The NST-EXPERT project: the need to evolve

NST-EXPERT is a medical expert system designed to evaluate fetal condition (especially in 'high risk' pregnancies). The system reasons based on data from the Non-Stress Test (NST), a monitoring test widely used in obstetrics. From specific limited maternal-fetal context information together with the analysis of the NST results the system infers a diagnosis for each case, elaborates a therapeutic plan, and suggests a prognosis of an early neonatal outcome. This article describes a new version based on a previous research prototype. Such systems can aid clinicians of varied experience in assessing and managing complicated pregnancies.

Evaluation of current antepartum fetal tests

Three hundred high-risk pregnancies of at least 28 weeks' gestation were included in this prospective descriptive study. Fetal movement count was performed daily. Maternal perception of sound provoked fetal movement (MPSPFM), fetal acoustic stimulation test (FAST), amniotic fluid index (AFI) and doppler umbilical artery pulsatility index were tested weekly until delivery. All fetal testing performed within a week of delivery was compared with fetal outcome. Fetal outcome was considered poor when there was perinatal death, intrapartum fetal distress, a five minute Apgar score of less than 7, thick meconium-stained amniotic fluid or admission to the neonatal intensive care unit. Seventeen pregnancies were considered poor outcome (prevalence of 5.7%). Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and Kappa index (KI) of each test to predict poor fetal outcome were evaluated. A combination of FAST and AFI is the most reliable antepartum fetal test. The sensitivity, specificity, positive predictive value, negative predictive value, accuracy and Kappa index of the combination of FAST and AFI were 70.0%, 99.6% 87.5%, 98.8%, 98.5% and 0.77%, respectively.

Prenatal diagnosis in the 1990s

Prenatal diagnosis has become widely available and detects an increasing variety of birth defects and potentially harmful medical conditions. Many of the studies are complex and must be performed within a specific time period. Most prenatal diagnostic sampling techniques have some degree of risk for the mother or the fetus, and all produce at least transient anxiety. Nurses are involved in identifying families at risk, preparing women for the procedures, providing support, and counseling patients after the results are known; because of this role, nurses need updated information. This review describes current methods for early identification of a potential problem, discusses a variety of prenatal diagnostic procedures, reviews the most common types of laboratory studies, and introduces future trends in the field of prenatal diagnosis.

Prenatal diagnosis

The standards for the practice of nurse-midwifery declare competence in prenatal diagnosis as one of the core competencies for basic nurse-midwifery practice. Encompassing the most frequently encountered situations that involve prenatal diagnostic counselling, this article aims at providing insight to the practicing nurse-midwife into the risks and benefits of invasive prenatal diagnostic procedures and prenatal diagnostic testing, thereby enabling the midwife to counsel the woman and help her to choose an invasive procedure according to her individual needs.

Transabdominal thin-gauge embryofetoscopy: a technique for early prenatal diagnosis and its use in the diagnosis of a case of Meckel-Gruber syndrome

OBJECTIVE

Our aim was to develop and evaluate a transabdominal endoscopic technique to visualize the embryo or fetus with thin-gauge needles and submillimetric fiberoptic endoscopes.

METHODS

Under ultrasonographic guidance, an 18- or 19-gauge thin-wall needle was introduced into the uterus of 28 patients undergoing first-trimester or early second-trimester termination of pregnancy. A 0.7 mm endoscope was threaded through the lumen of the needle after removal of the stylet. Visualization of the embryo-fetus was attempted before 14 weeks' gestation (n = 20). From 16 to 20 weeks (n = 8), the needle and endoscope were directed to the placental insertion of the umbilical cord, and a cordocentesis was performed.

RESULTS

Excellent visualization of the surface anatomy of fetuses from 7 to 13 weeks was obtained in 85% of cases (17/20). A diagnosis of Meckel-Gruber syndrome was made at 11 weeks' menstrual age by visualizing postaxial polydactyly and an occipital encephalocele. Endoscopically assisted cordocentesis allowed visualization of the lumen of the umbilical vein and of the blood flow within it.

