Dichorionic Placentas Research Articles

Whole-genome sequences reveal zygotic composition in chimeric twins

While most dizygotic twins have a dichorionic placenta, rare cases of dizygotic twins with a monochorionic placenta have been reported. The monochorionic placenta in dizygotic twins allows in utero exchange of embryonic cells, resulting in chimerism in the twins. In practice, this chimerism is incidentally identified in mixed ABO blood types or in the presence of cells with a discordant sex chromosome. Here, we applied whole-genome sequencing to one triplet and one twin family to precisely understand their zygotic compositions, using millions of genomic variants as barcodes of zygotic origins. Peripheral blood showed asymmetrical contributions from two sister zygotes, where one of the zygotes was the major clone in both twins. Single-cell RNA sequencing of peripheral blood tissues further showed differential contributions from the two sister zygotes across blood cell types. In contrast, buccal tissues were pure in genetic composition, suggesting that in utero cellular exchanges were confined to the blood tissues. Our study illustrates the cellular history of twinning during human development, which is critical for managing the health of chimeric individuals in the era of genomic medicine.

Distinct Placenta Increta and Percreta in the Setting of Dichorionic Diamniotic Twin Gestation: A Unique Histological Finding

Multiple gestations have been reported as a risk factor for placenta accreta spectrum (PAS) but the evidence is limited. Previous reports showed that PAS degrees (creta, increta, percreta) were similar in multiple gestation placentas. To our knowledge, there have been no reports of PAS in dichorionic placentas with different degrees of invasion. Here, we report dichorionic diamniotic placentas with two different degrees of invasion, one increta and another percreta.

Factors Related to Late Intrauterine Fetal Death in a Tertiary Referral Center: A Retrospective Study

Backgroun: Intrauterine fetal death (IUFD) is a contributor of perinatal outcome and is an important indicator of the quality of antenatal care. Despite efforts, risk factors cannot be identified in cases of intrauterine fetal deaths. This study aims to identify the maternal, fetal, placental and cord related factors related to it. 
 Methods: It is a retrospective cross-sectional study conducted analyzing patients admitted with IUFDs after 28 weeks of pregnancy at Tribhuwan University Teaching Hospital from April 2019 to March 2020. It was conducted after taking ethical approval from Institutional Review Committee (IRC) of Institute of Medicine. Data were collected from review of charts of individual patients in MS Excel and was analyzed using SPSS.
 Results: There were 5496 births and 46 intrauterine fetal deaths during the study period giving stillbirth rate of 8 per 1000 births. It was common in the age group of 26-30 years (34.8%), 62.2% were from inside Kathmandu valley,43.5% were just literate, 13% were illiterate, 84.8% were housewives, 56.5% were primigravida and 69.57% of the babies were preterm. Only four percent had previous history of intra uterine fetal deaths. Hypertensive disorders complicating pregnancy were found in 30.5% followed by heart disease in 10.9% of the mothers. There were no known co-morbidities in 26.1% of the patients. Out of total 46 cases, 62% were female. Two had Rh isoimmunization and four had congenital malformations. Placenta previa was seen in four percent and abruptio placenta in two percent. Twin pregnancy with diamniotic dichorionic placenta was present in four percent. Seventeen percent of the babies had cord around the neck and two percent had thrombosis of the umbilical cord. 
 Conclusion: Low level of maternal education and maternal comorbidities like hypertensive disorders complicating pregnancy were found to be most common factors seen in cases of intrauterine fetal deaths.

Genetic and Early-Life Environmental Influences on Dental Caries Risk: A Twin Study.

To explore the relative contributions of genetic and environmental influences on dental caries risk and to investigate fetal and developmental risk factors for dental caries. We recruited children from 250 twin pregnancies midgestation and collected demographic, health, and phenotypic data at recruitment, 24 and 36 weeks' gestational age, birth and 18 months, and 6 years of age. 25-hydroxyvitamin D was quantified in mothers at 28 weeks' gestation and in infants at birth. Dental caries and enamel defects were measured at six years of age. We compared concordance for the presence of any caries and advanced caries in monozygotic and dizygotic twin pairs. To investigate environmental risk factors for caries, we fitted multiple logistic regression models using generalized estimating equations to adjust for twin correlation. A total of 345 twins underwent dental assessment, with 111 (32.2%) showing signs of any caries and 83 (24.1%) having advanced caries. There was no evidence of higher concordance in monozygotic twins compared with dizygotic twins, with a difference of 0.05 (95% confidence interval -0.14 to 0.25; P = .30) and 0.00 (95% confidence interval -0.26 to 0.26; P = .50) for any caries and advanced caries, respectively, suggesting that environmental factors, rather than genetics, are the predominant determinant of caries risk. After adjusting for potential confounders, lack of community water fluoridation, hypomineralized second primary molars, dichorionic placenta, and maternal obesity were associated with caries. Environmental rather than genetic factors drive dental caries risk and arise as early as prenatal life.

