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Biomedical subjects

L Chik

Publications and source records attributed to L Chik.

At least 19 recordsLinked to original sources
PubMed2000

Correctly identifying the macrosomic fetus: improving ultrasonography-based prediction.

OBJECTIVE: Our goal was to improve the accuracy of estimating fetal weights among macrosomic fetuses with the traditional measurements of abdominal circumference, femur length, and head circumference. STUDY DESIGN: We used 4831 cases without anomalies from an ultrasonography laboratory database with an estimated fetal weight obtained a maximum of 14 days before delivery. Abdominal circumference, femur length, and head circumference were each regressed on birth weight to obtain estimated fetal weight by abdominal circumference, femur length, and head circumference, respectively. We compared the individual variation for estimated fetal weight by abdominal circumference, femur length, and head circumference by calculating a within-subject standard deviation to quantify the level of disparity. We adjusted the estimated fetal weight to the date of delivery and for dependencies on maternal diabetes mellitus, weight, and height. We then weighted cases with birth weight >4500 g and diabetic cases with birth weight >4000 g 20-fold (weighted estimated fetal weight) for the purpose of creating a favorable bias for classifying these cases. The equation of Hadlock et al, with abdominal circumference, femur length, and head circumference, was applied as a benchmark estimated fetal weight. RESULTS: Of the 4831 newborns, 308 (6.4%) had a birth weight >4000 g, and 56 (1.2%) had a birth weight >4500 g. There were 154 pregnancies complicated by diabetes mellitus; 26 (16.9%) of the resulting infants weighed >4000 g, and 5 (3.2%) weighed >4500 g. At 95% specificity, the weighted estimated fetal weight had a sensitivity of 85.7% at a cut point of 3912 g, compared with a sensitivity of 71.4% at 3604 g by use of the estimated fetal weight of Hadlock et al. CONCLUSIONS: We were able to improve the accuracy of identifying the macrosomic fetus compared to reliance on the equation by Hadlock et al. A fetus was found to be at significantly increased risk for birth weight >4000 g when the estimated fetal weight based on abdominal circumference is larger than that based on either head circumference or femur length or when there is a large within-subject variance in estimated fetal weight based on abdominal circumference, femur length, and head circumference. We also found that there were significantly different groups of patients whose estimated fetal weights require different equations for better estimates. Even given ultrasonographic measurements, taking into account maternal height, weight, and presence of diabetes mellitus can improve macrosomia detection. Although these findings remain to be optimized and validated, the approach used here appears to yield better predictions than the current "one function fits all" approach.

Anthropometry↗
PubMed1997

Precise gaussian distribution functions of maternal serum alpha-fetoprotein and free beta-subunit of human chorionic gonadotropin for trisomy 21 screening: improved accuracy for patient counseling.

OBJECTIVE: Gaussian equation curves are used to generate baseline curves against which a priori maternal age Down syndrome risks are adjusted to develop likelihood ratios for individual patients. We sought to evaluate the accuracy of these calculations, minimize the affects of outliers, and to make improvements. STUDY DESIGN: Gaussian distribution functions were used to investigate the best model for alpha-fetoprotein and free beta-human chorionic gonadotropin multiples of the median with use of nonlinear regressions. Parameters from distribution functions can be used to compute a more precise likelihood ratio for the decision logic for trisomy 21. A total of 58,297 normal cases and 348 cases of trisomy 21 were computed. RESULTS: Log normal distribution functions generated by nonlinear regression produced excellent but exaggerated goodness of fit R2 to the frequency distributions of the data. For normal cases values were as follows (in mean, SD, and R2, respectively): log alpha-fetoprotein -0.07199, 0.15681, and 0.9970; log beta-human chorionic gonadotropin -0.15203, 0.24284, and 0.9987. For trisomy 21 cases the values were (in mean, SD, and R2, respectively) for log alpha-fetoprotein -0.19303, 0.15802, and 0.9828 and for log beta-human chorionic gonadotropin 0.19996, 0.29760, and 0.9669. Distributions reconstructed with use of statistical means and SDs generated goodness of fit R2 from 0.585 to 0.914. Use of means and SDs derived from distribution functions increased the R2 to 0.855 and 0.999. The change in the model produces, at a 5% false-positive rate, a sensitivity of 57.18% (199/348). A 1 in 113 cutoff point risk is obtained and is tighter than the 1 in 251 without the distribution functions, as versus 1 in 270 by age calculations alone. CONCLUSIONS: Our data suggest that (1) normality of log transforms of alpha-fetoprotein and normality of log transforms of beta-human chorionic gonadotropin are reasonable models, (2) distribution functions can minimize the effect of outliers, which produces more realistic risk estimates, and (3) the effect of distribution functions versus standard mean and SDs cannot automatically be extrapolated to other parameters, which must be tested individually.

