Ultrasonographic criteria for the prenatal diagnosis of placental chorionicity in twin gestations

The Outcome after Laser Therapy of Monochorionic Twin Pregnancies Complicated by Twin-Twin Transfusion Syndrome with Coexistent Selective Fetal Growth Restriction

Background: Most previous studies evaluated outcomes of twin-twin transfusion syndrome (TTTS) without considering the coexistence of selective fetal growth restriction (sFGR). The objectives of this study were to compare twin survival and pregnancy complications after laser therapy of TTTS with and without sFGR. Methods: For this purpose, a retrospective cohort study including 98 monochorionic diamniotic twins and three dichorionic triamniotic triplets treated in a single tertiary center was conducted. Results: Overall, 46 twins had selective fetal growth restriction (26 type I, 13 type II, 7 type III). At birth, donor survival (61% vs. 91%), double survival (57% vs. 82%), and overall survival (75% vs. 88%) were significantly lower in the group with coexistent sFGR. Recipient survival (89% vs. 86%), miscarriage (7% vs. 2%), PPROM < 32 weeks (48% vs. 29%), and preterm delivery < 32 weeks (52% vs. 45%) were not significantly higher in the group with coexistent sFGR. Donor twins with sFGR type I (69% vs. 91%) and types II-III (50% vs. 91%) showed significantly lower survival than those without sFGR. Multivariate regression analysis identified sFGR and its subtypes as independent predictors of donor demise. Conclusions: the coexistence of sFGR in TTTS pregnancies was associated with poor donor outcomes and is probably the most important predictor of donor survival.

The heart after surviving twin-to-twin transfusion syndrome

BACKGROUND

The persistent changes in cardiac structure and function in children who survived twin-to-twin transfusion syndrome remain a matter of concern and controversy. Current fetal echocardiographic parameters and their postnatal evolution can help improve our understanding of the subject.

OBJECTIVE

To describe the echocardiographic changes of monochorionic fetuses affected by twin-to-twin transfusion syndrome, the recipient and the donor, before and after laser photocoagulation and to determine their evolution in the third trimester and during their first year of life.

STUDY DESIGN

An observational study was conducted including 55 uncomplicated monochorionic diamniotic twins and 78 pairs with twin-to-twin transfusion syndrome, 44 stage I-II and 34 stage III-IV, prospectively enrolled from 2015 until 2018. Comprehensive echocardiography was performed at 4 time periods: before laser photocoagulation, at 24 to 72 hours after surgery, at 28 to 30 weeks of gestation, and at 6 to 12 months after birth. Echocardiographic parameters were transformed to z-scores or indexed for heart area, estimated fetal weight, or body mass surface.

RESULTS

At diagnosis, recipients in all stages presented larger hearts (cardiothoracic ratio z-score: 2.77 [0.8] vs controls: -0.03 [0.5]; P<.001) and signs of ventricular hypertrophy (left end-diastolic ventricle wall thickness: 2.68 [0.7] vs controls -0.03 [0.7]; P<.001), along with systolic (cardiac index recipients: 317 [114] mL/min/kg vs controls: 400 [120] mL/min/kg, P<.001) and diastolic impairment (isovolumetric relaxation time z-score: 2.76 [0.6] vs controls: 0.05 [0.6]; P<.001). Donors presented smaller ventricular areas and diameters when compared with controls (left end-diastolic ventricle area z-score: -1.48 [1] vs 0.03 [0.9]; P<.001), along with decreased longitudinal motion (tricuspid annular plane systolic excursion z-score: -0.9 [1] vs controls -0.04 [1]; P<.001) and shorter ejection time z-score (-1.5 [0.7] vs controls: 0.0 [0.7]; P<.001). After surgery, an improvement in functional parameters was observed in both fetuses, whereas most morphometric changes prevailed in donors and recipients in the prenatal period. Postnatally, cardiac remodeling persisted in recipients (left relative wall thickness: 0.34 [0.02] vs controls: 0.30 [0.02]; P<.001), whereas donors mainly presented a decreased longitudinal motion in infancy (tricuspid annular plane systolic excursion z-score: -0.72 [0.7] vs controls: 0.23 [0.9]; P<.05).

CONCLUSION

Cardiac remodeling is present in both fetuses at the twin-to-twin transfusion syndrome diagnosis, whereas diastolic dysfunction is only significant in the recipient. Fetal therapy improves most echocardiographic parameters, although postnatally, the echocardiographic changes persist in both fetuses.

Left myocardial performance index in monochorionic diamniotic twin pairs complicated by selective fetal growth restriction with abnormal umbilical artery Doppler

OBJECTIVE

To evaluate left myocardial performance index (MPI) and its time intervals in monochorionic diamniotic (MCDA) twin pairs complicated by selective fetal growth restriction (sFGR) with abnormal (persistent -type II- or intermittent -type III- absent or reversed end-diastolic flow) umbilical artery Doppler.

METHODS

Retrospective study including 16 MCDA twin pairs with sFGR type II, 26 MCDA twin pairs with sFGR type III and 42 gestational age-matched uncomplicated MCDA twin pairs in a single tertiary center. Left isovolumetric contraction time (ICT), ejection time (ET), and isovolumetric relaxation time (IRT) were measured and MPI calculated by conventional Doppler at diagnosis of sFGR.

RESULTS

In sFGR type II, the smaller twin had shorter ET and prolonged IRT and MPI, while the larger twin showed prolonged ICT and MPI as compared to uncomplicated MCDA twins. In sFGR type III, the smaller twin had shorter ICT and ET, while the larger twin showed prolonged ICT, IRT, and MPI in comparison to controls.

CONCLUSION

A differential pattern of MPI time intervals could be observed in MCDA twins with sFGR type II and III. All twins had echocardiographic signs of pressure/volume overload, except the smaller twin type III with shorter systolic times probably reflecting reduced volume load.

Prescriptive standards of echocardiographic morphometric and functional parameters in uncomplicated monochorionic diamniotic fetuses

OBJECTIVE

To create prescriptive standards of cardiac morphometric and functional parameters in a cohort of uncomplicated monochorionic diamniotic (MCDA) twins.

METHOD

Fetal echocardiography was performed in a cohort of uncomplicated monochorionic twin fetuses scanned longitudinally, including comprehensive morphometric and functional parameters, using 2-D imaging, M-mode and conventional Doppler. A multilevel polynomial hierarchical model adjusted by gestational age and estimated fetal weight was used to fit each cardiac parameter.

RESULTS

The global heart dimensions including the atrial and ventricular areas, the ventricles dimensions and myocardial wall thicknesses and most of the functional parameters, such as the longitudinal myocardial motion and the biventricular cardiac output showed a positive quadratic increment throughout pregnancy. On the other hand, the left ejection fraction, shortening fraction and right fractional area change decreased with gestational age. Scatterplots for the main structural and functional parameters and ratios by gestational age, with mean, 5th, 10th, 90th, and 95th percentiles are provided. Regression equations by estimated fetal weight are also created.

CONCLUSION

We provide specific comprehensive echocardiographic prescriptive standards for uncomplicated MCDA twin fetuses following current standardized methodology. The implementation of these charts will potentially help to better identify abnormal cardiovascular parameters associated to monochorionic complications.

