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Amniocentesis
Published in Hung N. Winn, Frank A. Chervenak, Roberto Romero, Clinical Maternal-Fetal Medicine Online, 2021
Aris Antsaklis, Marianna Theodora
As far as zygosity represents the genetic makeup of the developing entity, accurate determination of this parameter is considered a prerequisite in multiple pregnancy prenatal screening for aneuploidies. In the clinical setting, zygosity is usually inferred from the ultrasound diagnosis of chorioni-city (44), the latter best achieved in the first trimester. In diamniotic (DA) pregnancies with fused placentas, measurements of the thickness of the dividing membrane using a cutoff value of 2 mm can differentiate MC from dichorionic (DC) twinning, though a high inter- and intra-observer variability has been reported. Sonographic detection of the “lambda” or “twin peak” sign is reported as a more reliable indicator of DC placentation with an accuracy of 100% in 10 to 14 weeks of gestation (45). Delayed sonographic evaluation in the second trimester is associated with a 10% to 12% chorionicity misinterpretation rate (46,47), while after 20 weeks of gestation, the determination may turn out impossible. Therefore, in the absence of the “lambda” or “twin peak” sign in a DA twin pregnancy, single placentation and monozygosity is concluded, when the rare cases of MC-DZ (dizygotic) gestations following ART reported are not taken into consideration. However, when a single amniotic sac is detected, monochorionicity is indisputable. Given that the great proportion (80–90%) of DC twins are DZ (48,49), chorionicity may roughly correspond to zygosity (50).
Multiple pregnancy and infertility
Published in Janetta Bensouilah, Pregnancy Loss, 2021
Multiplets have a more complicated life in utero than singletons and, as previously mentioned, monozygotic twins are at higher risk than dizygotic twins, but it is chorionicity and amnionicity rather than zygosity that determines the degree of risk. The particular challenges of a monochorionic (MC) pregnancy arise from the unique structure of the shared placenta, with vascular structures connecting the umbilical circulations of both twins. This leads to unpredictable and significant blood volume shifts between the fetuses causing problems such as twin–twin transfusion and acute fetal transfusion following the intrauterine death of one twin. Furthermore, the shared placenta is often unequally divided, which explains the increased incidence of discordant fetal growth. Perinatal mortality is two to three times higher in MC twins than in DC twins, and morbidity rates are similarly raised.1
Genetics and metabolic disorders
Published in Jagdish M. Gupta, John Beveridge, MCQs in Paediatrics, 2020
Jagdish M. Gupta, John Beveridge
The vascular anastomosis in monozygotic twins may be artery to artery, vein to vein, or artery to vein. Monozygotic twins show a higher incidence of congenital malformations than dizygotic twins. It is not possible to establish monozygosity with 100% certainty by examination of the placenta and membranes. However, the diagnosis of dizygosity can be made with more certainty if the presence of two chorions is shown or, more reliably, the twins are of opposite sex. DNA 'fingerprinting' is now the method of choice if zygosity needs to be determined with certainty. The incidence of monozygotic twins is less than that of dizygotic twins. Monozygous twins are rarely familial but there is a familial tendency for dizygous twinning.
Monocyte secretory profiling in a clinical and MEFV genotype-characterized cohort of Danish familial Mediterranean fever patients: diagnostic potential of CCL1 and CXCL1.
Published in Scandinavian Journal of Rheumatology, 2023
SB Mortensen, AE Hansen, K-E Byg, L Diederichsen, C Schade Larsen, MI Goldschmidt, MA Jakobsen, K Assing, KL Lambertsen, DC Andersen, IS Johansen
MEFV genotypes were assessed by sequencing of the entire coding MEFV region and zygosity was resolved in all except five patients (see Supplemental Table S6 for a full list of MEFV genotypes). MEFV genotypes with no detected variants or variants classified as VUS were present in 23 patients (5.8% and 20.1%, respectively), and these were grouped in MEFV group 1, whereas MEFV groups 2 and 3 constituted 17 patients (19.8%) and 46 patients (53.5%) with monoallelic and biallelic presence of variants classified as pathogenic or likely pathogenic, respectively. Five patients with inconclusive variant zygosity were excluded from the genotype groups. In five patients, where MEFV screening was negative, targeted sequencing of 16 autoinflammatory-related genes identified one patient, with a yet undescribed intron variant [NG_007507.1(NM_014646.2):c.590 + 8 T > G] in the gene responsible for the Majeed syndrome, LPIN2 (43).
Facial asymmetry and chewing sides in twins
Published in Acta Odontologica Scandinavica, 2022
Elina V. Heikkinen, Ville Vuollo, Virpi Harila, Antanas Sidlauskas, Tuomo Heikkinen
This study included 106 Lithuanian twin pairs of the same sex where 59 pairs were MZ and the rest were DZ twins. The twins were selected to the study on the basis of their willingness to participate in the research conducted by the Lithuanian University of Health Sciences Twin Centre. The exclusion criteria were facial trauma, permanent dental extraction, congenital disorders as well as pregnancy. The mean age of the twins was 20.2 years, ranging from 8.6 to 45.7. The number of male and female pairs was 46 and 60, respectively. For each twin pair, a blinded DNA test (AmpFlSTR® Identifiler® PCR) was done to determine true zygosity. The test compared genetic profiles, which ensures quick and authentic determination of zygosity by utilizing specific DNA markers (D8S1179, D21S11, D7S820, CSF1PO, D3S1358, TH01, D13S317, D16S539, D2S1338, D19S433, vWA, TROX, D18S51, D5S818, FGA) and Amel fragment STRs (short tandem repeats). In the asymmetry analyses, one male pair was excluded because of facial hair which caused erroneous roughness on the 3D surface. Furthermore, one female pair was excluded because chewing side preference had not been registered. Thus, the number of twin pairs with both 3D asymmetry analysis and PCS is 104.
Prenatal Sonographic Detection of Monochorionic Twins with Bipartite Placenta
Published in Fetal and Pediatric Pathology, 2021
Mehmet Serdar Kutuk, Taha Takmaz, Arslan Bayram, Sule Ozturk
Determination of chorionicity and zygosity is important for the correct risk assessment, counseling, and management of complications in multifetal pregnancies. For this purpose, ultrasonographic criteria were determined and have long been used. Although the presence of opposite-sex fetuses is a clear-cut sign of dizygocity, it is difficult to predict zygosity in same-sex fetuses. The presence of a twin peak sign (also called a lambda or delta sign), a triangular extension of chorionic tissue between the base of the two amniotic sacs, and the presence of two separate placentas are indicative of dizygosity. The presence of a T-sign strongly suggests monozygocity and monochorionicity [1–3]. However, even in tertiary centers, sonography misclassified 4.0% of dichorionic twins and 19.0% of monochorionic twins [4].