Chorionic Gonadotropin, beta Subunit, Human↗
PubMed1995

MOMs (multiples of the median) and DADs (discriminant aneuploidy detection): improved specificity and cost-effectiveness of biochemical screening for aneuploidy with DADs.

OBJECTIVE: Our purpose was to assess the efficacy of double- and triple-screening paradigms for Down syndrome and to develop a more logical, statistical approach to risk prediction that will decrease the cost of screening and allow the incorporation of new parameters appropriately weighted for their contribution. STUDY DESIGN: Data from 24,504 patients who had biochemical screening for Down syndrome by single (alpha-fetoprotein), double (alpha-fetoprotein, beta-human chorionic gonadotropin), or triple screening (alpha-fetoprotein, beta-human chorionic gonadotropin, unconjugated estriol) who had complete outcome information were analyzed by (1) existing gaussian-based methods, (2) the Glasgow ratio method, and (3) a new statistical approach (i.e., directly adjusted data sets for discriminant aneuploidy detection [DADs]) RESULTS: By use of individual risk-based thresholds for "at risk" status, both double and triple screening performed far better than single screening, but the percentages of patients at risk varied widely. When the percentages at risk were held constant, the sensitivity of double and triple screenings was similar, suggesting that there are no benefits of using estriol as a third marker. For 25,000 patients the use of only alpha-fetoprotein and beta-human chorionic gonadotropin would save about $500,000, with no decrease in sensitivity. With the DADs approach a statistically sound model giving more stable estimates was developed that permits each factor to be analyzed for its own explained proportion of variance and allows each parameter to have different weighting. For this data set the same sensitivity was seen with, conservatively, a 1% reduction in the percentage of patients at risk, which would reduce by 250 the number of amniocenteses, at a further savings of about $400,000. CONCLUSIONS: By use of existing methods, double screening is equally as effective as triple screening, so that the expense of estriol is unnecessary. The DADs approach, by allowing for variable weighting of parameters, lowers the at risk percentage and will permit a much more flexible approach as new parameters become available. Changing to DADs and eliminating estriol should achieve higher specificity for the same sensitivity and save, conservatively, about $900,000 in this series. Extrapolated nationally, if confirmed, the annual savings could approach $72,000,000.

Adolescent↗
PubMed1994

A gestational-age-independent model of birth weight based on placental size.

A placental weight (P) to birth weight (W) relationship, W = P1.5 x constant (A), was presented in 1966. However, based on histological and theoretical studies, placental efficiency increases proportionally to the square of the gestational age in weeks. The purpose of this study was to develop and validate a gestational-age-independent model of birth weight based on P2. Data were prospectively entered into a computerized database for liveborn, structurally normal neonates at a tertiary, urban center. 29,989 neonates had gestational ages based on menstrual dating, ultrasound and Ballard examination, 81.4% were African American. The 'best fit' of W = A x P1.5 had errors in predicting the mean birth weight by at least 10% from 24 to 33 weeks of gestation. In contrast, there was significant improvement (p < 0.05) when the model W = 0.0071 x P2 was used; errors of greater than 10% only occurred at 28 and 43 weeks of gestation. This model had similar accuracy when stratified according to gender or ethnicity. A gestational-age-independent model of mean birth weight can be based upon the square of placental weight. We hypothesize that this model may have utility in understanding disorders of intrauterine fetal growth.

