Monochorionic Placentation Research Articles

Twin growth problems: Causes and sonographic analysis

Understanding the significant increased risks associated with twin pregnancies requires knowledge of the embryogenesis of twins and the unique placental characteristics seen only in twin gestations. Dizygotic "fraternal" twins, 70% of all twins, are at relatively low risk when compared with monozygotic twins, largely due to abnormalities seen in association with monochorionic placentation. The sonographic determination of chorionicity and amnionicity allows better estimation of pregnancy risk--up to 50% mortality in monochorionic-monoamniotic twins. Careful evaluation of intrauterine twin growth assists in the early identification of fetal abnormalities because normal twin growth should parallel that of singleton pregnancies until late in the third trimester. A number of the unique complications affecting growth in twin pregnancies are discussed, including twin transfusion syndrome, the "stuck twin" phenomenon, twin embolization syndrome, and development of acardiac twins.

Intrauterine death in multiple gestation.

Intrauterine death of one fetus in a multiple gestation is associated with significant morbidity and mortality in the surviving infant. This study is a retrospective review of 38 twin and 3 triplet gestations involving the intrauterine death of at least one fetus. The obstetrical history, placental pathology, autopsy findings, and neonatal history of the surviving infant are reviewed. Three cases involved the recent stillbirth of both twins, the remaining cases involved a surviving infant. In one case, neonatal death of a surviving twin occurred on day 19. In two sets of triplets, two stillbirths occurred, in the third case two infants were liveborn. The incidence of preterm delivery was 34%, which decreased to 18% if fetal cotwin death had occurred before 20 weeks gestation. Cesarean section was the method of delivery in 16 cases. There was an excess of velamentous cord insertions, which was most pronounced in the stillborn twin. Monochorionic placentation was found in 72%, also an excess. Neurological damage was known to have occurred in 19 of the 39 surviving infants. Fifteen of these 19 (79%) were associated with monochorionic placentation. The neurologically damaged twin infants, when compared to the normal infants, had the cotwin die later in gestation (31 vs 16.5 weeks), had a shorter duration between the death of the cotwin and delivery (2.5 vs 21 weeks), and delivered earlier in gestation (36.5 vs 39.5 weeks). The probable cause of neurological damage, in our opinion, was either exsanguination into the dead twin fetus, or disseminated intravascular coagulation which occurred in at least 13 cases. The incidence of antepartum death in a multiple gestation, and the potential for neurological damage is probably higher than previously thought. A review of the literature is presented and the clinical implications of this phenomenon are discussed.

Twin gestation: Influence of placentation on fetal growth

To study fetal growth in twin gestation, morphometric autopsy data of 52 midgestation twin pairs who were stillborn or who died less than or equal to 24 hours after birth were analyzed. Twins were divided into three groups: (1) monozygotic: diamniotic, monochorionic placenta (n = 18); (2) dizygotic: diamniotic, dichorionic placenta, unlike sex (n = 12); (3) like-sex: placenta diamniotic, dichorionic in 63.6%, unknown in 36.4% (n = 22). The monozygotic group had a significantly higher rate of growth discordance, which was defined as a greater than 20% difference in body weight (monozygotic 72.2%, dizygotic 16.7%, like-sex 0%), and polyhydramnios (monozygotic 50%, dizygotic 0%, like-sex 9.1%). Organ weight z scores for body weight and brain weight standards were calculated for the smaller and larger of each twin pair. In the monozygotic group highly significant z scores were obtained for brain weight in the smaller twin (z = 2.71, p = 0.003, body weight standards) and heart weight in the larger twin (body weight standards, z = 3.87, p less than 0.001; brain weight standards, z = 3.64, p less than 0.001). We conclude that monozygotic twins with diamniotic, monochorionic placentation have a high degree of brain-sparing growth restriction in the smaller twin and cardiac hyperplasia in the larger twin, most likely caused by hemodynamic inequalities.