The benefit of prophylactic cervical cerclage in twin pregnancies

Background: Despite the progress in modern obstetric practice, preterm labor is second leading cause of death in the 1st month of life and the main cause of perinatal morbidity and mortality; it remains a difficult problem to prevent, delay or even stop. It occurs in 5%–13% of all pregnancies before 37 weeks' gestation but its incidence in twin pregnancies is about 25%. Objectives: This study aimed to determine the effect of prophylactic cervical cerclage (CC) in comparison to others methods: vaginal progesterone and bed rest in prolongation of gestational age in twin pregnancies to prevent preterm labor. Materials and Methods: A retrospective descriptive study was conducted between January 2012 and September 2018, in a private obstetric antenatal care clinic in Duhok/Kurdistan Region/Iraq. It involved 150 women with twin pregnancies attending this clinic for follow-up, they divided into: Group 1 (N-86): women who received prophylactic CC; Group 2 (N-44): those who got the vaginal progesterone supplementation of 100 mg from 20 to 34 weeks of gestation; and Group 3 (N-20): those who asked for advisement of bed rest and restriction of physical activity. Results: Most of the total sample 95.3% had dichorionic placenta, the majority of them 84.7% were the result of assisted reproductive techniques. There was no statistically significant difference between the three groups in relation to maternal age, gravid, and previous preterm delivery, but there was in relation to the gestational age at delivery. In Group 1, 93% who delivered >37 weeks, whereas 16% and 10% in Group 2 and Group 3 who delivered at this gestational age, respectively. The overall perinatal survival was 91.3% and 26.6% who admitted to Neonatal Intensive Care Unit. Conclusions: The current study found that the prophylactic CC was an effective method to prolong pregnancy among women with twin pregnancies.

516: Global transcriptomic analysis of sibling placentas in twin gestations complicated by preeclampsia

Preeclampsia (PE) is a disease of incompletely understood etiology that is the leading contributor to iatrogenic preterm birth (PTB). Our objective was to identify if PE in dichorionic pregnancies is characterized by similarities or dissimilarities in the transcriptome profile of the two placentas. Total RNA was extracted from 60 placental villous tissue samples and subjected to RNA-seq using the Illumina platform. Our study was designed to include two analytical stages: In the first stage placental samples (n=18) originated from singleton pregnancies with unambiguous clinical phenotypes: 1) severe features early-onset PE (sPE, n=8, GA: 30±1 wks); 2) idiopathic preterm birth (n=5, GA: 32±1wks) and 3) term non-labor (n=5, GA: 39±1wks). These samples were used to extract a generic transcriptomic signature of PE placenta. In the second stage placentas of 16 twin pregnancies classified based on chorionicity and PE diagnosis were included as follows: di-di nonPE (n=7, GA: 32±1 wks), mono-di nonPE (n=2, GA: 32±1 wks), di-di PE (n=5, GA: 33±2 wks) and mono-di PE (n=2, GA: 33±3 wks). Two separate biopsies were sequenced from monochorionic placentas. An additional set of singleton PE placentas (n=10, GA: 33±1 wks) was sequenced interspaced among the twin placentas to control for batch effects. Principal components analysis (PCA) and statistical modeling for similarity and dissimilarity between sibling placentas were applied. Our first stage analysis extracted a subset of 613 transcripts differentially expressed between sPE and non-PE singleton placentas. This molecular classifier showed linear separability among first stage samples independent of GA at birth. When applied to twin gestation placentas the classifier revealed several characteristics: 1) In the non-PE cases, biopsies from monochorionic placentas had more similar expression patterns of the genes composing the PE signature than dichorionic placentas which were more scattered in the PCA space (Fig. A); 2) Monochorionic nonPE placentas have closer proximity to the PE space compared to singleton nonPE placentas; 3) Dichorionic sibling placentas of pregnancies complicated by PE were the most discordant (Fig. B). In dichorionic pregnancies complicated by PE, the disease affects each placenta individually. Conversely, PE in twins could be the result of a single diseased placenta.

