[Validity of classical fetal weight charts in the Portuguese population]. / Validade das tabelas de peso fetal clássicas para a população Portuguesa.

PURPOSE: to assess the validity of several fetal weight charts, commonly used in Portugal, to classify its population. METHODS: observational retrospective study. Singleton birth data was analyzed, from a two- year period (May 2008 to April 2010), from pregnancies with an ultrasound in the same institution, between the 8th and 14th gestational week. Upon data validation, percentiles for each completed gestational week were created, smoothed by a quadratic function, analyzed and compared to the tables more commonly utilized, in the institution and country, by using Z-scores, percentile comparison, sample 10th percentile detection sensibility and birthweight means comparison. RESULTS: a total of 5,378 newborns (NB) were born in the period; 2,195 (42%) NB were included, born from the 24th to 42nd gestational week, allowing statistical analysis from the 34th to the 41st week. There were differences in the mean birthweight for each gestational age, between references and with the sample, as well as between sexes. The 10th percentile from some references has shown differences ranging from -288g at 37 weeks (-11% in Lubchenco et al. data), with and +133g at 34 weeks (+7,6% with Carrascosa et al. data) compared to the values found with the sample. Differences were also found concerning the sensitivity of the identification of a sample birthweight below the 10th percentile, which was between 14.1 and 100%, depending on the reference used. DISCUSSION: the limitation of these kinds of reference values must be remembered and minimized, with the adoption of regionally or nationally produced references, contemplating other variables, such as sex, with precisely known gestation duration and with validation of the utilized references in loco.

Validade das tabelas de peso fetal clássicas para a população Portuguesa / Validity of classical fetal weight charts in the Portuguese population

OBJETIVO: avaliar a validade de várias tabelas de peso fetal, habitualmente usadas em Portugal, para classificar a sua população. MÉTODOS: estudo observacional retrospectivo. Foram analisados os registos de nascimentos no período de dois anos (Maio de 2008 a Abril de 2010), decorrentes de gestações unifetais com datação precisa por ecografia entre as 8ª e 14ª semanas de gestação, na mesma instituição. Após validação dos registos, foram analisados os percentis de peso gerados para cada semana de gestação completa, suavizados por uma função polinomial de dois graus, comparando-os com as tabelas mais usadas na instituição e no país, através do uso de Z-scores, valores de percentis, sensibilidade para detecção do percentil 10 (P10) da amostra e comparação de médias de peso. RESULTADOS: um total de 5.378 recém-nascidos (RN) foi registado no período; 2.195 (42 por cento) RN corresponderam aos critérios de inclusão, com idade gestacional (IG) entre as 24ª e 42ª semanas, permitindo uma análise estatística entre as 34ª e as 41ª semanas. Foram detectadas diferenças no peso médio por IG entre tabelas e em relação à amostra, bem como diferenças entre os sexos. O P10 de outros trabalhos mostrou diferenças entre -288g na 37ªs (-11 por cento nos dados de Lubchenco et al.) e +133g na 34ªs (+7,6 por cento nos dados de Carrascosa et al.) em relação ao obtido na amostra. A sensibilidade para detecção de um RN abaixo do P10 na amostra variou, às 39ªs, entre 14,1e 100 por cento, dependendo da tabela usada. DISCUSSÃO: as limitações deste tipo de valores de referência devem ser tidas em consideração, tentando minimizá-las, nomeadamente pela criação de valores locais/regionais ou nacionais, com a contemplação de outras variáveis, sobretudo o sexo do RN, em gravidezes rigorosamente datadas e pela validação in loco dos valores utilizados.

PURPOSE: to assess the validity of several fetal weight charts, commonly used in Portugal, to classify its population. METHODS: observational retrospective study. Singleton birth data was analyzed, from a two- year period (May 2008 to April 2010), from pregnancies with an ultrasound in the same institution, between the 8th and 14th gestational week. Upon data validation, percentiles for each completed gestational week were created, smoothed by a quadratic function, analyzed and compared to the tables more commonly utilized, in the institution and country, by using Z-scores, percentile comparison, sample 10th percentile detection sensibility and birthweight means comparison. RESULTS: a total of 5,378 newborns (NB) were born in the period; 2,195 (42 percent) NB were included, born from the 24th to 42nd gestational week, allowing statistical analysis from the 34th to the 41st week. There were differences in the mean birthweight for each gestational age, between references and with the sample, as well as between sexes. The 10th percentile from some references has shown differences ranging from -288g at 37 weeks (-11 percent in Lubchenco et al. data), with and +133g at 34 weeks (+7,6 percent with Carrascosa et al. data) compared to the values found with the sample. Differences were also found concerning the sensitivity of the identification of a sample birthweight below the 10th percentile, which was between 14.1 and 100 percent, depending on the reference used. DISCUSSION: the limitation of these kinds of reference values must be remembered and minimized, with the adoption of regionally or nationally produced references, contemplating other variables, such as sex, with precisely known gestation duration and with validation of the utilized references in loco.