Twin pregnancy: the role of ultrasound in management

Determining chorionicity and amnionicity in twin pregnancies: Pitfalls

Although the accuracy of chorioamnionicity determination in multiple pregnancy is nearly 100%, some pitfalls do exist. These pitfalls may arise from some confusing sonographic appearance or because of certain rare variations of twinning going against the general principles. Pitfalls in chorionicity determination include (1) the disappearance of the twin peak sign with the regression of chorion frondosum and thinning of the intertwin membrane with advancing gestation; (2) fake twin peak sign because of other structures creeping into the intertwin membrane-placental junction; (3) intrauterine septum or synechia being mistaken as a thick intertwin membrane; (4) bipartite placenta in monochorionic twin being misinterpreted as two separate placentas of dichorionic twin; (5) erroneous fetal sex determination in sex chromosome mosaicism, monogenic disorders, and malformed genitalia in one fetus; and (6) rare twinning types such as dizygotic monochorionic twin and sesquizygotic twin. Pitfalls in amnionicity determination are (1) the lack of correlation between the number of yolk sacs and amnionicity and (2) failure to visualize the intertwin membrane because of technical issues.

Management of Twin Pregnancies: A Comparative Review of National and International Guidelines

Importance

Twin pregnancies are associated with a higher risk of perinatal mortality and morbidity compared with singleton and require more intensive prenatal care.

Objective

The aim of this study was to review and compare the recommendations from published guidelines on twin pregnancies.

Evidence Acquisition

A descriptive review of guidelines from the Royal College of Obstetricians and Gynaecologists, the International Society of Ultrasound in Obstetrics and Gynecology, the Royal Australian and New Zealand College of Obstetricians and Gynaecologists, the National Institute for Health and Care Excellence, the Institute of Obstetricians and Gynaecologists of the Royal College of Physicians of Ireland, the International Federation of Gynecology and Obstetrics, the Society of Obstetricians and Gynaecologists of Canada, and the American College of Obstetricians and Gynecologists on the management of twin pregnancies was conducted.

Results

All the guidelines highlight the importance of an accurate assessment of chorionicity, amnionicity, and gestational age in the first trimester. They also recommend the performance of nuchal translucency and a detailed anomaly scan. The ultrasound surveillance protocol is similar in all guidelines, that is, every 2 weeks for monochorionic and every 4 weeks for dichorionic twins. On the other hand, there are differences regarding the timing and mode of delivery, especially in monochorionic diamniotic twins, in the definition and management of fetal growth discordance, the use of cervical length to screen for preterm birth, and the timing of corticosteroids' administration.

Conclusions

The differences in the reviewed guidelines on the management of twin pregnancies highlight the need for an adoption of an international consensus, in order to improve perinatal outcomes of twin pregnancies.

Prediction of Amnionicity Using the Number of Yolk Sacs in Monochorionic Multifetal Pregnancy

The purpose of this article was to evaluate the accuracy of predicting amnionicity using the number of yolk sacs by diagnostic ultrasound examination in monochorionic (MC) multifetal pregnancies between 7 + 0 and 9 + 6 gestational weeks. A total of 97 patients with MC multifetal pregnancies underwent early ultrasound examination from 2004 to 2014 at Cheil General Hospital and Women's Healthcare Center. All patients for whom the number of yolk sacs was reported were included in this study. We compared the number of yolk sacs with amnionicity confirmed by an intertwine membrane. Overall, there was a 9.3% (9 cases) discrepancy in number of yolk sacs and amnionicity (4.3% for monochorionic diamniotic, 36.4% for monochorionic monoamniotic, and 33% for monochorionic triamniotic). Among the 9 cases with discrepancies, 4 cases with 2 yolk sacs were confirmed as monoamniotic pregnancies and 4 MC twin pregnancies showing a single yolk sac were diagnosed as diamniotic twin pregnancies. One case with 2 yolk sacs was identified as a triamniotic triplet pregnancy. In 9.3% of MC gestations, the number of yolk sacs was not correlated with the number of amnions in our study. To determine amnionicity in MC multifetal pregnancies, we recommend careful evaluation not of the number of yolk sacs but the presence or absence of intertwine dividing membrane after 8 gestational weeks.

Identical Twins Presenting with Dandy-Walker Malformation and Twin-Twin Transfusion

This report will describe the detection and treatment of 2 unusual entities: duplicated Dandy-Walker malformation as a result of identical twinning and twin-twin transfusion syndrome, which is unique to monochorionic pregnancies.Ultrasound plays a valuable role in the prenatal recognition of these anomalies, allowing for the option of fetal karyotyping, antenatal intervention, or postnatal follow up.

