Ultrasound Obstet Gynecol 2000; 16: 223±225. First trimester diagnosis of monoamniotic

N. J. SEBIRE, A. SOUKA, H. SKENTOU, L. GEERTS and K. H. NICOLAIDES Harris Birthright Research Centre for Fetal Medicine, King's College Hospital, London, UK

KEYWORDS: Cord entanglement, Monoamniotic, Twin

was made after mid-gestation. The introduction of the 11±14- ABSTRACT weekscan into routineantenatalcarehas now madeit possible This study reports the ultrasound findings and pregnancy to diagnosemonoamniotic from thefirst trimester. This outcome for a series of monoamniotic twin pregnancies study reports the ultrasound findings and pregnancy outcome diagnosed at 11±14 weeks' gestation. Of 315 monochorionic in a series of 12 monoamniotic twin pregnancies, including four twin pregnancies examined, there were 12 ,3.8%) mono- sets of , diagnosed at the 11±14-week scan. amniotic, including four sets of conjoined twins ,1.3%). The parents opted for termination of pregnancy in all cases of conjoined twins. In four other cases, there was discordancy for METHODS major structural fetal abnormality ,kyphoscoliosis, anen- Since 1992 pregnant women have attended our unit for cephaly, body stalk defect, diaphragmatic hernia), and the co- assessment of risk for fetal trisomy 21 by a combination of twin was structurally normal. In the four cases in which both maternal age and fetal nuchal translucency 9NT) measure- twins were structurally normal, ultrasound examination ment2. Ultrasound findings are entered into a computer demonstrated normal nuchal translucency thickness in all databaseat thetimeof thescan and data on pregnancy cases but cord entanglement was demonstrated from the first outcome entered when they become available. In all cases of trimester. Two cases were managed expectantly; one resulted multiplepregnancy, chorionicity and amnionicity arerou- in livebirth of both twins at 31 weeks' gestation and the second tinely recorded at the initial visit following ultrasonographic in intrauterine death of both at 21 weeks. Two examination for the presence or absence of an intertwin pregnancieswere treated with Sulindac; one resulted ina single membrane and, when present, the junction of the intertwin intrauterine death at 30 weeks and delivery of a normal co- membrane and . All pregnancies are subsequently twin, the other, in intrauterine death of both fetuses at 31 managed either in our unit or at the referring hospital. weeks'. Monoamniotic twin pregnancies are associated with a A computer search was carried out to identify monoamniotic high risk of fetal abnormalities and perinatal death and the twin pregnancies with two live fetuses, including those with mortality rate is higher than previously reported from series conjoined twins, and the individual patient notes were with recruitment later in gestation. examined with regard to management and pregnancy outcome.

RESULTS INTRODUCTION During thestudy period 91992±98), therewere315 mono- Twins account for about 1±2% of all pregnancies, with chorionic twin pregnancies and in 12 93.8%) cases the two-thirds being dizygotic and one-third monozygotic. All pregnancies were monoamniotic, including four sets of dizygotic and about one-third of monozygotic twins are conjoined twins 91.3%). The 11±14-week scan findings and dichorionic and therefore about 20% of all twins are pregnancy outcome for each case are shown in Tables 1 and 2. monochorionic. In , which occur in In four pregnancies one of the fetuses had a major structural about 5% of monochorionic pregnancies1, there is a single abnormality 9kyphoscoliosis, anencephaly, body stalk defect, amniotic cavity with a singleplacentaand thetwo diaphragmatic hernia), and the co-twin was structurally normal umbilical cords insert close to each other. In about 1% of 9Table1). In thecaseof anencephaly9case2), thewhole monochorionic pregnancies the twins are conjoined. pregnancy was terminated at the request of the parents, whereas Current knowledge on the natural history of monoamniotic in the case of body stalk defect 9case 3), the pregnancy was twins is mainly based on data derived from either postnatal managed expectantly and after elective Cesarean section at studies or prenatal sonographic reports where the diagnosis 34 weeks, the healthy twin survived and the abnormal one died

Correspondence: Professor K. H. Nicolaides, Harris Birthright Research Centre for Fetal Medicine, King's College Hospital, Denmark Hill, London SE5 8RX, UK

Received 10-1-00, Revised 3-8-00, Accepted 21-8-00

ORIGINAL ARTICLE 223 First trimester diagnosis of monoamniotic twin pregnancies Sebire et al.

