Estimating gestational age and its relation to the anthropometric status of newborns: a study comparing the Capurro and ultrasound methods with last menstrual period. Universidade Federal da Bahia. Salvador, BA, Brasil. Email: mfpnunes cox. OBJECTIVE: to assess the accuracy of the Capurro somatic and ultrasound methods, taking date of last menstruation as a reference point, for evaluating gestational age and anthropometric classification of term newborns. METHODS: a prevalence study was carried out involving pregnant women and their term newborns, 92 of whom were small for gestational age and appropriate sized for gestational age, at two public maternity hospitals in the Brazilian city of Salvador.
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Estimating gestational age and its relation to the anthropometric status of newborns: a study comparing the Capurro and ultrasound methods with last menstrual period. Universidade Federal da Bahia. Salvador, BA, Brasil. Email: mfpnunes cox. OBJECTIVE: to assess the accuracy of the Capurro somatic and ultrasound methods, taking date of last menstruation as a reference point, for evaluating gestational age and anthropometric classification of term newborns.
METHODS: a prevalence study was carried out involving pregnant women and their term newborns, 92 of whom were small for gestational age and appropriate sized for gestational age, at two public maternity hospitals in the Brazilian city of Salvador. The evaluation of the differences between the median gestational age according to the two methods was carried out using the non-parametric "Wilcoxon Signed-Rank Test.
RESULTS: compared to ultrasound, the Capurro method overestimated the gestational age in newbornsof less than 39 weeks and underestimated it in older newborns. Ultrasound underestimated gestational agein newborns with more than 37 weeks.
Key words: Gestational age, Infant, Small for gestational age, Sensitivity and specificity. Gestational age, measured in weeks or full days, is defined as the time that has elapsed since the first day of the last normal menstrual period LMP. At present, LMP and ultrasound are the principal methods used to estimate gestational age.
More precise ultrasound measures of gestational age up to the tenth week can be obtained by measuring the length of the fetus from head to buttocks, while, up to the 20 th week, measurement of the length of the femur or the biparietal diameter is the most appropriate. In the absence of ultrasound data or LMP, the Capurro somatic method 9 has been used in clinical practice. Although it is widely used, few studies have evaluated the accuracy of the Capurro somatic method 9 for estimating the gestational age and anthropometric parameters at birth compared with LMP and ultrasound.
These studies suggest that the Capurro method under- or overestimates gestational age compared with LMP and ultrasound. Despite these limitations, the Capurro method is still commonly used in maternity hospitals, especially when other methods are not available.
The use of this procedure has a direct impact on the accuracy of a diagnosis of the anthropometric status of a newborn and hence on the health conditions at birth.
In view of this, this study aims to evaluate the use of the Capurro somatic method and ultrasound, taking LMP as the point of reference, for the estimation of gestational age and anthropometrical classification of term newborns. The accuracy of the ultrasound and Capurro somatic methods for evaluation of gestational age and anthropometric status at birth was tested. The LMP method was taken as the point of reference. Given that the sample was not originally intended for this study and information on gestational age provided by the methods under study was not available for all the pregnant women, it was decided that the power of the sample for evaluating the accuracy of measurement of gestational age by each method should be calculated along with its capacity to classify the anthropometric status of newborns.
Thus, for a sample of newborns, for whom information on gestational age provided by LMP and Capurro was available, the following were taken into consideration: the difference between the means for the two procedures of 0. For evaluation of the difference between the mean gestational age provided by LMP and ultrasound, considering this difference to be 0.
The data were collected by duly trained researchers in accordance with the criteria and procedures outlined below. Weight at birth was obtained from the medical records. The newborns were weighed using the service's normal procedure, which consists of weighing the newborn immediately after birth, unclothed, with the umbilical clamped, using an electronic scale with a capacity of 15 kg, sensitivity calibrated at 5 g and reset for each weighing.
The gestational age was calculated in full months, according to the recommendation of the World Health Organization WHO. A gestational calendar was used to calculate the gestational age according to LMP and ultrasound. The LMP method was used with those mothers with a regular menstrual cycle between 25 and 31 days and date day and month as of the last menstrual period.
The estimation of gestational age using the Capurro method was carried out by neonatologists according to the standard procedure of the health center and registered in the medical records. When this was not available, it was acquired by a duly trained individual. The method is based on inspection in the first 12 hours of life of physical signs that are placed on a maturation scale 9,10 taking into consideration the following five characteristics of the newborn: skin texture, shape of the ear, size of the mammary nodule, formation of the nipple, and the folds of the sole of the foot.
The resulting figure was divided by 7 equivalent to the number of days in the week , to obtain the gestational age in full weeks. The ICC expressed as "rho" was equal to zero, indicating slight probability of the existence of variation from one observer to another and that the measurements taken contained no bias that would affect the study.
Anthropometric evaluation was carried out based on the information on birth weight and gestational age using the curve produced by Williams et al. Two groups were drawn up for the purposes of statistical analysis: one comprising newborns whose gestational age was estimated using the LMP and Capurro methods and another comprising newborns whose gestational age was ascertained using LMP and ultrasound. The LMP, ultrasound and Capurro methods were submitted to a normality test to see whether they exhibited a normal distribution, using mean, median and mode, arranged in histograms, by means of the Kolmogorov-Smirnov test.
The differences between the median gestational ages were tested using the Wilcoxon SignedRankTest. The receiver operating characteristic curve ROC curve 13 was used to establish the cut-off point with the greatest specificity and sensitivity for the gestational age estimation methods in diagnosis of anthropometric status at birth.
