A discordant twin gestation, in which one fetus is significantly growth restricted, compared to the other normal twin, is a unique model that can be used to elucidate the mechanism(s) by which the intrauterine environment affects fetal growth. In many model systems, placental transcription factor genes regulate fetal growth. Transcription factors regulate growth through their activation or repression of downstream target genes that mediate important cell functions. The objective of this study was to determine the expression of the placental HLX homeobox gene transcription factor and its downstream target genes in dizygotic twins with growth discordance. In this cross-sectional study, HLX and its downstream target genes’ retinoblastoma 1 (RB1) and cyclin kinase D (CDKN1C) expression levels were determined in placentae obtained from dichorionic diamniotic twin pregnancies (n = 23) where one of the twins was growth restricted. Fetal growth restriction (FGR) was defined as small for gestational age with abnormal umbilical artery Doppler indices when compared with the normal control co-twin. Homeobox gene HLX expression was significantly decreased at both the mRNA and protein levels in FGR twin placentae compared with the normal control co-twin placentae (p < .05). Downstream target genes CDKN1C and RB1 were also significantly decreased and increased, respectively, at both the mRNA and protein levels in FGR twin placentae compared with normal control co-twin placentae (p < .05). Together, these observations suggest an important association between HLX transcription factor expression and abnormal human placental development in discordant twin pregnancies.

Twinning is rare among humans, but there is much variability among populations. Several studies show that certain demographic and socioeconomic factors, such as maternal age, mother’s educational level and income, influence twinning rate. There is no background of analytical studies of twins in Uruguay. To the best of our knowledge, this is the first study that has focused on describing and analyzing Uruguayan twinning rates over a period of 17 years (1999–2015). The birth data were collected from the website of Uruguay’s Ministry of Public Health. Economic data were obtained from Uruguay’s Instituto Nacional de Estadísti’s website for the period 2001–2013, since these variables are defined specifically for that period of time. The statistical software R (The R Project for Statistical Computing) was used. The twinning rate varied from 8.51 to 13 in the studied period. Montevideo has the highest median and the smallest variability in comparison with the other departments. In Uruguay (1999–2015), the highest twinning rate (28.94%) was observed in women aged 45 and older. The analysis also showed a relationship between twin birth rates and the mother’s educational level. In three regions of the country (West, Center and East), twin births show a random pattern but in the other two (North and Metropolitan), there is an increasing trend in the number of twins over time. In conclusion, this study recognizes social, economic and demographic factors that influence in the rate of twin births in Uruguay.

Planning for the preterm birth of a fetus with known anomalies can raise complex ethical issues. This is particularly true of multiple pregnancies, where the interests of each fetus and of the expectant parent(s) can conflict. In these complex situations, parental wishes and values can also conflict with the recommendations of treating clinicians. In this article, we consider the case of a dichorionic twin pregnancy complicated by the diagnosis of vein of Galen aneurysmal malformation (VGAM) in one of the twins at 28 weeks’ gestation. Subsequent deterioration of the affected twin prompted the parents to request preterm delivery to prevent the imminent in-utero demise of the affected twin. However, given the associated risks of prematurity, complying with the parents’ request may have disadvantaged the health and wellbeing of the unaffected twin. This article canvases the complex ethical issues raised when parents request preterm delivery of a multiple pregnancy complicated by a fetal anomaly in one twin, and the various ethical tools and frameworks that clinicians can draw on to guide their decision-making in such cases.

Although the birth of twins has always attracted attention, there are no known genetic or environmental factors that can determine the birth of monozygotic (MZ) twins. And even for dizygotic (DZ) twins, genetic influences are not completely understood. A previous study from our group has shown that the C allele of polymorphism rs1042522 in the TP53 gene was more frequent in the mothers of twins than in the mothers of singletons in a small village in South Brazil. In order to clarify whether this was an isolated factor, we performed a population-based, observational case-control study. Samples were selected from a state-funded program of paternity investigation. Samples were considered cases when two of the children had the same date of birth, whereas controls were those samples in which at least two children were born in different dates. The first subsequent sample fulfilling control criteria was included after each case. From 2007 to 2013, 32,661 records were searched and 283 (0.9%) twins were found (119 MZ and 164 DZ). Genotypic and allele frequencies were not different between mothers of twins or mothers of singletons. However, mothers of MZ twins showed a higher frequency of GG genotype and lower frequency of the C allele when compared to mothers of DZ twins. Also, the proportion of MZ twins (42%) was higher than usually reported (30%). Finally, the proportion of twins found in this study seems to be more realistic, as this sample was allegedly not from users of assisted reproduction techniques.

Familial monozygotic (MZ) twinning reports are rare around the world, and we report a four-generation pedigree with seven recorded pairs of female MZ twins. Whole-genome sequencing of seven family members was performed to explore the featured genetic factors in MZ twins. For variations specific to MZ twins, five novel variants were observed in the X chromosome. These candidates were used to explain the seemingly X-linked dominant inheritance pattern, and only one variant was exonic, located at the 5′UTR region of ZCCHC12 (chrX: 117958597, G > A). Besides, consistent mitochondrial DNA composition in the maternal linage precluded roles of mitochondria for this trait. In this pedigree, autosomes also contain diverse variations specific to MZ twins. Pathway analysis revealed a significant enrichment of genes carrying novel SNVs in the epithelial adherens junction-signaling pathway (p = .011), contributed by FGFR1, TUBB6, and MYH7B. Meanwhile, TBC1D22A, TRIOBP, and TUBB6, also carrying similar SNVs, were involved in the GTPase family-mediated signal pathway. Furthermore, gene-set enrichment analysis for 533 genes covered by copy number variations specific to MZ twins illustrated that the tight junction-signaling pathway was significantly enriched (p < .001). Therefore, the novel changes in the X chromosome and the provided candidate variants across autosomes may be responsible for MZ twinning, giving clues to increase our understanding about the underlying mechanism.

Perinatal mortality is higher in twins. Effects of twin order have not previously been studied in the context of single fetal demise. Our objective was to determine whether death of the fetus more proximal to the cervix will result in worse perinatal outcomes. Our population included multiple pregnancies with two viable fetuses confirmed prior to 20 weeks’ gestation with the subsequent death of at least one twin. All the pregnancies were managed at The Royal Women's Hospital, Melbourne between 2006 and 2014. We excluded pregnancies of higher order multiples, the death of both twins simultaneously, and cases with incomplete outcome data. Maternal and neonatal data were reviewed. Of 46 pregnancies included, in 24 (52%), the dead twin was presenting. Gestational age at delivery was significantly earlier in these cases (mean difference: -5.0 weeks, 95% CI [-7.4, -2.6], p < .001), and emergency cesarean rates were higher 67% versus 32% (OR 4.29, 95% CI [1.25, 14.7], p = .02). There were no differences in the frequency of chorioamnionitis, preterm prelabor rupture of membranes, or placental abruption. Survival rates for co-twins were similar in both groups (presenting 83%; not presenting 91%; OR 0.41, 95% CI [0.07, 2.50], p = .29). The increase in neonatal morbidities was related to prematurity rather than to order. Findings were more common in dichorionic twins. Analysis was limited by a small sample size. If the dead twin is presenting, delivery is likely to occur earlier, with associated morbidity for the survivors. This is especially relevant for dichorionic twin pregnancies.