Surveillance of twin pregnancy with umbilical arterial velocimetry

Estimated combined cardiac output and laser therapy for twin-twin transfusion syndrome

INTRODUCTION

Twin-twin transfusion syndrome (TTTS) is the major cause for fetal demise in monochorionic diamniotic pregnancies. Estimated combined cardiac output (CCO) has not been studied in this setting. The primary aims of this study were to compare CCO in twin donor and recipient fetuses and assess differences in CCO before and after laser coagulation therapy. A secondary aim was to evaluate the relationship of CCO with perinatal mortality, defined as intrauterine or neonatal mortality (≤30 days of age) in fetuses that underwent laser coagulation therapy.

METHODS

We performed a retrospective review of fetuses with TTTS who received echocardiograms prior to laser therapy. Prelaser echocardiograms were performed in 66 fetuses, of which 45 (21 donor and 24 recipient) survived to the postlaser echocardiogram.

RESULTS

Donor CCO increased from a mean of 487±137 mL/min/kg prelaser to 592±128 mL/min/kg postlaser (P=.025). There was no significant change in mean recipient CCO from prelaser 551±165 mL/min/kg to postlaser 575±112 mL/min/kg (P=.564). In recipient fetuses, higher prelaser CCO correlated with increasing Quintero stage (P=.010) and perinatal mortality (P=.003). Thirty-day postnatal outcome data were available for 38 fetuses, of whom 34 (89%) survived. Amongst survivors, 25 (74%) experienced an increase in CCO, while 9 (26%) experienced a decrease in CCO (P=.010). Donor fetuses had higher CCO after laser therapy.

CONCLUSIONS

Higher prelaser CCO in recipient fetuses may indicate more advanced disease. Fetuses who exhibit a decrease in CCO after therapy laser may be at higher risk for perinatal mortality.

Twin-to-Twin Transfusion Syndrome: Definition, Staging, and Ultrasound Assessment

Objective: The purpose of this article is to review the definition of twin-to-twin transfusion syndrome (TTTS) and the sonographic diagnostic assessment of these cases prior to therapy.

Materials and Methods: The article addresses the terminology used to refer to the condition and describes the systematic ultrasound assessment of the condition, including the ultrasound diagnosis, the staging of the disease, cervical assessment and pre-operative mapping.

Results: From an etymologic and medical point of view, the term ‘fetofetal transfusion’ is more appropriate than ‘TTTS’. However, as the latter, and its attendant acronym TTTS, have been widely adopted in the English language, it is impractical to change at this point. TTTS is defined sonographically in the combined presence of a maximum vertical pocket (MVP) of 8 cm or greater in one sac and 2 cm or less in the other sac, regardless of the gestational age at diagnosis. Staging of the condition using the Quintero staging system is practical, reproducible, and accepted. Transvaginal cervical length assessment should be an integral part of the ultrasound evaluation. Pre-operative mapping to anticipate the location of the placental vascular anastomoses and avoid injuring the dividing membrane is also discussed.

Conclusions: The term ‘TTTS’ can continue to be used in the English medical literature. The condition can be diagnosed and assessed following a systematic ultrasound methodology. The use of such ultrasound methodology breaks the examination into a distinct set of components, assuring a comprehensive examination and proper communication among caregivers.

Do Doppler studies enhance surveillance of uncomplicated monochorionic diamniotic twins?

OBJECTIVES

To determine whether isolated abnormal Doppler indices before 28 weeks predict adverse pregnancy outcomes in uncomplicated monochorionic diamniotic (MCDA) twins.

METHODS

A retrospective cohort study of MCDA twin pregnancies receiving antenatal testing at a single center between 2007 and 2013 was conducted. Sonographic surveillance, including Doppler velocimetric studies of the umbilical artery, ductus venosus, and middle cerebral artery of each twin, was initiated by 28 weeks and repeated at least every 2 weeks. All pregnancies were deemed "uncomplicated" at initial sonography, without evidence of polyhydramnios, oligohydramnios, intrauterine growth restriction, twin growth discordance of at least 20%, structural or chromosomal anomalies, or unclear chorionicity. Pregnancies were divided into 2 groups: those with isolated Doppler abnormalities before 28 weeks and those with normal Doppler indices. The primary outcome was a composite including twin-twin transfusion syndrome, intrauterine growth restriction of more than 1 twin, growth discordance of at least 20%, preterm delivery before 34 weeks for fetal indications, or demise of more than 1 fetus.

RESULTS

Ninety-six patients were included, with 22 (22.9%) having isolated Doppler abnormalities before 28 weeks. The incidence of the primary outcome did not differ between groups (36.4% versus 28.4%; P = .47). The abnormal Doppler group underwent a greater number of sonographic examinations (15 versus 10; P= .001) and more antenatal admissions for fetal concerns (50.0% versus 12.2%; P < .001).

CONCLUSIONS

Isolated Doppler abnormalities are commonly encountered in uncomplicated MCDA pregnancies before 28 weeks yet are not clearly predictive of twin-specific complications. Doppler abnormalities were associated with increased sonographic surveillance and antenatal hospitalizations, suggesting an influence on physician practice patterns. Data may not support Doppler studies before 28 weeks for routine MCDA twin monitoring.

Umbilical and fetal middle cerebral artery Doppler reference ranges in a twin population followed longitudinally from 24 to 38 weeks' gestation

OBJECTIVE

To construct monochorionic diamniotic (MCDA) and dichorionic diamniotic (DCDA) twin reference ranges for umbilical artery (UA) pulsatility index (PI), UA resistance index (RI), fetal middle cerebral artery (MCA) PI and peak systolic velocity (PSV) and cerebroplacental ratio (CPR) from 24 weeks' to 38 weeks' gestation and compare these with published normal values for singleton pregnancies.

