The Usher test is a clinical method used to calculate the gestational age of a newborn. It is based on the evaluation of five physical criteria: plantar folds, pinna, hair, breast nipple and genitalia (male and female, according to their sex).
This method, along with other similar techniques such as the Dubowitz, Ballard and Capurro test, are used when there is no specific prenatal data, among which the date of the last menstrual period and imaging studies stand out..
Of all the methods mentioned for estimating gestational age, the Usher test is the fastest to perform but also the most inaccurate. This is because it is only based on anatomical characteristics, not taking into account the neurological capacities of the baby, as if the rest of the methods do..
As the Usher test is more limited in its observations, it only allows the gestational age to be established in the case of newborns 36 weeks and older. This means that this method is not useful to specify the gestational age of very premature babies, whose time of birth is below 36 weeks.
Another disadvantage of this method is that its results can be affected if the baby has suffered restrictions in intrauterine growth, that is, a delay in the growth and development of the fetus, which generates a low birth weight..
The parameters considered to estimate gestational age by this method are: characteristics and amount of hair present, strength of the cartilage of the pinna, presence and size of the nipple, characteristics of the genitalia (female or male as the case may be), presence and proportion of the folds of the soles of the feet.
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Before there were methods for estimating gestational age, birth weight was used as a criterion. Every child weighing 2,500 grams or less was said to be premature, but this method turned out to be a failure, as young children born at term were included and large premature children were underestimated.
The French Medical School was the pioneer in describing and adopting techniques for estimating gestational age after birth. The methods consisted of observing external anatomical characteristics, later including neurological parameters.
Dr. Robert Usher et al. In 1966 published an extremely simple and fast way to calculate gestational age. The method was quickly accepted by the medical community and in 1971 Gustin et al conducted a study at the Lima Maternity Hospital, where the Usher test was applied to 454 live births weighing 2,500 grams or less..
The objective of the work was to compare the characteristics included in the Usher test and its respective calculation with the gestational age calculated according to the method of the date of the last menstruation..
The work showed that the Usher method is much more effective at 37 weeks of gestation, with a coincidence percentage of 89.65%.
They also concluded that of all the parameters considered in this test, the observation of the plantar folds and the anatomical characteristics of the genitalia, both female and male, are the most accurate, coinciding with gestational age in 78%. While, they considered that the characteristics of the mammary gland is the least efficient with a 68.26% agreement..
When they analyzed the characteristics of the Usher test in isolation, they realized that for 37 weeks, the parameters with the greatest coincidence were that of the plantar folds (93.76%) and the characteristics of the genitalia (91%)..
Meanwhile, for newborns between 37-38 weeks, the characteristic of the pinna was the most appropriate with (86.96%). Finally, for newborns over 39 weeks, the most useful parameters are the plantar folds and external genitalia with 76.54% and 75% coincidence, respectively..
The method proposed by Usher only considers 5 somatic aspects, which are explained below:
The specialist evaluates the characteristics of the baby's hair, whether it is sparse or abundant, fine or thick, clumped or separable. Sparse, fine and clumpy hair is a sign of immaturity.
The specialist will observe how firm or weak the cartilage of the pinna is. The doctor will try to bend the pinna and if it bends easily and stays bent it is a sign of immaturity, on the other hand if the cartilage is difficult to bend and it quickly returns to its initial position it is a sign of maturity.
The specialist observes if the baby has a nipple, and if it is present, he proceeds to measure it. The smaller this is, the more premature the baby is.
In the male, the appearance of the scrotum smooth or with folds will be observed, as well as whether the testicles are descended or not. A smooth scrotum with undescended testicles is a sign of immaturity.
In girls, the disposition of the labia minora and majora will be observed. The normal thing is that the elders cover the minors, but if the opposite is observed, it is a sign of immaturity.
This characteristic is one of the most important that cannot be ignored, since together with the criterion of the genitalia, it represents the most unequivocal data in the calculation of gestational age. It is difficult to observe the soles of the newborn's feet, the presence of abundant folds is a sign of maturity.
For the interpretation of the above characteristics, specialists are guided by the Usher classification table shown below:
The Usher test can only classify into three gestational age ranges, being in this sense the most limited of the existing methods for this purpose.
The ranges are:
1st rank: less than 36 weeks
2nd rank: between 37 and 38 weeks
3rd rank: greater than 39 weeks
It is known that knowing the gestational age of a newborn is of vital importance, since a baby born prematurely will never behave in the same way as a full-term baby in the face of certain neonatal conditions, and therefore treatment and care are also different.
It is also known that the best methods to calculate gestational age are those obtained in the prenatal stage, such as the date of the last menstrual period and ecosonographic studies..
However, these data are not always available, the first perhaps due to factors such as: forgetfulness and ignorance and the second due to economic restrictions. Therefore, it was essential to have well-founded medical criteria to be able to estimate gestational age if the previous data are absent..
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