Uncomplicated Monochorionic Twins: Two Normal Hearts Sharing One Placenta

Cardiovascular dysfunction has been reported in complicated monochorionic diamniotic (MCDA) pregnancies; however, little is known whether hemodynamic changes occur in uncomplicated MCDA twins. A prospective observational study was conducted including 100 uncomplicated MCDA twins matched by gestational age to 200 low-risk singletons. Echocardiography was performed at 26-30 weeks gestation and cord blood B-type natriuretic peptide (BNP) was measured at delivery. In both groups, z-scores for echocardiographic parameters were within normal ranges; however the monochorionic group had larger atrial areas (mean (standard deviation) right atria-to-heart ratio: 17.0 (2) vs. 15.9 (1); p = 0.018; left atria-to-heart ratio: 17.0 (3) vs. 15.8 (2); p < 0.001) and signs of concentric hypertrophy (right relative wall thickness: 0.66 (0.12) vs. 0.56 (0.11); p < 0.001; left relative wall thickness: 0.69 (0.14) vs. 0.58 (0.12); p < 0.001). Longitudinal function was increased in twins, leading to higher tricuspid annular plane systolic excursion (6.9 mm (0.9) vs. 5.9 mm (0.7); p < 0.001) and mitral annular plane systolic excursion (4.9 mm (0.8) vs. 4.4 mm (1.1); p < 0.001. BNP levels at birth were also higher in MCDA twins (median [interquartile range]: 20.81 pg/mL [16.69-34.01] vs. 13.14 pg/mL [9.17-19.84]; p < 0.001). Thus, uncomplicated MCDA fetuses have normal cardiac shape and function, but signs of cardiac adaptation were identified by echocardiographic and biochemical parameters, when compared with singletons.

Structured evaluation and reporting in imaging of placenta and umbilical cord

The human placenta plays a pivotal role in development and growth of the fetus. Disorder of this multifunctional organ is central to various fetal disorders. Doppler sonography and MRI provide excellent diagnostic evaluation of the placental morphology and umbilical cord. Decades of experience in obstetric imaging have highlighted the need of careful prenatal assessment of placenta. However, in most of the routine obstetric scans, the evaluation and reporting of the placental examination is limited to the location and grade of the placenta. The purpose of this article is to review the existing literature and facilitate step-by-step evaluation of the placenta and umbilical cord by the radiologists.

Pitfalls in assessing chorioamnionicity: novel observations and literature review

Accurate diagnosis of chorioamnionicity in multiple pregnancies is the key to appropriate clinical management of multiple gestation. Although prenatal ultrasound assessment of chorioamnionicity is well established and highly accurate if performed in early pregnancy, exceptions and artifacts arise from anatomic variations in multiple pregnancies and unusual sonographic features do exist. We have summarized our own experiences and reports from the literature on these pitfalls as follows: (1) discordant fetal sex in monochorionic pregnancies due to sex chromosome abnormalities, genital malformation in 1 fetus, or dizygotic twins forming a monochorionic placenta; (2) separate placental masses in monochorionic pregnancies due to bipartite placenta; (3) false-negative and false-positive λ sign can arise for various reasons, and in partial monochorionic/dichorionic placentas both T and λ sign may co-exist; (4) intrauterine synechia appearing as a thick and echogenic intrauterine septum may lead to erroneous diagnosis of dichorionic twins; and (5) errors in ascertaining amnionicity by the visualization of thin intertwin amniotic membranes and the number of yolk sacs. The ultrasound techniques to reduce inaccuracy in prenatal determination of chorioamnionicity and the use of single nucleotide polymorphisms based on noninvasive prenatal test to determine zygosity are also reviewed.

ACR Appropriateness Criteria® Multiple Gestations

Women with twin or higher-order pregnancies will typically have more ultrasound examinations than women with a singleton pregnancy. Most women will have at minimum a first trimester scan, a nuchal translucency evaluation scan, fetal anatomy scan at 18 to 22 weeks, and one or more scans in the third trimester to evaluate growth. Multiple gestations are at higher risk for preterm delivery, congenital anomalies, fetal growth restriction, placenta previa, vasa previa, and velamentous cord insertion. Chorionicity and amnionicity should be determined as early as possible when a twin pregnancy is identified to permit triage of the monochorionic group into a closer surveillance model. Screening for congenital heart disease is warranted in monochorionic twins because they have an increased rate of congenital cardiac anomalies. In addition, monochorionic twins have a higher risk of developing cardiac abnormalities in later gestation related to right ventricular outflow obstruction, in particular the subgroups with twin-twin transfusion syndrome or selective intrauterine growth restriction. Monochorionic twins have unique complications including twin-to-twin transfusion syndrome, twin embolization syndrome, and acardius, or twin-reversed arterial perfusion sequence. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.

Ultrasound and histological measurements of dividing membrane thickness in twin gestations

OBJECTIVE

To determine how prenatal ultrasound measurements of dividing membrane thickness correlate with postnatal histological measurements and chorionicity in twin gestations.

METHODS

This was a prospective, longitudinal cohort study of twin gestations. Dividing membrane thickness was measured by transabdominal ultrasound, with the insonation beam both parallel and perpendicular to the membrane, in the second or third trimester, depending on when care was established. Ultrasound examinations were performed every 4 weeks following initial assessment until delivery. Measurements of membrane thickness from the first ultrasound examination were compared with histological measurements after delivery.

RESULTS

A total of 45 twin pregnancies (32 dichorionic, 13 monochorionic) were included. Mean gestational age at initial ultrasound examination was 24.1 ± 7.3 weeks. Parallel ultrasound measurements of membrane thickness were 1.6 ± 0.8 mm for monochorionic and 2.5 ± 0.9 mm for dichorionic gestations (P = 0.001). Perpendicular ultrasound measurements were 1.6 ± 0.3 mm for monochorionic and 2.2 ± 0.8 mm for dichorionic gestations (P = 0.009). Inter- and intraobserver reliability of ultrasound measurements were 0.847 and 0.950, respectively. Parallel and perpendicular ultrasound measurements correlated better with each other (R = 0.807, P < 0.001) than with histological measurements of membrane thickness (R_parallel  = 0.538, P < 0.001; R_{perpendicular}  = 0.529, P < 0.001). Receiver-operating characteristics curve analyses to predict histological membrane thickness > 50^th percentile resulted in an area under the curve (AUC) of 0.828 for parallel (P < 0.001) and 0.874 for perpendicular (P < 0.001) measurements with a cut-off value of 1.9 mm for both approaches. The AUCs for parallel and perpendicular measurements to predict dichorionicity were 0.892 (P < 0.001) and 0.823 (P < 0.001) with cut-off values of 1.9 and 1.8 mm, respectively.

CONCLUSION

Prenatal ultrasound measurement of twin dividing membrane thickness is positively correlated with postnatal histological measurement. Dichorionicity can be determined by a magnified dividing membrane thickness ≥ 1.9 mm. Measurements with the ultrasound beam parallel to the dividing membrane may be more accurate than perpendicular measurements. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.

