Orientador: Lilia Freire Rodrigues de Souza Li / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Ciências Médicas / Made available in DSpace on 2018-08-22T07:02:23Z (GMT). No. of bitstreams: 1 D'Agostini_Carla_M.pdf: 700861 bytes, checksum: be95f4db81c48e93d19398a6f8e880c2 (MD5) Previous issue date: 2013 / Resumo: O nascimento prematuro é a principal causa de morbidade e mortalidade perinatal. Os estudos avaliando a influência da adolescência na prematuridade são controversos, principalmente em gestantes acima de 16 anos, que não costumam ter desfechos piores que as gestantes adultas. Um dos principais marcadores de risco para o nascimento prematuro em uso é a medida do comprimento do colo do útero por ultrassonografia transvaginal. Avaliar se as gestantes abaixo de 16 anos têm risco aumentado de prematuridade e se têm colos mais curtos é necessário, pois pode ajudar a delinear estratégias de seguimento ou intervenções baseadas no comprimento do colo como marcador de risco. Este estudo subdivide-se em dois capítulos. O primeiro capítulo trata-se de um artigo de revisão sistemática que objetiva verificar se as gestantes com menos de 16 anos têm um risco de prematuridade maior que as gestantes adultas. Foi realizada pesquisa nas bases de dados MEDLINE e LILACS nos últimos dez anos com: os descritores gravidez na adolescência e nascimento prematuro; os descritores gravidez na adolescência e trabalho de parto prematuro; o descritor gravidez na adolescência e a palavra-chave: prematuridade. Foram incluídos 14 estudos, sendo a maioria coortes retrospectivas. Sete destes estudos realizaram controle de possíveis vieses em suas análises estatísticas. Dez dos quatorze estudos avaliados demonstraram associação da idade inferior a 16 anos com nascimento prematuro, sendo que quatro destes tiveram um grande número de pacientes avaliadas com controle de vieses em suas análises (odds ratios variando de 1,5 a 1,7). Podemos concluir que a gestação abaixo de 16 anos está provavelmente associada a um risco inerente de prematuridade quando comparada à gestação adulta. Medidas de prevenção da gestação nesta faixa etária, bem como programas de assistência com o objetivo de minimizar o risco de prematuridade destas pacientes devem ser empregados. O segundo capítulo trata-se de um artigo original que tem por objetivo comparar o comprimento do colo do útero de primigestas menores de 16 anos com primigestas adultas, sendo um estudo transversal, observacional e analítico realizado em primigestas do sistema público de saúde do município de Blumenau (Brasil). Aferiram-se os colos uterinos de primigestas menores de 16 anos e adultas através de técnica previamente validada entre 21 e 24 semanas de idade gestacional. A média do comprimento do colo uterino foi comparada entre os grupos (teste de Mann-Whitney) e a associação da adolescência com colos abaixo de 25 mm foi avaliada (teste exato de Fisher). Oitenta pacientes foram avaliadas (40 adolescentes e 40 adultas). A média do comprimento do colo encontrada nas adolescentes foi de 28 ± 6,6 mm, significativamente menor do que nas adultas (33 ± 4,1 mm) (p <0,0001). A proporção de colos abaixo de 25 mm foi de 27,5% nas adolescentes e 7,5% nas adultas (p <0,02). Assim, conclui-se que as primigestas adolescentes jovens formam um grupo de pacientes com colos mais curtos do que as adultas e com maior proporção de colos menores que 25 mm, merecendo atenção especial na assistência pré-natal quanto ao risco de nascimento prematuro / Abstract: Premature birth is the leading cause of perinatal morbidity and mortality. Studies evaluating the influence of adolescence on prematurity are controversial, especially in pregnant women over 16 years who do not usually have worse outcomes than adult pregnants. The measurement of cervical length by transvaginal ultrasound is one of the main markers of risk for preterm birth. Assess whether women under 16 have an increased risk of prematurity and have shorter cervices is important to outline strategies for follow-up or intervention