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.

Placental weight and birth weight to placental weight ratio in monochorionic and dichorionic growth-restricted and non-growth-restricted twins

OBJECTIVE:The aim of the present study was to compare the placental weight and birth weight/placental weight ratio for intrauterine growth-restricted and non-intrauterine growth-restricted monochorionic and dichorionic twins.METHODS:This was a retrospective analysis of placentas from twin pregnancies. Placental weight and the birth weight/placental weight ratio were compared in intrauterine growth-restricted and non-intrauterine growth-restricted monochorionic and dichorionic twins. The association between cord insertion type and placental lesions in intrauterine growth-restricted and non-intrauterine growth-restricted monochorionic and dichorionic twins was also investigated.RESULTS:A total of 105 monochorionic (intrauterine growth restriction=40; non-intrauterine growth restriction=65) and 219 dichorionic (intrauterine growth restriction=57; non-intrauterine growth restriction=162) placentas were analyzed. A significantly lower placental weight was observed in intrauterine growth-restricted monochorionic (p=0.022) and dichorionic (p<0.001) twins compared to non-intrauterine growth-restricted twins. There was no difference in the birth weight/placental weight ratio between the intrauterine growth restriction and non-intrauterine growth restriction groups for either monochorionic (p=0.36) or dichorionic (p=0.68) twins. Placental weight and the birth weight/placental weight ratio were not associated with cord insertion type or with placental lesions.CONCLUSION:Low placental weight, and consequently reduced functional mass, appears to be involved in fetal growth restriction in monochorionic and dichorionic twins. The mechanism by which low placental weight influences the birth weight/placental weight ratio in intrauterine growth-restricted monochorionic and dichorionic twins needs to be determined in larger prospective studies.

Comparison Between Monochorionic and Dichorionic Placentas With Special Attention to Vascular Anastomoses and Placental Share.

Placental vascular anastomoses in twins lead to a shared circulation and may subsequently enable the development of severe complications such as twin-twin transfusion syndrome (TTTS) and twin anemia-polycythemia sequence (TAPS). The presence of vascular anastomoses has frequently and systematically been studied in monochorionic (MC) placentas, but only rarely in dichorionic (DC) placentas. The aim of this study was to compare the prevalence of vascular anastomoses and evaluate the sharing discordance in MC and DC placentas. All consecutive placentas of MC and DC twins delivered at the Leiden University Medical Center (the Netherlands) and Medical University of Warsaw (Poland) from 2012 to 2015 were routinely injected with colored dye and included in the study. We excluded twin pregnancies treated with fetoscopic laser surgery. A total of 258 placentas were analyzed in this study, including 134 MC placentas and 124 DC placentas. Vascular anastomoses were present in 99% (133/134) of MC placentas and 0% of DC placentas (p < .01). Placental share discordance between MC twins was significantly larger compared to DC twins, 19.8 (interquartile range [IQR] 8.1-33.3) and 10.8 (IQR 6.2-19.0), respectively (p < .01). Vascular anastomoses associated complications occurred in 16% (22/134) MC twins. Our findings show that vascular anastomoses are almost ubiquitous in MC placentas, but non-existent in DC placentas. In addition, unequal placental sharing appears to be more common in MC than in DC placentas.

Velamentous cord insertion in dichorionic and monochorionic twin pregnancies – Does it make a difference?

ObjectiveTo estimate the prevalence of velamentous cord insertion (VCI) in dichorionic (DC) and monochorionic (MC) twins with and without twin-twin transfusion syndrome (TTTS), and to study the associated outcomes. MethodsWe recorded the type of umbilical cord insertion in all consecutive DC and MC placentas examined in two European tertiary medical centers. The association between VCI and perinatal outcomes was estimated and compared. ResultsA total of 1498 twin placentas were included in this study (DC placentas n = 550, MC placentas without TTTS n = 513 and MC placentas with TTTS n = 435). The prevalence of VCI in DC, MC without TTTS and MC with TTTS groups was 7.6%, 34.7% and 36.1%, respectively (P < 0.001). In MC twins (non-TTTS and TTTS groups), VCI was associated with severe birth weight discordance (odds ratio [OR] 4.76 95% CI 2.43, 10.47 and OR 4.52 95% CI 1.30, 28.59, respectively). In MC twins without TTTS, VCI was associated with small for gestational age (OR 1.66, 95% CI 1.12, 2.50). VCI was significantly associated with increased risk of intrauterine fetal demise in MC twins, and this effect was greater in the non-TTTS group (OR 2.71 95% CI 1.38, 5.47). These associations did not occur in DC group. Gestational age at birth was lower in the presence of VCI in the DC and MC twins without TTTS. ConclusionOur findings confirm that the prevalence of VCI is higher in MC twins than in DC twin pregnancies. VCI is an important indicator of adverse perinatal outcome, particularly in MC twins.

