[New perspectives in intrauterine surveillance with the fetal magnetoencephalogram]

PURPOSE

Despite intensive research and surveillance up to now one has failed to reduce cerebral handicaps in newborn. Fetal heart rate tracing (CTG) and Doppler have reduced the number of subpartal severe asphyxia and fetal death. But, 90% of cerebral damage is a result of antepartal problems. Thus only 10% can be avoided by intensive surveillance during labor. Detection of antenatal cerebral injury is a rare case and its impact on later fetal life can only be estimated. Insight in fetal neuronal function is not possible. Factors and time pattern determining fetal cerebral injury are thus not known. This publication explains a new system with whom one might be able to get more insight in cerebral wellbeing during the fetal intrauterine life.

METHODS AND RESULTS

A new diagnostic approach is set up by recording fetal magnet encephalographic signals (fMEG) thus offering the opportunity to detect fetal brain function. An array which was especially designed to fit to the pregnant body consists of 151 sensors which are able to record the fMEG. Clinical testing is performed in the moment at the UAMS in Little Rock, Arkansas in Cooperation with the Institutes for Medical Psychology and the Frauenklinik in Tiibingen. First results and arising questions are published.

CONCLUSION

With this new system a deeper insight into the fetal neuronal development and fetal wellbeing during pregnancy might be achieved thus reforming the fetal surveillance in the 21st century.

3-dimensional colour power angiography for staging human placental development

Maldevelopment of placental villous trees and their blood vessels results in impaired fetal growth, which can greatly compromise fetal, neonatal, childhood, and adulthood health. There are no means of directly assessing such maldevelopment. We have applied a new technique of imaging (colour power angiography [CPA]) with 3-dimensional reconstruction to assess directly villous development in human pregnancy in vivo in 20 uncomplicated pregnancies from 13 to 38 weeks' gestation. The chronology of villous trees was much the same in 3-dimensional CPA, scanning electron micrography, and classical histology from controls matched by age. This approach provides a unique opportunity to examine normal placental development directly, and should provide the bases for real-time investigation of placental pathology and a robust method for diagnosis and surveillance during pregnancy.

Perinatal significance of diagnosing glucose intolerance during pregnancy with portable glucose meter

OBJECTIVE

To evaluate the effect on perinatal outcome of replacing glucose measurements for the diagnosis of gestational diabetes mellitus in central laboratories with those obtained by portable glucose meter.

STUDY DESIGN

Simultaneously, venous blood samples were taken at the 100-g glucose tolerance test, and finger capillary blood glucose levels were also measured with a portable glucose meter in 180 pregnant patients. Patient management was according to the venous plasma glucose results. Following deliveries, the women were reallocated to diagnostic groups by both methods of measurements and by using the same cutoff values, and the outcome data were compared.

RESULTS

By using glucose values obtained by portable glucose meters instead of the results attained in the central laboratory, more women were diagnosed with gestational diabetes (33 vs 25) and the perinatal outcome was comparable.

CONCLUSIONS

Obstetricians have to identify glucose intolerance during pregnancy in order to prevent macrosomia and its perinatal complications. These goals can be achieved with at least the same efficacy by performing the 100-g glucose tolerance test with a portable glucose meter as with current laboratory methods. Such an approach is time and resource saving and more convenient for both patients and health providers.

Noninvasive antepartum recording of fetal S-T segment with a newly developed 151-channel magnetic sensor system

OBJECTIVE

The objective of this study was to evaluate the efficiency of the detection of the S-T segment in the fetal PQRST complex that is recorded in the antepartum period with the use of a newly developed noninvasive 151-channel magnetic sensor array.

STUDY DESIGN

One hundred two fetal magnetocardiographic recordings were performed on normal fetuses with gestational ages that ranged from 27.5 to 39.5 weeks. After the removal of the interfering maternal heart signals, the fetal heart data were inspected to detect the presence of P, QRS, and T segments.

RESULTS

The QRS complex was detectable in 100%, the P wave was detectable in 95.1%, and the T wave was detectable in 87.3% of the recordings.

CONCLUSION

Fetal magnetocardiography was recorded successfully, the QRS complex was observed in all subjects, and the T detection rate increased, with the gestational age reaching a peak of 97%. Further study of the S-T segment through the antepartum period could lead to advances in the detection of fetal jeopardy before labor.