Twin gestation: Influence of placentation on fetal growth

To study fetal growth in twin gestation, morphometric autopsy data of 52 midgestation twin pairs who were stillborn or who died ≤24 hours after birth were analyzed. Twins were divided into three groups: (1) monozygotic: diamniotic, monochorionic placenta (n = 18); (2) dizygotic: diamniotic, dichorionic placenta, unlike sex (n = 12); (3) like-sex: placenta diamniotic, dichorionic in 63.6%, unknown in 36.4% (n = 22). The monozygotic group had a significantly higher rate of growth discordance, which was defined as a >20% difference in body weight (monozygotic 72.2%, dizygotic 16.7%, like-sex 0%), and polyhydramnios (monozygotic 50%, dizygotic 0%, like-sex 9.1%). Organ weight z scores for body weight and brain weight standards were calculated for the smaller and larger of each twin pair. In the monozygotic group highly significant z scores were obtained for brain weight in the smaller twin (z = 2.71, p = 0.003, body weight standards) and heart weight in the larger twin (body weight standards, z = 3.87, p<0.001; brain weight standards, z = 3.64, p < 0.001). We conclude that monozygotic twins with diamniotic, monochorionic placentation have a high degree of brain-sparing growth restriction in the smaller twin and cardiac hyperplasia in the larger twin, most likely caused by hemodynamic inequalities. To study fetal growth in twin gestation, morphometric autopsy data of 52 midgestation twin pairs who were stillborn or who died ≤24 hours after birth were analyzed. Twins were divided into three groups: (1) monozygotic: diamniotic, monochorionic placenta (n = 18); (2) dizygotic: diamniotic, dichorionic placenta, unlike sex (n = 12); (3) like-sex: placenta diamniotic, dichorionic in 63.6%, unknown in 36.4% (n = 22). The monozygotic group had a significantly higher rate of growth discordance, which was defined as a >20% difference in body weight (monozygotic 72.2%, dizygotic 16.7%, like-sex 0%), and polyhydramnios (monozygotic 50%, dizygotic 0%, like-sex 9.1%). Organ weight z scores for body weight and brain weight standards were calculated for the smaller and larger of each twin pair. In the monozygotic group highly significant z scores were obtained for brain weight in the smaller twin (z = 2.71, p = 0.003, body weight standards) and heart weight in the larger twin (body weight standards, z = 3.87, p<0.001; brain weight standards, z = 3.64, p < 0.001). We conclude that monozygotic twins with diamniotic, monochorionic placentation have a high degree of brain-sparing growth restriction in the smaller twin and cardiac hyperplasia in the larger twin, most likely caused by hemodynamic inequalities.

Central nervous system damage and other anomalies in surviving fetus following second trimester antenatal death of co‐twin. Report of four cases and literature review

Four cases of multiple gestation with second trimester death of one fetus and subsequent damage to a survivor are reported. Monochorionic placentation was documented in three of the cases. Central nervous system lesions occurred in all cases, and bowel injury was noted in two of the damaged fetuses. Although rare maternal clotting problems have been reported in similar situations, none was noted in any of these four cases. Prior reports have indicated that losses in the first half of gestation were of no consequence to the surviving fetuses. These four cases contradict this suggestion, and indicate that close sonographic observation of the survivors is important in any multiple gestation where on fetus has died.

Correlation between pathology findings and ultrasonic prediction in twin pregnancy

The macroscopic and microscopic pathology fIndings in 32 twin pregnancies were compared with the antenatal sonographic classification into monochorionic and dichorionic pregnancy. The latter was based on the thickness of the intervening septum. The ultrasound diagnosis was confirmed in 24 of 30 cases giving an accuracy of 80%. Thirteen of the 24 cases were dichorionlc diamniotic type while 10 showed monochorionic d1amn1ot1c placentation. Only one case of monochorionic monoamniotic twin pregnancy was found. In six of the remaining 8 cases there was discrepancy between the ultrasound prediction and pathology findings. Definite conclusions about the chorion type could not be drawn from either ultrasound or pathology examination 1n the remaining 2 cases. No monoamniotic twin pregnancy was missed in the latter 8 cases. This is important because of the associated high mortality. The detection of monochorIonic diamniotic placentatlon is also crucial because of the unique occurrence of vascular anastomoses between the two foetal circulations and potential of developing twin-to-twin transfusion and discordancy of foetal growth. Determination of chorion type also helps in the analysis of zygosity of the twin-pregnancy and bears implication 1n genetic amniocentesis.

