The ultrasonographic prediction of chorionicity in twin gestation

In a prospective study of 69 consecutive twin gestations, chorionicity was assessed ultrasonographically, by the new technique of counting the number of layers visualized in the dividing membrane. For purposes of the study the antenatal categorization of chorionic type was based only on the number of layers observed. The pregnancy was classified as monochorionic when only two layers were identified and as dichorionic if three or four layers were seen. Confirmation of chorionic type was obtained after delivery by histopathologic examination of the placenta. The ultrasonographic technique used correctly determined chorionicity in 68 of 69 twin pregnancies. The predictive accuracy was 100% for 51 pregnancies designated by ultrasonography as dichorionic and 94.4% for 18 pregnancies considered to be monochorionic. These results suggest that counting the number of layers seen in fetal membranes by ultrasonography examination is an accurate way of determining chorionicity in twin gestation.     

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.     

Perinatal outcome of twin pregnancies according to chorionicity: an observational study from tertiary care hospital

Objective: To assess the perinatal outcome in twin pregnancies according to chorionicity.

Methods: This was a retrospective cohort study of twin pregnancies from January 2001 to December 2012. Maternal and perinatal outcomes of monochorionic (MC) and dichorionic (DC) twins were compared by using chi-square and t-test. Perinatal complications were compared by adjusted odds ratio using logistic regression at 5% level of significance.

Results: Among 391 twin pregnancies, 116 (29.6%) were MC and 275 (72.95%) were DC. In MC twins, the rate of miscarriage was three fold higher than DC (12.6% versus 4.4%; p-value?p value?p value?=?0.042] more likely to be delivered preterm. Likewise, neonatal intensive care admission for MC was 2.23 times [CI (1.08–4.06), p-value?=?0.03], congenital anomalies were 4.75 times [CI (1.22–18.4), p value?=?0.024]. Fetal growth restriction was 1.86 times more common in the MC twin pair [CI (1.07–3.21), p-value?=?0.026].

Conclusions: MC twins were more at risk for adverse outcomes than DC twins. Determining chorionicity at early pregnancy will help the Obstetricians to plan the care of these patients. This will help not only in managing twin pregnancies but also help in counseling according to the local perinatal outcome.     

Influence of chorionicity in intra-partum management of twin deliveries

Objective: To analyze morbidity and mortality in twin pregnancies as a function of the type of delivery and chorionicity. Design: Retrospective cohort study. Methods: Analysis of the type of delivery, intertwin time interval, and perinatal variables of >1000 twin deliveries during a 10-year period. Main outcome measure: Influence of delivery type and chorionicity on perinatal outcome. Results: The rate of cesarean sections was 42.4%. No differences were found as a function of chorionicity or as a function of presentation of the second twin. Cesarean sections were performed after vaginal delivery of the first twin in 1.8% of cases, being more common if the second baby was in a non-cephalic presentation (6.9% vs. 0.4%, p < 0.05). The average twin-to-twin delivery time interval was longer in the cases where the second had a cephalic presentation (8.26?±?7.75?min vs. 6.81?±?5.97?min, p < 0.05). The umbilical artery pH was lower the longer the interval between the birth of the twins, both in monochorionic and dichorionic. Conclusions: According to the results, vaginal delivery is as safe as elective caesarean section in twin pregnancies where the first twin is in cephalic presentation and the intrapartum management should not vary due to chorionicity.     

Maternal cell-free messenger RNA in twin pregnancies: the effects of chorionicity and severe twin to twin transfusion syndrome (TTTS)

Objective. To investigate the effects of chorionicity and severe twin to twin transfusion (TTTS) on maternal circulating cell-free messenger RNA (cf-mRNA). Design. Prospective cohort study. Setting. A UK tertiary referral Fetal Medicine Center. Population. All monochorionic (MC) twins complicated by severe TTTS (n= 23) and a cohort of uncomplicated dichorionic (DC) (n= 10) and MC (n= 7) pregnancies, between October 2006 and December 2007. Methods. Maternal cf-mRNA encoding glyceraldehyde 3-phosphate dehydrogenase (GAPDH), vascular endothelial growth factor receptor 1(VEGFR-1(Flt-1)), vascular endothelial growth factor A (VEGF-A), Endoglin, placental growth factor (PlGF), tyrosine kinase with immunoglobulin-like and EGF-like domains 1 (Tie-1), angiopoietin 1 (Ang-1) and angiopoietin 2 (Ang-2) were measured by a quantitative two-step real-time PCR assay after extraction from maternal plasma. Results. The amounts of cf-mRNA detectable are reported for uncomplicated DC, MC and TTTS pregnancies, respectively: GAPDH - 80, 100 and 96%; VEGFR-1 - 10, 0 and 26%; VEGF-A- 80, 71 and 96%; Endoglin-70, 71 and 91%; PlGF-70, 57, 26%; Tie-1 0, 43, 0%; Ang-1 71, 50 and 60% and Ang-2 83, 50 and 89%. There was a significant difference in VEGF-A (medians DC -337.3, MC - 390.8, TTTS - 618.6 copies/mL plasma p= 0.024), Endoglin (medians DC-14.49, MC-1171, TTTS - 2896 copies/mL plasma p= 0.027) and Ang-2 (medians DC-13.66, MC-8.49, TTTS 44.80 copies/mL plasma p= 0.007). Conclusion. Maternal cf-mRNA could be reliably detected for GAPDH, PlGF, VEGF-A, Endoglin, Ang-1 and Ang-2 in twin pregnancies and a significant difference was demonstrated in VEGF-A, Endoglin and Ang-2 between uncomplicated twins and MC twin pregnancies complicated by TTTS. If such alterations in maternal cf-mRNA precede the onset of clinically apparent disease, this may be used as an adjuvant blood test to complement ultrasound screening.     