based on cervical length as a risk marker. This study has two articles. The first article aimed to verify whether pregnant women younger than sixteen years have a higher risk of prematurity than adult women. For this, we did a systematic review of studies comparing preterm birth in teenagers under 16 with adult pregnant women in the last ten years. Fourteen studies were included in the first article, mostly retrospective cohorts. Seven of these studies were accomplished with control of possible biases in its statistical analyses. Ten of the fourteen studies reviewed found an association of age below 16 years with premature birth, and four of these had a large number of patients evaluated, with control of possible biases in its statistical analyses (odds ratios ranging from 1.5 to 1.7). We conclude that pregnancy under 16 years old is probably associated with an inherent risk of preterm birth. Actions to prevent pregnancy in this age group should be employed, as well as specific assistance programs in order to minimize the risk of prematurity in these patients. The second article aimed to compare the length of the cervix in primigravidae under 16 years old with adult primigravidae. An analytical, observational and cross-sectional study was performed with primigravidae under 16 and adults in the public health system in the city of Blumenau (Brazil). Cervical measurements through transvaginal ultrasonography were performed by using a previously validated method, between 21 and 24 weeks of gestation to compare the mean cervical length (Mann-Whitney test) and the frequency of cervices below 25 mm among young adolescents and adult primigravidae (Fisher's exact test). The cervical lengths of 80 patients were measured (40 adolescents and 40 adults). The average length of the uterine cervix found in adolescents was of 28 + / - 6.6 mm and in adults 33 + / - 4.1 mm (p<0.0001) and the proportion of cervices below 25 mm were 27, 5% in adolescents and 7.5% in adults (p<0.02). We concluded that adolescent primigravidae under 16 have shorter cervices than adults, with a higher proportion of cervices shorter than 25 mm. This may be associated with increased risk of preterm delivery in those adolescents who need special attention in prenatal care / Mestrado / Saude da Criança e do Adolescente / Mestra em Ciências

No description available.

Bakgrund: Under en ortodontisk behandling med fast apparatur finns det en risk för att tänderna drabbas av rotresorption. Rotresorptioner kan mätas med hjälp av Cone Beam Computed Tomography (CBCT). Mätresultatet kan dock variera mellan olika observatörer och mätfel kan uppstå vilket påverkar metodens tillförlitlighet.Syfte: Att beräkna det mätfel som uppstår vid mätning av rotresorptioner som uppstår till följd av en ortodontisk behandling i CBCT-bilder och utvärdera mätmetodens tillförlitlighet. Metod: Tio ungdomar som genomgick ortodontisk behandling undersöktes med hjälp av CBCT-röntgen av båda käkar (tand 16-26 samt 36-46). Fem observatörer mätte tändernas rotlängd i utvalda CBCT-snitt. Studien omfattade 100 rötter från totalt 90 tänder. Mätningen upprepades av samma observatörer vid ett senare tillfälle. Tillförlitlighet utvärderades med intraklass-korrelationskoefficient (ICC 2.1) med 95% konfidensintervall. Mätfelet beräknades med Dahlbergs formel och standard moment of measure variance estimator (MME)-formel. Resultat: Tillförlitligheten mellan observatörer uppmättes till ICC = 0,88 under den första mätningen och ICC = 0,87 vid den upprepade mätningen. Inom observatörerna uppmättes tillförlitligheten till ICC = 0,84-0,92. Mätfelet uppmätt med Dahlbergs formel var 0,44-0,64 mm för samtliga tänder och observatörer. Det största mätfelet uppstod vid mätning av kuspider, 0,4-1,15 mm. Det minsta mätfelet uppstod vid mätning av molarer, 0,42-0,53 mm. Mätfelet vid mätning av premolarer och incisiver var 0,42-0,70 respektive 0,43-0,66 mm. När mätfelet beräknades med MME-formeln erhölls liknande resultat. Konklusion: Mätning av rotlängd i CBCT-bilder uppvisar hög