Magnetocardiographic rhythm patterns at initiation and termination of fetal supraventricular tachycardia

BACKGROUND

Using fetal magnetocardiography (fMCG), we characterize for the first time the electrophysiological patterns of initiation and termination of reentrant fetal supraventricular tachycardia (SVT), the most common form of life-threatening fetal arrhythmia.

METHODS AND RESULTS

In contrast to the expectation that reentrant SVT is initiated by spontaneous premature atrial contractions (PACs) and is terminated by spontaneous block, 5 distinct patterns of initiation and 4 patterns of termination were documented, with the most common patterns of initiation involving reentrant PACs. Waveform morphology and timing, including QRS and ventriculoatrial interval, were assessed. This enabled detection of such phenomena as Wolff-Parkinson-White syndrome, QRS aberrancy, and multiple reentrant pathways that were crucial for defining the rhythm patterns. In addition, fMCG actocardiography revealed an unexpectedly strong association between fetal trunk movement and the initiation and termination of SVT, suggesting that autonomic influences play a key role.

CONCLUSIONS

This study demonstrates that the patterns of initiation and termination of fetal SVT are more diverse than is generally believed and that the most common patterns of initiation involve reentrant PACs. The ability to discern such patterns can help elucidate the underlying mechanisms and guide antiarrhythmic drug therapy. fMCG provides a noninvasive means of analyzing complex tachyarrhythmia in utero, with efficacy approaching that of postnatal electrocardiographic rhythm monitoring.

Developments in laboratory techniques for prenatal diagnosis

Ongoing trends in prenatal diagnosis aim at early, rapid, and ideally noninvasive diagnosis as well as at the improvement of risk-screening for aneuploidy. Interphase-fluorescence in situ hybridization and quantitative fluorescence polymerase chain reaction are efficient tools for the rapid exclusion of selected aneuploidies in addition to the established direct preparation of chromosomes from chorionic villi. Interphase fluorescence in situ hybridization has also made possible the diagnosis of selected chromosome abnormalities in single cells (e.g. in preimplantation genetic diagnosis) or noninvasive diagnosis. More complex multicolor fluorescence in situ hybridization approaches are currently being evaluated. Single cell polymerase chain reaction is the key technique for the molecular diagnosis of a growing number of monogenic conditions before implantation or, still more experimental, in fetal cells retrieved from the maternal circulation. New sources for noninvasive diagnosis came into play such as fetal DNA or cell nuclei in maternal plasma. The combination of biochemical parameters in the maternal serum, namely free beta-human chorionic gonadotropin with pregnancy associated plasma protein A and sonographic markers, has already dramatically increased the sensitivity of risk screening in the first trimester of pregnancy.

Teaching ultrasound-guided invasive procedures in fetal medicine: learning curves with and without an electronic guidance system

OBJECTIVE

To compare the learning curves of inexperienced junior obstetrics/gynecology registrars for ultrasound-guided invasive procedures on a training model, with and without an electronic guidance system.

STUDY DESIGN

Four junior registrars performed their first 100 procedures on a training model with a new electronic guidance system, and four other junior registrars performed their first 100 procedures on the same training model without using the guidance system. All procedures were performed using a free-hand technique. We evaluated the quality of the procedure, which we defined as the time spent with the entire needle clearly visualized on the screen over the total duration of the procedure. We constructed learning curves for the eight junior registrars for comparative analysis.

RESULTS

Quality of the procedure increased over time for all trainees. The learning curves were significantly steeper for trainees using the electronic guidance system. Trainees using the electronic guidance system performed better in the middle of their learning curve (procedures 25-75). All trainees reached the same level of quality by the end of their 100 procedures.

CONCLUSIONS

The automated electronic guidance system helps faster learning but, after 100 procedures on a training model, both groups reached the same level of quality.