Birth Weight↗
PubMed1991

Ultrasound measurement of the fetal head: computer versus operator.

In obstetrical ultrasound practice, biparietal diameter, occipito-frontal diameter and head circumference are among the most commonly used fetal measurements. To minimize the limitations associated with manual measurement, we have undertaken an investigation with a focus on (1) the design of a personal computer-based system for automated measurements of biparietal diameter, occipito-frontal diameter and head circumference, and (2) integration of such a system (including measurements of abdomen and femur) into the routine obstetrical ultrasound examination. This report presents preliminary results of a comparison of computer-determined fetal head measurements with those obtained by an operator. Data were obtained from 75 consecutive singleton fetal ultrasound examinations free of any obvious structural anomalies. The computer obtained acceptable measurements of biparietal diameter, occipito-frontal diameter and head circumference from 74 images and failed on one image. There was a highly significant correlation between computer-determined measurements of biparietal diameter (r = 0.986), occipito-frontal diameter (r = 0.958) and head circumference (r = 0.972) and those obtained by the operators. The mean measurement difference (computer minus operator) was 1.87 +/- 1.94 mm for biparietal diameter, 2.82 +/- 4.13 mm for occipito-frontal diameter and -0.36 +/- 9.87 mm for head circumference. These differences were independent of the operator's identity, the instrument used and gestational age. The key finding of this study is that, with the use of inexpensive personal computer technology, it is possible to design and implement a system that can give fetal head measurements which correlate highly with manual determination by a skilled operator and which take a fraction of the time.

Journal Article↗
PubMed1991

The mammary stimulation test--a predictor of preterm delivery?

Clinical risk identification for preterm delivery, the major cause of perinatal morbidity and mortality, remains problematic. To test the hypothesis that a provocative test for uterine contractility at the beginning of the third trimester would reliably identify patients destined to be delivered before and at term, we designed the mammary stimulation test. Uterine contractions in response to nipple stimulation at a mean of 28.6 weeks' gestation, were evaluated in 94 gravid patients at risk for preterm delivery. The mammary stimulation test, the results of which were not used for clinical management, was positive in 50% of patients tested and had a sensitivity of 84% and a positive predictive value of 34% (chi 2 = 11.15, p less than 0.01). Ninety-four percent of patients predicted to be delivered at term actually were delivered at term (negative predictive value). Furthermore, no patients with a negative mammary stimulation test were delivered within 1 month of testing or were delivered of infants weighing less than 2000 gm. Discriminant analysis indicated that the mammary stimulation test provided information beyond that available from clinical risk factors alone. A cost analysis suggested that the use of the mammary stimulation test could reduce the cost of ambulatory uterine activity monitoring by nearly 50%. If these findings can be validated in additional samples, the mammary stimulation test may be useful in prematurity prevention programs.

Discriminant Analysis↗
PubMed1991

Morphometry of the neonatal fetal alcohol syndrome face from 'snapshots'.

Recognition of alcohol-related birth defects is less successful in the neonate than in older children. Clarren et al. (1987) were able to describe the geometry of the FAS face at age 7. To define neonatal facial features of FAS, 3 reference points were used to map 7 frontal and 7 profile landmarks coded as standardized cartesian coordinates. These landmarks were digitized from snapshots of 21 neonates, prospectively diagnosed as FAS blinded for prenatal alcohol exposure, and 76 non-FAS controls. In the controls, race was found to be a significant determinant of landmarks, as expected. Using discriminant analysis and controlling for race, the FAS face was characterized by landmark measurements which correspond to short palpebral fissure, scooping out of the nasal bridge and thin vermilion [F(4,71)-7.8, r sq-30%, p < .01]. Jackknifed sensitivity was 75%, specificity, 79%. These findings suggest that FAS-defining features can be quantified in the neonate via computer-based screening of infants from at-risk pregnancies.

Alcoholism↗
PubMed1989

Survey of maternal-fetal medicine subspecialists: professional activities, job setting, and satisfaction.