Fetal Aneuploidy Detection by Cell-Free DNA Sequencing for Multiple Pregnancies and Quality Issues with Vanishing Twins

Non-invasive prenatal testing (NIPT) by random massively parallel sequencing of maternal plasma DNA for multiple pregnancies is a promising new option for prenatal care since conventional non-invasive screening for fetal trisomies 21, 18 and 13 has limitations and invasive diagnostic methods bear a higher risk for procedure related fetal losses in the case of multiple gestations compared to singletons. In this study, in a retrospective blinded analysis of stored twin samples, all 16 samples have been determined correctly, with four trisomy 21 positive and 12 trisomy negative samples. In the prospective part of the study, 40 blood samples from women with multiple pregnancies have been analyzed (two triplets and 38 twins), with two correctly identified trisomy 21 cases, confirmed by karyotyping. The remaining 38 samples, including the two triplet pregnancies, had trisomy negative results. However, NIPT is also prone to quality issues in case of multiple gestations: the minimum total amount of cell-free fetal DNA must be higher to reach a comparable sensitivity and vanishing twins may cause results that do not represent the genetics of the living sibling, as described in two case reports.

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).

Influence of chorionicity on perinatal outcome in a large cohort of Danish twin pregnancies

OBJECTIVE

To assess outcome in twin pregnancies according to chorionicity.

METHODS

A cohort was retrieved from local ultrasound databases at 14 obstetric departments in Denmark, comprising all twin pregnancies with two live fetuses scanned between weeks 11 and 14 in the period 1 January 2004 to 31 December 2006. Outcome data were retrieved from the National Board of Health.

RESULTS

Among 2038 twin pregnancies, 1757 (86.2%) were dichorionic (DC) and 281 (13.8%) were monochorionic diamniotic (MC). In MC pregnancies, the rate of spontaneous fetal loss in both second and third trimesters was more than threefold higher than the comparable rate in DC pregnancies: 6.0% vs. 1.9% for at least one fetus in the second trimester (P < 0.001) and 2.1% vs. 0.7% in the third trimester (P = 0.03). In 98.4% of DC pregnancies and in 91.1% of MC pregnancies, at least one infant was liveborn. Amongst pregnancies with two live fetuses at 24 weeks, the proportion with two live infants at 28 days after delivery was 97.5% and 95.1%, respectively.

CONCLUSIONS

The increased incidence of fetal loss in MC pregnancies compared with DC pregnancies predominantly occurs before 24 weeks' gestation. After this stage, although the risk of intrauterine fetal death is still higher in MC than in DC pregnancies, if both fetuses are alive at 24 weeks, the chance of a woman having two live infants 1 month after delivery is similar in MC and DC pregnancies.

[Twin pregnancies in southern Reunion Island: a three-year cross-sectional study of risk factors and complications]

OBJECTIVES

To describe characteristics of multiples pregnancies in southern Reunion Island.

MATERIAL AND METHODS

A three-year [corrected] cross-sectional observational study aimed at describing risk factors, events and [corrcected] complications and associated with twin pregnancies from 22 weeks gestation onward, within a tertiary care hospital centre, the Groupe Hospitalier Sud-Réunion.

RESULTS

The study included 241 multiple pregnancies out of 15 837 pregnant women. The regional incidence of multiple pregnancies was 1.5%. Indicators of eligible twin pregnancies (n=234) were mother age up or equal to 35 years (63% of women, OR 8.4; CI95% 6.3-11.1), infertility treatments (15%): ovarian stimulations (OR: 50.2; CI95% 24.7-102) and in vitro-fertilisations (OR: 44.3; CI95% 22.6-86.3). A low maternal corpulence before pregnancy (BMI<20) and celibacy were negatively associated with twin pregnancies. Prenatal cares for twin pregnancies were globally adequate. The need for hospitalisation was 50% (30% of whom for preterm delivery threats). Twin pregnancies increased risks for pre eclampsia (OR: 3.0; CI95% 1.6-5.7) and gestational diabetes (OR: 1.9; CI95% 1.2-2.8). Caesareans and instrumental delivery rates were 50% and 12% (vs 16% and 7%), respectively. Twin infants were preterm for 62% and very preterm for 18%. Last, they were more likely to die than singletons (perinatal mortality: 78 per thousand for monochorionic twins, 57 per thousand for bichorionic twins vs 17 per thousand, p<0.0001, respectively).

CONCLUSION

In Reunion Island, the incidence of multiple pregnancies is similar to that seen in Europe, but seems less due to assisted reproduction techniques. In return, they are associated with higher morbidity and mortality rates.