reliabilitet inom och mellan olika observatörer. Precisionen varierar mellan olika tandgrupper och observatörer, men vid mätning av allvarliga rotresorptioner (>2 mm) är metoden pålitlig. CBCT anses vara en pålitlig metod för mätning av rotresorptioner som uppstått till följd av ortodontisk behandling. Vid studier där en mätning utförs bör reliabilitet och precision tas i beaktande. / Background: An orthodontic treatment may cause root resorption of varying extent on the involved teeth. The resulting root resorption can be measured in cone beam computed tomography (CBCT) images. However, measurement results may vary among different raters because of measurement errors, affecting the reliability of the method of measurement. Objectives: To evaluate reliability and precision of measurement of root length following orthodontic treatment in CBCT images. Methods: Ten adolescents participating in a trial of orthodontic treatment were examined with CBCT of both jaws. Five raters measured root length in preselected CBCT images of 100 roots from 90 teeth. The measurements were later repeated by the same raters. Reliability was expressed as intra-class correlation coefficient (ICC 2.1). Measurement error was calculated with Dahlberg’s formula and standard moment of measure variance estimator (MME)formula. Results: The inter-rater reliability for all raters had an ICC-value of 0,88 for the first measurement and an ICC-value of 0,87 for the second measurement. The intra-rater reliability for all raters had an ICC-value between 0,84-0,92. Measurement error calculated with the Dahlberg's formula ranged between 0,44-0,64 mm for all teeth for all raters. The largest difference of measurement error between raters was observed in canines, 0,44-1,15 mm. The smallest measurement error was observed in molars, 0,42-0,53 mm. Measurement errors calculated by the MME formula showed similar results. Conclusion: Root length measurements in CBCT-images show high intra- and inter rater reliability. The precision varies between raters and tooth groups but measurements of severe root resorptions (>2 mm) are reliable with this method. The reliability and precision of a method should always be considered when conducting measurement studies. CBCT could be considered a reliable method for measurement of root resorption following orthodontic treatment with different orthodontic appliances.

This thesis describes the design, construction and testing of a new interferometer for the absolute measurement of length standards. It is assumed that this study mainly formed of three parts. Firstly, it starts with an introduction to the subject of length standards and length measurement by interferometry. The design of the new interferometer is given in detail, including the stable lasers used as light sources, fiber, optical and opto-mechanical components. In the second part of this study, the mechanical construction of the interferometer chamber is presented with temperature stabilization and controlling system. The temperature variations inside the chamber at different points in air and along the surface of the length standard are given. After that, the techniques for measurement of the refractive index of the air inside the interferometer chamber are summarized. In the last part of the thesis, a review of fringe analysis techniques is given, with an emphasis on 5 position phase-stepping algorithms. The data processing of images digitized in the interferometer is described, including the techniques developed for discontinuity removal and surface fitting. The measurement of the variation in length and flatness of the measuring faces of the length standards is described and the experimental results are given. The automated method of multiple wavelength-exact fractions is used to combine phase measurements at three wavelengths to allow accurate calculation of the length of the length standards. The experimental results are given for length standards. The uncertainty budget of whole system is calculated and presented in a table.