Ultrasound in twin pregnancies

OBJECTIVE

To review the literature with respect to the use of diagnostic ultrasound in the management of twin pregnancies. To make recommendations for the best use of ultrasound in twin pregnancies.

OUTCOMES

Reduction in perinatal mortality and morbidity and short- and long-term neonatal morbidity in twin pregnancies. Optimization of ultrasound use in twin pregnancies.

EVIDENCE

Published literature was retrieved through searches of PubMed and the Cochrane Library in 2008 and 2009 using appropriate controlled vocabulary (e.g., twin, ultrasound, cervix, prematurity) and key words (e.g., acardiac, twin, reversed arterial perfusion, twin-to-twin transfusion syndrome, amniotic fluid). Results were restricted to systematic reviews, randomized control trials/controlled clinical trials, and observational studies. There were no date restrictions. Studies were restricted to those with available English or French abstracts or text. Searches were updated on a regular basis and incorporated into the guideline to September 2009. Grey (unpublished) literature was identified through searching the websites of health technology assessment and health technology assessment-related agencies, clinical practice guideline collections, clinical trial registries, and national and international medical specialty societies.

VALUES

The evidence collected was reviewed by the Diagnostic Imaging Committee of the Society of Obstetricians and Gynaecologists of Canada, with input from members of the Maternal Fetal Medicine Committee and the Genetics Committee of the SOGC. The recommendations were made according to the guidelines developed by The Canadian Task Force on Preventive Health Care (Table 1).

BENEFITS, HARMS, AND COSTS

The benefit expected from this guideline is facilitation and optimization of the use of ultrasound in twin pregnancy. SUMMARY STATEMENTS: 1. There are insufficient data to make recommendations on repeat anatomical assessments in twin pregnancies. Therefore, a complete anatomical survey at each scan may not be needed following a complete and normal assessment. (III) 2. There are insufficient data to recommend a routine preterm labour surveillance protocol in terms of frequency, timing, and optimal cervical length thresholds. (II-2) 3. Singleton growth curves currently provide the best predictors of adverse outcome in twins and may be used for evaluating growth abnormalities. (III) 4. It is suggested that growth discordance be defined using either a difference (20 mm) in absolute measurement in abdominal circumference or a difference of 20% in ultrasound-derived estimated fetal weight. (II-2) 5. Although there is insufficient evidence to recommend a specific schedule for ultrasound assessment of twin gestation, most experts recommend serial ultrasound assessment every 2 to 3 weeks, starting at 16 weeks of gestation for monochorionic pregnancies and every 3 to 4 weeks, starting from the anatomy scan (18 to 22 weeks) for dichorionic pregnancies. (II-1) 6. Umbilical artery Doppler may be useful in the surveillance of twin gestations when there are complications involving the placental circulation or fetal hemodynamic physiology. (II-2) 7. Although many methods of evaluating the level of amniotic fluid in twins (deepest vertical pocket, single pocket, amniotic fluid index) have been described, there is not enough evidence to suggest that one method is more predictive than the others of adverse pregnancy outcome. (II-3) 8. Referral to an appropriate high-risk pregnancy centre is indicated when complications unique to twins are suspected on ultrasound. (II-2) These complications include: 1. Twin-to-twin transfusion syndrome 2. Monoamniotic twins gestation 3. Conjoined twins 4. Twin reversed arterial perfusion sequence 5. Single fetal death in the second or third trimester 6. Growth discordance in monochorionic twins. Recommendations 1. All patients who are suspected to have a twin pregnancy on first trimester physical examination or who are at risk (e.g., pregnancies resulting from assisted reproductive technologies) should have first trimester ultrasound performed. (II-2A) 2. Every attempt should be made to determine and report amnionicity and chorionicity when a twin pregnancy is identified. (II-2A) 3. Although the accuracy in confirmation of gestational age at the first and second trimester is comparable, dating should be done with first trimester ultrasound. (II-2A) 4. Beyond the first trimester, it is suggested that a combination of parameters rather than a single parameter should be used to confirm gestational age. (II-2C) 5. When twin pregnancy is the result of in vitro fertilization, accurate determination of gestational age should be made from the date of embryo transfer. (II-1A) 6. There is insufficient evidence to make a recommendation of which fetus (when discordant for size) to use to date a twin pregnancy. However, to avoid missing a situation of early intrauterine growth restriction in one twin, most experts agree that the clinician may consider dating pregnancy using the larger fetus. (III-C) 7. In twin pregnancies, aneuploidy screening using nuchal transluscency measurements should be offered. (II-2B) 8. Detailed ultrasound examination to screen for fetal anomalies should be offered, preferably between 18 and 22 weeks' gestation, in all twin pregnancies. (II-2B) 9. When ultrasound is used to screen for preterm birth in a twin gestation, endovaginal ultrasound measurement of the cervical length should be performed. (II-2A) 10. Increased fetal surveillance should be considered when there is either growth restriction diagnosed in one twin or significant growth discordance. (II-2A) 11. Umbilical artery Doppler should not be routinely offered in uncomplicated twin pregnancies. (I-E) 12. For defining oligohydramnios and polyhydramnios, the ultrasonographer should use the deepest vertical pocket in either sac: oligohydramnios when < 2 cm and polyhydramnios when > 8 cm. (II-2B).

Ultrasound Determination of Chorionicity in Twin Pregnancy: Accuracy and Operator Experience

To evaluate the accuracy of ultrasound in early detection of chorionicity and amnionicity in twin pregnancies and evaluate the role of operator-experience, a prospective follow up of 87 consecutive twin pregnancies was performed. Chorionicity and amnionicity were determined by 17 different observers, divided in 2 groups on the basis of their experience, using a composite of US markers at the first US examination confirming a viable intrauterine twin pregnancy. Accuracy of prediction was determined for both groups by comparison with postnatal pathology. From the 87 pregnancies examined at 10.1 (minimum 5.5 weeks, maximum 26.0) weeks of gestation, pathology was available in 82 cases and a correct prediction of chorionicity was made in all but two cases, both being diagnosed as monochorionic while dichorionic by observers belonging the more experienced group. No monochorionic pregnancy was missed and amnionicity was correctly diagnosed in all cases, including two monoamniotic twins. We conclude that use of a composite of ultrasound markers for early detection of chorionicity and amnionicity is reliable in a clinical setting where physicians with a variable degree of experience perform ultrasound examination.

Efficacy of marlex mesh on posterior fixation suture: an experimental study in a rabbit model

PURPOSE

To develop a novel method of posterior fixation suture augmented by the application of Marlex mesh and to evaluate the surgical results in a rabbit model.

DESIGN

Animal study.

METHODS

SETTING

Prospective, masked-observer, controlled experimental study.

STUDY POPULATION

Sixty superior rectus muscles of 30 rabbits.

INTERVENTION

Each superior rectus muscle was randomly subjected to posterior fixation suture at a distance of 6 mm from the muscle insertion. The rabbits were divided into 3 groups: conventional posterior fixation suture (Conventional group), and modified posterior fixation suture using a silicone sponge (Silicone group) or using Marlex mesh (Marlex group). Nonabsorbable sutures were used for muscle-sclera (Conventional group) or muscle-implant fixation (Silicone and Marlex group) and absorbable sutures were used for implant-sclera fixation (Silicone and Marlex group).