IVF/ICSI twin pregnancies: risks and prevention

Since the 1970s, the national twin birth rates have been increasing worldwide. Apart from the increasing childbearing age, the main cause is the use of assisted reproductive technologies (ART). To explore the overall consequences of dual embryo transfer (DET), the literature has been reviewed systematically regarding short- and long-term outcomes of IVF/ICSI twin pregnancies i.e. pregnancy complications, maternal risks, obstetric outcome and long-term morbidity including neurological sequelae, cognitive development and family implications. Another consequence of DET is vanishing twins, which seems to be a possible cause of adverse outcome in IVF singletons. The sparse literature on vanishing twins in IVF pregnancies and the influence on the surviving co-twin were also addressed. Finally, to determine the effects of implementing elective single embryo transfer (eSET), trials concerning eSET versus DET were analysed. In the light of the steadily increasing twin birth rates and the findings in this overview, where IVF/ICSI twins carry adverse outcome, it should be emphasized that the major obstacle in IVF remains the high twin birth rate. Furthermore vanishing twins account for another hazard of DET. These problems can be resolved by implementing eSET, diminishing the twin birth rate without affecting the overall goal of achieving a healthy infant.

An association of chorionicity with preterm twin birth

OBJECTIVE

To assess the risk factors for preterm birth in twin pregnancies, particularly monochorionicity.

METHODS

A cohort study of 767 sets of twins, each twin weighing more than 500 g, born between January 1, 1992, and December 31, 2001, at St. Joseph's Health Care in London, Ontario. Statistical analysis was performed using forward stepwise logistic regression models, with gestational age at birth less than 28 or 32 weeks as the outcome.

RESULTS

Polyhydramnios and chorioamnionitis were significant risk factors for preterm birth prior to 28 or 32 weeks' gestation. Monochorionicity was a risk factor for preterm birth prior to 32 weeks' gestation. Past term birth and maternal age over 30 years were associated with reduced risk for preterm birth.

CONCLUSION

Monochorionic placentation is a significant risk factor for preterm twin birth.

Neonatal outcome in a Danish national cohort of 8602 children born after in vitro fertilization or intracytoplasmic sperm injection: the role of twin pregnancy

BACKGROUND

In Denmark, 4% of all infants are born after in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI) and 40% of these children are twins.

METHODS

We investigated neonatal outcome in a complete Danish IVF/ICSI birth cohort including 8602 infants born between 1995 and 2000: 3438 twins (40%) and 5164 singletons (60%). Births conceived after IVF or ICSI were identified by record linkage with the Danish IVF Registry and the National Medical Birth Registry. Data on neonatal outcome were collected from the National Patient Registry.

RESULTS

IVF/ICSI twins had a 10-fold increased age- and parity-adjusted risk of delivery before 37 completed weeks [odds ratio (OR) 9.9, 95% confidence interval (95% CI) 8.7-11.3] and a 7.4-fold increased risk of delivery before 32 completed weeks (OR 7.4, 95% CI 5.6-9.8) compared with singletons. Correspondingly, ORs of birthweight <2500 g and birthweight <1500 g in twins were 11.8 (95% CI 10.3-13.6) and 5.4 (95% CI 4.1-7.0), respectively. The stillbirth rate was doubled in twins (13.1/1000) compared with singletons (6.6/1000) (p = 0.002). The risk of cesarean section and of admittance to a neonatal intensive care unit (NICU) was 4.6- and 1.8-fold higher in IVF/ICSI twins than in singletons. The rate of major malformations was 40.4/1000 in twins and 36.8/1000 in singletons (p = 0.4), whereas the total malformation rate (major + minor) was higher in twins (73.7/1000) than in singletons (55.0/1000) (p = 0.001). After exclusion of patent ductus arteriosus (PDA), which is strongly associated with preterm birth, no significant differences in any malformation rates were observed between twins and singletons. Apart from the frequency of ICSI children with hypospadias, which reached a significance level of p = 0.05, malformation rates in ICSI children were similar to those in IVF children.

CONCLUSIONS

This study indicates that neonatal outcome in IVF/ICSI twins is considerably poorer than in singletons. Thus, the impact is to draw the attention of clinicians to the benefit of elective single embryo transfer (eSET).

Genetic amniocentesis in multiple pregnancy

OBJECTIVES

Second-trimester genetic amniocentesis is the most frequently used invasive prenatal diagnostic technique. Several reports have been published about the effect of genetic amniocentesis on fetal loss in multiple pregnancies over the past two decades. Here we analyze our experience with genetic amniocentesis in multiple pregnancies over the past 10 years.

METHODS

Details of 184 multiple pregnancies were processed in all cases in whom genetic amniocentesis was performed in women who presented at our department since 1990. The outcomes of 175 cases (95.1%) out of 184 genetic amniocenteses were available to us. As a control group, we followed up the outcome of 300 twin pregnancies in which no genetic amniocenteses were performed.