The accuracy of the Capurro and ultrasound methods for diagnosis of anthropometric status at birth considering newborns whose weight falls below the 10 th percentile to be SGA 14 was evaluated by calculating the sensitivity, specificity, and positive and negative predictive value. The percentage of agreement and disagreement between the methods was also calculated using the Kappa coefficient. Of the newborns who met the inclusion criteria, 66 were excluded, 20 because their gestational age could not accurately be determined, 25 because they were discharged early from hospital, making it impossible to obtain data, and 21 because their mothers refused to participate.
Likewise, newborns whose gestational age was estimated using only one of the three methods were excluded from the study. The final sample thus comprised newborns, of whom The gestational age of seven newborns whose medical records did not contain this information 2. The mean weight of the AGA term newborns was For the SGA term newborns the mean weight was A low birth weight was found in 2 0.
It was also observed that most of the mothers interviewed A significant number of them were adolescents Table 1 shows the median gestational ages and their respective differences, estimated using a combination of LMP and Capurro or a combination of LMP and ultrasound.
Comparison of the median gestational ages estimated using LMP and Capurro revealed that there were differences in the 37 th and 38 th weeks of gestation, with higher values being returned by the Capurro method. In the 39 th week of gestation there were no differences in the medians calculated using the two methods. After the 40 th and 41 st weeks the opposite trend was observed, with LMP returning higher figures.
It was also noted that this significance was due principally to the differences in the 40 th and 41 s t gestational weeks, this being the range within which more than half of the newborns included in this study Figures 2 and 3 show the ROC curves used to define the cut-off point with the higher specificity and sensitivity for the ultrasound and Capurro methods for assessing the gestational age compared to the LMP for diagnosing newborns as small for gestational age.
The bands between the 37 th and 41 st weeks were tested as cut-off points. Both the ultrasound and the Capurro methods did not show statistical significance between the 37 th and 39 th week of gestation data not given. After the 40 th week of gestation the areas under the ROC curve reached Table 2 shows the accuracy of the gestational ages estimated according to the different methods for diagnosing SGA newborns, using sensitivity, specificity, positive predictive value and negative predictive value.
The gestational age estimated using ultrasound showed a higher sensitivity However, the specificity of the Capurro method The positive predictive value was higher when the Capurro method was used By contrast, ultrasound revealed a proportion of This study found that, compared to LMP, the births covered by the study fell data not given.
This Capurro method overestimated the gestational age in distortion in the measurement of gestational age newborns of less than 39 weeks and overestimated it increases the chance of incorrect anthropometric in those with a higher gestational age. Ultrasound classification of newborns. Depending on the weight underestimated the gestational age of newborns with of the newborn, underestimation of gestational age more than 37 weeks. Ultrasound was found to have may lead to SGA newborns being wrongly classified greater sensitivity in the prediction of SGA as AGA, thereby impeding the adoption of procenewborns and the Capurro method greater speci-dures important for the health of these children.
The ficity. The best cut-off point for ultrasound was opposite situation leads to unnecessary costs for found to be the 41 st week of gestation. Comparison of the median gestational ages esti-The results found in this study are for term mated using the Capurro method, taking the LMP newborns alone and the scope for comparison is thus method as the point of reference revealed that the limited.
However, they are broadly in accordance former overestimated the gestational age in with the findings of Panvini et al. This difference between the medians became 39 weeks of gestation and to overestimate it for newborns with fewer than 39 weeks. The poor accuracy of the Capurro method in estimating gestational age, compared to the LMP method has also been reported by other researchers. In the present study a similar tendency to underestimate gestational age was found for the ultrasound method, taking LMP as the point of reference, in newborns with a gestational age of over 39 weeks.
Some studies that have compared these two methods for estimating gestational age have found a similar tendency for ultrasound to underestimate gestational age. However, recent studies also suggest discrepancies in gestational age as estimated using these two methods and present alternative data analysis procedures as a way of reducing the number of such discrepancies. In view of this, it can be supposed that the best cut-off point for estimating gestational age using the ultrasound method is the 41 st week of gestation.
The data in Table 2 show that the sensitivity of the ultrasound Analysis of the power of the two methods to discriminate true non-cases AGA newborns shows, however, that the Capurro method has greater discriminatory power with a specificity of The findings of the present study suggest that ultrasound was a better predictor of gestational age and anthropometric conditions at birth compared to the Capurro somatic method.
However, if it is to be used by health services, adequate validation measures need to be taken and the ultrasound should be carried out before the 20 th week of gestation. In this study, however, only The Capurro somatic method, despite having received criticism with regard to its validity for estimating gestational age, is often the only option available for post-natal estimation of gestational age and it is recommended that it be used with caution in such situations.
The limitations of the study include the fact that the sample only included term newborns, thereby restricting broader comparison between pre- and post-term births. A second limitation was the use of ultrasound and Capurro test results recorded on medical records filled in by different health professionals, which may have given rise to inter-observer bias.
A further limitation was the fact that a considerable percentage of mothers were excluded because the gestational age of their children had been evaluated using only one method, especially when this was ultrasound, thereby restricting the size of the sample. Furthermore, each method is known to have its own inherent limitations, which this study attempted to minimize by adopting inclusion criteria and procedures to ensure external validation. However, in view of the lack of consensus as to the best method for estimating the standard gestational age and the inherent limitations of each, it is perhaps reasonable to argue that evaluation of the state of health and nutrition at birth should include both parameters that estimate the length of gestation and those that include anthropocentric conditions at birth.
This suggestion requires further study. Recommended definitions, terminology and format for statistical tables related to the perinatal period and use of a new certificate for cause of perinatal deaths. Acta Obstet Gynecol Scand. Physical status: the use and interpretation of anthropometry. Geneva; Tech Rep Ser.
A comparison of LMP-based and ultrasound based estimates of gestational age using linked California live birth and prenatal screening records. Paediatr Perinatal Epidemiol.
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