METHODS

This prospective multicenter cohort study included 1028 unselected twin pairs recruited over a 2-year period. Participants with dichorionic twins underwent fortnightly ultrasound surveillance from 24 weeks' gestation, with monochorionic twins being followed every 2 weeks from 16 weeks until delivery. A total of 7536 fetal Doppler examinations in 618 twin pregnancies were included in the analysis, with reference ranges for MCDA and DCDA pregnancies constructed for each of the Doppler indices using multilevel modeling.

RESULTS

UA-PI and UA-RI appear to be higher in twins than in singletons, and MCA-PI and MCA-PSV appear to be lower. The CPR also appears to be lower in twins than in singletons. Similar MCA indices were observed in MCDA and DCDA twins.

CONCLUSION

We have established longitudinal reference ranges for UA-PI and UA-RI, MCA-PI and MCA-PSV and CPR in twin pregnancies, which appear to differ from those in singleton pregnancies. The derived twin-specific reference ranges may be more appropriate in the surveillance of these high-risk pregnancies. Applying the singleton CPR cut-off of ≤ 1.0 may lead to a large number of false-positive diagnoses of cerebral redistribution in twin fetuses.

Antenatal fetal assessment: multifetal gestation--an overview

As prevalence of multifetal gestation has increased in the United States, antenatal surveillance of these pregnancies has gained importance. This article focuses on the assessment of twin pregnancy, since critical data are lacking for the surveillance of higher order multiple gestations. Twin pregnancies encounter risks that differ in nature, frequency, and intensity from those seen in singleton pregnancies. Most of these risks stem from subnormal or discordant fetal growth or abnormalities of placentation. Sonographic modalities play key roles in antepartum surveillance. These include fetal biometry, serial growth studies, amniotic fluid volume assessment, Doppler velocimetry of fetal-placental circulation, and biophysical profile testing. Fetal heart rate testing, specifically nonstress testing, has also been used extensively in twin surveillance. This article examines the specific application of these modalities to twin gestation and reviews the best evidence available for their support. Assessment of unique risk conditions of twin-twin transfusion, monoamniotic twinning, and intrauterine death of one twin is addressed. Based on current data, a strategic outline for assessment of twin pregnancy is presented.

Twin-twin transfusion syndrome

The understanding and management of twin-twin transfusion syndrome has evolved significantly over the past few years. Improved and standardized sonographic diagnostic criteria, understanding of the heterogeneic nature of the syndrome, development of an anatomical and reproducible surgical technique for the identification of vascular anastomoses, and technological advances and developments now allow clinicians to view the disease as a more readily understandable and treatable condition. Many tasks remain, including education of peers, better screening and diagnosis, and further development of surgical instruments. Generalization of treatment outcomes should no longer apply given the varied results with disease stage. Confirmation of our tailored approach to management of the disease according to stage should soon be corroborated with an appropriate clinical trial.

Middle cerebral artery to umbilical artery resistance index ratio in the prediction of neonatal outcome

OBJECTIVE

The objectives of this study were to evaluate the usefulness of the middle cerebral artery to umbilical artery resistance index ratio (C/U ratio) as a predictor of adverse perinatal outcome, and to show that the absence of fetal umbilical artery end-diastolic velocity (AEDV) in SGA fetuses is associated with high morbidity and mortality.

METHOD

In this prospective study, color Doppler flow imaging was used for the estimation of the C/U ratio in fetuses that were small for their gestational age, in 70 singleton pregnancies between 29 and 42 weeks of gestation. The subjects were categorized into two groups, with Group A consisting of 35 small for gestational age (SGA) fetuses with a normal C/U ratio (1.05 or higher), and Group B comprising 35 SGA fetuses with an abnormal C/U ratio (below 1.05).

RESULT

The mean C/U ratio values for birth weight and gestational age were higher in group A than in group B. Fetuses born to mothers in group B stayed longer in the neonatal special care unit (NSCU), whereas the period from ultrasound examination to delivery was higher in the cases in group A. A higher percentage of mothers with an abnormal C/U ratio underwent cesarean section. Fetuses with an absent end-diastolic velocity of the umbilical artery had a higher morbidity. Three stillbirths occurred in fetuses with an absent end-diastolic velocity of the umbilical artery.

CONCLUSION

Our results suggest that the C/U ratio is a good predictor of neonatal outcome, and could be used to identify fetuses at risk of morbidity and mortality. Fetal umbilical artery AEDV with intrauterine growth restriction is associated with high perinatal morbidity and mortality.

Ultrasound in the diagnosis of twin-to-twin transfusion syndrome--a preliminary report

OBJECTIVE

The aim of this study was to show the diagnostic possibilities of ultrasound in twin-to-twin transfusion syndrome (TTTS), to demonstrate its usefulness in cases of hemoglobin difference < 5 g/dL in neonates as well as in cases complicated by intrauterine death of one or both twins.

STUDY DESIGN

The study included 4 pairs of twins. In two cases 3 fetuses died in utero. In the other two the hemoglobin difference in newborn infants was < 5 g/dL. The ultrasound examination, evaluating the fetal anatomy and biometry, amniotic fluid volume, placentation, was performed. The special attention was paid to polyhydramnios/oligohydramnios, discordant fetal growth (fetal weight, abdominal circumference), the presence of fetal hydrops, ascites, pericardial effusion. Doppler blood flow velocimetry has been done in umbilical vessels, middle cerebral artery. The data was compared with normal reference values for singleton pregnancies. The waveforms from both uterine arteries were also evaluated to exclude placental insufficiency. Additionally the blood flow through the AV valves was measured to exclude or confirm its regurgitation. Postnatally the hemoglobin difference was evaluated if available and compared with sonographic findings.

RESULTS

In all cases inter-twin difference in abdominal circumference was greater than 18 mm and inter-twin weight difference of more than 15%. We observed polyhydramnios/oligohydramnios in all twin pregnancies. It has been found decreased PI in middle cerebral artery in larger fetus (recipient) in all our cases (comparing to single pregnancy). PI values for this vessel in smaller fetuses were within normal range (for single pregnancy). PI values in umbilical arteries of recipients were abnormal (increased PI or absent end-diastolic flow).