In vorliegender Arbeit werden Aufbau und Charakterisierung des beidseitig antastenden Interferometers vorgestellt, mit dem die absolute Länge prismatischer Körper ohne Anschub an eine Referenzplatte gemessen werden kann, was Verformungen durch Wechselwirkungen von Endmaßen mit angeschobenen Platten verhindern kann. Die Messunsicherheit im Vergleich zum Prototypen konnte aufgrund eines verbesserten Temperaturmesssystems, eines temperaturstabilisierten Vakuumkessels, Optiken mit besserer Ebenheit und Kameras größerer Auflösung deutlich reduziert werden. Das entwickelte Justageverfahren mit Autokollimationsscan und die Korrektur von Wellenfrontaberrationen tragen ebenso zu einer reduzierten Messunsicherheit bei, wie der durch optimale Ausrichtung der keilförmigen Strahlteilerplatten reduzierte Einfluss von Störinterferenzen. Vergleichsmessungen eines Stahl- und eines Filterglasendmaßes mit einseitig antastenden Interferometern zeigten mit Differenzen im Bereich von 0,4 bis 2,6 nm im Rahmen der Unsicherheiten konsistente Probenlängen, was die gute Eignung des beidseitig antastenden Interferometers für absolute Längenmessungen zeigt. Vergleichsmessungen an Silizium ergaben für die beidseitig antastend gemessenen Längen gegenüber im einseitig antastenden Interferometer gemessenen Längen deutlich geringere Werte und eine reproduzierbare Differenz zwischen den mit 532 und 633 nm gemessenen Längen von etwa 4 nm. Diese Effekte sind vermutlich auf die sich beim beidseitig antastenden Verfahren deutlich stärker auswirkenden Material- und Oberflächeneigenschaften zurückzuführen. Das volle Potential des beidseitig antastenden Interferometers entfaltet sich aufgrund des großen Messunsicherheitsbeitrages der Rauheit und des Phasensprungs bei der Reflexion vor allem bei der Messung von Längenänderungen, wie der thermischen Ausdehnung oder der Langzeitstabilität verschiedener Materialien, für die die Effekte der Rauheit und des Phasensprungs eine vernachlässigbare Rolle spielen. / The present thesis adresses the setup and characterization of PTB´s double-ended interferometer, which allows for absolute length measurement of prismatic bodies without the need for wringing to a platen, which prevents deformation caused by their interaction. In comparison with PTB´s prototype, the measurement uncertainty has been substantially reduced due to an improved temperature measurement system, a temperature stabilized vacuum chamber, optics of better flatness and cameras with higher resolution. Further reduction of the measurement uncertainty has been achieved by the developed adjustment procedure including an autocollimation scanning and a correction of the influence of wavefront aberrations. Multiple configurations of orientation of the beamsplitter plate wedges were tested to minimize the influence of parasitic interferences. Comparison measurements against single-ended interferometers on a steel and a filter glas gauge block resulted in deviations of the measured length in the range of 0.4 to 2.6 nm, which is in good agreement with measurement uncertainties. This proves the capability of absolute length measurement of the double-ended interferometer. Comparison measurements on silicon gauge blocks resulted in significantly shorter lengths than those measured in single-ended interferometers with a reproducible length difference of 4 nm for the different used wavelengths of 532 and 633nm. Those effects are presumably based on material and surface characteristics which seem to have a much stronger impact on the measured length when the sample is not wrung to a platen. Due to the large contribution of the roughness and the phase change on reflection to the measurement uncertainty, the full potential of the double ended interferometer will unfold for measurements on lengths changes, like measurement of the thermal expansion or long term stability of different materials, for which the influence of the roughness and phase change on reflection can be neglected.

No description available.