RESULTS

We found that the proportion of spontaneous losses in multiple pregnancies between the 18th and the 24th gestational weeks was 2.39%, whereas if genetic amniocentesis was performed the loss rate before the 24th week was 3.87%. The perinatal mortality rate was 10.03/1,000 in the group who underwent amniocentesis, while it was 10.52/1,000 in the group without amniocentesis.

CONCLUSIONS

Our results suggest that the genetic amniocentesis performed in multiple pregnancies slightly increased (1.48%) the fetal loss rate until the 24th week. Beyond 5 weeks after the procedure, no consequent fetal loss should be expected. In our study the intervention did not have any undesired effect on perinatal mortality rates.

The Utility of fFN for the Prediction of Preterm Birth in Twin Gestations

OBJECTIVE

To determine the sensitivity, specificity, and positive predictive value (PPV) of fetal fibronectin (fFN) and to determine its usefulness, in conjunction with selected other clinical assessment measures, in the prediction of preterm birth for women with twin gestations.

DESIGN

A prospective, descriptive, longitudinal design.

SETTING

An obstetrical high-risk clinic that received patient referrals from several surrounding communities in central Texas.

PATIENTS/PARTICIPANTS

Forty-eight women identified with twin gestations prior to the 22nd week of pregnancy; primarily of Hispanic ethnicity.

MAIN OUTCOME MEASURES

A substantial number of outcome variables were assessed in this study. In the present report, data derived from weekly assessments for the identification of the presence of fFN, the diagnosis of bacterial vaginosis, and the measurement of cervical length were reviewed for their relationship to prematurity, birth weight, birth weight discordancy and placental chorionicity.

RESULTS

The relative risk of birth prior to 35 weeks gestation, fetal death, or discordance of twin birth weights of greater than 20% was 2.22 (CI: 1.09, 4.55, P < 0.015) when fFN was found to be positive at any weekly testing after 22 to 24 weeks gestation (sensitivity 76.82%, specificity 58.33%, PPV 66.7%). The presence of fFN was most highly predictive of preterm birth when performed during the 24th to 28th gestational week. Shorter cervical lengths were highly correlated with preterm birth (r = -0.6). An association between bacterial vaginosis and preterm birth was not demonstrated in this sample.

CONCLUSION

Sampling for the presence of fetal fibronectin can be easily accomplished by RNs in labor triage units and by advanced practice nurses in outpatient settings. The identification of fFN, particularly during the 24 to 28 weeks gestational time frame, is highly predictive of preterm birth, and particularly so for women with twin gestations.

Maternal risks and perinatal outcome in a Danish national cohort of 1005 twin pregnancies: the role of in vitro fertilization

BACKGROUND

Twin pregnancies constitute 25% of all in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) pregnancies. There is a lack of knowledge on maternal risks and perinatal outcome of IVF/ICSI twin pregnancies.

METHODS

National survey by questionnaire (n = 1769). The study population consisted of all IVF/ICSI twin mothers (n = 266) and the two control groups of all IVF/ICSI singleton mothers (n = 764) and non-IVF/ICSI twin mothers (n = 739) who delivered in Denmark in 1997. The response rate was 89% among IVF twin mothers and overall 81%.

RESULTS

In terms of maternal risks and perinatal outcome no significant differences were observed between IVF/ICSI twin and non-IVF/ICSI twin pregnancies after stratification for maternal age and parity. Nevertheless, IVF/ICSI twin mothers were more frequently on sick leave (OR 2.5, 95% CI 1.5-4.0) and hospitalized (OR 1.9, 95% CI 1.3-2.8) during pregnancy. Compared with IVF/ICSI singleton pregnancies, IVF/ICSI twin pregnancies were characterized by a higher incidence of preeclampsia (OR 2.4, 95% CI 1.5-4.2) and a higher frequency of sick leave (OR 6.8, 95% CI 4.4-10.5) and hospitalizations during pregnancy (OR 3.5, (95% CI 2.5-4.9); moreover, mean birthweight (p < 0.001) and gestational age (p < 0.001) were lower. No differences were observed in the incidence of pregnancy-induced hypertension and gestational diabetes between IVF/ICSI twin and singleton pregnancies.

CONCLUSION

Although this population study indicates that maternal risks in IVF/ICSI twin pregnancies are comparable with non-IVF/ICSI twin pregnancies, the IVF/ICSI twin mothers were more likely to be on sick leave or hospitalized during pregnancy. Furthermore, maternal risks were higher and obstetric outcome poorer in IVF/ICSI twin vs. IVF/ICSI singleton pregnancies.