COMMENTS

The sonographic criteria seem to be very useful in diagnosis of twin-to-twin transfusion syndrome, especially in cases where the measurement of hemoglobin level is impossible. Doppler blood flow velocimetry in fetal vessels helps to explain the changes in fetal hemodynamics in TTTS.

Prediction of discordant twins by real-time ultrasonography combined with umbilical artery velocimetry

OBJECTIVE

To evaluate the role of umbilical Doppler velocimetry combined with ultrasonographic intertwin differences derived from estimated fetal weight, biparietal diameter, abdominal circumference and femur length as a comprehensive test for the prediction of discordancy.

METHODS

The sets of twins were studied with real-time ultrasonography for morphometric measurements and with duplex Doppler velocimetry for the S/D ratio of the umbilical artery in third trimester. The following cutoff values were used to indicate abnormal test results: delta biparietal diameter > 6 mm, delta abdominal circumference > 20 mm, delta femur length > 5 mm, delta estimated fetal weight > 15% and delta systolic/diastolic ratio > 15%. Discordancy was identified when the birth weight difference exceeded 15%.

RESULTS

Among the 52 sets of twin pregnancies studied, 40 sets of twins fulfilled the study criteria. Thirteen sets of twins were discordant (32.5%) The mean gestational age at delivery was 37.15 +/- 2.24 weeks (range 28-41 weeks). The diagnostic accuracy provided by ultrasonographic morphometries was not significantly different from that provided by umbilical Doppler velocimetry. Overall the best predictors appeared to be the presence of either delta systolic/diastolic ratio > 15% or delta estimated fetal weights > 15% with sensitivity and specificity values of 92% and 70%, respectively.

CONCLUSION

Real-time ultrasonography combined with umbilical artery velocimetry is useful in predicting discordant twins.

Umbilical Doppler velocimetry prediction of discordant twins

OBJECTIVE

To evaluate the role of umbilical Doppler velocimetry as a comprehensive test for the prediction of discordant twins.

METHODS

The sets of twins were studied with duplex Doppler velocimetry for umbilical artery in third trimester. A systolic/diastolic ratio was measured for each twin. The average difference in the ratios between each twin > or = 0.4 was used to indicate abnormal test. Discordancy was identified when the birth weight difference of > 25%.

RESULTS

Among the 52 sets of twin pregnancies studied, 40 sets of twins fulfilled the study criteria. Eight sets of twins were discordant (20%). The mean gestational age at delivery was 37.15 +/- 2.24 weeks (range 28 to 41 weeks). The test correctly identified 6 of the 8 growth discordant twins which had a sensitivity of 75%, specificity of 68.75%, and accuracy of 70%.

CONCLUSION

Umbilical Doppler velocimetry is useful in prediction of discordant twins.

Doppler ultrasound in multiple pregnancies

This chapter aims to provide a current review of the use of Doppler ultrasound in the management of multiple pregnancies. OVID and Medline searches were undertaken. Randomized controlled trials, where available, were assessed by the Cochrane Review Manager (RevMan-version 3.0). The specific multiple pregnancy problems of fetal growth restriction (FGR), twin reversed arterial perfusion sequence and twin-twin transfusion syndrome (TTTS) were also reviewed. Historically, controlled and randomized controlled trials show a promising reduction in perinatal mortality in twin pregnancies where Doppler ultrasound is used. However, the numbers are small and further trials are recommended. In those twin pregnancies in which there is FGR as a result of placental dysfunction, Doppler ultrasonography will show intertwin discordancy. In those twin pairs where development is complicated by TTTS, there is often discordant fetal size, with concordant fetal Doppler results. Thus Doppler ultrasound appears to be useful in the management of twin pregnancies and in delineating those complicated by FGR and TTTS.

Ultrasound in twin pregnancy

This review evaluates the role of ultrasound in twin gestation. Ultrasound is essential in the diagnosis and management of perinatal complications common in twins, including fetal anomalies, conjoined twins, acardiac twinning, fetal demise, prematurity, intrauterine growth retardation, and twin-to-twin transfusion. Indications for first-trimester scanning are reviewed, as well as its use in determining type of placentation, chorionicity, and amnionicity. The focus of this article will be the use of ultrasound and Doppler velocimetry in the evaluation of fetal growth and subsequent management of intrauterine growth retardation in twins, as well as the value of real-time ultrasound and Doppler evaluation in the diagnosis of discordant growth and twin-to-twin transfusion syndrome.

Antenatal assessment of twin gestation

We have identified that twin gestation presents considerable risks to the well-being of both infants that can be traced to either related maternal or intrinsic fetoplacental factors. A protocol for the assessment of twin gestation is established, beginning with a basis in ultrasound identification of twinning and correct gestational dating. Because most hazards for twins are related to abnormal growth, discrepant growth between twins, and abnormalities of placentation, the approach to assessing well-being requires good serial biometry of twins. This critical review addresses the individual and combined application of standard tests used for evaluation of intrauterine health in single pregnancies: (1) ultrasound fetal growth curves; (2) Doppler velocimetry of the umbilical artery; (3) nonstress tests; (4) amniotic fluid assessment and (5) biophysical profile testing. The best current evidence suggests that there are clear deficiencies in the basis for growth nomograms for twin gestations, and with the exception of femur length, most individual anatomic measurements start to deviate from singleton standards between 21 and 30 weeks' gestation. Regardless of formulae used, estimated fetal weight provides the best discriminator for discordant growth. Dynamic assessment of fetal well-being is best provided by a combination of Doppler velocimetry and nonstress testing. Semiquantitative amniotic fluid assessment, other than establishing pathological conditions (eg, twin transfusion syndrome), is problematic and difficult to reproduce. Inadequate data exist to establish the value of the biophysical profile in twins. Given the limitations of present knowledge, serial assessment of twins beginning in the midtrimester with ultrasound observation, and adding combinations of Doppler velocimetry and nonstress testing in the third trimester, seems to represent the most reasonable current clinical approach to twin well-being.