Table 1 Ultrasound findings and pregnancy outcome in eight nonconjoined monoamniotic twin pregnancies examined at 11±14 weeks of gestation

Ultrasound findings Outcome

Case Gestation Twin 1 Twin 2 Twin 1 Twin 2

1 13 weeks CRL 42 mm, NT 2.0 mm CRL 38 mm, NT 4.4 mm, IUD TOP 13 weeks Kyphoscoliosis 2 13 weeks CRL 66 mm, NT 1.2 mm CRL 79 mm, NT 1.2 mm TOP 13 weeks TOP 13 weeks Anencephaly 3 11 weeks CRL 48 mm, NT 1.8 mm CRL 55 mm, NT 5.5 mm, LB 34 weeks NND 34 weeks Body stalk defect 4 13 weeks CRL 63 mm, NT 6.0 mm, CRL 66 mm, NT 2.0 mm IUD 21 weeks IUD 21 weeks Diaphragmatic hernia 5 12 weeks CRL 52 mm, NT 1.1 mm CRL 53 mm, NT 1.0 mm IUD 21 weeks IUD 21 weeks 6 10 weeks CRL 38 mm, NT 1.2 mm CRL 39 mm, NT 1.7 mm LB 31 weeks LB 31 weeks 7 12 weeks* CRL 59 mm, NT 1.5 mm CRL 58 mm, NT 1.5 mm IUD 30 weeks LB 34 weeks 8 12 weeks** CRL 61 mm, NT 2.1 mm CRL 67 mm, NT 2.1 mm IUD 31 weeks IUD 31 weeks

*Sulindac treatment from 23 weeks; ** Sulindac treatment from 20 weeks. CRL, crown±rump length; NT, nuchal translucency thickness; IUD, intrauterine death; TOP, termination of pregnancy; LB, livebirth; NND, neonatal death. soon after birth. In the case of increased nuchal translucency and development of mild 9vertical pool of 11 cm). diaphragmatic hernia 9case 4), the pregnancy was managed Subsequently, the was reduced 9deepest pool expectantly and both twins died at 21 weeks of gestation. In the 2 cm). Cesarean section was planned for 32 weeks but at case of severe kyphoscoliosis 9case 1), the parents requested 31 weeks both fetuses died. termination of the whole pregnancy and after discussion the In the four pregnancies with conjoined twins the parents option of selective fetocide by the injection of potassium chloride opted for termination of the pregnancy, which was carried into the pericardial space was chosen. There were no immediate out by dilatation and curettage in the first trimester. post-operative complications and the fetal heart rate of the normal co-twin remained normal throughout a period of 2 h of DISCUSSION observation. However, a follow-up scan demonstrated fetal death, which on the basis of the crown±rump length must have Thefindings of this study demonstratethat monoamniotic occurred within 3±4 days of the fetocide. twin pregnancies are associated with a high risk of fetal In four cases, both twins were structurally normal. Ultrasound abnormalities and perinatal death. At the 11±14-week scan examination demonstrated cord entanglement in all cases from the diagnosis of monoamniotic twins should be considered in the first trimester. Serial scans, every 2±4 weeks, showed normal all twin pregnancies in which the lambda sign3 is absent, and fetal growth and umbilical artery Doppler velocimetry. In two in such casestheintertwin membraneshould bespecifically cases the pregnancies were managed expectantly; one resulted in searched for. Further diagnostic clues include close insertion live birth of both twins after elective Cesarean section at 31 of thetwo umbilical cords into theplacenta, presenceof only weeks and 6 days and the second resulted in death of both fetuses oneyolk sac 4 and unusual intra-uterine positioning of the two at 21 weeks. Two pregnancies were treated with Sulindac fetuses in close proximity to each other. 9Merck,Sharp & DohmeLtd., Herts,UK). In onecasethe Our data do not provideinformation on thenatural history of mother received Sulindac 9200 mg per day) from 23 weeks of conjoined twins because, in all cases, the parents opted to have gestation. Both fetuses were growing normally and the amniotic termination of pregnancy. However, it is of interest that in all fluid volume, assessed subjectively, remained normal; one fetuses the nuchal translucency thickness was increased, died at 30 weeks and the co-twin was live born by elective presumably because of the hemodynamic disturbance associated Cesarean section at 34 weeks. Postnatal follow up, including with this condition. It is likely that there would be significant magnetic resonance imaging of the brain, showed normal intra-uterine lethality in many such cases presumably accounting development. In the second case, Sulindac 9200 mg per day) was for the apparently higher prevalence of conjoined twins in the started at 20 weeks but at 22 weeks and 26 weeks the dose was first trimester compared with live births. At present, counseling increased to 300 and 400 mg, respectively, because of the of parents of conjoined twins diagnosed in the first trimester

