364 SPO Abstracts

316 ULTRASOUND ASSESSMENT OF CERVICAL LENGTH (CL) IN PRETERM LABOR (J7J'L). J Paraskos' M Waxman', F Johnson', J Teteris', J lams. The Ohio State University Department of Obstetrics & Gynecology, Colwnbus, OH

Studies of PTL therapy are complicated by imprecision in diagnosis. \'ok performed transvaginal ultrasonic measurement of CL in 60 women with PTL treated with parenteral tocolysis between 24 - 34 weeks. Measurements were obtained as soon as possible after completion of parenteral medication. Each patient was examined once. Findings were not available for clinical care. Mean gestational age at examination was 31.0 ± 2.6 weeks. Mean CL was 2.2 ± 1.37 mm, range 6.6 - 45.0 mm. CL correlated with interval from admission to delivery(r= 0.48 , p=O.OOOI,by logistic regression analysis). No patient whose CL was ;" 3.0 em had an admission to delivery interval of <21 days. Digital assessment of CL also correlated with interval to delivery (r=0.43, p=O.OO06), but was less clinically useful because there was no clinical cutoff to predict low risk of preterm delivery. Ultrasound assessment of CL is useful in PTL to select a group at low risk of preterm birth. Transvaginal scanning may improve the accuracy of diagnosis of PTL.

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317 AGGRESSIVE PERINATAL INTERVENTION BASED ON GESTATIONAL

AGE DERIVED MORTALITY RATES. bM..l.!:!I!n • x S.B. EtTer, M. Whilfield, x Division Malemal Fetal Medicine, Univenity of British Columbia, Grace aDd BCCH Hoopitals, V8DCOliver, Cauada.

The aim of the study is to present outcome data, specific to each week: of gestatioo, focusing on weeks 23 \0 28, adjuatiDg for poIAmIiaI confOlinden aDd with enough power aDd precision \0 use in bocb clinical 1IIOI1IIgODIODI, deciaiDn malting, aDd cOUDBeIlint! patieDIB, appropriately informed. All birtha between 23 aDd 28 completed weeks gealalion, born in Grace Hospital, Vancouver, during 7-ycar period from JlIIIIW)' 1983 \0 December 1989, were ineluded for analysis. Gestational age errors pre_ in 34.3 % of the patients were corrected by early ultrasound reports available in 88.3% of patieDIB. Neonatal moItaIity wu calculated for each week of gestation (fable I). The efTects on neonatal mortality of: fetal sex, use of steroids. p_ rupture of mombranea (PROM) , aDd delivery mode in breech preseDlBtinn were statistically analyzed for each week of gestation. Significant difference was found in : feta1 sex 01 27 aDd 28 weeks; PROM at 27 weeks; de~very mode in breech at 25 weeks; aDd steroids at 28 weeks. Long term follow up in thia population waa limited to survivon with birthweight under 800 JI81D8. Major diaability decreased in frequency in each week from 23 to 26 weeks «71.4% \0 IO.O~) with. dramatic inereue at 27 weeks ( 5~). This , we pooIUIate ia due to the focI that 27 weeks survivon who weighted Ie .. than 800 JI81D8 , have a major degree of WGR. We conclude that these moI1ality rates, coupled with known severe degree of diaability should deter us from recommending asgreasive moasures with major risks \0

mother, with no IligDificant feta1 benefil, at gestational a ... 1 ... than 25 weeks. Table I - Neonatal Mortality - 1983-1989 Grace Hoopital-Vancouver, B.C. Wceb IObd LVB S8 NN. SUltV. NN. MORT. RATE

N Nfi Nil Nfi ~ 23 83 56 61.5 T1 32.5 9 16.1 83.9 24 133 lOB 81.3 2S 18.7 44 /fl.1 59.3 2S 184 161 81.5 23 12..5 88.54.6 4.5.4 26 193 177 91.7 16 8.3 III 62.7 37.3 T1 3n 188 93.5 I3 6.5 143 76.0 24.0 28 231 221 95.7 10 4.3 192 86.9 13.1 TcUl 1025 911 88.9 114 11.1 5Ir1 57.2 42,8