Severe twin-twin transfusion syndrome: current management concepts

The presence of functioning vascular anastomoses within the monochorionic placentation of a monozygotic twin pregnancy is responsible for the twin-twin transfusion syndrome. This is a heterogeneous disorder with a wide spectrum of severity. In the most severe form it results in the oligohydramnios-polyhydramnios sequence with a marked disparity in intertwin biometry and amniotic fluid volume. Without therapy, the perinatal mortality of severe twin-twin transfusion syndrome is 60-100%. Several therapeutic interventions have been attempted with therapeutic amniocentesis producing the most consistent improvement in fetal survival rates. The outcome of 10 cases of severe twin-twin transfusion syndrome, presenting as the oligohydramnios-polyhydramnios sequence, is presented. Gestational age at presentation ranged from 20-34 weeks. Three fetuses were hydropic at initial presentation and of these only 1 survived. All cases were treated with serial aggressive therapeutic amniocentesis, the number of procedures ranging from 1-9/patient. The volume of amniotic fluid removed ranged from 3,200-14,000 mL. Gestation was prolonged a mean of 46 days (range 1-106 days). The perinatal survival rate was 65% (13/20 infants). Preterm premature rupture of membranes and secondary preterm birth complicated 1 pregnancy treated with therapeutic amniocentesis. Short-term morbidity in the liveborn infants was predominantly secondary to prematurity and renal cortical necrosis. Severe twin-twin transfusion syndrome is the most common aetiology of the oligohydramnios-polyhydramnios sequence. Therapeutic amniocentesis offers an intervention that may reduce the high perinatal loss rate previously observed with this disorder.

Monofetal death in multiple pregnancies: risks for the co-twin, risk factors and obstetrical management

The intrauterine death of one fetus in the case of multiple pregnancies can have an impact on the development of the surviving twin. Based on a single-centre retrospective personal study of 248 multiple pregnancies, 10 of which presented a monofetal intrauterine death, the authors observed the type of placentation, the age and cause of the death, the way in which pregnancy continued and the outcome of the surviving twin. This investigation also includes a review of published documents. Monochorial pregnancies were more frequently encountered in the case of monofetal death in utero. The etiology of the death was not always found and one surviving twin presented lesions as microcephaly convulsions and was retarded on a psychomotor level. In this series these complications did not exist when the pregnancy was bichorial. The authors conclude by demonstrating the major risk of fetal contamination for a live twin coexisting with a dead twin in the case on monochorial pregnancy. Other parameters (cause of death, gestational age at death, delay and duration of cohabitation), do not seem to be significant. It would appear to be of fundamental importance to establish an accurate diagnosis of placentation and to implement specific surveillance of monochorial pregnancies. A decision tree is suggested for use in the case of monofetal death.

Cardiac and extracardiac flows in discordant twins

OBJECTIVE

Our purpose was to evaluate Doppler-detectable differences in the fetal circulation of discordant twins with a growth defect resulting from either placental insufficiency or twin-to-twin transfusion syndrome.

STUDY DESIGN

Serial weekly Doppler recordings were performed for at least 3 weeks preceding delivery in 15 pairs of dichorionic twins (group A) in which the smaller twin had fetal distress (i.e., antepartum fetal heart rate late decelerations) and in 10 pairs of diamniotic and monochorionic twins (group B) in which the diagnosis of twin-to-twin transfusion syndrome was confirmed postnatally. Doppler recordings were obtained from umbilical artery, descending aorta, and middle cerebral artery, and the pulsatility index values were calculated. Furthermore, peak velocity from cardiac outflow tract and the percent of reverse flow in the inferior vena cava were calculated. For all these index values the intertwin differences (delta value) were calculated by subtracting the values obtained in the larger twin with those of the smaller twin.

RESULTS

In group A significant changes of delta values were evidenced for all the parameters tested. In particular, delta values of pulsatility index from the umbilical artery and descending aorta progressively increased approaching the occurrence of late decelerations, whereas the delta value for the middle cerebral artery reached a nadir 2 weeks before delivery. Similarly, delta values of peak velocity from outflow tracts significantly decreased, whereas those of the percent reverse flow in the inferior vena cava increased during the time considered. In group B fetuses no significant intertwin differences in pulsatility index values were evidenced in the vessels investigated, resulting in absence of modifications in delta values during the time interval considered. Moreover, significant changes were found in delta values of both the peak velocity from the outflow tract and the percent of reverse flow in the inferior vena cava. However, these changes were limited to the last recording, where the former delta value increased and the latter decreased.

CONCLUSIONS

Serial Doppler recordings may show hemodynamic changes in the fetal circulation of discordant twins. Different trends occur according to the underlying pathophysiologic mechanisms of the growth defect. The knowledge of these temporal changes may be useful in the management of such fetuses.

The value of Doppler ultrasound in the diagnosis and management of twin-to-twin transfusion syndrome

To evaluate the efficiency of the Doppler examination of umbilical arterial blood flow for the antenatal diagnosis and the monitoring of fetal condition during intrauterine treatment of twin-to-twin transfusion syndrome (TTTS), we studied 33 pairs of twins including 5 TTTS cases. In all cases umbilical arterial blood flow was examined by Doppler ultrasound and pulsatility index (PI) was calculated as umbilical arterial impedance. In twins with TTTS, PI of the recipient was outside the normal range and the difference of PI was greater than +0.5. In discordant twins without TTTS and concordant twins, the PI was within the normal range and the difference of PI ranged from -0.5 to +0.5. In 2 cases these findings were found before the appearance of fetal hydrops. In 2 TTTS cases transmaternal digitalization prevented the development of hydrops in the recipient. The difference of PI decreased with improvement in the fetal condition, and vice versa. Our data suggested that, in cases with TTTS, Doppler examination of umbilical arterial blood flow was effective in predicting fetal hydrops. Doppler was also very useful for monitoring the fetal condition during intrauterine treatment.

