secondhand smoke.
• Don't use any drug, even over-the-counter medications or herbal preparations, unless recommended by a health care provider who knows they are pregnant.
• Eat a variety of nutritious foods, including foods containing folic acid, like fortified breakfast cereals, leafy green vegetables, dried beans, legumes, oranges and orange juice.
• Don't eat undercooked meat or change a cat's litter box. Both are possible sources of toxoplasmosis, an infection that can cause birth defects.
• Don't eat shark, swordfish, king mackerel or tilefish. These fish can have high amounts of mercury. It's all right for a pregnant woman to eat a limited amount of fish that have small amounts of mercury, including shrimp, salmon, pollock, catfish and canned light tuna. But she should not eat more than 6 ounces of albacore (white) tuna per week.Women also should check local advisories about the safety of fish caught in local waters.

In addition, the March of Dimes recommends that all women be tested for immunity to rubella (German measles) and chickenpox before becoming pregnant and consider being vaccinated if they are not immune. After being vaccinated, a woman should wait one month before becoming pregnant.

Pregnant women who are 35 or older face some special risks, but many of these risks can be managed effectively with good prenatal care. It's important to keep in mind that the increased risk, even for the oldest women, is modest.

References
1. American Society for Reproductive Medicine (ASRM). Age and Fertility: A Guide for Patients. ASRM, Birmingham, AL, 2003, accessed 11/4/05.