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Obstetrical & Gynecological Survey:
doi: 10.1097/01.ogx.0000446902.79394.34
Obstetrics: Preconception and Prenatal Care

A Randomized Controlled Trial of Third-Trimester Routine Ultrasound in a Nonselected Population

Skråstad, Ragnhild B.; Eik-Nes, Sturla H.; Sviggum, Oddvar; Johansen, Ole J.; Salvesen, Kjell Å.; Romundstad, Pål R.; Blaas, Harm-Gerd K.

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Abstract

ABSTRACT: Fetuses who are small for gestational age (SGA) and with intrauterine growth restriction have increased risk for perinatal morbidity and mortality. This study was undertaken to compare detection rates of SGA after 2 ultrasound (US) examinations and to evaluate detection rates of fetuses who are large for gestational age (LGA), congenital anomalies, and adverse perinatal outcomes.

This trial (1989–1992) included 6780 pregnant women to whom routine US examinations at 18 weeks of gestation were offered. In the study group, 1 additional routine US examination was offered at 33/0 wk ± 3 d. The fetal head, abdomen, growth deviation, and birth weight were assessed. The cutoff value for SGA was birth weight for gestational age of greater than −22% weight deviation, and that for suspected intrauterine growth restriction was growth deviation greater than −5%. The cutoff value for suspected LGA in utero was growth deviation greater than +10%, and that at birth was defined as weight for gestational age of more than +22%.

Data from a study group of 3175 women and a control group of 3224 women were analyzed. The groups did not differ in size or gestational age at birth. In the study group, 77 of 467 fetuses thought to be SGA in utero were SGA at birth; 19 of 2689 fetuses thought to be non-SGA in utero were SGA at birth. Sensitivity and specificity for detection of SGA infants in the study group were 80% (95% confidence interval [CI], 71%–88%) and 87% (95% CI, 86%–88%), respectively. In controls, 44 of 217 fetuses suspected to be SGA in utero were SGA at birth; 52 of 2984 fetuses without suspected SGA in utero were SGA. The sensitivity and specificity for detection of SGA in the control group were 46% (95% CI, 36%–56%) and 94% (95% CI, 94%–95%), respectively.

In the study group, 132 of 1039 fetuses suspected as LGA in utero were LGA at birth; 13 of 2117 fetuses not considered LGA in utero were LGA. Sensitivity and specificity for detection of LGA in the study group were 91% (95% CI, 85%–95%) and 70% (95% CI, 68%–72%), respectively. In the control group, 60 of 373 fetuses thought to be LGA in utero were LGA at birth; 105 of 2828 fetuses not considered LGA in utero were LGA. Sensitivity and specificity for detection of LGA in the control group were 36% (95% CI, 29%–44%) and 90% (95% CI, 89%–91%), respectively. The study group had a significant increase in induction of labor and elective cesarean deliveries because of suspected SGA and a significant decrease in these parameters because of suspected LGA. The groups did not differ in spontaneous abortions, termination of pregnancies, or perinatal morbidity or mortality.

The study results showed that routine third-trimester US gave better detection rates of SGA and LGA than US performed only for clinical indication. Although conducted more than 2 decades ago, this large randomized controlled trial should be of interest to current clinicians because the value of third-trimester routine US is still debated.

© 2014 by Lippincott Williams & Wilkins.

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