Monochorionic Diamniotic Placenta Research Articles

Complex morphological and computed tomographic characteristics of vascularization of monochorionic diamniotic placentas with discordant weight of newborns

Complex morphological and computed tomographic characteristics of vascularization of monochorionic diamniotic placentas with discordant weight of newborns

Unusual Twinning Resulting in Chimerism: A Systematic Review on Monochorionic Dizygotic Twins

Traditionally, it is understood that dizygotic (DZ) twins always have a dichorionic placenta. However, with 8% blood chimerism in DZ twins, placental sharing is probably more common than previously has been recognized. In this article, we will review all available cases of monochorionic dizygotic (MCDZ) twins. A total of 31 twins have been described in literature. A monochorionic diamniotic placenta is reported in all cases. Assisted reproductive technology is responsible for the origin of the pregnancy in 82.1% of the cases. In 15.4% of the sex-discordant twins, a genital anomaly was reported in one of the twins. Chimerism is demonstrable in 90.3% of the twins, leading to various diagnostic difficulties. As this review shows that most MCDZ twins are discovered by accident, it can be argued that it is far more common than has been assumed until now. However, the prevalence is still unclear. Awareness of MCDZ twinning is important, with subsequently correct medical strategies. Similarly, the resulting (blood) chimerism is essential to consider in diagnostic procedures, pre- and postnatally. More research on the effect of placental transfusion between sex-discordant twins is required.

A case of discordant monochorionic diamniotic twin with umbilical cord entanglement after spontaneous rupture of the dividing membrane

Spontaneous antepartum rupture of the dividing membrane in monochorionic diamniotic twins with discordancy is extremely rare. The rupture is difficult to diagnose prenatally and has a poor outcome. The authors report a case of cord entanglement after spontaneous rupture of the dividing membrane within discordant monochorionic diamniotic twins. The subject was a 30-year-old woman pregnant with discordant monochorionic diamniotic twin at 27+4 gestational weeks. The relatively thin dividing membrane was sound until it passed parallel to the two umbilical cords where it then became ill-defined. The patient was managed cautiously due to the possibility of spontaneous rupture of the dividing membrane and potential cord entanglement. Upon delivery at 29+3 weeks due to fetal compromise, the patient presented with a monochorionic diamniotic placenta, a remnant of the disrupted dividing membrane, and entangled umbilical cords. The authors report this subject with literature review.

Monochorionic placentas with proximate umbilical cord insertions: Definition, prevalence and angio-architecture

IntroductionNot much is known on the definition, occurrence and characteristics of proximate umbilical cord insertions (PCI) in monochorionic (MC) placentas. The purpose of this study was to establish a reference range for the distance between cord insertions and to evaluate the prevalence and angio-architecture of MC placentas with PCI. MethodsAll MC placentas not treated with laser surgery were included in this study. The reference range of distance between cord insertions was created using the standard methodology proposed by Royston and Wright. We defined PCI as a cord insertion distance below the 5th centile. Results and discussionA total of 369 MC placentas were analyzed during this study period. The 5th centile was calculated by the equation: 0.027 × gestational age (weeks) +2.91 (cm), and ranged from 3.3 to 4 cm throughout gestation. Accordingly, 18 of the 369 (5%) MC placentas fulfilled the definition criteria for PCI. PCI occurred frequently in MC monoamniotic placentas (53%, 9/17) but were rare in MC diamniotic placentas (3%, 9/352). The prevalence of arterio-arterial and veno-venous anastomoses in MC placentas with and without PCI was respectively 100% versus 80% (P = .12) and 56% versus 26% (P = .01). PCI may be representative of later splitting of inner cell mass. ConclusionThe threshold for PCI (5th centile) is approximately 4 cm throughout gestation. PCI are rare in MC diamniotic placentas, but are quite common in MC monoamniotic placentas. MC placentas with PCI are characterized by higher rates of superficial AA and/or VV anastomoses.

Placental characteristics in uncomplicated monochorionic diamniotic twin pregnancies

Objective To investigate the association between placental sharing,vascular anastomoses,cord insertion and perinatal outcome in uncomplicated monochorionic diamniotic (MCDA) placentas.Methods Between January 1,2012 and July 31,2013,60 uncomplicated (seclective fetal growth restriction,twin anemia-polycythemia sequence and twin-twin transfusion dyndrome) MCDA placentas were studied.These uncomplicated MCDA placentas were divided into the placenta equally shared group with placental territory discordance (PTD) ＜0.25 and the placenta unequally shared group with PTD ≥ 0.25.Angioarchitecture,cord insertion type and the distance between two cord insertions were compared using the Chi-square test and nonparametric test.Results Mean maternal age was (30.3±4.1) years.There were 39 cases (65％) in the placenta equally shared group and 21 (35％) in the placenta unequally shared group.Vascular anastomoses were observed in all placentas,arterioarterial anastomoses in 58 placentas (97％),and venovenous anastomoses in 17 placentas (28％).The overall diameter and the maximum diameter of arterioarterial anastomoses in the placenta equally shared group were (0.19±0.11) cm and (0.18±0.09) cm,respectively,and were lower than those in the placenta unequally shared group [(0.27±0.11) cm and (0.27±0.12) cm,respectively] (T were-2.39 and-2.94,P＜0.05,respectively).No significant differences in the number,the overall diameter and the maximum diameter of venovenous anastomoses were observed between the two groups (all P＞0.05).The incidence of cord velamentous insertion and cord velamentous insertion plus cord marginal insertion were 14％ (11/78) and 42％ (33/78),respectively,in the placenta equally shared group,and were similar to those in the placenta unequally shared group [14％ (6/42) and 33％ (14/42),x2 were 1.00 and 0.43,P＞0.05,respectively].The mean distance between two cord insertions was shorter in the placenta unequally shared group than in the placenta equally shared group [(14.3±6.3) cm vs (18.2±6.0) cm,T=2.37,P＜0.05].Conclusions In cases with unequally shared placenta,the distance between two cord insertions is shorter and the diameter of arterioarterial anastomoses is larger,which may compensate for their unequal placental territories,leading to no complications in these MCDA twin. Key words: Twin, monochorionic; Placental circulation; Umbilical arteries; Umbilical veins

