Chorionicity In Twin Pregnancies Research Articles

Yolk sacs in twin pregnancy.

The purpose of this study was to evaluate the relationship between the yolk sacs separated or not separated by septum and chorionicity twin pregnancies scanned early in the first trimester, and the relation between size and morphologic features of the yolk sac and the outcome of twin pregnancies. In all 38 sets of twins two yolk sacs were identified. During the first trimester of a dichorionic twin pregnancy, the yolk sacs were always separated by a septum and not separated ("Eight" sign) in monochorionic twin pregnancy. In five cases, one of yolk sac was abnormally large (> 8 mm) and had thin wall. Four of the five mothers spontaneously aborted during the next 2-3 weeks. In one case of monochorionic twin ectopic pregnancy two yolk sacs were seen normally. The sonographic identification of yolk sacs in multiple pregnancies allows an early and efficient recognition of presence and chorionicity of twin pregnancy, both in intra- and extrauterine. Identification of abnormal yolk sac or yolk sacs suggests death of one or all embryos.

The lambda sign at 10-14 weeks of gestation as a predictor of chorionicity in twin pregnancies.

Chorionicity was prospectively determined in 369 twin pregnancies by ultrasound at 10-14 weeks of gestation. Pregnancies were classified as monochorionic if there was a single placental mass in the absence of the lambda sign at the inter-twin membrane-placental junction, and dichorionic if there was a single placental mass but the lambda sign was present, or the placentas were not adjacent to each other. In 81 (22%) cases, the pregnancies were classified as monochorionic and in 288 (78%) as dichorionic. Pregnancy outcome was available in 279 cases and all 63 of these pregnancies classified as monochorionic resulted in the delivery of same-sex twins. Similarly, all 100 different-sex pairs were correctly classified as dichorionic. These findings demonstrate the high reliability of ultrasound examination at 10-14 weeks of gestation in determining chorionicity in twin pregnancies.

Ultrasonographic measurement of the dividing membrane in twin pregnancy during the second and third trimesters: A reproducibility study

OBJECTIVE: Our purpose was to examine the reproducibility of intertwin membrane thickness measurements used to predict chorionicity in twin pregnancies. STUDY DESIGN: Twenty-seven twin pregnancies were scanned with high-resolution ultrasonography on 52 occasions during membrane twice in five different sites (total measurements 1040). The data were log-transformed and the coefficient of repeatability calculated as a measure of intraobserver variability. Interobserver variability was estimated by the Bland and Altman 95% limits of agreement. Random variation was assessed with the restricted maximum likelihood procedure in Genstat. RESULTS: The overall estimate of the coefficient of repeatability was 2.14, indicating that 95% of repeated measurements would be expected to be within 114% of each other. Measurements taken close to the placenta (up to 3 cm) were the most repeatable and displayed no bias when repeated. Coefficients of repeatability at this site ranged from 1.42 to 1.91, with no evidence of consistent differences between monochorionic and dichorionic twins. Gestational age was not significantly associated with membrane thickness for any of the models. The pregnancy type × subject × observer and pregnancy type × subject × site interactions were statistically significant ( p < 0.001 and p < 0.005, respectively), implying that interobserver variability depends on the subject being measured, the site of sampling, and chorionicity. CONCLUSION: Ultrasonographic measurement of membrane thickness has high intraobserver and interobserver variability in the second and third trimesters. Our findings provide an explanation for the suboptimal accuracy reported with this method in determining chorionicity in the second and third trimesters.

Amnionicity and chorionicity in twin pregnancies: prediction using ultrasound.

A total of 66 twin pregnancies was studied antenatally with ultrasound, followed up clinically, and the placentae examined pathologically to determine if, solely on the basis of antenatal sonography, an accurate assessment of amnionicity and chorionicity could be made. Sonographic features noted included number of placental sites, whether a membrane separating the fetuses could be visualized, fetal position and amount of amniotic fluid, and in some cases fetal positioning vis-a-vis each other and the uterine wall. Documentation of two placental sites confirms the presence of a dichorionic and, therefore, a diamniotic pregnancy. Documentation of a membrane separating the fetuses confirms the presence of a diamniotic pregnancy; lack of visualization of a separating membrane does not reliably predict, but does suggest, a monoamniotic pregnancy. Other features frequently assist in prediction of amnionicity, chorionicity, and zygosity; the most helpful of these was the "stuck twin" sign, in which one twin moved freely but the other remained in a fixed position adjacent to the sidewall of the uterus despite changes in maternal positioning, indicating the presence of a nonvisualized membrane. Presence of absence of entanglement or intermingling of fetal parts or umbilical cords may also be helpful. In the absence of such sonographic features, antenatal sonographic diagnosis of a monoamniotic pregnancy cannot be made reliably.