Maternal age, the chance for Down syndrome, and prenatal testing

NEWBERGER D. Down Syndrome: Prenatal Risk Assessment and Diagnosis. Am Fam Physician. 2000 Aug 15;62(4):825-832.

NEWBERGER D. Down Syndrome: Prenatal Risk Assessment and Diagnosis. Am Fam Physician. 2000 Aug 15;62(4):825-832.

In 2007, the medical guidelines changed from only offering women 35 years old and older prenatal testing for Down syndrome to offering it to all expectant mothers. This, however, should not mean maternal age is irrelevant when considering prenatal testing. And, it turns out, something commonly reported about maternal age is incorrect.

When the American Congress of Obstetricians and Gynecologists (ACOG) changed the guidelines in 2007, it did so at the prompting of the then new prenatal test of nuchal translucency (NT). When combined with a test of certain components of the mother’s blood, NT reported comparable accuracy rates as existing second-trimester blood-based tests (namely the AFP and then the Quad test). NT, though, is performed in the first trimester. So, the earlier and just-as-accurate prenatal test justified offering prenatal testing for Down syndrome to all expectant mothers.

Another reason for offering prenatal testing to all expectant mothers was the assertion that most children with Down syndrome are born to women under the age of 35. Indeed, this is exactly what the Centers for Disease Control states:

The age of the mother is the only factor that has been shown to increase the risk of having a baby with Down syndrome. This risk increases with every year, especially after the mother is 35 years of age. However, because younger women are more likely to have babies than older women, 80% of babies with Down syndrome are born to women younger than 35 years of age.

This statistic–that 80% of all children born with Down syndrome are born to women under 35–has been cited by the March of Dimes and the National Coalition for Health Professional Education in Genetics (NCHPEG). And, it turns out, it is wrong.

ACOG did not just change its guidelines overnight. Instead, practitioners argued in professional journal articles that maternal age should not set an arbitrary cut-off rate for offering prenatal testing. And, with the advent of the then-new first trimester ultrasound test of NT, ACOG changed its guidelines. But, a point may have gotten lost in the change.

In response to one of the more popular articles arguing for dropping the age cut-off, Robert Resta, a genetic counselor in Seattle, Washington and former editor of the Journal of Genetic Counseling, wrote a letter making a key point.

In the main article, the authors had asserted that “the majority of children with Down syndrome are born to younger mothers.” Resta, however, countered:

This statement is incorrect. The percentage of pregnancies in women aged 35 years or older has tripled since 1975 and currently about 14% of births in the United States are to women aged 35 and older. The net result is that since about the year 2000, women aged 35 and older have accounted for slightly more than 50% of pregnancies with Down syndrome.

Rather than dispute Resta’s assertion, the authors who had argued for offering prenatal testing for Down syndrome to all women because most children with Down syndrome are born to mothers under the age of 35 reversed themselves:

Data from Dr. Resta’s article indicate that he is correct in stating that the increasing number of pregnancies occurring in women who are 35 years of age and older has recently resulted in that cohort accounting for slightly more than half the number of Down syndrome fetuses conceived in the United States. … In the FASTER trial, where 21.6% of the screened population was aged 35 or older, compared with 14% for the US population, 69% of the Down syndrome cases occurred among those older women.

The FASTER trial was the First and Second Trimester Evaluation of Risk trial that established the reliability of NT as a prenatal test and was the prompt for ACOG to change its guidelines.

In a previous post, I shared how, due to The Great Recession, overall births are at their lowest point but have remained the same or growing among mothers in their 30’s and 40’s. This, then, means that there is an even higher percentage of older mothers being pregnant and, ergo, even more cases of Down syndrome are due to pregnancies of women over the age of 35. Contrary to the CDC statement, women under the age of 35 account for a minority of Down syndrome pregnancies, and have since the start of this century.

To see the other posts in this series, see these links here and here.

Comments

  1. I find this article unscientific in nature due to the fact, several key factors are unaccounted for. Such as the health if the older women and the genetic factors. For example, how many of those women have special needs kids. There is more to be considered than just the ages. How about the ages of the fathers? If the women are older, the father must be older. But curiously, nobody brought the age of the father up.

    • I recall reading a piece on book reviews that explained how reviewing a book, one should review what is written, not what one wishes had been written. This post is to explain the inaccurate statement that 80% of all children with Down syndrome are born to women under 35 when the true ratio is that half of all children with Down syndrome are born to women under 35 and half are born to those over 35. You’re quite correct that there are other factors that contribute to the chance of conceiving a child with Down syndrome, but those have not been shown to disrupt the 50/50 ratio.

      • Julie g says:

        Nice try mark. The majority of DS babies are to women under 35 and many to teenage mothers. There is also the paternal factor. Men over 40 are more likely to produce babies with Chromosomal abnormalities than younger men. I understand that you may have a vested interest in your opinion piece, but facts are facts.

        • You’re not saying I’m incorrect, you’re saying that Robert Resta is incorrect in saying the majority of pregnancies positive for Down syndrome are to women over 35–a position that those who he challenged saying what you say ended up reversing themselves. So, back up your statement with a reference; mine are in this post for everyone to see. And, please, keep the debate on the issue rather than claiming some unstated motive.

    • Kimberly Lair-Parker says:

      The age of the father does not matter, as men daily produce new sperm. As were a woman is born with the eggs she will always have. Everyone knows this.

      • This is not exactly correct. Studies have shown that the chance for having a child with Down syndrome increases with the age of either parent, with fathers over 40 having shown a correlation to an increased chance of having a child with Down syndrome.

  2. If mom’s are testing just so they will know ahead of time….fine. but if they do this in order to consider abortion, no. Because we are all fearfully and wonderfully made. I have a niece that is handicapped. She has brought such happiness to our family. Don’t mess up what God creates.

    • Elizabeth Walker says:

      why find out?

      the second test that confirms can cause miscarriage..

      and what reason to find out other than to terminate? all knowing would do is cause unwanted stress and theres nothing to prepare differently to a typical birth/child.

  3. What does “prenatal” testing mean to insinuate? that if the find out the conceived life in the womb has the syndrome they provide the chance to assassinate him in the womb?

    • See this post here, though “assassinate” is not the exactly appropriate word since it is associated with a killing of a political, social, cultural, or religious leader.

Trackbacks

  1. […] post generated a lot of discussion on Facebook and off-line about the role of maternal age and the […]

  2. […] relation to maternal age, with graphs visually displaying the percentages. See these posts at this link and this […]

  3. […] world. This is due, primarily, to more mothers having more children later in life, since maternal age is associated with the chance for having a child with Down syndrome. As the authors put […]

  4. […] is that in that same time the average age of pregnant women steadily increased. With Down syndrome correlating to the age of the mother, the more moms having children later in life, the more likely those […]

  5. […] interest fact was pointed out to me this morning by Mark Leach, whose blog, “Down Syndrome Prenatal Testing,” is one I regularly rely on for accurate statistics and information. The link provided here […]

  6. […] for having a child with Down syndrome increases with the age of the mother. See the graph at this post for the chance based on maternal age. While this relationship has been known, the reason for it […]

  7. […] the child after the parents are gone. The latter is particularly a concern of older moms, who are more likely to give birth to a child with Down […]

  8. […] posts here, here, here, and here  explain the difference between sensitivity and specificity as compared to positive […]

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