Selective termination of multiple gestations.

Twenty-two selective terminations in multiple gestations were performed by a number of different methods. In 17 dichorionic pregnancies there was a successful delivery in surviving singletons or twins. In five monochorionic pregnancies undergoing selective termination there was a successful delivery in only one and a pregnancy loss in the other four. Six of the 18 delivered pregnancies were complicated by premature labor and delivery. Among the several methods used for selective termination, intracardiac potassium chloride injection appears to be the procedure of choice in dichorionic pregnancies.

Placental injection studies in twin gestation

Vascular communication between placental vessels can occur when there is a fused placental mass in twin gestation. The presence of anastomotic channels can lead to the twin-twin transfusion syndrome in the fetuses. A study was conducted on 278 twin pairs to determine the incidence of vascular communication in fused twin placentas and the frequency of twin-twin transfusion syndrome. Anastomotic communication was found almost universally in monochorionic placentation and very rarely with dichorionic placentas. Twin-twin transfusion syndrome occurred uncommonly despite the high frequency of occurrence of cross-placental vascular communication. Misdiagnosis of intrauterine growth retardation in one twin can be avoided by determination of chorionicity by inspection of the placentas of twin gestation.

Congenital anomalies in twins in Aberdeen and Northeast Scotland.

Data with regard to the proportion of congenital malformations found at birth are presented from a survey of 657 pairs of twins of known zygosity and placentation delivered in Aberdeen and Northeast Scotland between 1968 and 1979. There was an excess of malformed individuals from monozygotic (MZ) pairs, but this did not reach statistical significance. The possible effect of monochorionic placentation in the causation of malformations in MZ twins in general is discussed. It seems that this type of placentation may be of less causative importance than has been previously suggested.

Twinning in Nigeria.

SummaryTwinning rates in Nigeria are much higher than in Europe and USA, and appear to be highest in its western and eastern parts. The twinning incidence in a representative population in a town in Western Nigeria, Igbo-Ora, is approximately four times that in Europe and USA.Zygosity determination has shown that only 8.6% of newborn twin pairs in Ibadan are MZ, compared to approximately 30% in Caucasian populations. Studies in Igbo-Ora have also given similar results, confirming the view that high twinning incidence in Nigeria is due to a very high DZ twinning rate, the MZ rate being the same as in Europe and USA.The proportion of twins with monochorionic placentae in Ibadan is about 5%, against approximately 20% in UK and USA. The twinning rates in the two populations are 45‰ and 11‰ respectively. This inverse relation (between the twinning rate and the proportion of monochorionic placentae) may be used in calculating the twinning incidence in a population in which the proportion of twins with monochorionic placentation is known.

Placental circulation of human twins: Constant arterial anastomoses in monochorionic placentas

Seventy-five twin placentas were examined by careful vascular injection studies after accurate diagnosis of the monochorionic or bichorionic state. Two triplet placentas were similarly examined. The injections were designed to study the precapillary circulation.Anastomoses between the arterial systems of the two embryos were definitely identified in every well-formed monochorionic placenta in this series. In all but one placenta these anastomoses were grossly visible, but in one they were first detected with the radiopaque injection mass.The size of the anastomoses was partially related to the distance separating the two umbilical cords.No anatomic cause for any preferential direction of flow, no venous valves, and no thrombus was found in any placenta. In one instance, one of the twins had died in utero and the anastomosis showed partial occlusion at the probable line of junction of the two placentas, due to vascular swelling.No arteriovenous precapillary anastomoses were demonstrated. Only one placenta showed a venous-venous anastomosis. Cross circulation at a capillary level could be shown in associated studies. There was no demonstrable anastomoses in any bichorionic placenta.A hypothesis is presented that the anemiapolycythemia syndrome develops in monochorionic placentation if the anastomoses are relatively large and the intrauterine twin in its high pressure environment is permitted to infuse the delivered twin in its low pressure environment.