Effects of placental chorionicity on outcome in twin pregnancies. A cohort study.

OBJECTIVE: To examine the effects of the chorionicity of the placenta on infant outcome at 1 year of age in twin pregnancies. STUDY DESIGN: Cohort study and retrospective review of the medical records of 44 monochorionic (MC) and 164 dichorionic (DC) twin gestations that had been followed at our institution since < 20 weeks' gestation. Physical and neurologic status was assessed at 1 year of corrected age in infants born to these 208 women. RESULTS: Adverse infant outcomes, such as death, cerebral palsy and mental retardation, occurred in 9 (10%) of 88 MC infants (4 deaths and 5 disabled infants) as compared with 12 (3.7%) of 328 DC infants (6 deaths and 6 disabled infants) (P < .05). Although delivery occurred one week earlier in MC than in DC twins (34.7 +/- 2.8 vs. 35.7 +/- 2.3 weeks, P < .01), there was no significant difference in gestational age at birth or birth weight between the 9 MC and 12 DC infants with adverse outcomes. A presumptive antenatal diagnosis of twin-twin transfusion syndrome (TTTS) was made in 14 (32%) of the 44 MC twin gestations. TTTS was considered to be responsible for adverse outcome in 7 MC infants. All 9 MC infants with adverse outcomes and 4 (33%) of 12 DC infants with adverse outcomes belonged to pairs that had weight discordance > or = 25% (P < .01). CONCLUSION: MC twins had an increased risk of adverse outcomes as compared with DC twins, mainly because of TTTS. In both MC and DC twins, a birth weight discordance > or = 25% was associated with adverse infant outcomes. The number of infants with disabilities at 1 year of age was equal to the number of deaths.     

Adverse perinatal outcome of twin pregnancies according to chorionicity: review of the literature

Twin gestations are at significant increased risk for adverse perinatal outcome. As a result, although prospective randomized data is lacking, increased fetal surveillance has been advocated for twins. Growth concordance is considered a reassuring sign in twins and conversely, discordancy to possibly reflect a hostile intrauterine environment at least to the smaller twin. Consequently, increased surveillance of discordant twins is commonly practiced. Monochorionic twins are at further risk for type-specific perinatal complications, for example, twin-twin transfusion syndrome. Recently, precise first-trimester depiction of chorionicity has enabled early antepartum stratification of twin gestations according to chorionicity, in comparison with previous later (mid- and third-trimester) ultrasonographic diagnosis of chorionicity. This immediately leads to the question whether antenatal testing of twins should differ according to chorionicity? Review of the literature supports that despite the existence of complications unique to monochorionic twin gestations, dichorionic twins sustain an increased risk of adverse perinatal outcome (such as fetal growth restriction) in comparison with singletons, and that close antenatal fetal surveillance of twins should be performed, irrespective of chorionicity.     

The impact of chorionicity on umbilical cord acid-base values in twin gestations.

