Volume 166 N umber I, Part 2

618 MA THEMA'OCAL MODELING OF FETAL WEIGHT PREDICTION C,Exacoustos X , P,Rosatt", A,Carusox, S,Mancusox, Dept, ObiGyn, CatboUc University, Rome, Italy

Previous studies suggested that birth weight (BW) prediction was enhanced by using formulas specifically derived from different gestational periods,!n 440 pregnant patients between 24-40 weeks of gestat10n an ultrasound examination was performed within 72 hours of delivery. The following ultrasound parameters were considered: biparietal diameter(BPD), head circumference (HC),mean abdominal diameter (AD), abdominal circumference(AC), femur(FL) and humerus length(HL). Ultrasound measurements were correlated to fetal weight with multiple stepwise regression analysis in three different gestational periods: before 32 wks, 33-37 wks and 38-40 wks.The best mathemalfcal models in predicting fetal weight in the different gestational periods were selected on the basis of the largest value of R 2 and the lowest mean unsigned and signed percent error: BW= 705.05-11.428 AC + 0.083 BPD2 + 0.036 AC2 + 0.244 FL2 before 32 weeks; BW- -1374.397 + 0.128 BPD2 + 0.198 AD2 + 0.298 HL2 between 33-37 weeks; BW= -5431.362 +19.17 BPD + 43.745 AD + 30.838 FL between 38-40 weeks. The accuracy observed during model development was confirmed during testing upon 809 non-model cases for the different gestational periods with an ultrasound examination obtained between 7 days of delivery(R2=0.95; 0.90; 0.85 respectively). Comparison with other weight estimation procedures showed that our models gives weight estimates that are more accurate as those obtained with other methods proposed in the literature for different gestational ages. Partially supported by grant 91.00110.PF41 from Progetto Finalizzato FATMA, CNR.

620 InIrauterine Growth ReIardation 0verestimaIi0n by UIIrasou1d Predicted EstimaIed Felal Weighl C. J. Sims, J. Y. Fang: D. R. Burholt: H. R. Giles, Dept. OblGyn, Medical College of Pennsylvania/Allegheny Campus, Pittsburgh, PA

Intrauterine growth retardation (IUGR) is a significant antepartum diagnosis that is associated with a marked increase in fetal and neonatal morbidity and mortality rates. Assuming an ultrasound estimated fetal weight less than the 10th percentile per gestational age, a diagnosis of IUGR was made. Clinical obsetVation at delivery hinted towards an overestimation of the diagnosis in our population, based on birth weight criteria only. Between September 1987 and May 1991, 102 singleton pregnancies were identified as less than the 10th percentile estimated fetal weight (Acuson 128, OB calculation package). A retrospective review of matemal and neonatal records was undertaken. Parameters analyzed included matemal body mass index, amniotic fluid volume, fetal position, the number of ultrasound measurements obtained, placental grade, placental position, gestational age at the time of measurement and the interval between ultrasound measurements and delivery. A miscalculation of ultrasound predicted IUGR was identified as a birth weight greater than the tenth percentile. 28/102 (27.5%) were miscalculated (expected 12-20%). None of the individual factors analyzed were statistically significant in predicting a miscalculation. We conclude from these data that there are other factors influencing the ultrasound overestimation of IUGR in our population. Institutional derived birth weight curves correlated with the OB calculation package may allow for a more accurate prediction in our population.

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SPO Abstracts 437

THE EFFECT OF GESTATIONAL AGE AND AMNIOTIC FLUID INDEX ON THE ABILITY TO VISUALIZE THE FETAL AIIDIJIINAL WALL CORD INSERTION BY ULTRAsaJNO $.J. Carlan, A.Pena\ M.Gore", \.I.F. O'Brien Depts. OB/GYN,U of S Fl, Tall1"', FL,and ORMC, Orlando, FL.

Fetal abdominal wall defects, especially C>q)haloceles, can be difficult to detect by ultrasound because of fetal trunk flexion, and/or small part crowding. This study was designed to investigate whether successful imaging of the urbilical cord at the fetal abdominal wall was related to gestational age and/or amiotic fluid index. Fourteen normal women were scanned every 2 wks from 20 wks to del ivery. The amiotic fluid index was obtained and if the cord insertion into the abdomen could be visual ized, the diameter was obtained. There were no maternal disorders, amiotic fluid, or fetal abnormalities. The mean birth was weight 3569.169 grams. WEEKS CORD DIAMETER (em) # (X) VISUALIZED M.!

20 9.2 • 1.2 13/14 (92.9) 129.3 • 30.7 22 10.1.1.1 12/14 (85.7) 135.8.33.7 24 11.2 • 1.0 12/14 (85.7) 139.6 • 24.5 26 12.3 • 1.3 10/14 (71.4) 153.3 • 26.7 28 14.0 • 2.1 7/14 (50) 154.5 34.6 30 14.3 • 2.5 7/14 (50) 147.1 30.9 32 15.3. 2.3 4/14 (28.5) 147.1. 24.8 34 14.0 1/14 (7.1) 156.0 • 36.3 36 19.0 1/14 (7.1) 166.4 • 35.6 38 18.0 1/14 (7.1) 156.7 • 45.5 40 0/12 165.0 • 36.2

IJe conclude that in spite of a trend toward a progressively increasing armiotic fluid index, the unbi 1 ical cord at the abdominal wall insertion becomes progressively more difficult to image. In fact, from 28 wks unti 1 term, the incidence of visualization well enough to obtain a measurement was less than or equal to 50%.

SINGLE UMBILICAL ARTERY: IMPLICATIONS OF SONOGRAPmC DIAGNOSIS

V Catanzarite, C Maidal:, A Mendoza"', L Cousins, J Schneider

Maternal-Fetal Medicine and PatholollY, Sharp Memorial Hospital Women's Center, San Diego

Eighteen cases of single umbilical artery (SUA) were diagnosed in utero over a 3 year period. There was one false positive dlagnosis (at 18 weeks) and one patient is yet undelivered. Of the remaining 16 cases, 11 were referred for various obstetric indications, one for 2V cord, and 4 for fetal anomalies. Eight patients had isolated 2V cord, including one with unexplained polyhydramnios. Each was correctly identified by sonography. Eight patients had identified associated anomalies; including one case each of Trisomy 13, Trisomy 18, Trisomy 21 and Turner Syndrome. The remaining cases were: VACTERL (2), holoproseneephaly (I), and omphalocele with bladder extrophy (1). In each case, sonography differentiated normal from abnormal babies, but in two of the anomalous infants, one or more major anomalies were missed by sonography. Based upon this experience, our current approach to the patient with SUA detected in utero is as follows: If careful sonographic evaluation shows no associated defects, we offer but do not recommend chromosomal studies. If other defects are seen, patients are counselled accordingly and amniocentesis is advised.