Prenatal diagnosis of QT prolongation by fetal magnetocardiogram--use of QRS and T-wave current-arrow maps

To determine the T wave of a fetal magnetocardiogram (FMCG), we have evaluated the T/QRS ratio and obtained current-arrow maps that indicate weak currents. We measured FMCG signals for 52 normal fetuses and two abnormal fetuses with prolonged QT waves by using three superconducting quantum interference device (SQUID) systems: a nine-channel system, a 12-channel vector system and a 64-channel system. The T/QRS ratio was calculated for all the normal fetuses from the maximum magnitudes of the QRS complex and the T wave. Current-arrow maps of the QRS complex (R wave) and T wave were obtained by using the 64-channel system, and the phase differences of the total-current vectors were calculated by using the current-arrow maps. The results showed that the T/QRS ratio had a wide variability of 0.35 for the normal fetuses. However, the magnitude of the prolonged T wave was as weak as the detection limit of the SQUID magnetometer. Although the T/QRS ratios for the fetuses with QT prolongation were within the normal range (< 0.35), the weak magnitude of the prolonged T wave could be evaluated. On the other hand, by comparing the current-arrow maps of the R and T waves for the normal fetuses, we found that the maximum-current arrows were indicated as either in the same direction or in opposite directions. These patterns could be identified clearly by the phase differences. Very weak prolonged T waves for the two abnormal fetuses could be determined by using these current-arrow maps and phase differences. Consequently, although the T/QRS ratios of FMCG signals have a wide distribution, we have concluded that the current-arrow map and phase difference can be used to determine the T wave of an FMCG signal.

Challenges of recording human fetal auditory-evoked response using magnetoencephalography

OBJECTIVE

Our goals were to successfully perform fetal auditory-evoked responses using the magnetoencephalography technique, understand its problems and limitations, and propose instrument design modifications to improve the signal quality and success rate.

METHODS

Fetal auditory-evoked responses were recorded from four fetuses with gestational ages ranging from 33-40+ weeks. The signals were recorded using a gantry-based superconducting quantum interference device. Auditory stimulus was 1 kHz tone burst. The evoked signals were digitized and averaged over an 800 ms window.

RESULTS

After several trials of positioning and repositioning the subjects, we were able to record auditory-evoked responses in three out of the four fetuses. Since the superconducting quantum interference device array design was not shaped to fit over the mother's abdomen, we experienced difficulty in positioning the sensors over the fetal head.

CONCLUSIONS

Based on this pilot study, we propose instrument design that may improve signal quality and success rate of the fetal magnetic auditory-evoked response.

Nurse versus machine: slaves or masters of technology?

As the millennium approaches nurses are challenged to reflect on the evolving role of technology on the profession. A preview of the technologies coming to the clinical arena in the not-so-distant future is provided. Eight guidelines for wise technology integration are offered to assist providers in appropriately using technology while preserving humanity in an increasingly high-technology world.

[Study and application on the device of the drop volume of amniotic fluid in estimating fetal lung maturity]

A novel device of drop volume of amniotic fluid has been made to estimate fetal lung maturity. The design of the device is based on the principle that the surface tension of amniotic fluid is inversely proportional to the quantity of surfactant in the solution. The device measures the falling time of fluid drops from drop-tube and estimates the fetal lung maturity by using the method of comparison and electric-optic timing-counting. 148 samples of amniotic fluid were measured by the device and the data were compared with those obtained by biochemical method. The results demonstrate that this device has high stability and accuracy, and the rate of agreement between the two methods is as high as 93%.

In utero fetal muscle biopsy: a precious aid for the prenatal diagnosis of Duchenne muscular dystrophy

Prenatal diagnosis for Duchenne muscular dystrophy can usually be performed using DNA analysis. This approach would be impossible when there is only one prior affected male and no identifiable gene deletion. Therefore, in utero fetal thigh muscle biopsy with direct examination of muscle by dystrophin analysis may provide the only means of prenatal diagnosis. We report such a case in which fetal muscle biopsy was able to exclude Duchenne muscular dystrophy. A detailed literature review of the topic is provided.

Evaluation of the Abbott system in maternal serum screening for Down syndrome: the AxSym analyzer, AFP and hCG reagents and Maciel Prenatal Interpretive Software

Multi-marker maternal serum screening for Down syndrome in the second trimester is now part of routine care in many centers. Most protocols use a combination of hCG (or its free beta-subunit) and alpha-fetoprotein (AFP) or unconjugated estriol (UE3), or both. Risk calculation is based on these maternal serum marker values combined with maternal age and trisomy 21 maternal age-related risk. Computer programs are therefore necessary. Both technical and statistical efficiency are included in the final risk evaluation. We studied the Abbott system, comprising AxSym analyzer, AFP and hCG kits and Prenatal Interpretive Software (Maciel). Median values were established between 14 and 18 weeks of amenorrhea in a population of 1822 patients and in twin pregnancies in 157 cases. Forty maternal sera from trisomy 21 affected pregnancies were analyzed. Software was evaluated in a population of 429 patients and in 124 cases of trisomy 21. We conclude that this system constitutes an accurate and efficient method of maternal serum screening for Down syndrome.