Factors affecting the outcome in multiple gestations

Introduction: Twin births are the commonest form of multiple births. Twins have attracted considerable attention and excited curiosity from early times as a biological variety in the study of the human species. Twin pregnancy is considered as high risk pregnancy. There is poor neonatal outcome in terms of mortality and morbidity. Materials and methods: A retrospective study was conducted from Jan 2015 to Jan 2014 Mac Gann Government General Hospital. During this period there were 2643 deliveries occurred out of which 48 twins and 8 were triplets. Results: In the present study, Incidence of twin pregnancy is 18/1000 live birth. Monozygotic twinning rate is 4.2/1000 live births, while dizygotic twinning rate is 14.2/1000 live births. Perinatal mortality in twins is 177/1000 births as compared to 74.3/1000 births in singleton pregnancy i.e., 2.38 times that of singleton pregnancy. In twin pregnancy Perinatal mortality rate in 1st twin is 62.5/1000 live births while in second twin it is 114.5/1000 births. Frequency of IUGR in twin pregnancy is 85.4%. Risk of preterm labour in twin pregnancy is 64.5%. IUGR babies are more in monochorionic than in dichorionic placenta. Conclusion: Perinatal mortality in twin is higher than in of singleton pregnancy. Risk of single fetal loss (antepartum deaths) in twin pregnancy is higher than risk of both fetal losses. Perinatal mortality rate in 2st twin is double compared to first twin. Perinatal mortality increases as the gestational age decreases. Frequency of IUGR in twin pregnancy is very high and more in monochorionic than in dichorionic placenta.

Umbilical Cord Coiling and Zygosity: Is there a Link?

Introduction: The aim of this study was to analyze abnormalities of umbilical coiling index (UCI) in twin gestation to test whether the coiling is genetically influenced by zygosity.Methods: Data retrieved comprised gestational age (GA), chorionicity, fetal gender, and UCI. Results: The mean UCI of hypercoiled cords in monochorionic placentas was 0.55 coils/cm and 0.49 coils/cm in dichorionic placentas with discordant fetal gender (P = 0.2629).Discussion: In conclusion, no significant statistical difference between UCI in monochorionic and dichorionic twin placentas with discordant fetal gender was identified, suggesting that zygosity does not play a role in umbilical coiling induction.

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.

Umbilical Artery Doppler Ultrasound for the Determination of Chorionicity in Twin Pregnancies

Background: Maternal and perinatal complications are higher in twins than in singleton pregnancies. This complications rate is directly related to placental chorionicity in twin pregnancies. Early diagnosis of twins and their chorionicity is necessary to reduce the perinatal mortality. It can be determined by different methods in the first trimester. Ultrasonography is a valuable tool in management of twin pregnancy. Ultrasound in evaluation of the chorionicity decreases later in gestational weeks. The aim of this study is to determine the chorionicity by using Doppler ultrasonography in second and third trimesters. Methods: Patients were divided into two groups according to their chorionicity. Pregnancies with dichorionic placentas were included into group 1, while with monochorionic placentas were included into group 2. In both groups, PI, RI and S/D indices of umbilical artery were measured in each fetus. Whether there is a significant difference between the groups in the Doppler parameters was evaluated. Results: The PI, RI and S/D indices of umbilical artery doppler ultrasonography were different between the twins with dichorionic placentas (p < 0.05), but they were similar in twins with monochorionic placentas. Conclusions: Based on our study results, we suggest that the Doppler ultrasonography can be useful method for chorionicity determination of twin pregnancies at second and third trimesters, if chorionicity has not determined until the end of second trimester. doi:10.4021/ jcgo29w

