Early and simple determination of chorionic and amniotic type in multifetal gestations in the first fourteen weeks by high-frequency transvaginal ultrasonography

First-trimester ultrasound

There has been an increase in the use of fetal ultrasound in the first trimester. This article reviews the published literature with emphasis on fetal nuchal translucency (NT). When measured according to well-defined guidelines, increased NT identifies about 80% of chromosomal anomalies for a false-positive rate of about 5%. Increased NT may indicate the presence of structural defects or genetic disorders, and it is relatively frequently seen in monochorionic pregnancies prone to develop twin-twin transfusion syndrome.

Twin pregnancy: the role of ultrasound in management

Determination of chorionicity is one of the most important issues in the management of twin pregnancy. Modern ultrasound equipment has made it possible to accurately assess placentation already in the first trimester with the lambda sign. With regard to prenatal diagnosis, it is important to know the chorionicity in order to calculate the risk of chromosomally abnormal fetuses. Accurate chorionicity offers the obstetricians the opportunity to observe the monochorionic twins more intensively than is required for twins with dichorionic placentation. This review gives an update of the state of the art for clinicians caring for twin pregnancies.

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.

Sono-endoscopic delineation of the placental vascular equator prior to selective fetoscopic laser ablation in twin-to-twin transfusion syndrome

OBJECTIVE

To assess the safety and efficacy of a new fetoscopic technique in the management of twin-to-twin transfusion syndrome.

STUDY DESIGN

Prospective study of fetoscopic treatment and outcome in 10 pregnancies complicated by severe twin-to-twin transfusion syndrome before 24 weeks' gestation. The sono-endoscopic approach was used to identify the placental vascular equator and photocoagulate any vessels crossing this threshold.

RESULTS

The mean gestation at treatment was 20 weeks and 3 days. An average of three to four vessels were ablated during each procedure, with a mean operative time of 24 min (range, 14-31 min). The overall survival rate was 55% (11 of 20) with at least one survivor in 70% (seven of 10) of pregnancies.

CONCLUSIONS

Fetoscopic laser ablation is a safe and effective form of treatment in the management of severe twin-to-twin transfusion syndrome. This technique, where vessels crossing the placental vascular equator are identified and photocoagulated fetoscopically, is an alternative to the non-selective and selective methods described previously. This new approach is associated with a shorter operating time, less damage to the normal placental surface vasculature and with survival results that are at least as promising as previously reported techniques.

Yolk sacs in twin pregnancy

OBJECTIVE

The purpose of this study was to evaluate the relationship between the yolk sacs separated or not separated by septum and chorionicity twin pregnancies scanned early in the first trimester, and the relation between size and morphologic features of the yolk sac and the outcome of twin pregnancies.

RESULTS

In all 38 sets of twins two yolk sacs were identified. During the first trimester of a dichorionic twin pregnancy, the yolk sacs were always separated by a septum and not separated ("Eight" sign) in monochorionic twin pregnancy. In five cases, one of yolk sac was abnormally large (> 8 mm) and had thin wall. Four of the five mothers spontaneously aborted during the next 2-3 weeks. In one case of monochorionic twin ectopic pregnancy two yolk sacs were seen normally.

CONCLUSION

The sonographic identification of yolk sacs in multiple pregnancies allows an early and efficient recognition of presence and chorionicity of twin pregnancy, both in intra- and extrauterine. Identification of abnormal yolk sac or yolk sacs suggests death of one or all embryos.

Prenatal diagnosis in multiple pregnancy

Fetal abnormality is more common in multiple than in singleton pregnancies. This, together with the requirement to consider the risks with at least two babies to sample correctly each fetus and to undertake accurately-targeted selective termination, amounts to a major challenge for obstetricians involved in prenatal diagnosis. Early determination of chorionicity should be routine, since this influences not only the genetic risks but also the invasive procedure chosen for karyotyping or genotyping. Assessment of nuchal translucency identifies individual fetuses at risk of trisomy. Contrary to expectation, invasive procedures in twins appear to have procedure-related miscarriage rates that are similar to those in singletons. Instead, contamination remains a concern at chorionic villus sampling. Elective late karyotyping of fetuses may have a role in some countries. Whereas management options for discordant fetal abnormality are relatively straightforward in dichorionic pregnancies, monochorionic pregnancies are at risk of co-twin sequelae after any single intrauterine death. Techniques have now been developed to occlude completely the cord vasculature by laser and/or ultrasound guided bipolar diathermy. Given the complexities associated with prenatal diagnosis, all invasive procedures in multiple pregnancies should be performed in tertiary referral centres.

First trimester ultrasound with nuchal translucency measurement for Down syndrome risk estimation using software developed by the Fetal Medicine Foundation, United Kingdom--the first 2000 examinations in Newcastle, New South Wales, Australia

In September 1997 screening for Down syndrome using first trimester ultrasound to measure nuchal translucency, with risk estimation by the software program developed in the United Kingdom by the Fetal Medicine Foundation, was introduced in Newcastle, New South Wales. In the first 2,000 such risk estimations 134 women (6.7 %) were screen positive (with a risk of greater than 1 in 300 at that gestation for Trisomy 21). In the first 1,000 of these 2,000 fetuses delivered thus far there were 8 cases of Trisomy 21, 2 of Trisomy 18 and 1 of 47 XXX. Nine of these 11 were screen positive, the only false negative results being for 2 cases of Trisomy 21. The detection rate for Trisomy 21 was 6 out of 8 (75%) and for every case of Trisomy 21 (Down Syndrome) detected by this process, 11.3 invasive tests would have been needed to make that diagnosis in a screen positive woman.