CONCLUSION

Endoscopic visualization of the embryo or fetus can be performed transabdominally in the first trimester with small-delivered endoscopes. This represents a clear advantage over previous endoscopic approaches to the human pregnancy. Potential applications of this technique include a precise description of fetal anatomy and physiologic features, diagnosis of anomalies, and therapeutic fetal interventions.

[Chorionic villus needle sampling by the transabdominal route or by placental centesis. A series of 930 cases]

The authors report on a series of 930 chorion villus sampling diagnoses made with a needle by the transabdominal route, from January 1991 to October 1992 at the Prenatal Diagnosis Center in Marseille. Indications for prenatal diagnosis were: raised maternal age in 75% of cases (N:698); ultrasound findings in 11% (N:106), chromosome abnormalities in the family in 6% cases (N:53), raised human chorionic gonadotrophin in 4% cases (N:38), parental rearrangement in 2% cases (N:20), and sex linked disease in 1% (N:15). The success rate was 97% with 29 failures; the number of needle insertions was one in 97% cases and two in 3% cases. The average gestational age at sampling was related to the indications; 16 weeks of amenorrhoea for raised maternal age, and 22 weeks of amenorrhoea for ultrasound findings. Thirty one abnormalities were observed, four balanced translocations, and seven placental mosaicisms. Forty eight pregnancies terminated in abortion. The rate of fetal loss was 3.5% (7 cases) for the 200 first cases and 1% (8 cases) for the 730 following cases. Choriocentesis through the transabdominal route provides a diagnosis within a few days and the rate of fetal loss is close to that of amniocentesis. These arguments are in favour of an extension of this method of sampling.

Rapid fetal lung maturity testing: commercial versus NBD-phosphatidylcholine assay

We compared the TDx Fetal Lung Maturity test and the fluorescence polarization method using 1-palmitoyl-2(6-[(7-nitro-2,1,3-benzoxadiazol-4- yl)amino]caproyl)phosphatidylcholine (NBD-phosphatidylcholine). Using 76 paired human amniotic fluid samples, the fluorescence polarization values of the two methods were found to have a strong nonlinear correlation (r2 = 0.946). Both assays can be completed in less than 1 hour, have excellent precision (between-day variation less than 2%), and indicate the amount of surfactant phospholipid relative to albumin. The FLM assay is calibrated with surfactant/albumin standards; therefore, the reported results (in mg/g) correlate inversely with polarization of NBD-phosphatidylcholine. Strong correlations were seen for both assays with the lecithin-sphingomyelin ratio and phosphatidylglycerol. The correlations indicate that the recommended reference range for FLM will have more false predictions of immaturity than the NBD-phosphatidylcholine assay.

[The use of acoustic stimuli for assessing fetal status ante- and intranatally]

Modified acoustic fetal stimulation test was used in 311 pregnant and parturient women. The technique of acoustic stimulation at the end of pregnancy and at the beginning of labor is described. Specific features of fetal cardiac activity in response to stimuli in health and intrauterine suffering were detected. The modification of acoustic stimulation of the fetus was found to be an informative method of functional diagnosis in clinical perinatology. The test permits obtaining supplementary information on the fetal status and helps detect chronic intrauterine hypoxia at the early stages of its development.

[Color-coded M-mode Doppler echocardiography in the diagnosis of fetal arrhythmia]

Colour-coded M-mode Doppler echocardiography is a simultaneous registration of the conventional M-mode echocardiogram and of the pulsed wave colour-coded Doppler echocardiogram with simultaneous analysis of several sample volumes along the ultrasound cursor with a high timely resolution, guided by the two-dimensional imaging. Within 9 months, 36 foetuses with arrhythmias were prospectively examined (24 foetuses with atrial premature beats, 9 foetuses with supraventricular tachycardia, and 3 foetuses with complete heart block). The classification of arrhythmia by the colour-coded M-mode Doppler echocardiography was always possible at first examination. The most important advantage of this method is the simultaneous registration of the information of conventional M-mode and Doppler echocardiography. Therefore, the intervals between atrial and ventricular contractions can also be analysed even when the angle of insonation to the foetal heart is unfavourable, since contractions cannot only be identified by wall movements but also by the flow velocities. Furthermore, the duration of regurgitation of atrioventricular valves can be exactly measured by colour-coded M-mode Doppler echocardiography. In foetal supraventricular tachycardia, it appears that severity of congestive heart failure is correlated with the duration of atrioventricular valve regurgitation up to a holosystolic insufficiency. Thus, it seems possible, that the duration of insufficiency of atrioventricular valves is a good parameter for evaluation of cardiac function and for modifying antiarrhythmic treatment in cases of supraventricular tachycardia.