January 1992 Am J Obstet Gynecol

318 CERVICAL DILATION IS THE BEST PREDICTOR OF RISK FOR PRETERM BffiTH J. Smeltzer, J. Lewis?,P. VanDorsten, D. Cruikshank, Depts. OB/GYN, Medical College of Virginia, Richmond, VA, Washington University, St. Louis MO

Preterm birth is the most important cause of death and disability of the normally-formed infant. Interventions to prevent preterm birth must be able to identifY those at highest risk. To evaluate the importance of the factors which can lead to preterm birth, data on social, historical and current pregnancy risk factors were collected from 971 patients with 1067 consecutive pregnancies referred to a special treatment clinic by city public clinics for fixed criteria. Of these, 981 participated at or after 25 weeks, with 63786 days of observation from 25 to 37 weeks. Complete data were available on 973 (99.2%). Cervix exam data were prospectively collected semi­weekly to 34 weeks on outpatients. Intensive treatment was used to 34 weeks. There were preterm labor or ROM in 40.8%, and birth in 30.1%, perinatal death in 10.4 per 1000. The effects of the factors were estimated in a stepwise fashion by a censored regression iterative least squares (lLS) model on cohorts by weeks at exam. Of social, historical and pregnancy scores, only twins had a consistent effect. Cervix dilation at the internal os was a consistent predictor of a shortened pregnancy across gestational ages. Other parts of the exam were much less important, but of expected direction.

Effect of factor on mean interval to delivery Week, (n) Dilation Length Station' Twins

days/cm days/em days/score days 27 (202) -10.148' 5.094b -8.027b -18.218' 28 (336) -5.087' 2.283 -0.524 -4.088 29 (313) -9.164' 2.535 -3.570 -20.535' 30 (348) -6.332' 2.937' -5.904 -1.658 31 (320) -7.142' 0.103 -2.093 -14.631b 32 (355) -4.623' 1.863 -2.404 -5.567 33 (321) -4.789' 1.347 -1. 770 -3.147 34 (348) -4.639' 0.552 0.373 -2.683 '"High"=0;Minus=1;Engaged=2;Positive=3. p < "0.05, bO.01, '0.001.

319 EARLY CERVIX DILATION WARNS OF PRETERM LABOR J. Smeltzer, J. Lewis", D. Cruikshank, P. VanDorsten Depts. OB/GYN, Medical College of Virginia, Richmond, VA, Washington University, St. Louis MO Effective treatment of preterm labor requires its early recognition. Only when the condition is recognized prior to advanced cervical dilation or rupture of membranes can the labor be effectively arrested. Home uterine monitoring and periodic clinic monitoring are available for this purpose. Their high cost and low specificity make them useful only for high-risk groups. Most preterm births occur in women without prior risk factors. An ideal system would be low cost and identify most of those with truly high risk. Hendricks described an exponential increase in cervix dilation in the weeks prior to labor in term patients. This study addresses the ability of cervix exam to predict new onset preterm labor from 26 to 35 weeks gestation. Cervical exams were recorded semi-weekly in this period from 2070 exams of 842 pregnancies at risk for preterm birth but with no preterm labor in the index pregnancy. Data were analyzed using a regression model for censored data by weekly cohort. Independent variables were social risk score, obstetric history, twins, cervix consistency, station, length, and dilation. Other variables' coefficient estimates were weaker and inconsistent, but cervix dilation had a strong, consistent effect on time to spontaneous labor. Controlled fOf all other variables, the estimated change in mean time to labor ranged from -5.09 days/cm dilation at 32 weeks gestation to -13.39 days/cm at 27 weeks, with high estimates at early ages (p < .0001). The power of cervix dilation alone to predict preterm labor in this sample was computed by week from exam for exams <31 weeks. Labof before end of week= > 1 2 3 4 Sensitivity .603 .524 .457 .419 Specificity .771 .778 .781 .783 Positive predictive value .157 .217 .263 .303 Negative predictive value .965.933 .893 .858 Cervix dilation predicts most labors within two weeks of exam.