Submitted by Fabíola Silva (fabiola.silva@famerp.br) on 2016-07-07T17:27:31Z No. of bitstreams: 1 gustavohenriquedeoliveira_dissert.pdf: 920807 bytes, checksum: dd35cbbf5e85078e466e6f5bcd2d444e (MD5) / Made available in DSpace on 2016-07-07T17:27:31Z (GMT). No. of bitstreams: 1 gustavohenriquedeoliveira_dissert.pdf: 920807 bytes, checksum: dd35cbbf5e85078e466e6f5bcd2d444e (MD5) Previous issue date: 2010-12-09 / Aim: To evaluate the importance of cervical gland area (CGA) to predict spontaneous preterm birth (SPB). Method: A prospective study was performed from October 2008 to September 2009 of 102 singleton pregnancies at 20 and 24 weeks. A transvaginal ultrasound during the routine morphological scan investigated: the cervical length, CGA, its thickness and signs of cervical funneling. A preterm birth is defined as one that occurs at less than 37 weeks gestation. Ultrasound and clinical variables were submitted to univariate analysis by calculations of descriptive statistics, the Student t-test, percentages, and two-dimensional associative arrays evaluated using the Fisher exact test and odds ratio. The level of significance was set at 5%. Results: Of the 102 patients, four were lost in the follow up and seven were excluded as delivery was induced prematurely; ten patients presented spontaneous preterm births and 81 at term. The mean maternal age was 28.8 years old (18-41 years) without significant difference between the spontaneous preterm birth and term groups. There were statistical differences in the mean (33.9 vs. 36.1 cm), median (33.5 vs. 37.0 cm) and spread (standard deviation: 9.6 vs. 7.0) of the cervical length between the two groups. Risk factors for SPB gave an odds ratio of 15.06. All patients presented a CGA with a mean thickness of 8.4 mm (5.1 to 15 mm – SD: 3.1) for SPB and 8.9 mm (3.0 to 13.9 mm – SD: 2.3) for term individuals. Conclusion: The results suggest that the presence or absence and thickness of CGA are not correlated to SPB even in clinically or ultrasonographically high-risk patients. Further studies are necessary to reevaluate the parameters used to predict SPB. / Objetivo: Avaliar a importância do eco glandular endocervical (EGE) na predição de parto prematuro espontâneo (PPE). Método: Estudo prospectivo de 102 gestações únicas, entre 20-24 semanas, de outubro/2008 a setembro/2009. Na ecografia morfológica, o exame transvaginal avaliou: comprimento do colo uterino, EGE, espessura e sinal do afunilamento. Foi considerado PPE interrupção antes de 37 semanas de gestação. As avaliações ultrassonográfica e clínica foram submetidas à análise univariada pelos cálculos de estatísticas descritivas, teste t de Student, distribuições percentuais, tabelas associativas para análises bidimensionais, teste exato de Fisher e odds ratio no nível de significância de 5%. Resultados: Das 102 pacientes, quatro perderam seguimento, sete foram excluídas por parto prematuro induzido, dez pacientes apresentaram PPE e 81 parto a termo (PT). A idade materna média foi de 28,8 anos (18-41 anos), sem diferença nos dois grupos (PPE e PT). No comprimento do colo observaram-se diferenças na média (33,9 x 36,1 cm), mediana (33,5 x 37,0 cm) e na dispersão (desvio–padrão 9,6 x 7,0). Fatores de risco para PPE mostraram odds ratio de 15,06. Todas as pacientes apresentaram EGE, com espessura média de 8,4 mm (5,1 a 15 mm - desvio padrão 3,1) para PPE, e de 8,9 mm (3,0 a 13,9 mm - desvio padrão de 2,3) para PT. Conclusão: Os resultados indicam que a presença, ausência ou espessura do EGE não se correlacionou com PPE, mesmo naquelas pacientes com alto risco clínico e/ou ultrassonográfico de PPE. São necessárias novas pesquisas para reavaliação dos parâmetros indicadores de PPE.

This diploma thesis deals with the proposal of internal methodology for measurement of products and parts on CMM UPMC Zeiss at CMI Brno. The first part of this work analyzes the current state of knowledge in the field of accurate measurement on coordinate measuring machines (CMM), which includes the definition of basic metrological concepts, methodology for determining and expressing uncertainties of measurement and a general description of CMM. The diploma thesis also contains a detailed description of the UPMC 850 CARAT S-ACC device from the company Zeiss and summarizes the requirements for the testing laboratory in accordance with the standard ČSN EN 17 025: 2018. The next part of the work is focused on defining and determining the measurement uncertainties for this CMM and on developing a testing procedure for measurements on this machine. The final part of this thesis summarizes the achieved results and recommendations for practice.