We analyzed the job setting, professional activities, and satisfaction of subspecialists in maternal-fetal medicine. A two-page questionnaire was mailed to all members of the Society of Perinatal Obstetricians. The results were analyzed by multiple regression and multivariate analysis. Of 603 questionnaires mailed, 496 (80%) were returned; 70% of all certified maternal-fetal medicine subspecialists responded. The job setting of respondents was university hospital-based faculty in 66%, community hospital-based salaried in 15%, private practice in 10%, and other in 9%. The average percent of professional time devoted to each area was as follows: clinical work, 57% of all professional time; research, 18%; administrative, 15%; and educational, 11%. Time distribution, volume of hysterectomies, and number of peer-review publications were the only significant differences among job settings. For university hospital-based faculty, the time distribution was 50% clinical, 23% research, 16% administrative, and 11% educational. For community hospital-based salaried physicians, it was 63% clinical, 10% research, 16% administrative, and 11% educational; for private practice, it was 84% clinical, 7% research, 5% administrative, and 6% educational. Types of activities of maternal-fetal medicine subspecialists included ultrasound (75% of respondents, mean 436 studies per year), gynecologic procedures (71% of subspecialists, volume of 8.7 hysterectomies per year), genetic procedures (83%; 125 procedures per year), research (87%), recent peer-review publications (80%), grants (40%), and medicolegal reviews (64%). Ninety-five percent had a medical-school faculty appointment.(ABSTRACT TRUNCATED AT 250 WORDS)

Female↗
PubMed1988

A prototype system for perinatal knowledge engineering using an artificial intelligence tool.

Though several perinatal expert systems are extant, the use of artificial intelligence has, as yet, had minimal impact in medical computing. In this evaluation of the potential of AI techniques in the development of a computer based "Perinatal Consultant," a "top down" approach to the development of a perinatal knowledge base was taken, using as a source for such a knowledge base a 30-page manuscript of a chapter concerning high risk pregnancy. The UNIX utility "style" was used to parse sentences and obtain key words and phrases, both as part of a natural language interface and to identify key perinatal concepts. Compared with the "gold standard" of sentences containing key facts as chosen by the experts, a semiautomated method using a nonmedical speller to identify key words and phrases in context functioned with a sensitivity of 79%, i.e., approximately 8 in 10 key sentences were detected as the basis for PROLOG, rules and facts for the knowledge base. These encouraging results suggest that functional perinatal expert systems may well be expedited by using programming utilities in conjunction with AI tools and published literature.

Expert Systems↗
PubMed1988

From mainframe to micro: decentralization of perinatal epidemiology.

To evaluate the feasibility of analyzing large perinatal datasets on smaller computers, the 1980 National Natality Survey was downloaded first to a minicomputer and then to a microcomputer. Operating system utilities were used to minimize programming and storage requirements. Accuracy was confirmed by comparing descriptive statistics with published values derived on mainframes. Based on a typical analytic problem, implementation on the microcomputer compared favorably to implementation on the minicomputer. Our results suggest that the microcomputer may be a practical alternative to the mainframe for perinatal epidemiological analysis.

Computers↗
PubMed1988

Interobserver variability. A source of error in obstetric ultrasound.

Several sources of error encountered in obstetrical ultrasound examination have been analyzed from a computerized ultrasound database. The variability in measuring fetal landmarks and visualization of fetal structures were found to be significantly different among three registered sonographers who examined 1,410 consecutive second and third trimester patients. The rate of successful measurement of biparietal diameter (BPD) and average abdominal diameter (AAD), as well as successful visualization of fetal stomach and/or kidneys were statistically different among the three sonographers. Only the fetal femur length was consistently measured by all three sonographers. The bias in terms of actual millimeters measured was significantly different for both BPD and AAD. The bias related to the BPD was in the magnitude of 1 mm, while the bias related to the AAD was almost 3 mm. The clinical significance of these findings and the value of the computer to perform periodic checks to assure quality control in a busy ultrasound service are discussed.

Diagnostic Errors↗
PubMed1985

Maximizing the efficiency of a study on alcohol-related birth defects by means of data collection and analytic strategy dissociation.