Blood Chimerism in a Dizygotic Dichorionic Pregnancy

Blood chimerism in twins is known to occur through the transfer of hematopoietic stem cells between the fetuses via a common placenta. We present a case of blood chimerism in a dizygotic dichorionic twin pregnancy. The female twin was delivered at 34 weeks of gestation, and the male twin was stillborn. Pathologic examination confirmed dichorionic diamniotic placentas. The karyotype of the female child was obtained using peripheral blood sample, and it revealed a mixture of 46,XX and 46,XY cells (chi 46,XY[13]/46,XX[7]). FISH analysis performed on the buccal cells by using CEP X/Y probe (Abbott Molecular Inc., USA) revealed 100% XX signals (nuc ish Xcen(DXZ1x2)[500]). Gross examination of the external genitalia and abdominal ultrasonography revealed no definitive abnormal findings in relation to sex differentiation. When XX/XY chimerism is present in blood lymphocytes, careful examination of external genitalia and reproductive organs and further studies are required to detect chimerism in non-hematopoetic tissues. This is a rare case of blood chimerism in dichorionic placentas, in contrast to those in monochorionic placentas.

Perinatal morbidity and mortality in twin pregnancies with dichorionic placentas following assisted reproductive techniques or ovarian induction alone: a comparative study

Objective To compare maternal and perinatal outcome in non-spontaneously and spontaneously conceived dichorionic twin pregnancies. Study design We report a retrospective study of all 350 twin pregnancies delivered ≥22 weeks of gestation between January 1, 2001 and December 31, 2005 in a tertiary maternity unit. We compared maternal outcome, perinatal morbidity and neonatal mortality between spontaneous and non-spontaneous dichorionic twin pregnancies, with a subgroup analysis separating pregnancies following assisted reproduction technology (ART group) from those following ovarian induction alone (OI group). Generalized linear model and multivariate analysis were performed. Results The proportion of primiparous women and the mean maternal age were higher in the non-spontaneously conceived dichorionic twin pregnancy group as expected (70.2% vs. 38.2%, p < 0.001 and 32.1 ± 3.8 vs. 30.7 ± 4.6 years, p < 0.01). Multivariate analysis, adjusted for maternal age and parity, revealed that non-spontaneously conceived dichorionic twin pregnancies were associated with a higher risk of very preterm birth (OR 2.20, 95% confidence interval 1.02–4.77, p < 0.05), low birth weight (1.77, 1.21–2.61, p < 0.01), very low birth weight (1.99, 1.13–3.49, p < 0.05), NICU admission (1.66, 1.14–2.43, p < 0.01), and fetal or neonatal death (3.21, 1.30–7.95, p < 0.05). Multivariate analysis confirmed that the mean gestational age ( p < 0.01) and mean birth weight of the first ( p < 0.05) and second twins ( p < 0.01) were lower in the non-spontaneously conceived dichorionic twin pregnancy group. These associations were confirmed in the OI group analysis ( n = 39) but not in the ART group ( n = 65). Ovarian induction was associated with an increase in the risk of preterm and very preterm births (2.25, 1.06–4.75, p < 0.05 and 3.47, 1.42–8.49, p < 0.01, respectively), low and very low birth weights (2.87, 1.63–5.05, p < 0.001 and 2.59, 1.33–5.07, p < 0.01, respectively), NICU admission (2.92, 1.67–5.11, p < 0.001) and fetal or neonatal death (4.20, 1.40–12.56, p < 0.05). The mean gestational age ( p < 0.001) and mean birth weight of the first ( p < 0.01) and second twins ( p < 0.001) were also lower in the OI group. Conclusions Twin pregnancies with dichorionic placentation following non-spontaneously conceived pregnancy are associated with a higher risk of adverse perinatal outcome compared with dichorionic spontaneously conceived twin pregnancies especially in case of ovarian induction alone.