OBJECTIVE: To evaluate the impact of chorionicity on inter-twin differences in acid-base status at birth. METHODS: Records for twin pregnancies delivered at > or = 24 weeks' gestation from 1 January 1990 to 31 June 2000 were reviewed. Collected data included maternal demographics, gestational age, fetal presentation, anesthesia, delivery mode, inter-twin interval, umbilical artery (UA) and venous (UV) acid-base values, Apgar scores and birth weights. The influence of chorionicity on umbilical cord biochemistry was evaluated. (p < 0.05 was considered significant.) RESULTS: Analysis was carried out in 87 twin pairs (29 monochorionic, MC; and 58 dichorionic, DC). MC and DC twins were similar in maternal age (25.5 vs. 28.2 years), estimated gestational age (33.7 vs. 33.6 weeks), Cesarean delivery (55.2 vs. 52.6%), delivery interval (10 vs. 5 min) and respective birth weights (twin A, 1882 vs. 1981; and twin B, 1828 vs. 1872 g). MC first twins had a higher UA pH (7.31 +/- 0.05 vs. 7.26 +/- 0.08; p = 0.0005) than DC first twins. MC first and second twins had higher UA and UV bicarbonate levels than their DC counterparts (DeltapH = 21.7 +/- 5.1 vs. 18.5 +/- 3.1 mmol/l and 22.0 +/- 3.5 vs. 19.6 +/- 2.5 mmol/l, respectively; p = 0.003). MC twins were more discordant in UA pH than DC twins (DeltapH = 0.043 +/- 0.09 vs. 0.003 +/- 0.07; p = 0.009). MC and DC twins had a similar venous pH (DeltapH = 0.01 +/- 0.06 vs. 0.02 +/- 0.06; p = 0.5). CONCLUSIONS: There is a significant association between placental chorionicity and umbilical cord biochemistry in twins. Although it is possible that the mechanism of this finding is related to placental angioarchitecture, it is unlikely to be a result of simple mixing of blood volumes between twins. The physiology of underlying processes requires further study.     

The Northwestern University multihospital twin study: IV. Duration of gestation according to fetal sex

Recently MacGillivray has observed that the average duration of male twin gestations is shorter than that of either female twin or male/female twin gestations. The data from 562 twin gestations from the Northwestern University multihospital twin study were used to test this observation. Male twin gestations were slightly but significantly shorter than other twin gestations as measured by pediatric examination (p < 0.005). Approaching significance at the 0.05 level were findings that male twin gestations were shorter than other twin gestations when measured by dates, and that the male twins were slightly shorter and lighter than other twins. No significant differences were found between male/female twin gestations and female twin gestations. No relationship could be found between twin sex combinations and a variety of maternal and obstetric factors. Taken together, the results suggest that male twin gestations differ in some distinctive biologic sense from other twin gestations.     

Sonographic evaluation of growth discordance and chorionicity in twin gestation.

Ninety-four twin gestations had serial ultrasound examinations for evaluation of fetal growth, with special attention to prediction of weight discordance and chorionicity. Fetal weight estimations were made a mean of 3.2 days before birth and then compared to actual birthweights. The average error in intertwin discordance prediction was 1 +/- 9%. In 56 patients ultrasonic detection of membrane thickness was compared with placental pathologic conditions. If a membrane was seen between twins, it was confirmed by placental pathologic study in all cases. No membrane was seen in four twin pairs, but only one of these actually had monochorionic monoamniotic membranes. The three cases with false-positive diagnoses of monoamniotic twin gestation were initially seen late in pregnancy. If clinical decisions in twin gestations are based on ultrasound determination of discordance and chorionicity, the level of accuracy demonstrated by these data must be considered.     

Second-trimester Down syndrome maternal serum screening in twin pregnancies: impact of chorionicity

OBJECTIVE: To evaluate the diagnostic value of second-trimester maternal serum screening for Down syndrome in twin pregnancies. METHOD: On the basis of a prospective study of second-trimester maternal serum screening, we studied the distribution of alpha-fetoprotein (AFP) and free ss hCG in 3043 twin pregnancies with known outcome. There were 1561 dichorionic and 244 monochorionic pregnancies. The placental type was not available in 1238 cases. We compared 5 screening policies with the same risk, 1/250, cut-off: maternal age, maternal age corrected for the risk of having at least one affected twin in dichorionic pregnancies, maternal serum marker screening using observed AFP and free ss-hCG values divided by a factor of 2, by using the median values actually observed in the global twin population, or by the median values specific to mono- or dichorionic twins. RESULTS: When expressed in singleton-derived MoMs, the median was 2.10 for AFP and 2.11 for free ss-hCG. The median AFP did not differ between monochorionic and dichorionic pregnancies. The distribution of free ss-hCG was significantly shifted towards greater values in monochorionic (2.16 MoM) compared to dichorionic (2.07) pregnancies (p < 0.0001). Screened-positive and detection rates were, respectively, 6.6% and 27.3% using maternal age alone, 24.6% and 54.5% using maternal age corrected for the risk of having at least one affected twin in dichorionic pregnancies, 7.75% and 54.5% using observed AFP and free beta-hCG values divided by a factor of 2, 8.05% and 54.5% using the median values actually observed in the global twin population, and 7.75% and 54.5% using the median values specific to mono- or dichorionic twins. CONCLUSION: Trisomy 21 second-trimester maternal serum screening is feasible in twins, and is better than a policy based on maternal age alone.     