Doppler velocimetry in pregnancy

Since the late 1970s, Doppler velocimetry has been investigated extensively for use in obstetrics. Initially, this technique showed promise for the management of certain complications of pregnancy; this promise has yet to be fulfilled. Doppler velocimetry of either the uterine or umbilical vessels, which showed some merit in selecting growth-retarded fetuses at particular risk, has neither become a screening tool for intrauterine growth retardation nor proven clinically successful in improving fetal outcome. Likewise, its use for other complications of pregnancy (eg, postdate pregnancy, twin pregnancy, and diabetes) has not led to improved pregnancy outcome. More recently this technique has been used to study other vascular beds. Changes in the Doppler characteristics of these vascular beds may demonstrate the fetal response to its environment. These investigations provide the potential for a better understanding of fetal physiology; however, it has yet to be shown by prospective evaluation that their application results in improved pregnancy outcome. This review defines the uses and limitations of Doppler ultrasound in current obstetric practice.

Doppler velocimetry and umbilical cord blood gas assessment of twins

In 25 pairs of twins delivered by cesarean section, the flow velocity waveform in the umbilical artery was measured and the resistance index calculated. Umbilical artery and vein blood gases were measured at delivery. Results were tabulated by taking the difference in resistance indices between each fetus and plotting these values against the pO2-differences. The data revealed that index differences of more than 10 were of little value in detecting a pO2-difference of > 1 kPa, despite a sensitivity of 100%. The predictive value was only 41%, and specificity 44%. It was obvious, however, that a pO2-difference > 1 kPa occurred only when the resistance index was 76% or more in one fetus and below 76% in the other. The sensitivity of this index parameter was 100%, predictive value 64%, and specificity 78%. In conclusion, the pO2-level in a fetus seems to be unaffected by the impedance in umbilical circulation as long as the resistance index is below 76%. Above this value, there is a significant risk for fetal hypoxaemia.

Twin growth problems: causes and sonographic analysis

Understanding the significant increased risks associated with twin pregnancies requires knowledge of the embryogenesis of twins and the unique placental characteristics seen only in twin gestations. Dizygotic "fraternal" twins, 70% of all twins, are at relatively low risk when compared with monozygotic twins, largely due to abnormalities seen in association with monochorionic placentation. The sonographic determination of chorionicity and amnionicity allows better estimation of pregnancy risk--up to 50% mortality in monochorionic-monoamniotic twins. Careful evaluation of intrauterine twin growth assists in the early identification of fetal abnormalities because normal twin growth should parallel that of singleton pregnancies until late in the third trimester. A number of the unique complications affecting growth in twin pregnancies are discussed, including twin transfusion syndrome, the "stuck twin" phenomenon, twin embolization syndrome, and development of acardiac twins.

Diastolic zero-flow in the umbilical artery in twin pregnancies

Clinical arterial blood flow measurements in single pregnancies can not be precisely estimated yet. ARED (absent or reverse end diastolic) flow of the umbilical artery (UA) commonly indicates a symptom of fetal jeopardy. The interpretation of blood flow measurement in twin pregnancies is still controversial. On one hand, no differences in a single pregnancies are found, and on the other hand, increased resistance indices have been reported. In the feto-fetal transfusion syndrome mostly there are normal blood flow measurements. When pathological blood flow occurs, usually it affects the donor. By means of 4 case reports with ARED flow, the value of the investigation method in management of twin pregnancies is demonstrated. Three out of four fetuses with an ARED flow in the UA have died. Case fetus with a normal flow velocimetry survived. Even feto-fetal transfusion syndrome may cause pathological blood flow curves. In fetuses with ARED-flow in the UA fetal hypoxia and acidosis are to be expected. A careful evaluation of the cardiotocogram is indicated with a viable fetus. A possible fetal disturbance may be seen early in blood flow curves and may help provide better obstetrical management.

Ultrasonography and Doppler studies in twin-to-twin transfusion syndrome

In 40 twin pregnancies, the evaluation of hemodynamics by ultrasound was performed during the period January 1986 through September 1991. The blood flow velocities' waveforms in the umbilical artery, umbilical vein and tricuspid valve, and the total cardiac dimension, were obtained by ultrasonography in conjunction with 3.5 MHz pulsed Doppler ultrasound. Six patients with twin pregnancies were identified as having twin-to-twin transfusion syndrome (TTS), on the basis of like-sex twins with monochorionic diamniotic placentation, vascular anastomosis in the placenta, and umbilical cord venous blood hemoglobin difference exceeding 5 g/dl at delivery. No distinctive findings for TTS were revealed by the measurement of umbilical artery blood flow velocity waveforms. However, cardiomegaly in 5 recipient fetuses and tricuspid regurgitation and biphasic umbilical vein waveforms in 3 recipient fetuses constituted characteristic features of TTS. Ultrasonography and a Doppler study might be beneficial in diagnosing TTS and evaluating the hemodynamics in a recipient fetus.

Term birth after midtrimester hysterotomy and selective delivery of an acardiac twin

OBJECTIVE

Our aim was to determine whether hysterotomy and selective removal of an acardiac twin could improve the outcome of the "pump" twin.

STUDY DESIGN

A literature and case review of the outcome of the acardiac twin malformation was performed. When an acardiac malformation was diagnosed at 19 weeks' gestation the patient was monitored with weekly ultrasonographic examinations. At 23 weeks' gestation, no blood flow could be demonstrated to the acardiac twin and it was thought that the continued presence of the acardiac twin posed a risk to the "pump" twin. A midtrimester hysterotomy was performed and the acardiac twin was delivered.