MAIN OUTCOME MEASURES

The efficacy of posterior fixation suture was determined by forced duction testing toward the operated-on muscle immediately after the operation and at 8 weeks postoperatively. Eyes were enucleated at 8 weeks after surgery to measure the stability of the bond using a push pull gauge, and finally the histologic findings were evaluated.

RESULTS

Immediately after posterior fixation suture and at 8 weeks postoperatively, the restrictive motion during duction toward the operated-on muscle was greater in the Marlex group compared to the other groups (P < .001). The resistance to separation of the myoscleral union was greatest in the Marlex group (P < .001).

CONCLUSIONS

Posterior fixation suture can be effectively reinforced and stabilized using Marlex mesh.

Intrauterine growth in multiple pregnancies in relation to fetal number, chorionicity and gestational age

OBJECTIVES

To examine birth weight in dichorionic and monochorionic twins and trichorionic triplets, and to estimate the relative independent importance on growth of fetal number, chorionicity and gestational age.

METHODS

Four groups of pregnancies were examined: 12,816 singleton pregnancies, 302 monochorionic twin pregnancies, 569 dichorionic twin pregnancies, and 97 trichorionic triplet pregnancies. Chorionicity was determined at 10-14 weeks on the basis of the presence or absence of the lambda sign in twins, and by examining the ipsilon zone in triplets. The relationship between birth weight and gestational age in singletons was established, and using this equation the expected mean birth weights for all gestational ages were calculated. For each case in all groups, the difference between the observed birth weight for each fetus and the appropriate normal mean for gestation in singletons was calculated (Z-score). Multiple regression analysis was used to examine the independent contribution of gestational age, number of fetuses and chorionicity in the prediction of actual birth weight and birth weight Z-score.

RESULTS

Birth weight Z-score was significantly lower than the expected mean in singletons for dichorionic twins, monochorionic twins and trichorionic triplets (t = 15.4, P < 0.0001, t = 21.7, P < 0.0001 and t = 19.9, P < 0.0001, respectively). Furthermore, the reduction in expected birth weight was significantly greater for monochorionic twins and trichorionic triplets compared with dichorionic twins (t = 6.3, P < 0.0001 and t = 7.8, P < 0.0001, respectively). Multiple regression analysis demonstrated that number of fetuses, presence of a monochorionic placenta and gestational age were independently associated with birth weight Z-score, the strongest effect being fetal number, followed by monochorionicity (t = - 23.4, P < 0.0001, t = - 8.3, P < 0.0001 and t = - 4.9, P < 0.0001, respectively).

CONCLUSIONS

The finding that monochorionic twins were of lower adjusted birth weight than dichorionic twins, and the significant independent effect of chorionicity on birth weight suggest that monochorionic placentation in itself has an effect on intrauterine growth. The effect of fetal number independent of chorionicity is demonstrated by the lower birth weight of trichorionic triplets compared with dichorionic twins.

Determining chorionicity in twin gestations: three-dimensional (3D) multiplanar sonographic measurement of intra-amniotic membrane thickness

OBJECTIVES

Measuring the thickness of the membranes to determine chorionicity in twins using two-dimensional (2D) ultrasound may provide uncertain results, given the possibility of measuring in an oblique view. We aimed to determine whether chorionicity can be assessed during the second and third trimesters by measuring the thickness of the membranes with three-dimensional (3D) multiplanar ultrasound, which ensures the measurement is perpendicular to the membranes, and to evaluate the reproducibility of the technique.

METHODS

This was a prospective study of 84 twin pregnancies (30 monochorionic and 54 dichorionic) between 20 and 35 weeks of gestation. The dividing membranes between the fetuses were visualized with 2D and 3D transabdominal sonography and the thickness of the membranes was measured by the multiplanar technique. Intraobserver variability was assessed by comparing the measurements obtained in sagittal and axial views by the same observer. We examined the frequency distributions to determine the optimal cut-off point of the thickness of the membranes to predict chorionicity. Kappa index, intraclass correlation coefficients and 95% limits of agreement were calculated to evaluate the inter- and intraoperator variability. We also compared membrane-thickness measurement, during the second and third trimesters, using 2D and 3D ultrasound.

RESULTS

In monochorionic and dichorionic pregnancies, respectively, the mean thickness was 1.42 (SD, 0.31) mm and 2.48 (SD, 0.47) mm. With 3D ultrasound, the intraclass correlation coefficient was 0.99 in all cases. The 95% limits of agreement were all within +/-0.2 mm. The best cut-off for membrane thickness for discriminating monochorionic from dichorionic twinning was 1.8 mm. Using this cut-off, there were one false-negative (sensitivity, 97%; 95% CI, 83-99%) and three false-positive (specificity, 94%; 95% CI, 85-99%) diagnoses of monochorionic twins. Kappa indices for intra- and interoperator variability were all above 90%, suggesting almost perfect agreement. Measurements with 2D sonography were less accurate (sensitivity and specificity, 83%).

CONCLUSION

Prenatal assessment of dividing membranes using 3D multiplanar ultrasound is reproducible and may be a useful alternative method for determining chorionicity in twin pregnancies during the second and third trimesters.

Additional benefits of first trimester screening

The goal of first trimester screening for aneuploidy is to provide patients their risk assessment for fetal Down syndrome. Nonetheless, it has been noted that combined screening offers physicians and patients other important pregnancy information. For example, first trimester ultrasound results in accurate pregnancy dating and enables the early diagnosis of multiple gestations during the period when amnionicity and chorionicity is best discerned. It also detects a limited number of fetal anatomical abnormalities, affording patients time to make decisions regarding the management of their pregnancies. A cystic hygroma, one of the most powerful ultrasound markers for fetal aneuploidy, can be detected on first trimester ultrasound. An enlarged nuchal translucency may identify fetuses at risk for other adverse outcomes and for congenital heart defects. In addition, abnormal first trimester serum markers are associated with adverse pregnancy outcomes, and knowledge of these abnormalities may help with patient counseling and management.

Antenatal Detection of Arterio-Arterial Anastomoses by Doppler Placental Assessment in Monochorionic Twin Pregnancies

OBJECTIVES

To evaluate the reproducibility of Doppler antenatal detection of arterio-arterial anastomoses (AAA) in monochorionic (MC) twin pregnancies.

METHODS

Between October 2002 and February 2004, 21 MC diamniotic twin pregnancies and one dichorionic triamniotic triplet seen at the Twin Clinic at the University of Brescia were recruited. After routine ultrasonographic assessment, AAA were searched using Color or Power and spectral Doppler. The presence of AAA was confirmed postnatally by placental injection studies.

RESULTS

Data of 19 patients were available for the analysis. AAA were detected in 12 cases (63%) antenatally and in 16 (84.2%) at injection study. Sensitivity and specificity of Doppler for detecting AAA were 75 and 100%, respectively. Detection rates increased at advanced gestations and with anterior/fundal placentae. The incidence of twin-twin transfusion syndrome was higher in the group with no AAA detected in vivo compared to the group with AAA found with Doppler (28.5 vs. 16.6%), but the difference was not statistically significant (p = 0.5).