Application of the terms "prospective" and "retrospective" to quasi/experimental research designs used in clinical investigations is often ambiguous; they often lack specification as to whether they apply to data acquisition, analytic strategy, or both. Data may be collected prospectively by preplanned protocol or retrospectively by chart review. In addition, the direction of analysis may be prospective--comparing differential outcomes for at-risk and not at-risk (exposed/not exposed) groups--or retrospective--comparing differential preceding risks for affected and nonaffected groups. Prospective data collection is advantageous in assuring the availability of crucial variables for an entire sample, but prospective analytic strategies may be inefficient, underestimating effect sizes, particularly when the outcome of interest is rare or the effect, even if large, is seen in only a small proportion of cases. In a prospective multilinear regression model of risks for lowered birthweight for gestational age, 2% of the variance was explained by alcohol variables after adjustment for confounding. In comparison, a similar multilinear regression of case-control sample, in which the frequency of the abnormal outcome is raised, showed 18% of the variance explained by alcohol variables. Data collection and analytic strategies may be dissociated. Although some statistical power may be lost because of reduced sample size, synthetic case-control analysis is efficient in examining small effects. It also has the advantage of decreasing the size of the database to be managed and the time required for analysis. Using this approach, it is feasible to perform virtually any analysis that can be done on a mainframe on medium-sized departmental computer system.

Birth Weight↗
PubMed1984

The association between cesarean birth and outcome in vertex presentation: relative importance of birth weight, Dubowitz scores, and delivery route.

The effect of the obstetrician's choice for delivery route on infant outcomes was studied in 17,260 mothers in labor, with the fetus alive at the onset of labor, in vertex presentation, and without major congenital anomalies. At birth weight categories, stratified by 500 gm increments, there was no improvement in intrapartum and neonatal mortality or in neonatal morbidity associated with the cesarean birth route. The major dependent variables important in neonatal outcome were birth weight and neonatal maturity. The association between cesarean section delivery and outcome in vertex presentations is limited. This information documents the need for prospective randomized and controlled studies with respect to proposed changes in birth route for the very low-birth weight fetus.

Apgar Score↗
PubMed1984

What affects fetal pulmonary maturation during diabetic pregnancy?

Previous studies differ as to whether the fetus of the woman with diabetes mellitus has altered formation of lung surfactant. The factors responsible for these differences remain unclear. In this study, measures of blood glucose control, including birth weight percentile and the presence of factors potentially influencing fetal pulmonary maturation, such as diabetic class, maternal chronic hypertension, and preeclampsia, were compared with the amniotic fluid lecithin/sphingomyelin ratio, phosphatidylglycerol, and phosphatidylinositol within a group of 90 diabetic pregnancies. The factors were evaluated in combination with the techniques of canonical correlation and multiple regression analysis. Gestational age had the strongest effect in determining levels of amniotic fluid phospholipids, and hypertension was found to significantly accelerate the appearance of phosphatidylgycerol (p less than 0.05). The effect of hypertension was one third as important as that of gestational age. Neither diabetic blood glucose control, White classification, nor the remaining explanatory variables were found to play a significant role in determining the amniotic fluid phospholipid levels. This study suggests that, in the clinical management of diabetes, gestational duration remains the single most important determinant of amniotic fluid phospholipid levels.

Amniotic Fluid↗
PubMed1984

The effect of delivery route on outcome in breech presentation.

This study was undertaken to determine the effect of choice of birth route on infant outcome in fetal breech presentation. The study group excluded infants who were footling breeches and infants with major congenital anomalies. The mothers were in labor with the fetal heartbeat present at entry into the labor room. Outcome variables were intrapartum and neonatal deaths and neonatal neurological morbidity. Delivery route was not significantly associated with neonatal death in the 500 to 999 gm (p = 0.43) and 1,000 to 2,499 gm (p = 0.43) categories. Over 2,500 gm, there were no neonatal deaths. In similar manner, delivery route was not significantly associated with neonatal neurological morbidity. In both neonatal death and morbidity, birth weight and modified Dubowitz score explained the largest proportion of the variance for outcome in breech presentation.

Breech Presentation↗