Academic literature on the topic 'Twin primes'

Although twin-spotted rattlesnakes (Crotalus pricei ) were first identified more than a century ago, little has been published about the ecology of this species and no information has been available regarding population characteristics. During 1997--99, I captured, measured, and marked 117 C. pricei in the Chiricahua Mountains to address this need for information. Lizards constituted the bulk of C. pricei prey, but their diet also included mammals, birds, and snakes. Mating and parturition were concentrated in August and early September. Movement patterns varied dramatically from year to year, as males moved substantially farther during the 1998 monsoon season (July--September) than in 1997. Crotalus pricei are sometimes collected illegally for the pet trade. About 90 people may have hunted for C. pricei at a well-known site during 1997--98. On average, snakes at this site were 38.1 mm smaller than snakes at other sites, an observation that could be attributed to collecting pressure.

Esta tesis está basada en dos artículos: Articulo 1: Early first-trimester free-β-hCG and PAPP-A serum distributions in monochorionic and dichorionic twins Objetivo: Examinar la distritución en primer trimestre de los marcadores bioquímicos de aneuploidias en gestaciones gemelares dependiendo de su corionicidad. Métodos: La free-β-human chorionic gonadotropin (hCG) en sangre materna y la pregnancy-associated plasma protein A (PAPP-A) fueron analizadas entre las semanas 8–13 + de gestación como parte del cribado rutinario del primestrimestre en conjunción con la translucencia nucal medida a las 11-13+6 semanas. Se analizaron los datos de 279 gestaciones multiples extraidos de nuestras bases de datos. Los casos con síndrome de Down fueron excluidos. Las concentraciones individuales de los marcadores fueron expresadas y corregidas según peso, étnia, hábito tabáquico y diabetes materna. Para com parar las distribuaicones de los parámetros bioquímocso se utilizo un modelo aditivo generalizado con un modelo de regresión suave con los valores transformados en logaritmo en base a 10’’ usando el sftware R (modelo aditivo generalizado- modelo suave de regresión lineal) . Resultados: Las distribuciones de Free-β-hCG y PAPP-A analizadas con un modelo aditivo generalizado ajustados a modelo suave de regresión lineal, fueron significativamente diferentes dependiendo de la corionicidad. Mostramos graficamente la relación entre la concentración esperada de free-β-hCG y PAPP-A y la edad gestacional en días para gemelares monocoriales y bicoriales ajustados por peso. Conclusión: Los valores de Pregnancy-associated plasma protein A y free-β-hCG son espefícios para la edad gestacional. Es necesario hacer una distinción entre gestaciones monocoriales y bicoriales porque los marcadores bioquímicos son más bajos en las gestaciones monocoriales que en las bicoriales. Artículo II: First trimester risk assessment for trisomy 21 in twin pregnancies combining nuchal translucency and first trimester biochemical markers Objetivo: El objetivo es describir la eficacia del riesgo combinado para el asesoramiento de síndrome de Down en las gestaciones múltiples. Métodos: Los niveles maternos de free beta-human chorionic gonadotrophin y pregnancy-associated plasma protein A (PAPP-A) se determinaron entre las semanas 8-12 de gestación y la translucencia nucal fetal se midió entre las semanas 11-13+6 de gestación. El riesgo individual para cad feto fue estimado mediante el test combinado en las gestaciones bicoriales. En las gestaciones moncoriales, se utilizó el riesgo medio de los dos fetos. SE ofreció una técnica invasiva cunado el riesgo era mayor de 1/270 para uno de los fetos. Resultados: Desde febrero 2007 hasta junio 2011, se incluyeron 447 gestaciones múltiples en el estudio. From February 2007 to June 2011, 447 twin pregnancies were enrolled in this study. 