In vivo perfusion measurements in the human placenta using echo planar imaging at 0.5 T

This paper presents the first in vivo measurements of perfusion in the human placenta from 20 weeks gestational age until term, using the non-selective/selective inversion recovery echo-planar imaging sequence, in which data is alternately acquired following a selective and non-selective inversion pulse. Twenty pairs of images were collected, two each at the following inversion times: 20, 310, 610, 910, 1110, 1410, 1910, 2810, 3310, and 4510 ms with the sequence being repeated with a repetition time (TR) of 10 s. The results of these measurements were used to suggest the optimum sequence for future work in terms of the signal to noise ratio in the measured perfusion rate in a given measurement time. The sequence was also analyzed to determine the expected variability in the measurements. In normal pregnancies the average value of perfusion rate was found to be 176 (standard error = +/-24) ml/100 mg/min. (n = 16, standard deviation = 96 ml/100 mg/min). The expected variability in the measured parameters due to signal to noise ratio considerations alone was calculated to be 71%. For a maximum scanning time of 400 s, the optimum sequence for measuring placental perfusion was found to require 8 repetitions at each of 10 inversion times which were geometrically spaced (given by a(o), a(o)r, a(o)r2, a(o)r3, . . .), with a(o) = 850 ms, r = 1.073 and TR = 5 s, giving a pixel variability of 38%. Other timing schemes are recommended for measuring perfusion in other anatomical regions with different values of perfusion rate and longitudinal relaxation time.

Doppler velocimetry in the umbilical and middle cerebral arteries in fetuses with intrauterine growth retardation or fetal distress

To clarify the usefulness of Doppler velocimetry in high-risk fetuses, i.e. with intrauterine growth retardation (IUGR) or with fetal distress, nomograms of the age-related changes in resistance and pulsatility indices in the fetal umbilical and middle cerebral arteries were made, and the best cut-off values for each parameter were determined. Included were 505 and 684 fetuses as the control and subject groups, respectively, between 22 and 41 weeks' gestation. Using the color-coded pulsed Doppler method, the resistance index in the umbilical and middle cerebral artery (RIUA, RIMCA), the pulsatility index in both these arteries (PIUA, PIMCA), and the RI and PI ratios between these arteries (RIUA/MCA, PIUA/MCA) were measured. In normal fetuses, RIUA and PIUA showed a gradual decrease with advance in gestational age. RIMCA and PIMCA showed a parabolic fashion with a peak around 30-31 weeks' gestation. RIUA/MCA and PIUA/MCA ratios decreased until 30-31 weeks' gestation and then increased to term. Analyses with receiver-operating-characteristic (ROC) curves revealed that PIUA is the most appropriate parameter in identifying IUGR under the cut-off point of 1.5 S.D., with a sensitivity, specificity, positive and negative predictive value, and accuracy of 60.6%, 93.3%, 75.2%, 87.6%, and 85.0%, respectively. As for fetal distress, the PIUA/MCA ratio was the most efficacious parameter under the cut-off point of 2.0 S.D., with a sensitivity, specificity, positive and negative predictive value, and accuracy of 67.3%, 97.4%, 72.9%, 96.7% and 94.6%, respectively. The findings obtained indicate that the measurement of PI value in the umbilical artery is enough to detect IUGR per se, probably due to the reflection of the decrease in the placental vascular bed, and that the ratio of indices between the umbilical artery and middle cerebral artery is more accurate than independent evaluations in identifying fetuses developing fetal distress, reflecting a brain sparing effect as well as fetoplacental insufficiency.

