346 spa Abstracts

166 THE LEMON SIGN: NOT A SPECIFIC INDICATOR OF MENINGOMYELOCELES. RH....B..alI., RA Filly" RB Goldsteinx, and PW Callenx. Department of Obstetrics, Gynecology and Reproductive Sciences, and Department of Radiology. University of California San Francisco. OBJECTIVE: The association of the "lemon sign" with myelomeningoceles has been well documented. This study was performed to determine if this sign is exclusive to myelomeningoceles. STUDY DESIGN: The study population included all abnormal fetuses in our data base with this sonographica\ly observed finding, from 1988 to 1991. RESULTS: There were 23 cases all together of the "lemon sign" in fetuses with another morphologic anomaly. Twelve fetuses were found to have a myelomeningocele and six an encephalocele. Five fetuses with the "lemon sign" demonstrated a variety of structural anomalies not involving the neural tube. These were, skeletal dysplasia, cystic hygroma, fetal hydronephrosis, an umbilical vein varix in a two vessel cord, and a case with a diaphragmatic hernia and agenesis of the corpus callosum. None of the fetuses with anomalies not involving the neural tube had sonogrnphic evidence of the Amold-Chiari malformation. CONCLUSIONS: This sonographic finding appears not be limited to cases of myelomeningoceles. Based on the diversity of anomalous fetuses seen in this study, it is unfortunately even more difficult to speculate on a pathophysiologic explanation for the abnormal cranial development that results in the "lemon sign". This study does not clarify the cause of this malformation. However it does appear fair to state that the Amold-Chiari malformation is not the sole cause of this finding.

167 SONOGRAPHIC SCREENING FOR TRISOMY 21: FETAL HUMERUS:FOOT LENGTH RATIO, A USEFUL NEW MARKER. Jeffery Michaelson*, Mason Barr Jr·, Marjorie C Treadwell·. Mark I Evans, Nelson B lsada, Peter G Pryde*. Mark P Johnson·. DeplS. OB/GYN & Pathology, Hutzel HospitaVWayne State University. Detroit, MI, and OB/GYN, Pediatrics & Pathology, University of Michigan, Ann Arbor, MI. OBJECTIVE: To evaluate the use of arm length and humerus length as prenatal markers for Trisomy 21. STUDY DESIGN: Direct necropsy measurements were analyzed on 703 midgestational fetuses (641 normal, 62 trisomy 21) between 100 and 200 days gestational age (GA). Arm and foot length were found to be linear vs GA. Necropsy arm:foot length rntio vs GA was found to be linear in both groups, but the regressions were significantly different between normals and trisomy 21 (p<.OOI). Encouraged by the necropsy data, 128 midgestational pregnancies (117 karyotype normal, 11 trisomy 21) were sonographically evaluated for humerus:foot length ratio vs GA as a marker to identify fetuses at risk for trisomy 21. RESUL TS: Sonographic humerus and foot length vs GA were found to be linear for both groups between 100 and 200 days GA. The humerus:foot length ratio was linear for both normals and trisomy 21, but the regressions were found to represent significantly different populations (p<.OOI). When compared to women ~ 35 years old in our high risk population with a normal sonographic fetal survey, a sonographic humerus:foot length ratio ~ 0.85 correctly identified 45% of trisomy 21 fetuses (spec = 0.93, PPV = 0.38, NPV = 0.95) and had a odds ratio of 52.7 (99% confidence limits = 9.72 - 285.23) for trisomy 21. CONCLUSIONS: The humerus:foot length ratio vs GA is an additional sonogrnphic marker for identification of fetuses at increased risk for trisomy 21.

January 1993 Am J Obstet Gynecol

168 DIAGNOSIS OF GROWTH RETARDATION IN SMALL-FOR-GESTATIONAL AGE FETUSES. n;; Qmng, SC Robson, Xs Gallivan, xJAD Spencer. Dept. Ob/Gyn, University College Hospital, London, England. OBJECTIVE: To compare serial and isolated measurements of abdominal circumference (AC) and estimated fetal weight (EFW) in the prediction of intrauterine growth retardation (IUGR) in small-for-gestational age (SGA) fetuses (EFW<lOth centile). STUDY DESIGN: Serial measurements were performed in 105 SGA fetuses during the third trimester. The final AC and EFW measurements were compared with o..AC and /i-EFW (change in AC and EFW between recruitment and delivery). Ultrasound measurements > 2 SO below our population mean were regarded as abnormal. IUGR was defined as two or more abnormal neonatal morphometric indices (subscapular and triceps skinfolds, ponderal index and MAC/HC ratio > 2 SO below mean). RESULTS: Median gestation at delivery was 275.5 (range 252-297) days. 95 (90.4%) had a birtbweight < 10th centile for gestation and 23 (21.9%) were growth retarded.

Last EFW Last AC /i-AC /i-EFW Sensitivity(%) 81.8 82.6 56.5 56.5 Odds ratio 3.7 3.5 6.7 5.5 (95% CI) (1.1,12.2) (1.1,11.5) (2.4,19.0) (2.0,15.2) Kappa index 0.17 0.16 0.3 0.35 CONCLUSIONS: IUGR, as assessed by neonatal morphometry, was poorly predicted by ultrasonic measurements. Of those studied, /i-AC was marginally superior to other measures in the prediction of IUGR.

169 SONOGRAPHIC IDENTIFICATION OF THE LARGE FOR GESTATIONAL AGE FETUS - THE EFFECT OF GESTATIONAL AGE ON DIAGNOSTIC ACCURACY. R N PollackX, M.Simardx, N.Brossardx, A.K.Joshix. Dept. of OB/GYN, McGill University , Montreal , Canada. OBJECTIVE: To assess the ability of sonography to Identify the large for gestational age (LGA) fetus remote from term, and to establish the optimal time when sonographlc estimation of fetal weight should be performed. STUDY DESIGN: 544 sonographlc examinations were performed In the third trimester. The sonographlcally derived fetal weight percentile was compared with the actual blrthwelght percentile . RESULTS: 1096 of examinations revealed the presence of a LGA fetus. 22% of neonates were LGA. The sensitivity, specificty, positive & negative predictive values of a sonographlc diagnosis of LGA was 23.8%,93.8%,53.6% &80.3% , respectively. The positive predictive value (PPV) of a sonographlc diagnosis of LGA was greatest at between 28-30 weeks when It was 81.8%.The sensitivity at this time was only 22.5%. The sensitivity was maximal at between 34-36 weeks gestation, when it was 62.5%. The PPV of the test when performed during this Interval was 5096. CONCLUSION: The ability of sonography to Identify the LGA fetus Is dependent upon the gestational age at which time the examination Is performed.