This final thesis is dealing with stating uncertainty of optical measuring device Micro-Vu Sol 311, which is located at Faculty of mechanical engineering in Brno. Overview of coordinate measuring machines (CMM for short) and analyzed present status of optical CMM is in summation. This part also includes basic metrology concepts and methodology of determination of uncertainty of measuring instrument. Content of following parts of thesis is detailed description of Micro-Vu SOL 311 machine and etalons that were used in determination of enhanced uncertainty of measurement such as gage blocks, laser interferometer and glass scale. Last part of this thesis includes summary of achieved results and recommendations for practice.

OBJETIVO: O objetivo do presente estudo é comparar o poder da medida do comprimento do colo uterino quando obtida no período de 18-21 semanas com a obtida no período de 22-25 semanas de gestação na predição do parto prematuro espontâneo em gestações gemelares e analisar o valor do encurtamento cervical observado entre essas duas medidas. MÉTODO: estudo retrospecto envolvendo 383 gestantes gemelares que foram avaliadas entre a 18ª e a 21ª semanas (GRUPO 1- 241 pacientes) e a 22ª e a 25ª semanas de gestação (GRUPO 2- 266 pacientes). Esses dois períodos foram avaliados de maneira independente e as pacientes foram incluídas em um deles ou em ambos, com ao menos 3 semanas entre os exames. Pacientes incluídas nos dois períodos (GRUPO 3- 124 pacientes) permitiram a análise do encurtamento cervical. Não foram incluídas gestações com as seguintes complicações: síndrome da transfusão feto-fetal, poliidrâmnio, malformação fetal, patologia uterina, gestações submetidas a procedimento invasivo, cerclagem uterina, parto prematuro eletivo e os casos em que não foi possível obter o desfecho da gestação. O parâmetro avaliado foi o comprimento do colo. Curvas ROC foram usadas para comparar a capacidade de predição do parto prematuro. Na determinação de sensibilidade, especificidade, VPP e VPN foi usado como ponto de corte o 5º percentil do comprimento do colo determinado por Fujita et al (2002) em nossa população. RESULTADO: GRUPO 1- o comprimento médio do colo com 19,5 semanas (IG média no grupo) foi 38,2 ±8,7 mm. A taxa de PPE (parto prematuro espontâneo) abaixo de 28, 30, 32 e 34 semanas de gestação foi 3,7%, 6,2%, 7,8% e 16,1%, respectivamente. A incidência de colo curto foi (14/241) 5,8%. Análise da curva ROC revelou área sob a curva de 0,64 (CI95% 0,53-0,75). Sensibilidade de 33,3%, 33,3%, 30% e 23% e VPN de 97,3%, 95,6%, 93,8% e 86,8% para parto abaixo de 28, 30, 32, e 34 semanas de gestação foram obtidos. GRUPO 2- o comprimento médio do colo com 23,3 semanas (IG média no grupo) foi 35,6 ±10,5 mm. A taxa de PPE abaixo de 28, 30, 32 e 34 semanas de gestação foi 2,6%, 5,2%, 7,1% e 12,8%, respectivamente. A incidência de colo curto foi (22/266) 8,2%. Análise da curva ROC revelou área sob a curva de 0,80 (CI95% 0,72-0,88), e essa área é maior do que a do GRUPO 1 (p0,001). Sensibilidade de 71,4%, 57,1%, 52,6% e 38,2% e VPN de 99,1%, 97,5%, 96,3% e 91,4% para parto abaixo de 28, 30, 32, e 34 semanas de gestação foram obtidos. GRUPO 3- Análise da curva ROC revelou área sob a curva de 0,81 (CI95% 0,73-0,89). O melhor ponto de corte para encurtamento cervical foi dado pelo joelho de curva e foi 2 mm/semana. Sensibilidade de 80%, 90%, 78,5% e 60,8% e VPN de 98,9%, 98,9%, 96,8% e 90,6% para parto abaixo de 28, 30, 32, e 34 semanas de gestação. CONCLUSÃO: nas gestações gemelares, a medida do colo uterino entre 22-25 semanas de gestação é melhor preditora do