S80 SPO Abstracts January 1997 Am J Obstet Gynecol

250 COMPARISONS OF FETAL GROWTH IN THE MACAQUE AND MAN: A LONGITUDINAL ULTRASONOGRAPHIC STUDY. Nigel Simpson ~, Carl Nimrod, Rosa De Vermette ~, Jocelyn FournieK, Laurie Coadf , Colette Daudelin x, AndreDabrow~ki x. Division of Perinatology, Ottawa General Hospital, Animal Resources Division, Health Canada, and Department of Mathematics, University of Ottawa, Ontario, Canada.

OBJECTIVE: The macaque monkey and the human, as catarrhines, both exhibit villous haemochorial placentation, with sinfilar fetal:placental weight ratios. The monkey has been used as a model for early human growth and development. We therefore set out to compare prenatal growth in these two species.

METHODS: 24 cynomolgus monkeys (Macacafasciculmis) were scanned on a weekly basis throughout pregnancy from 30 days gestation (term = 165 days). The following measurenmnts were recorded: biparietal diameter, abdominal circunfference, femur length. Regression analysis was applied to each data set. The resulting growth curves were compared to those obtained in human studies.

RESULTS: In both species there is a deceleration in the growth velocity in all three parameters as term approaches, and growth rates up to 165 days are similar in both species�9 Individual macaque fetuses show differing growth velocities.

CONCLUSION: Prenatal growth in the macaque is similar to that seen in man over the first 165 days of gestation. This would indicate that the macaque may be a suitable model in studying factors governing early human development.

255 SKELETAL DYSPLASIA: OUTCOME PREDICTION USING FEMUR LENGTH T O ABDOMINAL CIRCUMFERENCE RATIO (FL/AC). R.D. Wilson, A. Rahemtullah, ~ B. McGiUivra~3 Depts. of Obstetrics & Gynecology and Medical Genetics, Univ. of British Columbia, Vancouver, Canada.

OBJECTIVE: A previous study (Ranms et al, 1996) reported that a femur length/abdominal circumference ratio of less than 0.16 suggested the diagnosis of a skeletal dysplasia. This finding was tested in a population of fetuses referred to Medical Genetics with a possible ultrasound diagnosis of skeletal dysplasia.

METHODS: Eighteen patients were identified. The FL/AC ratio was calculated from the initial ultrasound at this center. Control ratio for similar gestational ages was calculated fi-om a local large prospective bimneUy population. Pregnancy outconms were available for all patients including autopsy for therapeutic abortion, stillbirth and neonatal deaths.

RESULTS:

0.16 to 0.18 to OUTCOME <0.16 <0.18 <0.20

TA, SB, NND 9 0 0 Non-lethal skeletal dysplasia 0 2 3 No evidence skeletal dysplasia 0 1 3

CONCLUSION: A FL/AC ratio of <0.16 correctly predicted a lethal skeletal dysplasia in 9 /9 with gestational age range 15-26 wks. This study supports the Ramus et al, 1996 findings. (R Ramus, L Martin, D. Twickler. Sonographic prediction of fetal outcome in suspected skeletal dysplasia using the fenmr length to abdominal circumference ratio. J Ultrasound Med, 1996;15:537.

254 QUALITY ASSURANCE VALIDATION OF ULTRASONOGRAPHIC FE- TAL WEIGHT ESTIMATION. DR Bryant ~, 1 ZadoK, L ChiU. Deparmmnt of Obstetrics and Gynecology, Wayne State University, Hutzel Hospital, De- troit, Michigan.

OBJECTIVE: To determine the relative quality and need 1or adjustment of estimated fetal weight (EFW) procedures in an active obstetrical ultra- sound unit.

STUDY DESIGN: 3331 fetuses delivering within seven days of sono- graphic evaluation were randomly split into quality assurance (QA) and validation datasets. The EFW formula currently in use (Hadlock, 1984) and the Hadlock (1985) formula were separately modeled by zero intercept regression using birth weight (BW) as the dependent variable�9 The coeffi- clen �9 t of determination ( r ) and fit standard errors (FSE) were used as criteria of goodness of fit. Regression coefficients (b) outside the range 0.95 to 1.05 were used as criteria to determine the need for proportional adjustnlents.

RESULTS:

Quality Assurance Group (N = 1656)

Fo~wmla Current Hadlock (l 985)

r 2 0.881 0.886 FSE 332.6 326.1 b 1.059 1.110

Validation Group (N = 1675)

Formula Current Hadlock (1985)

r 2 0.884 0.887 FSE 323.5 319.6 b 1.003 1.002

CONCLUSIONS: In this population, birth weights were approximately 6% higher that EFW generated by the current fbrmula and 11% higher than estimates using the Hadlock (1985) formula. Adjustment resulted in appropriate estimates, as validated (b = 1.003). The overall accuracy of both formulas was lower than that reported by Hadlock et al (1985). Reasons for this observation likely include the use of log weight equations, which maximize r 2 in smaller versus larger estimates, and disproportional sample sizes in the birth weight populations.

256 IMPROVED ULTRASOUND DETECTION OF FETAL ANOMALIES IN A STATE DESIGNATED PRENATAL DIAGNOSIS CENTER. J~ Weiss, S. Lovett, M. Diogo, P. Williams, K. Sarem, R. DePalma. East Bay Perinatal Medical Associates, Oakland CA.

OBJECTIVE: To determine the efficacy of ultrasound screening for the detection of major congenital anomalies at a prenatal diagnostic center.

STUDY DESIGN: Of 3447 women undergoing routine second trimester ultrasound screening, data were retrieved for 2176 of them. Only those scans performed up to 24 weeks were analyzed. Perinatal outcomes were determined by examining insurance reimbursement records of the sole referring managed health care provider with verification from the attending obstetrician or pediatrician as required.

RESULTS: There were 60 major congenital anomalies (2.8% of total). Fort}, (67%) were either identified on the sonogram directly or frmn subsequent genetic testing. Correction for cardiac anomalies (12 VSD, 1 mild puhnonic stenosis) which frequently are undetectable antenatally, improves the detection rate to 85%. Pregnancy termination was opted for 20 of the 40 abnormal fetuses. Specific incidence and detection rates were as follows:

Abnormality Terminations

Genetic 9 9 100% 7 + 2 IUFD All Cardiac 25 9 36% 6 Corrected Cardiac 12 9 75% 6 CNS 7 7 100% 6 Pulmonaly 3 3 100% 1 + 1 IUFD All Other 19 15 79% 3

(note: three fetuses had both genetic and major cardiac anomalies)

CONCLUSIONS: The high detection and termination rates suggest that prenatal ultrasound screening at or before 24 weeks gestation is efficacious when performed at a prenatal diagnostic center.