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Inherited Disorders and Birth Defects

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03/20/2007

Question:

My wife is 13 weeks pregnant.

Married in the year 1992 had difficulties for 8 months since marriage for conceiving due to delay in menstrual cycle but after some oral treatment got conceived and had a normal child in the year 1994.

Now it is 14 years since our marriage, i am now 44 and she is going to be 42. Since the first child we have done some treatement but not able to conceive, injections were administered for proper ovulating and was under observation in last year January but it failed without ovulating.

Now since December,06 she did not menstruate so we consulted doctor and found she is pregnant. We delayed to visit the doctor hoping it might be delay in menstruation cyucle.

Doctor order for ultrasound marker used for identifying Down syndrome is the nuchal translucency . And the result showed 1 in 36. Is this a very risky ratio and what should be the normal ratio for her age of 42 years.

Now the doctor ordered for tripple blood test to still confirm further. What should be the normal ratio for this test for her age ?.

We had a first child normal at the age of 29 years, as she is now 42 the doctor fear and also as she was not ovulating properly and has a fibroid in uterus.

Is it more risky that the ovary is old and stopped working as she was not menstruating and ovulating regularly every month.

Please advise.

Answer:

You have a number of important questions and I would highly recommend that you speak to a genetic counselor or geneticist if you have not already done so. These experts would be able to discuss your specific situation in detail.

That being said, there is a well-known association between older mothers or what is called advanced maternal age (age 35 or older) and chromosome errors that happen during cell division in eggs and sperm. These errors can lead to chromosome abnormalities such as Down syndrome, which is the most common chromosome disorder seen. Down syndrome is seen in about 1 in 800 live born infants.

Statistically, a woman who is 42 years old has about 1 in 65 chance to have a baby born with Down syndrome. This chance can go up or down if you do other screening tests. One of those screening tests is an ultrasound done during the first trimester to look at the back of the baby’s neck and measure it - called nuchal translucency. If this measurement is increased, this can increase the chance that the baby has Down syndrome. This is a screening test - it cannot tell you for sure that the baby has Down syndrome or other problems.

The screening test you had, a triple check, looks at 3 types of biochemical products that have been found to be associated with chromosome problems; the most common one again is Down syndrome, also called trisomy 21. Like the nuchal translucency, this blood test is a screening test, not a diagnostic test - it can only tell you about your potential chance or risk to have a baby with Down syndrome. It cannot tell you for sure if the baby will have Down syndrome.

There are no specific normal ratios at age 42 for either nuchal translucency or the triple check - there is a formula that is used to calculate the risk based on the specific findings in each pregnancy. In your case, the calculation was 1 in 36 based on the nuchal translucency and you are waiting results from the triple check.

The only way to know for sure if the baby has Down syndrome is to do an amniocentesis – inserting a thin needle into the amniotic sac, obtaining fluid from around the baby which contains the baby’s cells and doing a chromosome analysis (a diagnostic test). This is the only way to tell you what your true chance is to have a baby with Down syndrome.

Again, I would recommend that you ask your doctor about a referral to talk to a genetic counselor or geneticist to discuss these issues in depth. This is an area that they have a lot of expertise. You can locate a genetics center near you through the National Society of Genetic Counselors Resource Center website below.

Related Resources:

National Society of Genetic Counselors Resource Center

For more information:

Go to the Inherited Disorders and Birth Defects health topic, where you can:

Response by:

Anne   Matthews, RN, PhD Anne Matthews, RN, PhD
Associate Professor of Genetics
School of Medicine
Case Western Reserve University