Volume 166 Number I, Part 2

181 "FETAL GROWTH CHARTS":COMPARISON OF CROSS SECTIONAL ULTRASOUND EXAMINATIONS WITH BIRTHWEIGHT. 1M Bernstein, MC Meyer, GM Simmons, EL Capeless. Dept. Ob/Gyn, Univ. Vermont, Burlington, VT.

We examined the hypothesis that fetal growth curves derived from birthweight data under­represent normal fetal weight in pre term gestation due to a high incidence of growth deficiency in premature newborns. We compared growth curves created from. birthweight data with curves generated from. ultrasound exam­inations collected cross-sectionally. We matched 350 ultrasound exam{nations with 350 newborn weights. Groups were evenly distributed by gestational age between 26 and 39 weeks gestation (25/wk). Ultrasound examinations were performed for size/dates discrepancy. Menstrual dating was confirmed by early ultrasound or index examination BPD. Regression lines for the growth curves were different (p<O.OOl). Between 26 and 35 weeks the ultrasound derived regres­sion predicted higher fetal weights (p<0.05). We conclude that for pre term infants «35 weeks) estimation of percentile rank for growth will differ between birthweight and ultrasound derived growth curves. Sonographically derived "fetal growth charts" provide an improved standard when characterizing ultrasound' estimates of fetal weight.

182 FETAL SACRAL LENGTH IN THE ASSESSMENT OF GESTATIONAL AGE. D.ID'id M. Sherer Jacques S. Abramowicz, Mark A. Plessinger·, James R. Woods, Jr. University of Rochester, Rochester, NY. The fetal sacrum is a consistent sonographically identifiable structure. In a prospective cross·sectional study of 506 singleton fetuses between 15·41 weeks, with normal growth and no structural anomalies, the sacral length (SL) ranged between 15-43 mm. Models to predict SL based on gestational age (GA), biparietal diameter (BPO), head circumference (HC) and femur length (FL) and 95% confidence limits were derived by least squares regression analysis. The SL was analyzed as the dependent variable paired with the GA, BPO, HC and FL as the independent variables. Scatterplots of the data for each model along With the standard error of the estimate (SEE), coefficient of determination (R2) and adj. R2 demonstrated excellent correlation:

SUGA: SEE=0.1707, R2=95.9%, Adj. R2=95.9% SUBPO: SEE=0.2082, R2=93.9%, Adj. R2=938% SUHC: SEE=0.2048, R2=94.1%, Adj R2=94.0% SUFL: SEE=0.2352, R2=92.2%, Adj. R2=92.1 %

The following is a graphic representation of SL as a function of GA: 45

E'40

.s 35

B, 30 c .5 25

~ 20 g (J) 15

10

~

~" ...... . 'f.' ". ~

~ ~

"'" . ~ ~~~ . "

~ y. -.108 + .102(GA) ". ,. - Predicted Sacral Length (mm) . ___ 95% Confidence umllS

I I I I I I I 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42

Gestational Age (weeks) Subsequently the SL of 40 LGA (EFW >90th percentile) and 40 SGA (EFW <10 'h percentile) fetuses were found !l.Q1 to be statistically different from that of the 506 fetuses with normal growth. Conclusion: We define the normal limits of SL and demonstrate that SL may be utilized in the assessment of GA irrespective of fetal size.

SPO Abstracts 329

183 UNEXPLAINED MIDTRIMESTER POLYHYDRAMNIOS: SONOGRAPHIC FOLLOW-UP AND PERINATAL SIGNIFICANCE Jacques S. Abramowicz MD David M. Sherer, MD, J. Christopher Glantz, MD, James R. Woods, MD. University of Rochester, Rochester, NY.

Third trimester polyhydramnios has been associated with sub­optimal perinatal outcome such as higher incidence of preterm labor, pre-eciampsia,plaGental abruption, and fetal anomalies. The significance of midtrimester polyhydramnios is less clear. We examined the outcomes of 47 singleton gestations from 16 to 27 weeks gestation with unexplained polyhydramnios but with no known structural anomalies or evidence of maternal diabetes. Polyhydramnios was defined as mild­moderate if the greatest vertical fluid pocket visualized on ultrasound measured > 6cm and severe if it measured> 1 Ocm. A group of 87 gestations with normal amniotic fluid and identical inclusion criteria constituted the control group. Results: Demographic and obstetrical data were similar in both groups. In the study group, 44 patients (94%) were diagnosed as mild-moderate and 3 as severe polyhydramnios. Follow-up scans were performed on 40 patients. Among these, polyhydramnios had resolved in 30 (75 %). Of those with mild-moderate polyhydramnios who were rescanned, it had resolved in 74%. In severe polyhydramnios with subsequent scans, it resolved in all (n=2). Gestational age at delivery, mean birthweight, 5min Apgar scores, incidence of pre-eclampsia, and placental abruption were similar in both groups. In the study group, 3 infants were subsequently diagnosed as having an anomaly: two cases of trisomy 21 and a third with unilateral multicystic dysplastic kidney. No anomalies were demonstrated in the control group (p<0.025). Conclusions: Resolution of unexplained midtrimester polyhydramnios is common. Further antenatal investigation, however, may be indicated, even in the absence of additional abnormal sonographic findings.

184 FOOT:LEG LENGTH AND FOOT:FEMUR LENGTH RATIO IN NONINVASIVE SCREENING FOR TRISOMY 21. MliK Paul Johnsonx, Mason Barr Jr.2x, Marjorie C. Treadwellx, Nelson B.

Isada, Peter G. PrydeX, David B. Cotton, Mark I. Evans. Dept. OB/GYN, Hutzel Hospital/Wayne State Univ., Detroit, MI., and Depts. OB/GYN, Pediatrics & Pathology, Univ. of Michigan, Ann Arbor, MI.

UHrasound screening for trisomy 21 has had limited SUCCeSS. However, fetuses w~h T21 tend to be growth restricted and may have shortened limb lengths. In order to delineate the pattern of IUGR in T21, gravimetric measurements were collected from 436 fetal necropsies (gestational ages (GA) 100-200 days) from the Teratology Database at the Univ. of Michigan (391 morphologically normal and 45 karyotype confirmed T2t fetuses) Using the power equation analytical approach we have previously described, we confirmed that fool lenglh and leg lenglh VS. GA are linear relationships. We then generated a fool 10 leg lenglh ralio and found it to be linear vs. GA in both normal and T21 populations. However, the generated regression curves were found to be significantly different between groups (p<.0001) with higher ratios noted in T21 . Using a fool 10 leg lenglh ralio of >0.44 to screen for T21, the following were calculated: sensitivity=0.69, specificity-0.91, +PV=0.61, and -PV.0.94. In this population, with a T21 prevalence of 17%, this measurement provides a high +PV and -PV for the ident~ication of T2t. We conclude that 1) fool 10 leg lenglh ralios vs. GA is a linear relationship, and 2) regression curves are sign~icantly d~ferent between T21 and normals. This finding now provides a rational anatomic basis for ultrasound screening for T21. Since completion of this analysis, and based on our observations that T21 s have shortened upper leg lengths, we have begun a prospective study using fool 10 femur lenlh ralios measured by uHrasound during routine prenatal screening. Preliminary data reflects the differences found in our fool to leg lenglh necropsy studies and has encouraged our continued work to define the role of this measurement in prenatal screening for T21 in a low risk population.