parto prematuro abaixo de 34 semanas do que a medida obtida entre 18-21 semanas. O encurtamento cervical 6mm/3 semanas entre 18 e 25 semanas de gestação é bom preditor de parto prematuro em subgrupo de alto risco. / OBJECTIVE: The aim of the present study is to compare the value of cervical assessment in twin pregnancies in predicting risk of spontaneous preterm delivery when performed at 18-21 weeks and 22-25 weeks gestation and to examine the value of cervical shortening observed between both periods. METHODS: This retrospective study involved 383 women carrying twins who were scheduled between 18-21 completed weeks (GROUP 1- 241 patients) and 22-25 completed weeks of gestation (GROUP 2- 266 patients). These two periods were assessed independently, and patients could be included in one or both with at least three weeks between the exams, whose delivery data was obtained. Patients included in both periods (GROUP 3- 124 patients) allowed the analysis of cervical shortening. Pregnancies presenting with the following complications where not included in the analyses: twin-twin transfusion syndrome, polihidramnius, fetal malformation, uterine patology; cases that underwent invasive procedures or uterine cerclage, premature delivery indicated for maternal or fetal complications and cases in which pregnancy outcome was impossible to obtain. Cervical length was the analyzed parameter. Area under the ROC curve was used to compare the predictive capacity of spontaneous preterm birth. To determine sensitivity, specificity, PPV and NPV, cervical length cut-off for short cervix was determined by Fujita et al (2002) curve, designed in our population. RESULTS: GROUP 1- The mean cervical length at 19.5 weeks (mean gestational age in the group) was 38.2 +- 8.7 mm. The rate of spontaneous preterm delivery (SPD) < 28, <30, <32 and < 34 weeks of gestation was 3.7%, 6.2%, 7.8% and 16.1%, respectively. The incidence of short cervix in the group was (14/241) 5.8%. Receiver operating characteristic curve analysis revealed area under the curve 0.64 (CI95% 0.53-0.75). Sensitivities of 33.3%, 33.3%, 30% and 23% and negative predictive values of 97.3%, 95.6%, 93.8% and 86.8% for delivery at <28, <30, <32, and <34 weeks gestation were achieved. GROUP 2- The mean cervical length at 23.3 weeks (mean gestational age in the group) was 35.6 +- 10.5 mm. The rate of SPD < 28, <30, <32 and < 34 weeks of gestation was 2.6%, 5.2%, 7.1% and 12.8%, respectively. The incidence of short cervix was (22/266) 8.2%. Receiver operating characteristic curve analysis revealed area under the curve 0.80 (CI95% 0.72-0.88), and this is larger than GROUP 1 area (p0,001). Sensitivities of 71.4%, 57.1%, 52.6% and 38.2% and negative predictive values of 99.1%, 97.5%, 96.3% and 91.4% for delivery at <28, <30, <32, and <34 weeks gestation were achieved. GROUP 3- Receiver operating characteristic curve analysis revealed area under the curve 0.81 (CI95% 0.73-0.89). The best cut-off for cervical shortening was reveled by the inflection point of the curve and was 2 mm/week. Sensitivities of 80%, 90%, 78.5% and 60.8% and negative predictive values of 98.9%, 98.9%, 96.8% and 90.6% for delivery at <28, <30, <32, and <34 weeks gestation were achieved. CONCLUSION: In twin gestations, assessment of cervical length at 22-25 weeks is better than __________________________________________________________________ assessment at 18-21 weeks to predict preterm delivery before 34 weeks. Cervical shortening of 6 mm/ 3weeks between 18 and 25 weeks gestation was a good predictor of spontaneous preterm birth in high risk population.