Second-trimester multifetal pregnancy reduction facilitates prenatal diagnosis before the procedure

OBJECTIVE

To evaluate the pregnancy outcome of selective second-trimester multifetal pregnancy reduction (MFPR) compared to first-trimester MFPR.

DESIGN

Cohort analysis.

SETTING

In Vitro Fertilization Unit, Tel Aviv Sourasky Medical Center, Tel Aviv, Israel.

PATIENT(S)

The study groups comprised 38 and 70 patients who underwent selective second-trimester MFPR (group 1) and first-trimester MFPR (group 2) at mean gestational ages of 19.7 +/- 3.3 weeks and 11.7 +/- 0.7 weeks, respectively.

INTERVENTION(S)

Ultrasonographically guided intracardiac injection of potassium chloride (KCl) solution.

MAIN OUTCOME MEASURE(S)

Pregnancy outcome and obstetric complications.

RESULT(S)

No statistically significant difference was found between group 1 and group 2 regarding mean gestational age at delivery (35.4 +/- 3.4 weeks and 35.9 +/- 3.1 weeks, respectively); mean birth weight (2,318.9 +/- 565.7 g and 2, 138.1 +/- 529.4 g); and the incidence of obstetric complications. These complications included pregnancy loss (5.2% and 15.7%), pregnancy-induced hypertension (0 and 10%), discordancy (12% and 18. 4%), intrauterine growth restriction (0 and 40%), and gestational diabetes (0% and 6%). However, the rate of all pregnancy complications was lower among second-trimester MFPR patients.

CONCLUSION(S)

Selective second-trimester MFPR is associated with favorable perinatal outcome and may facilitate detection of structural and chromosomal anomalies before the procedure and selective reduction of the affected fetus.

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.

Obstetric sonography. Who to scan, when to scan, and by whom

Most patients in the United States have an indication for and receive sonography during pregnancy. The issue of routine sonography for low-risk women continues to be contentious even though the randomized trials have not been able to demonstrate a clear benefit. Clinics that routinely offer sonography for all pregnancies usually schedule such a procedure at 16 to 20 weeks of gestation. Although great progress is being made in the first-trimester diagnoses of congenital anomalies, most targeted studies are performed at 18 to 20 weeks of gestation. Although many private obstetricians perform in-office sonography, the highest rates of detection of congenital anomalies are seen in tertiary care settings such as a university medical center. In difficult or otherwise high-risk cases, a consulting perinatologist is commonly the physician most likely to integrate the ultrasound findings with a rational management plan for the remainder of the pregnancy and for delivery.

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.

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.

Fetal growth in multifetal gestation

Multiple gestations present a significant increase in fetal growth abnormalities in direct relationship to the number of fetuses present. Various definitions of birth weight discordancy exist (> or = 15%-40%). When first trimester discordancy in CRL or gestational sac diameter or early second trimester discordancies of BPD, HC, AC, or femur length are detected, genetic counseling and further work-up, including chromosomal analysis, should be considered. AC and SEFW are the best sonographic predictors of second and third trimester growth discordancy of twins. Discordant Doppler velocimetry of the umbilical arteries enhances ultrasonographic diagnosis of twin discordancy. Karyotyping also should be considered on second or third trimester diagnosis of growth discordancy. Twin-twin transfusion should be considered when growth discordancy is diagnosed in monochorionic gestations. Concordant twins with appropriate-for-gestational-age growth parameters should be followed with repeated sonographic assessment of fetal growth at approximately 4-week intervals. Discordant twins should be followed by repeat sonographic assessment of fetal growth at closer intervals, most probably every 2 weeks. Surviving singleton fetuses, after spontaneous fetal death of a twin at > 16 weeks of gestation, should be followed with antepartum surveillance similar to that of discordant twins. In rare cases of extremely premature twins with discordant growth and deteriorating fetal well-being of the growth-restricted twin, conservative management should be considered in favor of the normally grown fetus.

Effects of embryo reduction from trichorionic triplets to twins

Sixty-six trichorionic triplet pregnancies reduced to twins were compared with 47 triplet pregnancies that were not reduced. The miscarriage rate was higher (7.6% compared with 2.6%) but the number delivering between 24 and 32 weeks was lower (8.2% compared with 24.0%). Since severe preterm delivery is associated with risks of neonatal death and severe handicap, embryo reduction of triplets to twins may not improve the chance of survival but may reduce the rate of handicap.

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.

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.

Molecular genetic etiology of twin reversed arterial perfusion sequence

OBJECTIVE

Our purpose was to determine whether the twin reversed arterial perfusion sequence (acardiac anomaly) results from fertilization of the first or second polar body.

STUDY DESIGN

Placental or fetal tissue was obtained from nine twin sets discordant for twin reversed arterial perfusion. After deoxyribonucleic acid extraction, the polymerase chain reaction was used to amplify five polymorphic microsatellite repeats. The products were differentiated by polyacrylamide gel electrophoresis, and patterns were compared within twin sets.

RESULTS

Deoxyribonucleic acid fingerprinting patterns were identical in all twin sets for all primer pairs. It is calculated that the chance that any of the acardiac twins resulted from fertilization of either the first or second polar body is <4% and the chance that they all resulted from polar body fertilization is <0.001%.

CONCLUSION

Twins discordant for the twin reversed arterial perfusion sequence anomaly are monozygous. Our results exclude polar body fertilization as a likely cause of this condition.

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.

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.

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.