Fetal and fetal brain volume estimation in the third trimester of human pregnancy using gradient echo MR imaging

The Cavalieri method has been applied in combination with gradient echo magnetic resonance imaging (MRI) to investigate the increase in the volume of the fetus and fetal brain in the third trimester of pregnancy. Eighteen women with singleton pregnancies were recruited. Birthweights for the fetuses all lay within the 10-90th centile based on Liverpool data. A regression analysis, weighted using values derived from the coefficient of error predicted for each volume estimate, revealed a linear relationship between total fetal volume and gestational age (R2 = 0.88) and between fetal brain volume and gestational age (R2 = 0.71) during the third trimester. Fetal volume increased by an average of 25.2 ml per day and fetal brain volume increased by an average of 2.3 mL per day. Fetal brain volume is on average a constant proportion (10%, SD = 2%) of total fetal volume throughout the third trimester. Volume data were also obtained for eight fetuses diagnosed as abnormal. The volume of seven of the eight abnormal fetuses fell outside the 95% confidence interval established from the data obtained for the normal fetuses. However, for only three of the eight abnormal fetuses did brain volume fall outside the 95% confidence interval established for normals, possibly due to brain sparing occurring in asymmetrical growth retardation. The volume of the fetus and fetal brain may be readily estimated directly using the Cavalieri method and magnetic resonance imaging. These parameters represent potentially useful information for assessing fetal growth.

In vivo relaxation time measurements in the human placenta using echo planar imaging at 0.5 T

This paper presents the first in vivo measurements of the nuclear magnetic resonance relaxation times T1 and T2 at 0.5 T in the human placenta from 20 weeks gestational age until term, in both normal and compromised pregnancies. T1 measurements were performed by using both an inversion recovery sequence and the Look-Locher echo planar imaging (EPI) sequence on a total of 41 women with normal pregnancies and 11 women with compromised pregnancies. T2 measurements were performed by using a spin-echo EPI sequence on 36 women with normal pregnancies and 14 women with compromised pregnancies. In normal pregnancies, both the T1 values measured with the inversion recovery sequence and the T2 values were found to decrease with gestational age, the linear regression results gave T1 = -9.1t + 1538 r2 = 0.23 p = 0.03. T2 = -4.0t + 338 r2=0.47 p =410(-6) where t is the gestational age in weeks, and T1 and T2 are the relaxation times in milliseconds. T1 values measured very rapidly with the Look-Locher EPI sequence, but, therefore, with a much lower signal-to-noise ratio, showed no significant trends. The T1 values measured in the abnormal group were significantly lower than those measured in the normal group. Four out of eight patients with compromised pregnancies had placental T1 values lying outside the 90% confidence limits for the normal population based about the regression line, significantly more than expected by chance (p = 0.005). Ten out of fourteen of the T2 measurements in the abnormal group were below the regression line established for the normal group, with 4 lying below the 90% confidence interval, although these trends were only just significant (p = 0.06 and p = 0.03).

Is a speculum examination sufficient for excluding the diagnosis of ruptured fetal membranes?

OBJECTIVE

To determine the false negative rate of a sterile speculum examination for the diagnosis of rupture of the membranes in women not in labor and without visible amniotic fluid at speculum examination. Furthermore, possible risks to the mother and the baby after suspected rupture of the membranes were analyzed.

STUDY DESIGN

In women not in labor with suspected rupture of the membranes between gestational weeks 34 and 42, a sterile speculum examination was performed. If no amniotic fluid was visible, a test for Diamine oxidase was carried out. The results of tests were not known to the obstetricians or the women. The women were allowed to return home with no further controls if no amniotic fluid was visible at the speculum examination. Neonatal and obstetric outcome was recorded prospectively.

RESULTS

Of 27,502 deliveries, 2,099 women not in labor attended the delivery ward for suspected rupture of the membranes after week 34. Amniotic fluid was visualized in 1,580 women. In 519 women in whom no amniotic fluid was seen at the speculum examination, the Diamine oxidase test was negative in 456 and positive in 63. Antibiotics were given to eleven children (2.4%) in the group with a negative Diamine oxidase and to one infant (1.6%) in the positive Diamine oxidase group (p>0.05). No differences in obstetric outcome were recorded.

CONCLUSIONS

The false negative rate of a speculum examination for the diagnosis of rupture of the membranes in women without amniotic fluid visible at a speculum examination was 12% when Diamine oxidase was used as the standard for the diagnosis of rupture of the membranes. This study did not show any disadvantages for mothers and infants if the women were sent home after a false negative speculum examination. The value of biochemical methods in the management of women not in labor with rupture of the membranes after thirty-four weeks of gestation could be questioned.