Curves of Placental Weights of Live-Born Twins

AbstractThe purpose of this study is to present curves of estimated placental growth in twins and to evaluate the relative contribution of gestational age, zygosity, chorionicity, fusion of the placentas, sex of the individual and of the twin pair, site of the umbilical cord insertion, birth order, maternal age, and parity. Perinatal data and placental data were obtained from 6315 live-born twin pairs from the East Flanders Prospective Twin Survey. Of 4318 twin pairs, with no missing values, the placental weights of different gestational ages were analyzed using a nonlinear multivariate Gaussian regression. Two groups were distinguished: (1) twins with two separate placentas, and (2) twins with only one placental mass (one placenta in case of monochorionic twins or two fused placentas in case of dichorionic placentas). Overall, placental weight was influenced by gestational age, fusion of the placentas, and parity. In the case of one placental mass, monozygotic dichorionic twins had the lowest weights. If two separate placentas were present, birth order played a role in favor of the first-born twin. For parity and zygosity, the differences were most pronounced between 27 and 29 weeks, whereas the difference for birth order was most pronounced between 33 and 37 weeks. In conclusion, basic physiological characteristics, routinely examined at birth, influence placental weight. Taking these covariates into account allows a better evaluation of the placental weight given a gestational age, as an indicator of growth.

Curves of Placental Weights of Live-Born Twins

The purpose of this study is to present curves of estimated placental growth in twins and to evaluate the relative contribution of gestational age, zygosity, chorionicity, fusion of the placentas, sex of the individual and of the twin pair, site of the umbilical cord insertion, birth order, maternal age, and parity. Perinatal data and placental data were obtained from 6315 live-born twin pairs from the East Flanders Prospective Twin Survey. Of 4318 twin pairs, with no missing values, the placental weights of different gestational ages were analyzed using a nonlinear multivariate Gaussian regression. Two groups were distinguished: (1) twins with two separate placentas, and (2) twins with only one placental mass (one placenta in case of monochorionic twins or two fused placentas in case of dichorionic placentas). Overall, placental weight was influenced by gestational age, fusion of the placentas, and parity. In the case of one placental mass, monozygotic dichorionic twins had the lowest weights. If two separate placentas were present, birth order played a role in favor of the first-born twin. For parity and zygosity, the differences were most pronounced between 27 and 29 weeks, whereas the difference for birth order was most pronounced between 33 and 37 weeks. In conclusion, basic physiological characteristics, routinely examined at birth, influence placental weight. Taking these covariates into account allows a better evaluation of the placental weight given a gestational age, as an indicator of growth.

OP05.09: Preliminary experience in Poland with fetoscopic laser surgery for severe TTTS

Objective: To compare the transfer of technetium-99m labelled red blood cells (99mTc RBCs) in monochorionic (MC) placentas, MC placentas after laser coagulation of the vascular anastomoses for TTTS and fused dichorionic (DC) placentas. Methods: Placental perfusion study with 99mTc O Rh – RBCs in 5 MC, 5 lasered MC and 5 fused DC placentas. The arteries of twin 1 were injected with 20–30.10 × 9 99mTc RBCs diluted in 100 mL NaCl, whereas the vessels of twin 2 were rinsed with 200 mL NaCl. The % of transferred 99mTc RBCs was calculated by dividing the radioactivity measured in the rinsing solution of twin 2 by the initial radioactivity injected in twin 1. Afterwards, each placenta was injected with dyed barium sulphate to document the angioarchitecture. Results: GA at birth was similar in the 3 groups. None of the lasered MC and fused DC placentas had visible anastomoses, whereas all 5 MC placentas had visible anastomoses-1 had only small arteriovenous (AV)-venoarterial anastomoses (VA) without an arterioarterial (AA) anastomosis, 4 had an AA with AV/VA. The % of transferred 99mTc RBCs in lasered MC placentas (0, range: 0–000012) was similar to fused DC placentas (0, range: 0–001760) (NS), but significantly lower than in MC placentas (8.5, range: 1–66) (p < 0.01). In MC placentas, the larger the AA, the higher the % of transferred 99mTc RBCs. Conclusion: In MC placentas successfully separated by laser coagulation of the vascular anastomoses, the transfer of 99mTc RBCs was not significant and similar to fused DC twin placentas. Therefore, laser seems to functionally separate the 2 fetal circulations.

1099: Importance of chorionicity in fetal medicine

Chorionicity, rather than zygocity, is the main determinant of perinatal outcome in multiple pregnancies. Monochorionic (MC) twins have a 6-fold increase in fetal miscarriage before 24 wk, and for those reaching 24 wk there is a 2-fold increase in perinatal death, growth restriction and severe premature delivery compared to dichorionic (DC) twins. Most of these complications are attributed to unequal placental sharing and the presence of vascular anastomoses, which are invariably present in all MC placentas but not in DC placentas.