CONCLUSION

This study confirmed the feasibility of AAA Doppler detection in vivo in MC pregnancies.

Ultrasound in multiple gestations: twins and other multifetal pregnancies

Ultrasound has an important role not only in assessing amnionicity and chorionicity but also in diagnosing abnormalities and providing fetal surveillance throughout the duration of gestation.

Evidence-based care of women with a multiple pregnancy

Women with a multiple pregnancy face greater risks for themselves and their infants than women pregnant with one child. Pre-pregnancy care should focus on avoiding multiple pregnancy. Early prenatal care centres on determining chorionicity and screening for fetal anomalies, with later care focusing on the presentation, prediction and management of preterm birth, and intrauterine growth restriction. The optimal timing and mode of birth are the focus of current multicentre, randomised, controlled trials. However, the data from such trials on care for women with a multiple pregnancy are limited. Many areas of care require better-quality information, including when using assisted reproductive techniques, the optimal number of embryos to be transferred, care after the diagnosis of chorionicity, and the benefits of specialised multiple pregnancy clinics. Better-quality information is required to inform clinical practice for women with complications of multiple pregnancy, including monoamniotic twin pregnancy, treatment of twin-to-twin transfusion syndrome, and care following single intrauterine fetal death.

The sonographic diagnosis of chorionicity

The differentiation between mono- and dichorionic placentation in twin pregnancies is of clinical importance because of the significant difference in perinatal morbidity and mortality between the two, and the increased surveillance indicated in monochorionic gestations. Application of ultrasonography has enabled very precise prenatal determination of chorionicity. While this is best performed in the first trimester when accuracy approaches 100%, even in the third trimester, using a composite cascade of available sonographic features, accuracy has been reported to approach 97%. While two clearly separate placentae or discordant fetal gender conform to dichorionicity, in most twin pregnancies other features need to be assessed to determine chorionicity. The presence of the 'lambda' or the 'T' sign in the presence of a single placenta, best determined in the first trimester, is the most reliable indicator of chorionicity, with measurements of the inter-twin membrane thickness and counting of the membrane layers being less reliable. In this article, we review the sonographic features that help in the accurate depiction of chorionicity.

Twin pregnancies discordant for anencephaly—management, pregnancy outcome and review of literature

AIMS AND METHODS

To examine the prognosis of conservative management in twin pregnancies discordant for anencephaly, we review the literature and report on four of our own cases, which were analyzed retrospectively.

RESULTS

In the University Hospital of Erlangen, six twin pregnancies discrepant for anencephaly were observed during an 8-year period (1992-2000). Four of these pregnancies were managed conservatively. Preterm delivery occurred in all of the cases, but the unaffected fetuses all had favorable long-term outcome. Delayed interval delivery was performed in two cases due to extreme immaturity in the healthy fetus.

CONCLUSIONS

Our data show that in twin pregnancies with early diagnosis of anencephaly in one fetus, the risk of premature delivery of the healthy fetus may be more increased than is already known in the literature. Therefore, selective fetocide of the anencephalic fetus is a management option, at least in dichorionic pregnancies, to prevent polyhydramnios and to reduce the risk of preterm delivery.

Prediction of chorionicity in twin pregnancies at 10-14 weeks of gestation

OBJECTIVE

To examine the accuracy of sonographic determination of chorionicity in twin pregnancies at 10-14 weeks of gestation.

DESIGN

Prospective study on the sonographic prediction of chorionicity at 10-14 weeks of gestation.

PARTICIPANTS

During a 30 month period, from October 1997 to May 2000, 165 women attending the departments of fetal medicine or ultrasound.

METHODS

Sonographic criteria used in the diagnosis of chorionicity were the number of placental sites, the lambda (lambda) and T signs and the thickness of the inter-twin membrane. The diagnosis of chorionicity was made at the time of the ultrasound examination using all these features and subsequently compared with the postnatal diagnosis, confirmed either by placental histology or discordancy in infant sex.

RESULTS

In 150 cases with confirmation of chorionicity following delivery, 116 were postnatally classified as dichorionic and 34 monochorionic. Prenatal ultrasound examination correctly identified chorionicity in 149 (99.3%) cases. The most reliable indicator for dichorionicity was a combination using the lambda sign or two separate placentae with a sensitivity and specificity of 97.4% and 100%, respectively. The most useful test in predicting monochorionicity was the T sign with a sensitivity of 100% and specificity of 98.2%. Measurement of the inter-twin membrane thickness was a less reliable indicator where the sensitivity for dichorionicity and specificity for monochorionicity was only 92.6%.

CONCLUSIONS

Ultrasound examination of twin pregnancies at 10-14 weeks of gestation predicts chorionicity with a high degree of accuracy using a combination of the number of placentae, lambda and T signs and inter-twin membrane thickness. All hospitals should encourage departments providing ultrasound services to undertake chorionicity determination when examining women with twin pregnancies at this gestation.

Outcome of first-trimester chorionic villus sampling for genetic investigation in multiple pregnancy

OBJECTIVES

To evaluate the efficacy of and risk associated with chorionic villus sampling for genetic investigations in multiple pregnancies, and to evaluate the accuracy of the ultrasonographic detection of chorionicity during the first trimester.

PATIENTS AND METHODS

A total of 198 sets of twins and nine sets of triplets from 10 087 consecutive first-trimester pregnancies undergoing chorionic villus sampling were considered. Gestational age ranged from 7 to 12.6 weeks. Assessment and confirmation of chorionicity was based on a multiplicity of features. Dichorionicity was established in 169 sets of twins (85.3%) and trichorionicity in all triplet cases, while 29 twins were considered monochorionic. Chorionic villus sampling was performed transabdominally in all but one case, and identification of the placental insertion of the umbilical cord was the main benchmark for sampling. Sampling risks were evaluated by comparing clinical outcome with that of a control population of 63 dichorionic twin pregnancies which underwent no invasive procedure.

RESULTS

Determination of the presence or absence of the lambda sign led to a correct assignment of chorionicity in all cases, while the presence of a membrane thickness of 2 mm or more reflected a 100% specificity with a 22% false negative rate. Sampling was successfully performed in all cases and in only four cases (1.0%) were two needle insertions needed. At follow-up no evidence of incorrect sampling was reported. Karyotyping was provided to all patients, and in 94.1% of cases both short and long-term culture methods were carried out. No difference in fetal and perinatal losses between the study and control populations was found, but a higher rate of deliveries before 37 weeks and of low birth weight babies was noted amongst controls.

CONCLUSIONS

Chorionicity in twin pregnancy can be determined with certainty between 7 and 12 weeks of gestation; in cases of confluent placentas reliability is provided by determining the presence or absence of the lambda sign. This study indicates that first-trimester transabdominal chorionic villus sampling is a highly efficient, reliable, and relatively safe approach for genetic diagnosis in twin pregnancies. Although a precise evaluation of the relative risks of chorionic villus sampling and mid-trimester amniocentesis in twins must await randomized control studies, the advantages of a first-trimester diagnosis to enable early decision-making about selective fetal reduction are obvious.