[Adnexal torsion with hemorrhagic infarct in early pregnancy. Diagnosis by color-coded vaginal Doppler sonography]

A 25 year-old woman presented with left lower quadrant pain in the 11th week of gestation. Transvaginal sonography showed a 7 x 8 x 5 cm cystic-solid mass with an adjacent 9 mm echogenic structure on the left side corresponding to the adnexal stalk. Color Doppler sonography revealed the absence of central or peripheral flow within the mass suggestive of adnexal torsion and subsequent infarction. Laparoscopic detorsion of the left adnexa was not followed by restoration of perfusion ad a left adnexectomy was performed. Transvaginal color Doppler sonography is useful for preoperative diagnosis of adnexal torsion.

Transabdominal fetoscopy in fetal anomalies diagnosed by ultrasound in the first trimester of pregnancy

The ability of ultrasound to diagnose fetal anomalies is limited in the early stages of gestation. We describe a microendoscope that can be used with an 18-gauge needle at the time of amniocentesis to provide more precise diagnostic information when the first-trimester ultrasound examination suggests a problem.

[Magnetic resonance imaging of the fetus. Contribution to antenatal diagnosis]

Magnetic resonance imaging (MRI) of the fetus has been developed over the last 10 to 15 years. This new imaging technique cannot remplace ultrasonography which remains the key examination for antenatal diagnosis but can add further improvements over ultrasonographic findings, particularly in evaluating the fetal brain. MRI of the fetus has thus been focused in this area, the main studies aiming at analyzing brain malformations and at searching for ischemic or hemorrhagic lesions and possible gyration anomalies. Advances in data processing software and volume acquisition and the development of the echo-planar technique and T2-weighted sequences are currently under study. MRI of the fetus has thus progressed rapidly. It is however a long costly examination which may not be well tolerated by pregnant women. Currently, routine MRI of the fetus is not possible, because of the requirement for specialized facilities. This new technique, still in the evaluation phase, should be studied using strict protocols reserved for centers specialized in antenatal diagnosis.

An expert diagnostic system based on neural networks and image analysis techniques in the field of automated cytogenetics

In this study, we introduce an expert system for intelligent chromosome recognition and classification based on artificial neural networks (ANN) and features obtained by automated image analysis techniques. A microscope equipped with a CCTV camera, integrated with an IBM-PC compatible computer environment including a frame grabber, is used for image data acquisition. Features of the chromosomes are obtained directly from the digital chromosome images. Two new algorithms for automated object detection and object skeletonizing constitute the basis of the feature extraction phase which constructs the components of the input vector to the ANN part of the system. This first version of our intelligent diagnostic system uses a trained unsupervised neural network structure and an original rule-based classification algorithm to find a karyotyped form of randomly distributed chromosomes over a complete metaphase. We investigate the effects of network parameters on the classification performance and discuss the adaptability and flexibility of the neural system in order to reach a structure giving an output including information about both structural and numerical abnormalities. Moreover, the classification performances of neural and rule-based system are compared for each class of chromosome.

Single uterine entry for genetic amniocentesis in twin pregnancies

In 176 diamniotic twin pregnancies at 10-20 weeks of gestation, amniotic fluid for cytogenetic studies was successfully obtained from both sacs by the use of a single uterine entry. There were no cases of discordancy between sex at amniocentesis and birth. There were six pregnancies with fetal unbalanced chromosomal defects; in one pregnancy both fetuses were abnormal and in five pregnancies only one fetus was abnormal. The total fetal loss rate was 5.7% (20 of 352 fetuses), including six (1.7%) terminations or selective fetocides and 14 (4.0%) spontaneous deaths. In the 176 pregnancies there were five (2.8%) with no survivors, including one termination and four (2.3%) spontaneous miscarriages or intrauterine deaths. There are only two (1.1%) pregnancies in which amniocentesis could have contributed directly to the losses and therefore the procedure-related rate of fetal loss may be similar to that in singleton pregnancies. The median gestation at delivery was 37 (range 16-40) weeks and delivery before 32 weeks occurred in 9% of the pregnancies. The birth weight distribution was similar to that reported in singleton pregnancies. This study demonstrates that in twin pregnancies amniotic fluid for cytogenetic studies can be obtained successfully from both sacs by use of a single uterine entry. The risk of fetal loss from this procedure appears to be similar to that in singleton pregnancies.