The impact of assisted reproductive technology and chorionicity in twin pregnancies complicated by obstetric cholestasis

Objective: To assess in a cohort of twin pregnancies the prevalence of obstetric cholestasis (OC) and its correlation with the type of conception and chorionicity.

Methods: A retrospective cohort study including all the twin pregnancies delivered between 2005 and 2013 at our University Hospital was carried out. In the study population, the prevalence of OC was investigated in relationship to the impact of assisted reproductive technology (ART) and of chorionicity.

Results: Overall, 569 twin pregnancies were included in the study population. Among those complicated by OC, the rate of ART was 3-fold higher (OR 3.4, 95% CI 1.2–9.5, p?=?0.02), whereas the rate of dichorionicity did not differ significantly (OR 1.6, 95% CI 0.3–7.9, p?=?0.53).

Conclusion: The risk of developing OC seems to be significantly higher among twin pregnancies obtained after ART in comparison with those conceived spontaneously.     

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. (Am J Obstet Gynecol 1996;175:1529-33.)     

A practical approach to the sonographic diagnosis of chorionicity and amnionicity in twin gestations

Sonography has a unique diagnostic role in establishing chorionicity and amnionicity in twin gestations. The period in which the most accurate diagnosis can be reached is during the first trimester. The first step is to exclude monochorionicity, by demonstrating signs of dichorionic placentation such as the 'two-ring', 'twin-peak' or 'lambda' sign. If monochorionicity cannot be excluded, finding signs such as the 'one-ring' or 'tau' sign should confirm it When monochorionicity is diagnosed, an attempt to establish amnionicity should be carried out. The sonographer must be aware of various pitfalls that may reduce the diagnostic accuracy. As pregnancy progresses, the diagnosis may become difficult in like-sexed twins with a single placental disk Counting the number of layers and measuring the width of the membrane may help in reaching the correct diagnosis.     

Perinatal mortality and morbidity in twin pregnancies: the relation between chorionicity and gestational age at birth

Aim  

To investigate perinatal mortality and morbidity rates of twin pregnancies and to determine the underlying factors responsible for the increase in these rates.     

双胎妊娠的膜性和卵性诊断以及胎儿的特殊异常

邵小光教授 在西方国家，妇产科的诊治常规早已强调B超和胎盘检查对双胎妊娠膜性诊断的重要性和不可或缺性，但是在区别单卵妊娠还是双卵妊娠的卵性诊断上却不太重视，所以膜性和卵性经常混淆。1987年英国有一项以妇产科和小儿科医生为对象的调查，结果表明，能正确理解双胎妊娠的膜性和卵性关系的调查对象竞不足20％（Fisk N．Br J Obstet Gynecol，1993，100：975-977）。     

Ultrasound determination of chorionicity and perinatal outcome in twin pregnancies using dividing membrane thickness

OBJECTIVE: To assess the value of ultrasound measurement of twin dividing membrane thickness in predicting chorionicity and perinatal outcome. To compare magnified with unmagnified images, and measurements taken with dividing membranes parallel and perpendicular to the ultrasound beam. METHODS: This was a prospective, observational cohort study of twin-pregnancy ultrasound examinations during the second and third trimesters with chorionicity confirmed by a pathologist. Ultrasound measurements of the dividing membrane thickness were recorded in 44 twin pregnancies using unmagnified and magnified images. Measurements were taken at various membrane sites either horizontal or vertical to the ultrasound beam, depending on the orientation of the dividing membrane. We compared the mean membrane thickness between monochorionic and dichorionic pregnancies as well as between pregnancies with good and adverse perinatal outcome. RESULTS: Membranes were significantly thicker in dichorionic pregnancies when compared with the monochorionic pregnancies (2.35 vs. 1.69 mm, p = 0.021). A cut-off point of >/=2.0 mm provided a sensitivity of 75.7%, a specificity of 85.7%, a positive predictive value of 96.6%, and a negative predictive value of 40.0%, for determining dichorionicity. Two of 7 monochorionic and 24 of 37 dichorionic pregnancies (59.1%) had good perinatal outcome. These pregnancies had significantly thicker membranes (2.44 vs. 1.96 mm, p = 0.022). Even among the dichorionic pregnancies, a membrane thicker than 2.2 mm was associated with a significantly higher proportion with good perinatal outcome (80.0 vs. 47.1%, relative risk 1.7, p = 0.036). Magnified images obtained with the ultrasound beam parallel to the membrane identified adverse outcome more accurately than unmagnified and perpendicular images. A cut-off point of >2.2 mm for membrane thickness was found to be the best predictor of good outcome. CONCLUSIONS: Membrane thickness can be used to identify chorionicity and adverse perinatal outcome, particularly if the ultrasound images are magnified and parallel to the ultrasound beam.