Prenatal diagnosis of heterokaryotypic mosaic twins discordant for fetal sex

The presence of a monozygotic twin gestation with discordant sex of the twins is a very rare constellation, which is referred to as heterokaryotypic monozygotic pregnancy. This constellation can develop either due to a chromosomal aberration after twinning or is - as in the following case - due to a mitotic error before twinning and an unequal distribution of mosaicism in both embryos. So far the diagnosis of heterokaryotypic monozygotic pregnancy has always been made postnatally, with only one exception (Gonsoulin et al., 1990). In this case we suspected the presence of monozygotic twins ultrasonically because of the chorionic and amniotic membrane characteristics. Surprisingly the sex of the fetuses was discrepant. As one of them had hydrops and a structural heart defect, we carried out an amniocentesis, which revealed mosaicism [45,X/46,X,i(Y)(p10)] of both fetuses. The female fetus with a predominant 45,X set of chromosomes and the typical intrauterine signs of the Ullrich-Turner syndrome (massive hygroma colli, hydrops fetalis and multiple cardiac defects) died during the 25th week of gestation due to cardiac decompensation. The other fetus appeared to be male with a predominance of a 46,X,i(Y)(p10) set of chromosomes and was born a few days after the intrauterine death of the hydropic fetus. In conclusion, our observation shows that ultrasonic evidence of discordant fetal sex in twins does not necessarily exclude monozygosity.

Sonographic considerations with multiple gestation

Determination of chorionicity is of paramount importance in risk assessment and management. Best performed in the first trimester, dichorionic placentation can be reliably assumed when the membrane is easily seen, there is a "twin peak" sign, there are clearly separate placentas, and there is discordant fetal gender. In a monochorionic twin pregnancy, there is a single placental mass, the dividing membrane is difficult to visualize until the end of the first trimester, and the membrane inserts onto the placental surface without a peaked appearance. Amniotic fluid volume assessment is important in the management of twin pregnancy. Polyhydramnios-oligohydramnios may be a manifestation of twin-twin transfusion syndrome, although oligohydramnios with normal amniotic fluid volume in the other twin's sac may more likely be a sign of velamentous cord insertion, infection, or chromosomal or structural abnormality. Fetal growth discordance is common in twin pregnancy and is associated with increased perinatal mortality and morbidity. The most sensitive indicator of discordant twin growth is thought to be estimated fetal weight, and an intertwin difference of > or = 20% is considered significant. In the clinical care of a patient with twins, it is reasonably standard to confirm chorionicity with ultrasonography in the first or early second trimester. At about 20 weeks, a level II ultrasound for anatomic survey is indicated. In dichorionic pregnancies, ultrasound examinations are then performed at 26 to 28 weeks and every 3 to 4 weeks thereafter to follow growth and amniotic fluid volume. In monochorionic twins, we generally do an additional ultrasound at about 23 to 24 weeks, because of the risk of twin-twin transfusion syndrome. In the late third trimester, careful attention should also be given to fetal position, to help with delivery planning.

First trimester ultrasonography of multiple gestations: a review

The objective was to review current literature pertaining to first trimester ultrasonography of multiple gestations. To this goal, all manuscripts published in the English language regarding this topic were selected and reviewed in a MEDLINE search from 1966 through May 1998. Additional sources were identified through cross-referencing. Current widespread application of first trimester ultrasonography and especially transvaginal sonography has introduced a new dimension in both diagnostic and management aspects of multiple gestations. Application of first trimester ultrasonography in multiple gestations enables an earlier and more precise depiction of important anatomical details regarding fetal viability, chorionicity, pregnancy outcome, structural abnormalities, pathophysiology of developmental disorders (such as twin reverse arterial perfusion [TRAP] sequence), early sonographic signs associated with fetal aneuploidy (nuchal translucency and abnormal crown-rump length), and potential fetal growth discordancy. First trimester ultrasonography also assists in guiding operative procedures including: amniocentesis, chorionic villus sampling, and selective fetal reduction. Enhanced information obtained with high-resolution, first trimester transvaginal ultrasonography is rapidly becoming a standard for establishing critical information that will assist clinicians to stratify management of multiple gestations. Given the increasing incidence of multiple gestations because of various assisted reproductive technology modalities, it is important that obstetricians become aware of the potential advantages of first trimester ultrasonography in clinical management of multiple gestations.

Ambulatory management of multiple gestation

Ambulatory management of multiple gestation requires careful and continuing care by the obstetrician. The initial evaluation should include a comprehensive history, including use of fertility enhancing drugs and ART, family history, social history; a general physical examination, including a pelvic examination; laboratory evaluation, including complete blood cell count, dipstick urinalysis for protein and glucose, urine culture, blood type, Rh factor and irregular blood antibody determination, serology for rubella, syphilis, hepatitis B surface antigen and varicella (if there is no history). A Papanicolaou smear should be done at the time of the pelvic examination, as should evaluation for bacterial vaginosis. Ultrasound assessment of placentation should be done at 14 weeks' gestation, but vaginal or perineal ultrasound of cervical length should be done at the initial visit. Other testing procedures should include repeat ultrasound evaluation for fetal growth every 4 weeks in a dichorionic placentation and every 3 weeks if monochorionic placentation is present. Triple screen MSAFP at 16-18 weeks' gestation and blood sugar screening at 22-26 weeks should be performed. After the first trimester, the patient should schedule physician visits every 2 weeks or less. Routine medications should include one prenatal vitamin per day, additional folic acid supplementation of 1.0 mg per fetus, supplemental iron preparation, and additional calcium to equal 1500 mg/day. The use of low-dose aspirin to prevent preeclampsia in twin gestations has not been adequately studied. Continuing vigilance by the knowledgeable obstetrician should occur. Multiple gestations should not be cared for by non-physician providers or by family physicians. Referral to a maternal-fetal medicine unit is recommended.

Very early and simple determination of chorionic and amniotic type in twin gestations by high-frequency transvaginal ultrasonography

OBJECTIVE

The aim was to determine the chorionic and amniotic types in multifetal pregnancies with transvaginal ultrasonography at very early stage of gestation.

STUDY DESIGN

Twenty-one spontaneous multifetal pregnancies were scanned transvaginally before 8 weeks' gestation (four of them from 4th week). The chorionic and amniotic type was determined ultrasonographically. All twin gestations had postpartum pathologic evaluation of the placenta and histologic determination of the chorionic and amniotic type.

RESULTS

Ultrasonographic evaluation of the 21 pregnancies demonstrated 20 twin and 1 triplet gestation. Four of the twin pregnancies were monochorionic-diamniotic. Triplet was monochorionic-triamniotic (spontaneously aborted in 8th week of gestation). In all 20 twin pregnancies, transvaginal ultrasonography correctly predicted the chorionic and amniotic type before 8 weeks of gestation.

CONCLUSION

Transvaginal ultrasonography allows a reliable, simple and rapid determination; the dichorionic twin pregnancy in 4 weeks, monochorionic in 5 weeks, and differentiation of mono- or diamniotic in 7 weeks of gestation.