RESULTS

After the midtrimester hysterotomy, the pregnancy progressed to term and a healthy female infant was delivered by elective cesarean section at 37 weeks' gestation.

CONCLUSION

Midtrimester hysterotomy may be a useful intervention in cases of twinning when one fetus is a threat to the health of the other.

Umbilical artery blood flow velocity waveforms in twin pregnancies

To detect discordant fetal growth in twin pregnancies and assess a possible role for Doppler ultrasound measurements of blood flow velocity waveforms in umbilical arteries in such cases, 32 twin pregnancies were examined on 125 occasions. The last examination was within 14 days of delivery. There was postpartum death of one pair of twins with the twin transfusion syndrome. Birthweight was appropriate for gestational age in 15 twin pairs, both infants were small for gestational age (SGA) in 5, and one of the infants was SGA in 12 twin pairs. The correlation coefficient of RI difference at the last examination and percentage birth weight difference in twin pairs was 0.68. Cutoff points for the delta RI and weight difference were established. The sensitivity of delta RI (0.1) was 77.8%; specificity, 95.8%; positive predictive value, 87.5%; and negative predictive value, 92.0%.

The relationship between umbilical artery Doppler velocimetry and fetal biometry

The relationship between peak-systolic/end-diastolic ratio of the umbilical artery waveform and fetal biometry was studied in 127 uncomplicated pregnancies with established dates between 20 and 40 weeks' gestation. At each ultrasonographic examination fetal biometry included measurement of the biparietal diameter, head circumference, abdominal circumference, and femur length. The peak-systolic/end-diastolic ratio was measured by either a continuous or a pulsed-wave method. There were significant linear negative correlations between all the biometric parameters, as well as between the ultrasonographically estimated fetal weight and peak-systolic/end-diastolic ratio. Of the individual ultrasonographic parameters the femur length (for gestations less than 30 weeks) and the abdominal circumference (for gestations greater than or equal to 30 weeks) were found to be best correlated with the peak-systolic/end-diastolic ratio. Regression curves, including the 10th and the 90th percentile, were developed between each biometric parameter (biparietal diameter, head circumference, abdominal circumference, and femur length), as well as between estimated fetal weight and peak-systolic/end-diastolic ratio. The estimated fetal weight nomogram had the best sensitivity (48%) in predicting intrauterine growth retardation. These nomograms should prove most useful in assessing downstream placental vascular resistance in high-risk patients with unknown dates.

The definition, diagnosis, and management of growth-discordant twins: an international census survey

In order to establish a protocol considering the definition, diagnosis, and management of growth-discordant twin gestations, a questionnaire was sent to 96 authors of twin-related obstetric articles. The views of the 61 responders comprise this international census survey. The data suggest that a clear cut-off value for discordancy is still needed; however, the data indirectly supported a two-grade definition, namely, mild (greater than 15% and less than 25% birth-weight disparity) and severe (greater than 25%) growth discordants. Expectant management was advocated by the majority of participants with out-patient follow-up for mild discordants, while severe discordants may preferably be hospitalized. Follow-up should be done by non-stress testing (daily - 2/wk), biophysical profile (1-2/wk), Doppler velocimetry (1/wk - bi-weekly) and sonographic biometry (bi-weekly). The opinions considering termination of pregnancy because of intertwin growth discordancy were divided; however, discordancy per se, was not considered an indication for cesarean delivery. An adapted management flowchart that summarizes the survey's data is presented and may be used as a standard for future investigations.

Is pulsed Doppler velocimetry useful in the management of multiple-gestation pregnancies?

Few studies have addressed the significance of umbilical artery pulsed Doppler velocimetry in multiple gestation. Level II ultrasonography and pulsed Doppler studies were performed in 94 twin pairs and seven sets of triplets, which yielded data on 207 fetuses. A systolic/diastolic ratio was calculated for each fetus; abnormal pulsed Doppler velocimetry showed high correlation with adverse pregnancy events. Those with abnormal Doppler findings tended to be born 3 to 4 weeks earlier and to exhibit a greater number of stillbirths and structural malformations, as well as greater morbidity, when compared with fetuses without abnormal Doppler results. Fifteen of 17 infants with abnormal antenatal waveforms suffered serious morbidity. Seven were small for gestational age, and two were borderline for small for gestational age. An additional five infants with abnormal waveforms were appropriate for gestational age but were either recipient or donor in the twin transfusion syndrome. Eleven fetuses with this syndrome are described. Donor twins tended to be severely small for gestational age, with 7 of the 11 infants showing elevated systolic/diastolic ratios. Amniotic fluid volume tended to be diminished in the donor's sac but normal or increased in the recipient's sac. The observations in the study correlate with suspected physiologic changes of this syndrome. Because present findings suggest that fetuses with abnormal velocimetry suffer increased morbidity and mortality, a more rational method of management that uses Doppler data is suggested for multiple gestations.

Maternal-fetal Doppler sonography: potential or reality

Doppler sonography, in its varying forms, has been used by numerous researchers to evaluate the maternal-fetal circulation. Unfortunately, as can be seen from this review, few sweeping conclusions can be drawn from the literature to date. Doppler certainly seems a worthwhile adjunct in the evaluation of patients with any of a number of abnormalities that affect maternal-fetal circulation. Unfortunately, considering the discrepancies in the literature and the recent controversy regarding the use of pulsed and color Doppler in pregnancy, the examination is often avoided. However, there are certainly instances where Doppler can provide unique and valuable information. In these situations, the prudent use of Doppler should be encouraged.

Middle cerebral artery blood flow in normal and growth-retarded fetuses

Doppler ultrasonography of the middle cerebral artery was performed on 17 fetuses that were small for gestational age at the time of delivery. Results were compared with a group of 25 fetuses that had a normal weight for gestational age at the time of delivery. Despite a significant difference in fetal weight and systolic/diastolic ratio of the umbilical artery between the two groups, no difference was found in either the systolic/diastolic ratio or in the Pourcelot index of the middle cerebral artery. This may reflect a protective effect on the brain circulation in the small-for-gestational-age fetus.

