Archived Issues

2002, Volume 13, Number 3

Prenatal Information That We Need

by David M. Keren, M.D.

In this issue of the Warde Report, I review some of the features of our new QUAD test that make it more useful for Prenatal screening than the triple test. It will give fewer false positives and more true positives. I also review clinical and laboratory features of the Smith-Lemli-Opitz Syndrome (SLOS) that is now detectable in about 60% of affected pregnancies. Optimal information results from a combination of our analytical results and the information provided by the doctor's office. Below are the pieces of information that are key.

1. Date of birth of the person whose ovum is used. Usually this is the pregnant woman's birthdate. However, in cases of a donated ovum, we must have the age of the woman who donated the ovum for our calculation. Risk goes up or down with the age of the ovum. A 40 year old woman with the ovum of a 21 year old woman would have a much lower risk than with her own ovum. Conversely, a 21 year old woman who receives an ovum from a 30 year old woman would have a higher risk than if she could use her own ovum. Please provide date of birth of the woman whose ovum was used. And indicate that this is a donor (otherwise, we might be confused by the two birthdates).

2. Weight in pounds. The fetal analytes that we measure are diluted in the mother's blood and tissue fluids. The greater the weight, the greater the dilution. We cannot calculate risk estimates without maternal weight at the time of the assay.

3. Insulin-dependent diabetes mellitus (IDDM). Patients with IDDM have different risks for neural tube defects and have different mean values for some of the fetal analytes.

4. Race. African-Americans have slightly different risks for neural tube defects than other races. Also, the AFP analyte is slightly different.

5. Gestational Age. We recommend using the ultrasound information after 6 weeks 0 days of age to have the fewest false positive results compared to LMP data. If ultrasound information is not available, and the LMP is uncertain, an ultrasound should be performed.

6. Family history of neural tube defects. What is the relation to the fetus, eg. first degree (siblings or parents) versus second degree (uncles or aunts) versus third degree (any other affected relative).

7. Down Syndrome history. Has the patient had a previous Down Syndrome pregnancy or not (either live birth or not)?

As always, when your office has any questions, call Warde Medical Laboratory at 800 876-6522. Many of your questions may already be answered by the catalogue or past issues of the Warde Report that are available on this website.