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Differentiation of Monochorionic and Dichorionic Twin Placentas by Antenatal Ultrasonic Evaluation
Author(s) -
Cheung A.,
Wan M.,
Collins R.J.
Publication year - 1990
Publication title -
australian and new zealand journal of obstetrics and gynaecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.734
H-Index - 65
eISSN - 1479-828X
pISSN - 0004-8666
DOI - 10.1111/j.1479-828x.1990.tb03244.x
Subject(s) - obstetrics , polyhydramnios , twin to twin transfusion syndrome , medicine , monochorionic twins , gestational age , pregnancy , twin pregnancy , incidence (geometry) , gestation , fetus , biology , physics , optics , genetics
EDITORIAL COMMENT: Any lead that promises improved results in twin pregnancy warrants scrutiny since the condition accounts for more than 10% of perinatal deaths (78 of 677 in Victoria in 1987). Twins are monozygotic or identical in about 1 in 4 cases in Caucasian populations and about 1 in 2 in Asian populations (15 of the 31 consecutive cases in this series from Hong Kong). Differences in incidences of spontaneous twin pregnancies in different populations is accounted for by differences in rates of dizygotic twinning, monozygonic twinning apparently having a similar incidence (about 1 in 300 pregnancies) in all populations. This study shows that ultrasound is reasonably accurate at identification of dichorionic from monochorionic twins (70% of monozygotic twins) by assessment of the thickness of the septum between the 2 gestational sacs. The higher perinatal mortality rate in monozygotic compared to dizygotic twins is mainly due to complications that occur exclusively in the monochorionic variety (twin to twin transfusion and its various complications, acute polyhydramnios) but there is also an increased incidence of fetal growth retardation (about 25 %). This paper discusses the advantages of knowing if twins are monochorionic from the point of view of antenatal management. In the editor's opinion the principles of management of all twin pregnancies are: I) The patient should be encouraged to have extra rest at home, whether she believes it to be necessary or not, from 20 weeks' gestation until delivery. 2) Extra surveillance (more frequent testing) for anaemia and preeclampsia. 3) Ultrasonographic assessment of fetal growth every 3–4 weeks from 20 weeks. 4) Weekly cardiotocography from 30 weeks' gestation, especially if the twins are thought to be monochorionic, or if polyhydramnios is present, in order to detect severe fetal compromise (twin to twin transfusion, fetal growth retardation of 1 or both fetuses). Recognition of the rare monoamniotic twin pregnancy alters management only at delivery, the time at which the astute clinician makes the diagnosis by noting that there is only one amniotic sac, since the 25% incidence of cord entanglement or knotting indicates immediate delivery of the second twin if this condition is diagnosed antenatally by ultrasound, elective Caesarean section at 37 weeks' gestation has many advocates. ABSTRACT The prenatal identification of various types of placentation is important for the antenatal management of twin pregnancies. Such classification can be achieved with the use of ultrasound examination. In 32 cases of twin pregnancy the intervening septum was classified as either a thick (dichorionic) or thin (monochorionic) type. Macroscopic and microscopic examination of the placenta after delivery confirmed the ultrasound diagnosis in 24 of the 30 cases, an accuracy of 80%.