Table 2 Ultrasound findings in four conjoined monoamniotic twin pregnancies examined at 11±14 weeks of gestation

Case Gestation Ultrasound findings

1 13 weeks CRL 58 mm, NT 7.0 mm and CRL 60 mm, NT 3.5 mm, thoraco-omphalopagus 2 11 weeks CRL 50 mm, NT 4.2 mm and CRL 49 mm, NT 7.5 mm, thoracopagus 3 13 weeks CRL 77 mm, NT 2.4 mm and CRL 75 mm, NT 3.6 mm, thoraco-omphalopagus 4 11 weeks CRL 55 mm, NT 6.5 mm and CRL 56 mm, NT 0.5 mm, thoracopagus

CRL, crown±rump length; NT, nuchal translucency thickness.

224 Ultrasound in Obstetrics and Gynecology First trimester diagnosis of monoamniotic twin pregnancies Sebire et al. relies on data from postnatal series. Survival depends heavily from the first trimester of pregnancy 12,13. Therefore, a more upon thesiteof conjoining and theorgans involved.About 50% likely cause of fetal death in monoamniotic twins, which of conjoined twins are stillborn. About one-third of the live occurs suddenly and unpredictably, is acute `twin-to-twin births have defects which are not amenable to surgical correction transfusion syndrome'. Thecloseinsertion of theumbilical and theydiein theneonatalperiod.In thoselivebirths where cords into the placenta is associated with large-caliber surgery is attempted about 60% of babies survive5. anastomoses between the two fetal circulations14. Conse- Half of our non-conjoined monoamniotic twin pregnan- quently, an imbalancein thetwo circulations could not be cies were associated with discordancy for a fetal structural sustained for prolonged periods of time 9which is necessary for abnormality. This is similar to the data reported in a review the development of the classic features of twin-to-twin by Baldwin6, in which five of 13 938%) sets of non-conjoined transfusion syndrome), but would rather have major hemo- monoamniotic twins were associated with structural defects dynamic effects, causing sudden fetal death. Furthermore, in in one or both fetuses. Monoamniotic twins occur when diamniotic monochorionic pregnancies, increased fetal nuchal embryonic splitting takes place after day nine following translucency thickness at the 11±14-week scan is associated fertilization. Abnormalities, which are usually discordant, with adversepregnancy outcomedueto thesubsequent may therefore potentially be a consequence of the twinning development of severe twin-to-twin transfusion syndrome15. process itself, hemodynamic factors or amniotic abnormal- In the current study however, all fetuses had normal nuchal ities, as suggested by our case of body stalk defect. translucency thickness and there was no difference between In the management of monoamniotic twins that are thosethat survivedand thosethat subsequently died. discordant for a major abnormality, selective termination of pregnancy is expected to be associated with a high risk of REFERENCES death of thenormal co-twin. In dichorionic twins, therisk of death or handicap of the co-twin when one of the fetuses dies 1 Quigley JK. Monoamniotic twin pregnancy. 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