189

Volume 166 Number 1, Part 2

RECOGNITION OF THE LARGE FOR GESTATIONAL AGE (LGA) FETUS USING GESTATIONAL AGE INSENSITIVE PARAMETERS. Joseph M. Miller, Jr., LSU Medical Center, New Orleans, LA.

Accelerated abdominal circumference (AC) growth occurs in the LGA fetus of diabetics and may allow improved recognition. The utility of the AC growth rate (AGR) and the ratio of the femur length (FL) to AC were evaluated in 35 diabetic and 52 nondiabetic patients, scanned after the 31st week on >2 occasions at least 2 weeks apart. The initial and final scans were analyzed. Birthweight (BW) tables of Brenner defined the median BW and LGA (>90%). AGR cor­related with LGA status in diabetics but not in nondiabetics. FL/AC from the last study was strongly associated with LGA status in both groups. Both AGR and FL/AC correlated with rel­ative BW (RBW) = BW~median BW for GA, r=.408 and -.675, respectively, and may explain why these indices work better for larger LGA new­borns of diabetics (RBW=I.37±.17) than nondia­betics (RBW~I.25±.08), p=.03. FL/AC may be more useful than AGR, particularly in diabetics

Diabetics Nondiabetics LGA NonLGA p LGA NonLGA p

AGR >1.2 10 4 5 6 cm/wk <1.2 4 17 .004 7 34 .100

FL/AC <.21 13 4 7 5 1 17 .000 5 35 ~.21

.003

190 TRANSVERSE CEREBELLAR DIAMETER/ABDOMINAL CIRCUMFERENCE RATTO IN PREGNANCY: A NOMOGRAM W. Meyer,X D. Gauthier,x S. Warsof, A. Bieniarz University of III inois at Chicago, Chicago, IL

In fetal growth disturbances, cerebellar growth has been shown to remain constant while abdominal circumference may vary considerably. To determine whether a relationship exists be­tween fetal transverse cerebellar diameter (TCD) and abdominal circumference (AC), 138 patients with well dated pregnancies between 14-42 weeks were evaluated in a cross-sectional study. All pregnancies were normal, with no maternal or fetal factors which are associated with abnormal fetal growth. The TCD, AC and TCD/AC ratio were calculated for each patient and correlated to gestational ;lge with linear regression analysis. RESULTS. Excellent correlation exists between TCll and gestational age (r=0.97) as well as TCD and AC (r=0.98). TeD/AC was normally distributed with a meCll1 of !J.b5 +/- 0.887" (median=13.64%, mmle=13.611). The 5th and 95th percentiles were 12.27 and 15.287 respectively. The TCD/AC ratio rernillned constant tllroughout pregnancy when cumpared to gestational age (r=0.03). CONCLUSlON: THE TCD/AC RATIO IS A STABLE FETAL BlOMETRIC PARAMETER WHICH IS INDEPENDENT OF CESTATlONAL AGE. THIS RATIO HAY BE USEFUL IN THE PRENATAL DETECTlON OF SOMATIC FETAL GROIHH ABNORHAL ITI ES.

191

SPO Abstracts 331

FETUSES WITH DOWN'S SYNDROME HAVE DISPRO­PORTIONATELY SHORTENED FRONTAL LOBE DIMENSIONS ON ULTRASOUND. Bahado-Singh R, Wyse L.' Dorr MA: Copel JA, and Hobbins JC. Department of OB/GYN, Yale University School of Medicine, New Haven, CT.

Shortened occipital frontal diameter (due to short frontal lobe) occurs in Down syndrome (OS) post­natally. We assessed frontal lobe size in mid-trimester OS fetuses. Frontal lobe length (FLL) and frontal lobe­cavum septum pellucidum (FLL-CSP) were measured from inner table to anterior and posterior aspect of cavum, respectively. Fronto-thalamic distance (FTD) from inner table to posterior thalamus and FTD/BPD were obtained. Nomograms were generated for 125 normals (15-21 weeks) and compared to 19 OS fetuses. FTD and FTD/BPD proved the most useful parameters. When expressed as multiples of the median to eliminate variation due to gestational age, significant shortening in mean FTD in OS fetuses compared to normals (p<0.0019) and FTD/BPD (p<0.0177) was seen. In the OS group, 32% had FTD < 10th percentile. If an observed-to-expected FTD ratio of 0.84 is used as a screening test for OS, sensitivity 21.1 %, specificity 95.2%, and positive predictive value 0.6 would be obtained in a population with 1 :250 risk of OS. Conclusion: Frontal lobe dimension is significantly shortened in OS fetuses. Prospective evaluation of this finding is planned.

192 AN EVALUATION OF RESIDENT USE OF LABOR AND DELIVERY lJLTRASOUND: VALUE AND LIABILITY. L. Coultrip, C. Ludowese', L. Hawkins', V. Lupo. Hennepin Medical Center, Minneapolis, MN.

In this ongoing study, ultrasound (US) use by obstetric residents assigned to Labor and Delivery is prospectively monitored to determine the usefulness and limitations of LIS performed by second year residents without formal LIS training. Of 1225 patients evaluated on L&D for acute problems and 480 service deliveries during a four month interval, 191 LIS cxaminalion~ have been uocumcntco. Indications included amniocentesis (15')1), placentation (13%), EFW (10'/(.) and other (15';;.). The most common indication for a scan is dating (47';{') in the absence of prenatal care. 55':1 of these patients presented at 28 weeks or ks\. {)5(/(, of (fA estimates were deemed accurate when confirmed by subsequent .scan by trained technicians or newborn exam. lIsing BPD/AC, 19';', of EFWs fell within 5"(. and 4S'{ within IO'/r, of fetal delivery weight within 48 hours of scan (N=30) compared to 27% and 58':1 respcctively for FL/ AC. Misscd diagnoses included a term twin gestation and a gastroschisis. In an indigent population presenting with erratic prenatal care, L&D scanning affords an opportunity to accurately date the pregnancy in a population in which 35'/r would otherwise he poorly dated.