Screening for fetal abnormalities in multiple pregnancies

Multiple gestations account for 1-2% of all pregnancies but contribute disproportionately to the incidence of both perinatal loss and fetal structural abnormalities. Ultrasound examination provides essential information about screening for, and the management of, such defects, including accurate determination of chorionicity, assessment of risk, invasive testing and selective termination if appropriate.

The consequences of monochorionic placentation

Monochorionic (MC) placentation occurs in two-thirds of monozygous twins and approximately 0.3% of all spontaneous conceptions. Vascular anastomoses within the placenta allow intertwin transfusion to occur, which is in most cases a normal event. However, imbalance in this flow may lead to the clinical sequelae observed, with acute, chronic or reverse intertwin transfusion. Acute transfusion describes the events following the death of one of an MC twin pair in utero, with an approximately 1 in 4 chance of demise or neurological damage in the co-twin. Chronic intertwin transfusion, otherwise termed feto-fetal transfusion syndrome, arises following the gradual flux of blood from one twin (the donor) to its sibling fetus (the recipient). The ensuing polyhydramnios places the pregnancy at risk of preterm amniorrhexis and/or labour, notwithstanding the specific sequelae seen in these fetuses following chronic in utero insult. Reverse transfusion describes the most bizarre form of intertwin transfusion: acardiac twinning. Retrograde perfusion of one of the twins with deoxygenated blood leads to the formation of a non-viable acardiac parasite and a 'pump twin' struggling to maintain the cardiac output required to perfuse both twins.

The aetiology and management of twin-twin transfusion syndrome

Twin-to-twin transfusion syndrome presents in the mid-trimester with gross discordance in amniotic fluid volume, and complicates 10-15 per cent of monochorionic twins. Recent studies suggest a primary vascular basis in which a paucity of the bidirectional superficial anastomoses normally found in monochorionic twins is unable to compensate for haemodynamic imbalance resulting from unidirectional transfusion along deeper arterio-venous anastomoses. It is associated with high rates of perinatal mortality from ruptured membranes, hydrops and growth restriction, and a significant morbidity from cardiac and neurological sequelae in particular. Serial aggressive amnioreduction is the current treatment of choice, with survival in around two thirds of cases. In the remaining third, with features suggesting a poor outcome, selective fetocide may have a role. Current attempts at vascular ablative therapies have been associated with inferior survival rates, but the long term therapeutic goal remains the identification and ablation of the shared chorionic vasculature.

Determination of chorionicity in twin gestations by high-frequency abdominal ultrasonography: counting the layers of the dividing membrane

OBJECTIVE

Our aim was to determine whether chorionicity in twin gestations can be diagnosed by use of high-frequency ultrasonography to count the layers of intraamniotic membrane.

STUDY DESIGN

This prospective study of 66 twin pregnancies between 13 and 38 weeks' gestation used transabdominal ultrasonography at 10 MHz. The pregnancy was classified as monochorionic when two layers were counted and as dichorionic when three or four layers were counted. The findings of the examiner, who had no other information about chorionicity, were compared with those of the histopathologic examination of the placenta.

RESULTS

Ultrasonography allowed chorionicity to be determined correctly in 60 of 63 cases (95%; 100% in the second trimester and 92% in the third. The predictive value for dichorionicity was 100% (48/48) and the sensitivity 94% (48/51). The 12 monochorionic diamniotic pregnancies in which the membrane was visualized were all correctly diagnosed. In a thirteenth case, with severe oligohydramnios, the membrane could not be seen. Two patients were lost to follow-up. In 95% of the cases (63/66) only one examination was required to diagnose chorionicity. Intraobserver variability was 0% (0/26). Interobserver variability, tested by photographs, was 3% (2/65).

CONCLUSIONS

This technique should be the first-line method for determining chorionicity in the second and third trimesters because it is the most effective. Its excellent reproducibility may be attributable to the use of high-frequency ultrasonography.

Late selective termination of fetal abnormalities in twin pregnancies: a multicentre report

OBJECTIVE

To evaluate the outcome of late selective fetal termination based on combined data from eight tertiary perinatal centres.

DESIGN

Israeli law requires institutional committee approval for pregnancy termination. Moreover, after 24 weeks only a district superior committee can approve the termination. A total of 36 bichorionic twin pregnancies who underwent selective fetal termination after 24 complete gestational weeks were identified in eight Israeli centres.

RESULTS

In 23 women (63.9%) the indication for selective termination was structural anomaly, and in 13 (36.1%) the indication was chromosomal abnormality. The mean gestational age at the time of diagnosis was 24.1 +/- 1.9 weeks. The termination procedure was performed at a mean gestational age of 25.5 +/- 2.0 weeks (median 25, range 24-33 weeks). There was one case of immediate procedure-related complication (i.e. amnionitis) and the unaffected infant died, which was the only perinatal death in this series. No evidence of coagulopathy was reported. Only five women (13.8%) delivered before 34 completed weeks. The mean gestational age at delivery was 36.9 +/- 2.9 weeks (28-41 weeks), and the mean procedure-to-delivery interval was 11.8 +/- 3.2 weeks (median 13, range 3-17 weeks).

CONCLUSIONS

Late (> 24 weeks) selective termination in twin pregnancies is associated with favourable perinatal outcome of the healthy twin. In countries where the law permits late pregnancy termination, the parents should be informed of that possibility.

The sequential in utero death of heterokaryotic monozygotic twins. A case report and literature review

A case of monozygotic twins in a 19-year-old primigravida is presented. Ultrasound examination at 15 weeks' gestation showed one twin to have a cystic hygroma and hydrops fetalis. The other twin appeared normal. The twins appeared to occupy the same amniotic cavity. Fluid was taken from the cystic hygroma under ultrasound guidance for karyotyping and this showed 45,XO chromosomes. Conservative management was adopted. Serial ultrasound examination showed deteriorating hydrops and at 26 weeks the first twin died. Intensive monitoring of the remaining twin was undertaken with weekly ultrasound, cardiotocography (CTG), and clotting screens. At 29 weeks' gestation the CTG and clotting were normal, but ultrasound revealed that multicystic encephalomalacia had developed in the second twin. A very thin dividing membrane was seen for the first time between the twins. The parents decided to terminate the pregnancy. Prior to an intracardiac potassium chloride injection, a fetal blood sample was taken which revealed 46,XX chromosomes and a normal clotting screen including natural anticoagulant levels. Labour was then induced. Delivery took place 5 h later and the woman made an uneventful recovery. The mechanism for genetic differences between monozygotic twins is discussed and the literature reviewed. A non-disjunction event around the time of splitting of the twins is proposed as the cause. The prognosis for the remaining twin is also discussed, as is the pathogenesis of the cerebral damage.

Sonographic determination of first trimester twin chorionicity and amnionicity

OBJECTIVE

To determine the reliability of first trimester sonography in the detection of twin chorionicity and amnionicity.

MATERIALS AND METHODS

Sets of twins (179) were evaluated sonographically in the first trimester. Chorionicity was determined by identifying the number of gestational sacs. The presence or absence of an amnion about each embryo/fetus was also recorded. The placentas for each case were evaluated to determine chorionicity and amnionicity.

RESULTS

Of the 179 twin pairs, 158 were dichorionic/diamniotic; 19 were monochorionic/diamniotic, and two pairs were monochorionic/monoamniotic. Chorionicity and amnionicity were correctly determined in each case.