402 (89.9%) eran bicoriales y 45 (10.1%) monocoriales. En los gemelos bicoriales, la media de crown–rump length (CRL) era 63.9mm; La media de los múltiples de la mediana de NT (MoM) fue de 0.97; la media de los múltiples de la mediana hCG fue de 1.74; la media de los múltiples de la mediana de PAPP-A MoM fue de 1.72. En las gestaciones monocoriales, el CRL medio fue de 61.9mm; la media de NT MoM fue de 0. 98; la media de hCG MoM was 1.44; y la media de median PAPP-A MoM fue de 1.51. 2 gestaciones fueron diagnosticadas de síndrome de Down, las dos en gestaciones bicoriales. La tasa de falso positivos fue de 5.7% (95% Intervalo de confianza 4.1–7.3)y de 4.4% (95% intervalo de confianza interval 0.1–8.8%) en gestaciones gemelares bicoriales y monocoriales, respectivamente. Conclusiones: El test combinado en gestaciones gemelares parace ser un buen método para el cribado de Síndrome de Down con una alta tasa de detección y una tasa aceptable de falsos positivos.<br>This thesis is based in two articles: Article I: Early first-trimester free-β-hCG and PAPP-A serum distributions in monochorionic and dichorionic twins Objective: To examine the distribution of first-trimester biochemical markers of aneuploidy in twins according to chorionicity. Methods: Maternal serum free-β-human chorionic gonadotropin (hCG) and pregnancy-associated plasma protein A (PAPP-A) were measured between 8–13 + 6 weeks as a part of a routine first-trimester screening program in conjunction with fetal nuchal translucency measured at 11 to 13 + 6 weeks’ gestation. Data from 279 twin pregnancies were extracted from our fetal databases. Down syndrome cases were excluded. Individual marker concentrations were expressed as weight, ethnicity, smoking and maternal diabetes corrected. To compare the distributions of the biochemical parameters, a generalized additive model was used adjusted to a smoothing regression model with the values transformed with base 10’’ logarithm using R software (generalized additive model-smoothing spline regression). Results: Free-β-hCG and PAPP-A distributions, analyzed with a generalized additive model adjusted to a smoothing regression model, were significantly different depending on the chorionicity. We graphically displayed the relationship between the predicted concentration of the free-β-hCG and PAPP-A and the gestational age in days for monochorionic and dichorionic twins adjusted by weight. Conclusion: Pregnancy-associated plasma protein A and free-β-hCG values are gestational age specific. It is necessary to make a distinction between monochorionic and dichorionic twins because biochemical markers are lower in monochorionic than in dichorionic twins. Article II: First trimester risk assessment for trisomy 21 in twin pregnancies combining nuchal translucency and first trimester biochemical markers Objective: The aim is to describe the performance of first-trimester combined risk assessment in twin pregnancies. Methods: Maternal serum free beta-human chorionic gonadotrophin and pregnancy-associated plasma protein A (PAPP-A) were determined at 8 to 12 weeks and fetal nuchal translucency (NT) was measured at 11 to 13+6 weeks. The individual risk was estimated for each fetus using the combined test in dichorionic twins. In monochorionic twins, the mean risk assessment of the two fetuses was used. An invasive diagnostic procedure was offered when the risk was fi1 : 270 in either one of the fetuses. Results: From February 2007 to June 2011, 447 twin pregnancies were enrolled in this study. There were 402 (89.9%) dichorionic and 45 (10.1%) monochorionic twins. In dichorionic twins, mean crown–rump length (CRL) was 63.9mm; median NT multiples of the median (MoM) was 0.97; median !-hCG was MoM 1.74; median PAPP-A was 1.72. In monochorionic twins, mean CRL was 61.9mm; median NT MoM was 0. 98; median !-hCG MoM was 1.44; and median PAPP-A was 1.51. Two pregnancies with Down syndrome were detected by first trimester screening, both in dichorionic twins. The false positive rate was 5.7% (95% confidence interval 4.1–7.3) and 4.4% (95% confidence interval 0.1–8.8%) in dichorionic and monochorionic twins, respectively. Conclusions: The combined test in twins appears to be a good method for Down syndrome screening with a high detection rate and an acceptable false-positive rate.