Monozygotic twin pregnancy: diagnostic and Doppler ultrasound studies

Of 178 consecutive twin pregnancies, 63 were both monozygotic and also studied prenatally by real-time B-scan (and usually Doppler) ultrasound. The 48 pregnancies with monochorionic placentas (in which vascular anastomoses are almost universal) were compared with the 15 monozygotic pregnancies having dichorionic placentas. The type of placenta found at delivery was predicted with substantial accuracy by ultrasound examination in mid-pregnancy. We were unable to identify any inter-group difference in fetal growth rate, discordance of fetal growth between twins or pattern of umbilical artery flow velocity waveform. In the absence of the rare florid twin transfusion syndrome, the vascular anastomoses that have been shown to be common in monochorionic placentas do not exert a strong influence on fetal growth or fetoplacental blood flow.

Hydrops revisited: literature review of 1,414 cases published in the 1980s

This paper reviews 47 series of hydrops fetalis (804 cases) and 610 individual cases published since 1980. From this large number of cases, guidelines are derived for prenatal diagnosis and management.

Discordant twins--a prospective study of the diagnostic value of real-time ultrasonography combined with umbilical artery velocimetry

This study was undertaken to evaluate the role of Doppler velocimetry combined with intertwin differences in ultrasonographically derived estimated fetal weight, biparietal diameter, abdominal circumference, and femur length as a comprehensive test for the prediction of discordancy. The following cutoff values were used to indicate abnormal test results: delta biparietal diameter greater than 6 mm, delta abdominal circumference greater than 20 mm, delta femur length greater than 5 mm, delta estimated fetal weight greater than 15%, and delta systolic/diastolic ratio greater than 15%. Discordancy was identified when the birth weight difference exceeded 15%. The study population consisted of 58 consecutively evaluated third-trimester twin gestations. Eighteen sets of twins were discordant. None of these tests was uniformally successful in identifying twin discordancy; in three instances, all test results were normal. The diagnostic accuracy provided by ultrasonography was not significantly different from that provided by Doppler velocimetry. Overall the best predictor appeared to be the presence of either delta systolic/diastolic ratio greater than 15% or delta estimated fetal weights greater than 15%, which correctly identified 14 of the 18 discordant twins and misclassified only five of the 40 concordant pairs. This combination also had the highest positive and negative predictive values (73% and 90%, respectively).

Doppler velocimetry and placental disease

Quantitative placental examinations were performed on 47 women who had Doppler flow velocity studies of the umbilical artery during their pregnancy. The systolic-diastolic ratio of the umbilical artery was used as the measurement parameter to divide the study population into two groups. Group 1 consisted of women with normal systolic-diastolic ratios (systolic-diastolic less than 3), and group 2 consisted of women with an elevated systolic-diastolic ratio (systolic-diastolic greater than or equal to 3). The group with an increase in systolic-diastolic ratio had more perinatal complications as demonstrated by two stillbirths, a higher incidence of cesarean deliveries for fetal distress, and more admissions to the neonatal intensive care unit. Significant differences were found when gestational age at delivery, placental weight, birth weight, and the number of small muscular arteries in the placenta were compared. Since gestational age may have accounted for the difference in placental findings, patients were matched for gestational age. The placental weights were comparable, but there were fewer small muscular arteries in those patients with an increase in systolic-diastolic ratio (p less than 0.001). In addition, when these findings were examined to determine the influence of diminished uterine flow velocity, none was found.

Twin-to-twin transfusion syndrome: what are appropriate diagnostic criteria?

One hundred seventy-eight consecutive twin pregnancies were studied to reevaluate the standard diagnostic criteria for chronic twin-to-twin transfusion syndrome of an intertwin hemoglobin difference greater than 5 gm/dl and a birth weight difference greater than 20%. Hemoglobin differences greater than 5 gm/dl were found in six pregnancies with monochorionic placentas but also in seven with dichorionic placentas. Birth weight differences greater than 20% occurred no more commonly in monochorionic than in dichorionic pregnancies. Of the four pregnancies with a coexisting hemoglobin difference greater than 5 gm/dl and birth weight difference greater than 20%, only one had a monochorionic placenta and therefore likelihood of vascular anastomoses. Diagnosis of twin-to-twin transfusion syndrome cannot be definitively established by current standard diagnostic criteria.

Correcting umbilical artery flow velocity waveforms for fetal heart rate is unnecessary

We prospectively examined 55 normal pregnant women between 32 and 41 (means = 37) weeks' gestation. Five measurements of the umbilical artery peak-systolic/end-diastolic frequency ratio were obtained from each patient during one examination. Comparison of the fetal heart rate and the umbilical artery peak-systolic/end-diastolic frequency ratios between pregnancies less than 37 and greater than 37 weeks' gestation revealed no difference. Subsequently a total of 256 measurements were analyzed as one group. Plotting the individual peak-systolic/end-diastolic frequency ratios against the corresponding fetal heart rates revealed a moderate negative linear correlation: y = 4.15-0.012x, r = -0.36 and p less than 0.04. When only heart rates between 120 to 160 beats/min were plotted against peak-systolic/end-diastolic frequency ratios, a weaker correlation was found (r = -0.33, p = 0.15). The difference (mean +/- SD) between the obtained and the corrected peak-systolic/end-diastolic frequency ratios was 4.4% +/- 3.2%. The 95th percentile of the obtained peak-systolic/end-diastolic frequency ratio was 3.35 and the corrected ratio was 3.27. Averaging of the five measurements obtained from each patient for all 55 patients decreased the 95th percentile value to 3.09 whereas the same procedure for the corrected peak-systolic/end-diastolic frequency ratios decreased it to 3.07. We conclude that although there is a statistically significant negative linear correlation between the fetal heart rate and the umbilical artery peak-systolic/end-diastolic frequency ratio, this relationship is not clinically significant.