CONCLUSION

The chorionicity of twin pregnancies can be determined from the time that the gestational sacs are visualized within the uterus. Transvaginal sonography can reliably determine the amnionicity of monochorionic twin pregnancies after 7 weeks, menstrual age.

Ultrasonographic measurement of the dividing membrane in twin pregnancy during the second and third trimesters: a reproducibility study

OBJECTIVE

Our purpose was to examine the reproducibility of intertwin membrane thickness measurements used to predict chorionicity in twin pregnancies.

STUDY DESIGN

Twenty-seven twin pregnancies were scanned with high-resolution ultrasonography on 52 occasions during the second and third trimesters. Two observers, blind to other criteria of chorionicity, measured the dividing membrane twice in five different sites (total measurements 1040). The data were log-transformed and the coefficient of repeatability calculated as a measure of intraobserver variability. Interobserver variability was estimated by the Bland and Altman 95% limits of agreement. Random variation was assessed with the restricted maximum likelihood procedure in Genstat.

RESULTS

The overall estimate of the coefficient of repeatability was 2.14, indicating that 95% of repeated measurements would be expected to be within 114% of each other. Measurements taken close to the placenta (up to 3 cm) were the most repeatable and displayed no bias when repeated. Coefficients of repeatability at this site ranged from 1.42 to 1.91, with no evidence of consistent differences between monochorionic and dichorionic twins. Gestational age was not significantly associated with membrane thickness for any of the models. The pregnancy type x subject x observer and pregnancy type x subject x site interactions were statistically significant (p < 0.001 and p < 0.005, respectively), implying that interobserver variability depends on the subject being measured, the site of sampling, and chorionicity.

CONCLUSION

Ultrasonographic measurement of membrane thickness has high intraobserver and interobserver variability in the second and third trimesters. Our findings provide an explanation for the suboptimal accuracy reported with this method in determining chorionicity in the second and third trimesters.

Early first-trimester ultrasound provides a window through which the chorionicity of twins can be diagnosed in an in vitro fertilization (IVF) population

PURPOSE

Early and accurate diagnosis of placentation alerts the obstetrician to potential clinical sequelae. The reproductive endocrinologist has a unique opportunity to sonographically evaluate the very early intrauterine pregnancy. We undertook this study to determine whether chorionicity could accurately be predicted using early first-trimester transvaginal ultrasound.

RESULTS

Of 47 sets of twins conceived through our IVF-ET program, all underwent detailed transvaginal sonography. These findings were then compared with results of placental pathology examination, after birth. Transvaginal sonography was performed 41 days following embryo transfer. All 3 monochorionic placentas were correctly predicted by ultrasound, while the remaining 44 placentas were dichorionic.

CONCLUSIONS

The significance of our findings lies both in our 100% accuracy in diagnosis and in the extremely early gestational age at which we were able to establish correctly the diagnosis of chorionicity. The errors in diagnosis made by previous investigators were often the result of not recognizing single placentae which were later histologically shown to be the result of placental fusion. The infertility specialist has a unique window of opportunity to evaluate placentation and should provide useful information regarding chorionicity to the obstetrical team.

Prospective determination of chorionicity, amnionicity, and zygosity in twin gestations

OBJECTIVE

Our purpose was to determine the predictive accuracy of a composite ultrasonographic evaluation for chorionicity, amnionicity, and zygosity in a consecutive series of twins.

STUDY DESIGN

One hundred ten consecutive twins were seen for ultrasonography beginning January 1992. Chorionicity, amnionicity, and, zygosity were prospectively assessed with a composite of ultrasonographic findings (placental number, fetal sex, membrane thickness, and "twin peak" sign). Clinical and pathologic confirmation of chorionicity, amnionicity, and zygosity was available on 100 of these twins.

RESULTS

The 100 twins had 3.6 +/- 1.6 ultrasonographic scans each (mean +/- SD) with the first performed at 22.6 +/- 6.9 weeks. Chorionicity, amnionicity, and zygosity were each predicted with > or = 91% sensitivity and specificity. In 35 (35%) cases zygosity could not be determined by either ultrasonographic or clinical or pathologic assessment at delivery.

CONCLUSION

Chorionicity, amnionicity, and zygosity have important implications for antepartum management and prognosis of twins. By use of a composite of ultrasonographic findings, chorionicity, amnionicity, and zygosity were predicted with excellent reliability when they were prospectively tested in a heterogeneous consecutive series of twins.

Multifetal pregnancy reduction and selective termination

The incidence of multifetal pregnancies has increased dramatically since the advent of assisted reproductive technologies. Preterm delivery accounts for most of the mortality associated with multifetal pregnancies. Multifetal pregnancy reduction is a safe and effective procedure designed to decrease the adverse outcomes associated with very preterm deliveries. The increased incidence of multifetal pregnancies combined with reliable techniques for prenatal diagnosis of genetic and structural fetal anomalies have led to an increase in the diagnosis of abnormal fetal conditions in parents carrying multiple gestations. The development of the procedure of selective termination has provided prospective couples the option of selective termination of the abnormal fetus and continuation of the pregnancy.

Genetic diagnosis in multiple pregnancies

A twin gestation presents unique problems in both genetic counseling and prenatal diagnosis. This article describes the specific genetic counseling concerns for a twin gestation and outlines the available techniques for genetic prenatal diagnosis. The technical aspects, risks and benefits to the pregnancy of amniocentesis and of chorionic villi sampling are compared. Although the risk of miscarriage after amniocentesis in a twin gestation is at least double that for a singleton, much of this additional risk is secondary to the inherent hazards of twins and not procedure-related. In experienced centers, chorionic villi sampling is equally safe and efficacious, and allows an earlier diagnosis that may be beneficial when discordant results are found. The aspects of serum screening unique to twin gestations are also outlined. Prenatal diagnosis by both chorionic villus sampling and amniocentesis can be safely performed in twin gestations and higher-order multiple gestations. Serum screening is also useful, but appears to have a lower sensitivity and specificity than in singletons.

Placental transfer of lidocaine hydrochloride after prolonged continuous maternal intravenous administration

We treated a patient with arrhythmia during pregnancy with prolonged intravenous administration of lidocaine hydrochloride. This was a case of twin-to-twin transfusion syndrome and the arrhythmia was caused by ritodrine therapy. In total, 14.1 g lidocaine (50 mg.hr-1 for 282 hr) were used. Since there are no descriptions of human placental transfer of lidocaine after such a prolonged continuous intravenous administration, we measured lidocaine concentrations in maternal and fetal serum, and in the amniotic fluid (AF) at delivery. Fetal serum lidocaine concentrations (donor: 0.83 microgram.ml-1; recipient: 0.82 microgram.ml-1) were lower than in the maternal serum (1.6 micrograms.ml-1), while the AF lidocaine concentrations (donor: 1.05 micrograms.ml-1; recipient: 1.04 micrograms.ml-1) were higher than those of the fetal sera. The fetal/maternal concentration ratios of lidocaine were 0.52 for the donor and 0.51 for the recipient, which were similar to those described previously after administration of lidocaine in labour.