22 research outputs found
Significance of placental cord insertion site in twin pregnancy
Objective
To investigate the association between abnormal cord insertion and the development of twinâspecific complications, including birthâweight discordance, selective fetal growth restriction (sFGR) and twinâtoâtwin transfusion syndrome (TTTS).
Methods
This was a single center retrospective cohort study of twin pregnancies. Abnormal cord insertion was defined as either marginal (umbilical cord attachment site less than 2âcm to the nearest margin of the placental disc) or velamentous (cord attached to the membrane before reaching the placental disc with clear evidence of vessels traversing the membranes to connect with the placental disc), as described in placental pathology reports. Twins with major structural or chromosomal abnormalities and monochorionic monoamniotic twins were not included in the study. Information on the pregnancies, ultrasound findings, prenatal investigations and interventions was obtained from the electronic ultrasound database, while data on placental histopathological findings, pregnancy outcome, mode of delivery, birth weight, gestational age at delivery and admission to the neonatal intensive care unit were obtained from maternity records. Categorical variables were compared using the chiâsquare or Fisher's exact test, while continuous variables were compared using the Student's tâtest, ANOVA for multiple comparisons and the KruskalâWallis test.
Results
Of the 497 twin pregnancies included in the analysis, 351 (70.6%) were dichorionic and 146 (29.4%) were monochorionic. The incidence of birthâweight discordance of 25% or more was significantly higher in pregnancies with velamentous and those with marginal cord insertions compared to those with normal cord insertion (24.0%, 15.3% vs 7.6%, P <â0.001 and P =â0.020, respectively). In pregnancies with birthâweight discordance of 25% or more, the smaller twins had significantly higher prevalence of velamentous (13.8%) and marginal (34.2%) cord insertions compared with the larger twins (1.8% and 18.5%, respectively, P <â0.001). The smaller twins of the monochorionic diamniotic pregnancies showed an even higher prevalence of velamentous (29.5%) and marginal (40.9%) cord insertions compared with the larger twins (2.3% and 31.5%, respectively, P <â0.001). Compared with the normal cord insertion group, only velamentous insertion was associated significantly with the risk of sFGR (odds ratio (OR), 9.24 (95% CI, 2.05â58.84), P <â0.001) and birthâweight discordance of 20% or more (OR, 4.34 (95% CI, 1.36â14.61), P =â0.007) and 25% or more (OR, 6.81 (95% CI, 1.67â34.12), P =â0.003) in monochorionic twin pregnancies. There was no significant association between velamentous cord insertion and TTTS (P =â0.591), or between marginal cord insertion and the development of sFGR (P =â0.233), birthâweight discordance of 25% or more (P =â0.114) or TTTS (P =â0.487). Subgroup analysis of dichorionic twins showed that abnormal cord insertion was not associated with the risk of birthâweight discordance (P =â0.999), sFGR (P =â0.308), composite neonatal adverse outcome (P =â0.637) or intrauterine death (P =â0.349).
Conclusion
Monochorionic twins with velamentous cord insertion are at increased risk of birthâweight discordance and sFGR. Sonographic delineation of placental cord insertion could be of value in the antenatal stratification of twin pregnancies. Prospective studies are required to assess the value and predictive accuracy of this potential screening marker
The power of monitoring: optimizing survey designs to detect occupancy changes in a rare amphibian population
Biodiversity conservation requires reliable species assessments and rigorously designed surveys. However, determining the survey effort required to reliably detect population change can be challenging for rare, cryptic and elusive species. We used a tropical bromeliad-dwelling frog as a model system to explore a cost-effective sampling design that optimizes the chances of detecting a population decline. Relatively few sampling visits were needed to estimate occupancy and detectability with good precision, and to detect a 30% change in occupancy with 80% power. Detectability was influenced by observer expertise, which therefore also had an effect on the sampling design â less experienced observers require more sampling visits to detect the species. Even when the sampling design provides precise parameter estimates, only moderate to large changes in occupancy will be detected with reliable power. Detecting a population change of 15% or less requires a large number of sites to be surveyed, which might be unachievable for range-restricted species occurring at relatively few sites. Unless there is high initial occupancy, rare and cryptic species will be particularly challenging when it comes to detecting small population changes. This may be a particular issue for long-term monitoring of amphibians which often display low detectability and wide natural fluctuations