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Fundal height measures for IUGR often unreliable. (Sensitivity of 70%).

SAN FRANCISCO -- The most routine screening method for intrauterine growth restriction is also the least reliable, Dr. Robin Field said at a meeting on antepartum and intrapartum management sponsored by the University of California, San Francisco.

Studies show that fundal height measurement--usually a routine part of prenatal care--has a sensitivity of only 70% for intrauterine growth restriction (IUGR), said Dr. Field, director of perinatal services at Kaiser Permanente Medical Center in San Francisco.

"In real clinical practice, it probably misdiagnoses IUGR about 50% of the time. It's an important test to arouse our suspicions. And if you are suspicious that you have IUGR, you go on to the next step," he said.

Most experts accept fetal abdominal circumference as the most reliable measurement of fetal size. An abdominal circumference within the normal range reliably excludes IUGR with a false negative rate of less than 10%, according to studies. Animal studies show that abdominal circumference at the liver is actually an indirect measure of the nutritional status of the fetus. The liver is the most affected organ in IUGR.

"Unfortunately, taking abdominal circumference has more interobserver and intraobserver variation than either femur length or biparietal diameter," Dr. Field said.

Estimated fetal weight calculations all use abdominal circumference but also must utilize properly performed biometrics. These equations have an error rate of 10%. In clinical use, Dr. Field has found properly performed biometrics to be as accurate as ultrasound.

When ultrasound is used, assessment of intrafetal proportions is often critical in screening for growth restriction, Dr. Field explained. Whether the fetus has an asymmetrical or symmetrical IUGR often influences the diagnosis and outcome. Though studies show that asymmetry is not reliable for establishing etiology, it can increase the concern. When the IUGR is asymmetrical, liver size may be reduced, while head size and growth are maintained.

"In these cases, you have to think IUGR even if the estimated fetal weight is greater than the 10th percentile," Dr. Field said at the meeting.

Fetuses with symmetrical IUGR, however, are more likely to be normal, especially if their estimated fetal weight is not extremely low, he added.
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Author:Boughton, Barbara
Publication:OB GYN News
Date:Oct 1, 2002
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