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Trying to Conceive After 35 – What are the Risks of Birth Defects?

Age and Fertility

There is a decline in a woman’s fertility as she ages be due to less frequent ovulation or to problems such as endometriosis. Women generally have some decrease in fertility starting in their early 30s and it is normal for a woman over 35 to take longer to conceive than a younger woman.

But there is good news. Since the late 1970s, birth rates for women in their late 30s and 40s have increased dramatically. According to the National Center for Health Statistics, between 1978 and 2000, the birth rates for women age 35 to 44 more than doubled. However, women should be aware of the risks associated with childbearing after the age of 35 so that they can make informed decisions about their pregnancies.

According to the American Society for Reproductive Medicine, about one-third of women between age 35 and 39 and two-thirds of women over 40 have fertility problems. However, once they conceive, healthy women over 35 or into their 40s usually have healthy pregnancies. Pregnant women who are 35 or older face some special risks, but many of these risks can be managed effectively with good prenatal care. Keep in mind that the increased risk, even for the oldest women, can usually be successfully treated.

Risk of Birth Defects

The risk of having a baby with chromosomal disorders increase as a woman grows older. The most common of these disorders is Down syndrome, a combination of mental retardation and physical abnormalities caused by the presence of an extra chromosome. 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; and at 45, a 1-in-30 chance.

Chromosomal Birth Defects

One major reason for apprehension in a pregnancy after age 35 is increased risk of chromosomal abnormalities. Age-related chromosomal birth defects such as Down syndrome occur in only about 1 in 200 pregnancies for women aged 35. However, for women age 40 at the time of pregnancy, the risk rises to about 1-2 percent.

Age-related chromosomal problems typically originate at the time of meiosis, when the egg cell eliminates half of its 46 chromosomes to accommodate the male’s genetic material. Tiny filaments called spindles, which appear to become detached from the chromosomes as women age, separate the chromosomes. This detachment can result in an abnormal number of chromosomes in the egg, a condition called aneuploidy. This occurs in about 33 percent of eggs at age 35 and 50 percent of eggs at age 40.

The American College of Obstetricians and Gynecologists (ACOG) recommends that pregnant women older than 35 should be offered prenatal testing to diagnose or rule out Down syndrome and other chromosomal abnormalities. About 95 percent of women who undergo prenatal testing receive do not have babies with one of these disorders and if prenatal testing rules out chromosomal defects and the mother is healthy, the baby probably is at no greater risk of birth defects than if the mother were in her 20s.

Non-chromosomal Birth Defects

As you grow older, your risk also rises for non-chromosomal birth defects and pregnancy complications such as gestational diabetes, pre-eclampsia and intrauterine growth retardation. There is little information available to confirm this though.

How can a woman over 35 reduce her risks?

Thanks to research and development in this field, today most women in their late 30s and 40s who are planning pregnancy can look forward to having a healthy pregnancy and a healthy baby. However, older women should follow the following guidelines for a healthy pregnancy:

  • Plan for pregnancy by seeing a doctor before you try to conceive. You must review all you medical conditions, medications and immunizations at this time.
  • Take a prenatal vitamin containing 400 micrograms of folic acid daily before you become pregnant and through the first month of pregnancy to help prevent neural tube defects.
  • Get early and regular prenatal care.
  • Eat a variety of nutritious foods, including foods containing folic acid, like fortified breakfast cereals, enriched grain products, leafy green vegetables, oranges and orange juice and peanuts.
  • Begin pregnancy at a healthy weight.
  • Stop smoking or drinking alcohol before you try to conceive, and continue to avoid these during pregnancy.
  • Don’t use any drug, even over-the-counter medications or herbal preparations, unless recommended by a health care provider who knows you are pregnant.
  • Pam Tully

    This article doesn’t mention one of the most important risk factors for birth defects, which is paternal age. Many articles and papers quote statistics for birth defects or risks relating to the age of a mother, but these often do not mention how the age of the father may have more of an influence. Older fathers are more likely to have children and grandchildren with bipolar, schizophrenia, autism, ms and Downs syndrome. Research is now turning it’s attention to fathers and sperm quality and as geneticist John Crow writes;

    DNA in sperm degrades as men age and can then be passed along to children in permanently degraded and irreparable form, which they likely pass on as well, means that the “greatest mutational health hazard to the human genome is fertile older males”. He described mutations that have a direct visible effect on the child’s health and also mutations that can be latent or have minor visible effects on the child’s health; many such mutations allow the child to reproduce, but cause more serious problems for grandchildren, greatgrandchildren and later generations


Last modified: February 10, 2013


The information provided here should not be considered medical advice. It is based on the average experience of women trying to conceive and may not be what you may be experiencing. It's not meant to be a replacement for any advice you may receive from your doctor. If you have any concerns about your cycle or our ability to get pregnant, we advise you to contact your doctor.