WOMENS-HEALTH Messages for June, 1999: Re: complicated pregnancies

Re: complicated pregnancies

From: William D. McIntosh, MD (anonymous@obgyn.net)
Tue, 22 Jun 1999 17:05:01 -0500 (CDT)

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In reply to: Amber: "complicated pregnancies"

At Tue, 22 Jun 1999, Amber wrote: >
>I am pregnant now for the third time, and with each of my pregnancies.
>there have been major descrepancies of dating between ultrasound and
>using my Last menstrual period. With this pregnancy there is a five
>week difference in the two dates. I have been diagnosed as having SLE
>and Hashimoto's Hypothyroidism. I am wondering if either of these could
>somehow cause a slow fetal growth rate which is showing up in the
>ultrasounds and causing the misdating of the pregnancies. I have been
>questioned about the accuracy of my dates but I am sure that there was
>no intercourse within weeks of the date of conception given by the
>ultrasound

Dating is sometimes a more complicated thing than it would seem. Neither SLE nor Hashimoto's thyroiditis are going to significantly affect the fetal growth, at least in the first half of pregnancy. In the later half of pregnancy, then the results of these conditions, such as hypertension, nephrosis, hypothyroidism can dramatically affect growth.

Ultrasound dating is more accurate the earlier in the pregnancy it is performed. At 6-8 weeks, it is accurate to 3-4 days. At 18 weeks, the accuracy is more like 10 days. At 30 days, the sono could be as much as 4 weeks off.

Beyond that, I really don't know how else to answer your question. If this is an early ultrasound, then the reasonable and prudent OB is going to go with the dates provided in that fashion. LMP dating is only accurate to a +/- 4 weeks, and the least accurate dating method of all is recalled intercourse, which is virtually unusable in a general patient population (an obvious exception is pregnancies that result from Artificial Reproductive Technologies). That parameter is so unreliable for clinical use, that we don't even ask.

-- William D. McIntosh, MD Clarksville, TN

This is for educational purposes only. It is not intended to replace consultation and examination by your physician or other health care provider.

Next message: William D. McIntosh, MD: "Re: dysplasia was found inside my cervix"
Previous message: William D. McIntosh, MD: "Re: Colposcopy during pregancy"
In reply to: Amber: "complicated pregnancies"

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