Anencephaly in twin pregnancy: a series of 6 cases

To report a series of cases of anencephaly in twin pregnancies and assess the prognosis of the normal twin. Retrospective study covering 4 years, at the CHU Campus in Lomé, assessing the sonographic aspects and management of cases of anencephaly in twin pregnancies. Anencephaly was found in 6 twin pregnancies. The mothers' mean age was 31 years and all had a very low socioeconomic status. All had drunk a plant infusion of an unknown chemical composition in early pregnancy. Mean gestational age at diagnosis was 25 weeks. Ultrasound performed in all cases showed that 5 cases involved monochorionic diamniotic placentas, and 1 case a dichorionic placenta. Both fetuses were alive at diagnosis in all cases: one had anencephaly and the other twin was normal. The average estimated weight of the anencephalic twin at diagnosis was 659 grams, and of the normal twin, 749 grams; growth was thus discordant. Hydramnios was noted in all cases. Expectant monitoring was instituted; both twins died before 30 weeks in 4 cases. Anencephaly in twin pregnancy is a rare occurrence. Ultrasound can be involved in the diagnosis and management.

Evidence for blood chimerism in dizygotic spontaneous twin pregnancy discordant for Down syndrome

A monochorionic-diamniotic placenta (MCDAP) is rare in dizygotic (DZ) twinning. All reported cases have been documented in pregnancies achieved by the induction of ovulation alone or during the IVF cycle. We report a spontaneous pregnancy in a 39-year-old patient with evidence of MCDAP in DZ twins, discordant for trisomy 21. The first and second-trimester sonographic scans indicated male twins with MCDAP. Amniocentesis, performed because of advanced maternal age, revealed a normal karyotype in one fetus, and trisomy 21 in the other. Molecular studies, performed in order to confirm the zygosity and chorionicity, demonstrated that the fetuses were DZ. In order to identity the affected twin, a detailed sonographic examination was repeated, but no abnormal findings associated with Down syndrome were demonstrated in any of the fetuses. Therefore, umbilical cord blood samples were obtained from both fetuses. Chromosomal analysis revealed in both fetuses two cell lines: a normal cell line of 46,XY and a 47,XY,+ 21 cell line, in 65 and 80% of the cells, respectively. This result was independently confirmed by both FISH and G-banding. DNA extracted from both cord blood samples demonstrated an admixture of two distinct genotypes in each sample. We propose that this case represents a monochorionic-dizygotic twin pregnancy with blood chimerism. The most plausible mechanism underlying this phenomenon is placental fusion early in pregnancy, resulting in an architecturally single placenta originating from two distinct zygotes. The newly formed blood vessels created anastomoses between the DZ twins and allowed reciprocal blood chimerism between the normal and the trisomic twin.

Abundant vascular anastomoses in monoamniotic versus diamniotic monochorionic placentas

OBJECTIVE: The study’s aim was to compare the vascular anatomy of monoamniotic with uncomplicated diamniotic monochorionic pregnancies. STUDY DESIGN: The fetoplacental circulations of both twins in 18 monochorionic placentas were perfused after delivery under optimal physiologic conditions, and anastomoses were delineated by dye-contrast injection. Six were from pregnancies with monochorionic monoamniotic twins and 12 from uncomplicated monochorionic diamniotic twin pregnancies. RESULTS: The cord insertions in monochorionic monoamniotic placentas were central, with a median intercord distance of 3.2 cm (range 1.7 to 6.9 cm), whereas in monochorionic diamniotic control placentas the cord insertions ( n = 24) were rarely central (marginal, 13; velamentous, 2) or eccentric (6), with a mean intercord distance of 9.6 cm (5.2 to 16.7; P < .001). Cord entanglement was present in 5 of 6 cases of monochorionic monoamniotic placentas and in none of the monochorionic diamniotic placentas. Monochorionic monoamniotic placentas had more anastomoses than did monochorionic diamniotic placentas, both overall (median 13 vs 5 respectively, P < .01) and for each of the different types (arterioarterial, venovenous, and arteriovenous, P < .01). CONCLUSIONS: Monoamniotic monochorionic placentas have significantly greater numbers of both superficial and deep anastomoses than do uncomplicated monochorionic diamniotic pregnancies. This observation suggests a vascular basis for the extreme rarity of twin-twin transfusion syndrome in monoamniotic pregnancies. (Am J Obstet Gynecol 1998;179:788-93.)

The vascular anatomy of monochorionic diamniotic twin placentas and the transfusion syndrome

By the use of the corrosion technique vascular communications between the fetal vascular beds were studied in 22 dichorionic diamniotic and 23 monochorionic diamniotic placentas. The following observations were made: 1. 1. Vascular anastomoses were demonstrated in 20 monochorionic diamniotic placentas. 2. 2. Not in all of these cases superficial arterio-arterial were present, nor did each placenta show deep arteriovenous anastomoses. 3. 3. None of the placentas contained more than three cotyledons shared by both twins. 4. 4. Six main types of vascular communications were found; these appeared in twelve different combinations. 5. 5. The vascular connection in shared cotyledons is by way of the villous capillaries and the paravascular capillary network. 6. 6. Evidence of the twin transfusion syndromes was present in three cases of twins with monochorionic diamniotic placentas.