A comparative study of fetal umbilical velocimetry with continuous- and pulsed-wave Doppler ultrasonography in high-risk pregnancies: relationship to outcome

Systolic/diastolic ratios of umbilical velocimetry obtained with either continuous-wave or pulsed-wave Doppler ultrasonography have been used to assess downstream placental vascular resistance and fetal well-being. The purpose of this study is to compare the efficacy of systolic/diastolic ratios obtained by continuous-wave and pulsed-wave Doppler ultrasonography in the prediction of poor pregnancy outcome. Continuous-wave and pulsed-wave umbilical velocimetry was performed and systolic/diastolic ratios were measured in 200 high-risk pregnancies in the third trimester by use of Angioscan III and a General Electric RT 3600 scanner, respectively. A total of 165 study participants had normal systolic/diastolic ratios and 35 participants had elevated ratios (greater than 3.0) with both continuous-wave and pulsed-wave Doppler ultrasonography. Both methods identified 35 participants with abnormal ratios, and none of the women was misclassified by either method. The pulsed-wave and continuous-wave values for 35 participants with elevated ratios were 6.35 +/- 1.52 and 6.23 +/- 1.58, respectively; values for 165 participants with normal ratios were 1.95 +/- 0.40 and 1.96 +/- 0.41, respectively (not significantly different). Participants with elevated systolic/diastolic ratios within 7 days of delivery had significantly higher incidence of adverse pregnancy outcome as judged by small-for-gestational-age fetuses, presence of meconium at delivery, fetal distress in labor, cesarean sections and 5-minute Apgar scores less than 7. Fetuses with elevated ratios were delivered at an earlier gestational age (34 +/- 1.2 weeks), had lower birth weights (1422 +/- 151 gm), and spent more time in the neonatal intensive care unit (17.1 +/- 5.2 days), compared with fetuses with normal ratios (delivered at 38.5 weeks +/- 0.9 weeks, 3100 +/- 210 gm birth weights, and 2 +/- 0.2 days spent in neonatal intensive care units, respectively, p less than 0.05). We therefore conclude that continuous-wave and pulsed-wave Doppler ultrasonography produce similar results with regard to systolic/diastolic ratios in high-risk pregnancies, and either method appears to be a valuable adjunct in the surveillance of high-risk pregnancies.

Antepartum improvement of abnormal umbilical artery velocimetry: does it occur?

Absence of end-diastolic velocity on umbilical artery velocimetry suggests extreme elevation of placental vascular resistance and is associated with adverse pregnancy outcome. This study was undertaken to assess whether antepartum improvement of abnormal umbilical artery waveforms occurs. Thirty-one fetuses identified with absence of end-diastolic velocity between July 1985 and December 1987 at Women's Hospital underwent sequential umbilical artery velocimetry at 1- to 3-day intervals. The presence of end-diastolic velocity on subsequent scans was considered an improvement in waveforms. The mean diagnosis-to-delivery interval (20.5 +/- 4 days), gestational age at delivery (32.5 +/- 1.2 weeks), and birth weight (1440 +/- 210 gm) were significantly higher in five fetuses that showed improvement in waveforms, compared with the 26 fetuses that did not show improvement in waveforms (9.5 +/- 3.5 days, 29.5 +/- 0.9 weeks, and 940 +/- 70 gm, respectively). Ten perinatal deaths occurred, for a perinatal mortality rate of 32.3%. There was significant perinatal morbidity in the overall group as judged by intrauterine growth retardation, meconium, 5-minute Apgar scores less than 7, and cesarean section for fetal distress. We conclude that although absence of end-diastolic velocity is associated with adverse pregnancy outcome, antepartum improvement in umbilical artery waveforms occurred in 15% of the fetuses studied and was associated with an improvement in perinatal outcome. Factors that influenced this improvement, though unclear, might be related to maternal bed rest or medication and require further investigation.

Tape measurement of symphysis-fundal height in twin pregnancies

We hypothesized that tape measurement of symphysis-fundal height could be useful in detecting multiple pregnancies, and in such cases in predicting preterm labour and identifying small-for-gestational-age (SGA) fetuses. Although mean fundal height is substantially greater in twin than singleton pregnancies, the value of the technique to detect multiple pregnancies may be limited because combined birth-weight is less and the frequency of SGA fetuses is greater in undiagnosed than in diagnosed twin pregnancies. We found no evidence that the measured fundal height is greater in pregnancies going on to preterm delivery, and we suggest that the commonly accepted theory that the high rate of preterm labour in twin pregnancies results simply from uterine overdistension be reappraised. Nevertheless, fundal height measurement was of value in identifying pregnancies in which both babies were SGA and is therefore recommended as a simple, inexpensive and non-invasive technique.

Umbilical artery flow velocity waveforms in fetuses dying with congenital anomalies

Absent or reversed diastolic component in umbilical artery (UA) flow velocity waveform was observed in eight fetuses with major malformations. Because of the uncorrectable fetal conditions or the parents' reluctance to terminate the pregnancy, no interventions were undertaken and eventually all eight fetuses died in utero. The interval between the abnormal waveform recording and fetal death was between 1 and 7 days (mean 3.6 days). In two fetuses with abnormal diastolic flow, analysis of umbilical vein blood obtained by ultrasound-guided sampling revealed moderately severe acidosis and hypoxia (pH 7.228 and 7.241, PCO2 47.5 and 46.9 mmHg; PO2 14.6 and 14.7 mmHg, respectively). Our observation suggests that once the diastolic component of UA flow velocity waveforms becomes absent or reversed, the fetus is in a state of hypoxia and acidosis and fetal death is impending. This limited experience may help in formulating clinical management when using UA flow velocity waveforms in the monitoring of high-risk fetuses.