Monochorionic Placentas Research Articles

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.

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.

Character of placentation in twins, as related to hemoglobin levels.

Capillary hemoglobin values estimated simultaneously in liveborn partners of 86 pairs of dichorionic twins during the first week of life were comparable in the two partners. In 20 pairs of liveborn twins with monochorionic placentas the values were different, with the second-born having the higher hemoglobin concentration. This difference, which was small in the first hours after delivery but became greater later (12 to 24 hours), indicates that shunting of blood occurs during delivery. Because of the abundant and easily recognizable anastomoses this placentofetal transfusion is greater in monochorionic twins. Ergometrine injection immediately after delivery of the second twin may enhance this process. Estimations of venous hemoglobin in 17 dichorionic twins showed slightly higher values in the second-born partners. The corresponding capillary blood levels were an average of 2.5 Gm./100 ml. higher than the venous values.

Intrauterine disseminated intravascularcoagulation: A syndrome of multiple pregnancy with a dead twin fetus

Three infants with intrauterine disseminated intravascular coagulation are presented.Each was the product of a twin pregnancy with a macerated sibling. Renal cortical and cerebral necrosis were the predominant features. Two other similar patients have been previously reported. It appears likely that the feto-fetal exchange of thromboplastic material from a dead fetus through vascular shunts in a monochorionic placenta is responsible for this syndrome. With conservative management, the renal cortical necrosis may not necessarily be fatal, but the prognosis is probably poor because of the severity of the cerebral damage. Three infants with intrauterine disseminated intravascular coagulation are presented.Each was the product of a twin pregnancy with a macerated sibling. Renal cortical and cerebral necrosis were the predominant features. Two other similar patients have been previously reported. It appears likely that the feto-fetal exchange of thromboplastic material from a dead fetus through vascular shunts in a monochorionic placenta is responsible for this syndrome. With conservative management, the renal cortical necrosis may not necessarily be fatal, but the prognosis is probably poor because of the severity of the cerebral damage.

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.

Discordant abnormalities in monozygotic twins

Congenital abnormalities are more often seen in monozygotic twins, especially with a monochorionic placenta, than in dizygotic twins. Although abnormalities are more frequently concordant in monozygotic than in dizygotic twins, discordance for the abnormalities among the former is strikingly frequent. Among 24 consecutive pairs of monochorionic (i.e., monozygotic) twins, five sets were discordant for various phenotypic traits. During the same period, among 79 pairs of dichorial twins, an abnormality was noted in only one pair, and this was discordant. The twin method has not been extensively applied to the study of the relative contributions of heredity and environment in the development of congenital disease. Its use in such studies is described and the various factors which may account for intrapair differences in isogenic individuals are discussed.

Twin zygosity and placental form in relation to the outcome of pregnancy: Adair Award address

The zygosity of 80 per cent of 293 pairs of twins was established with certainty at birth; a placenta with a single chorion identified 22.8 per cent as monozygotic, differences in sex identified 30.2 per cent as dizygotic, and differences in blood groups of those of the same sex identified an additional 27.0 per cent as dizygotic. The remaining 20 per cent are probably although not positively monozygotic.The data corroborate Weinberg's rule which indicates the total number of dizygotic twins in any population should be twice the number of different sex and that this subtracted from the total should give the number who are monozygotic.Twins have a high mortality which in large measure is due to the high frequency of premature termination of pregnancy. Total neonatal mortality was seven times as great and fetal mortality three times as great for twins as for single infants. Neonatal deaths due primarily to premature delivery accounted for a mortality of 42.5 per 1,000 twin births and only 0.9 per 1,000 total births. However, among infants weighing 1,000 to 2,500 grams the perinatal mortality for twins was 10.5 per cent, for total infants it was 17.5 per cent.Twins known to be monozygous on the basis of monochorionic placentas, identical sex and blood groups had an increased frequency of premature delivery and consequently a greater mortality.Mortality was slightly higher for males (11.7 per cent) than females (9.4 per cent), for twins of like sex (12.2 per cent) than unlike sex (7.3 per cent), for second born (11.8 per cent) than first born (9.3 per cent), and for twins with monochorionic placentas (13.2 per cent) than dichorionic placentas (9.6 per cent).The only conditions that could be considered directly related to the fact of second birth were pneumonia and hyaline membrane disease. These were found in 5 first born and 13 second born. The difference in frequency of these 2 conditions made the only real difference in mortality of first and second twins as delivered at the Chicago Lying-in Hospital.

Multiple pregnancies at the Chicago Lying-in Hospital, 1941 to 1947

In the six and one-half year period prior to July 1, 1947, there were 22,943 deliveries at the Chicago Lying-in Hospital. Among these there were 257 multiple pregnancies, an incidence of 1:91 for twins and 1:4,580 for triplets.The mean birth weight in this series was 2,354 Gm.The mean length of gestation for twin pregnancies was 256.7 days and for multiple pregnancies (including triplets) in which the combined weight of the babies was over 5,000 Gm. is 271.2 days.The mortality for all infants and fetuses weighing more than 1,000 Gm. was 8.2 per cent and for those over 2,500 Gm. was 1.6 per cent. The mortality for single infants born in this hospital during the same period was 2.5 per cent over 1,000 Gm. and 1.6 per cent over 2,500 Gm.The mean ratio between the weight of the placenta and the combined birth weight of the twins was 1:6.7, a ratio only slightly different from that of 1:7 found for single infants.The twins associated with 48 monochorionic placentas were of the same sex in 46; of different sexes in 2. Those associated with dichorionic placentas were of the same sex in 92, of different sexes in 70.The incidence of pre-eclamptic and hypertensive toxemia in this series was 21 per cent, in comparison to approximately 8 per cent for all deliveries. Postpartum hemorrhage and polyhydramnios also occurred more frequently than in single pregnancies.Prematurity was the most important cause of death in this series of twin infants. Polyhydramnios, placenta previa, and abruptio placentae were the maternal complications most commonly associated with fetal mortality.