[Endosonography in early pregnancy]

Vaginal sonography has brought tremendous advantages in the diagnosis of early pregnancy both for the patient and the physician. In the first place it is easier to perform than abdominal sonography, since a filled bladder is not a prerequisite for the examination. Secondly, the intrauterine location of the pregnancy can be diagnosed as early as the 37th day of gestation. Thirdly, diagnosis of a disturbed intrauterine or an extrauterine pregnancy is possible earlier than with the abdominal approach. Vaginal sonography thus frequently reduces the period of anxious waiting for the patient and, where necessary, enables the physician to operate early with the least possible traumatization.

[A newly developed instrument of microbubble test for evaluation of fetal lung maturity]

A new instrument for Pattle's microbubble test was devised in order to improve the diagnosis of fetal lung maturity. This instrument consists of 4 needles fixed at 8mm intervals and an air pump. Microbubbles were produced in 175 microliter of amniotic fluid placed on a slide glass by injecting 10 ml of air at 400 ml/h with an air pump through 22 gage needles. After 4 minutes, the number of stable microbubbles less than 15 um in diameter were counted in 5 microscope fields. When over 6 microbubbles were observed, fetal lung maturity was diagnosed as positive. 72 samples of amniotic fluids were tested by our method as well as the other 5 methods. The percentage of accurate diagnostic results was 97.2% with our method, 93.1% with the L/S ratio, 83.3% with the DSPC method, 86.1% with the PG method, 93.1% with the shake method, and 94.4% with the Pattle's original method. It is concluded that ours is a reliable, rapid and simple method for evaluating fetal lung maturity.

[Sampling of the chorionic villi: transcervical fine-needle and endoscopic aspiration]

In 63 cases chorionic villi sampling has been performed under complete anesthesia just before legal abortion; nine of them were endoscopic transcervical and 54 transcervical by means of a catheter under direct ultrasonic control. 81% offered useful chorionic villi, 17.4% only decidual material. The last 21 aspirations by means of a catheter between the 8th and the 12th week of gestation (p.m.) caused no problem at all. From the first punction on useful chorionic material has been obtained.

A sonographic screening method for Down syndrome

We describe a potential screening method for the second trimester detection of the fetus with Down syndrome by the use of standard sonographic biometry. Retrospective assessment of the biparietal diameter, femur length, and biparietal diameter/femur length ratio in 55 fetuses with Down syndrome and 544 control fetuses was performed at two medical centers. Adequate numbers of cases and controls were available to permit statistically significant comparisons between the groups at 15 to 23 weeks' gestation. Fetuses with Down syndrome displayed no statistically significant differences in the cephalic index or the biparietal diameter compared with controls at a given gestational age. Significant femur length shortening was observed, but the greatest statistical difference was noted for the biparietal diameter/femur length ratio. This ratio was found to decrease with gestational age in the normal population and was consistently elevated in the Down syndrome population (compared with control) throughout the second trimester. With a cutoff value of 1.5 SD above the normal population mean for the biparietal diameter/femur length ratio, 50% to 70% of fetuses with Down syndrome could be identified in 6% of the total population (p less than 0.0001). This preliminary study suggests that the biparietal diameter/femur length ratio may prove superior to current Down syndrome screening methods and, as a third independent variable, may significantly enhance the sensitivity and specificity of combined maternal age/maternal serum alpha-fetoprotein screening modalities.

Clinical performance of a system for semiautomated chromosome analysis

Until recently equipment for automated chromosome analysis has not been used for routine purposes in clinical cytogenetic laboratories. During a 3 1/2-year period the chromosome laboratory of Rigshospitalet has tested the Magiscan chromosome system under routine conditions and performed the first evaluation of its clinical performance. The system consists of an image processor with a light pen for manual interaction connected to a hard-copy printer and a microscope with a TV camera and a motorized scanning stage for eight slides. Automated metaphase finding takes place without operator assistance. An operator is involved in the analysis after the metaphases are located. Using two of these complete systems, we have performed a total of 4,691 chromosome analyses comprising a count of 10 metaphases, of which three were "eyeball" karyotyped and one was "machine" karyotyped. Presently, two-thirds of our prenatal analyses (amniotic-cell cultures) are carried out with these two machines. A third Magiscan system without scanning stage is used as a "karyotyping-only" system to produce hard-copy karyograms in those cases in which metaphases are manually located and counted in the microscope. Since the end of 1984, 4,773 additional machine karyograms have been produced with this system. With a complete system, a prenatal analysis can be carried out in an average of 35 min. The average time for a machine karyotype is 7 min. Since 1984 the productivity of the laboratory has increased 17%-20% without enlarging the staff.

[Computer-assisted documentation and recording of findings of obstetrical ultrasound findings]

Since 1976 on our department obstetrical reports are generated and stored by computer. This kind of documentation has been also introduced for obstetrical ultrasound investigations. One year ago the part of our database for storing and recording the results of obstetrical ultrasound examinations was changed according to new purposes. This system was designed to support diagnosis of pathological findings and to arrange the results more clearly. Immediately after the investigation the results are entered in a terminal (3278 IBM). Our database is a CICS (Customer Information Computer System) application of the WAMIS (Wiener Allgemeines Medizinisches Informationssystem) from the IMC (Institut für Medizinische Computerdokumentation). The results of the investigation are printed after storage in the data base. The screen and the obtained print-out are divided into several sections according to medical purposes. Since the results of fetal measurement are displayed graphically, fetal growth and the change of normal or abnormal findings can be judged immediately. The new layout of the hardcopy of the results of our ultrasound investigations improves diagnosis of pathological findings. Each examinator is forced to visualize fetal organs, signs of fetal vitality and to perform standardized measurement. Therefore, the possibility to find pathological alteration is improved especially if the investigator is less experienced.

[Control of early pregnancies by vaginal sonography]

151 patients with suspected early pregnancies between 5 to 10 weeks were examined by transvaginal section scanning. Pregnancies could be verified as early as 16 days after conception while the first heart beat actions were seen after 21 to 22 days. In early pregnancies where heart actions could not be shown at first examination a second look was taken after the 6. week dated from conception. beta-HCG-units were found in a range of 59 to 55,000 mU/ml. 3 pregnancies in the 5th, 6th, respectively 7th week escaped our detection by the first examination. In 44 cases screened after the 6th week we did not prove heart actions. In all of these patients controlled measurements showed either values below or borderline low compared to normal scales.

[Actocardiograph--an instrument for the diagnosis of fetal behavioral stages?]

The investigation of fetal behaviour are an important clinical tool for assessing fetal well-being. However, they are time-consuming and at least 2 real-time scanners must be employed. The aim of this study was to find out if fetal behavioural states can be diagnosed by using only the "actocardiograph". Thus we compared tracings of the actocardiograph with simultaneously registered tracings from "polygraphic monitorings" including real-time observations of fetal eye, breathing and body movements. We could demonstrate that state 1F and 4F can be recognised in 93% resp. 82%. Periods without a definite state cannot be diagnosed from actocardiographic tracings. This suggested that the combined recording of fetal movements and fetal heart rate with the actocardiograph might be useful for the registration of fetal movements and for the overall diagnosis of fetal behavioural states. However polygraphic monitorings including real-time observations give the only precise picture of neuromotoric coordination.