Usefulness of measurement of proximal phalanx length by using ultrasonography in newborn infants

Abstract

The purpose of this study was to compare digit lengths and proximal phalanx lengths in newborn infants by using ultrasonography (USG) and to examine sex differences between the ratio of the second digit (2D) and fourth digit (4D) of digit length and that of proximal phalanx length and the associations of digit length and proximal phalanx length with birth weight and birth height. Sixty newborn infants (28 males and 32 females) were recruited. Digit lengths were measured by using a transparent ruler and proximal phalanx lengths were measured by using USG. There were significant correlations between digit length and proximal phalanx length in the left and right hands. There was no significant correlation between 2D:4D ratios of digit lengths and 2D:4D ratios of proximal phalanx lengths measured by using USG. In males, birth height was significantly associated with right fourth proximal phalanx length and with left second and fourth proximal phalanx lengths. Birth weight was significantly associated with proximal phalanx length in males. Proximal phalanx length measured by using USG was significantly associated with digit length in newborn infants. Hormonal exposure before birth may be involved in the associations of proximal phalanx length with birth weight and height in males.

Impact statement

• What is already known on this subject? The ratio of the second digit (2D) and fourth digit (4D) has been used postnatally to provide a retrospective indication of the foetal hormonal environment. Digit lengths have been measured by using a direct method, photocopies, digital scans and radiographs, but the results of a study on measurement of digit lengths by using ultrasonography (USG) have not been reported.

• What do the results of this study add? Proximal phalanx length measured by using USG was significantly associated with digit length in newborn infants. In males, birth height was significantly associated with right fourth proximal phalanx length and with left second and fourth proximal phalanx lengths. Birth weight was significantly associated with proximal phalanx length in males.

• What are the implications of these findings for clinical practice and/or further research? Measurement of proximal phalanx length by using USG may be useful for a study on gender differences in foetal development and the foetal hormonal environment. Hormonal exposure before birth may be involved in the associations of proximal phalanx length with birth weight and height in males.

Keywords:

• Digit lengths
• proximal phalanx lengths
• newborn infants
• ultrasonography
• digit ratio

Acknowledgements

The authors appreciate the support and cooperation of the subjects who participated in the present study.

Disclosure statement

No potential conflict of interest was reported by the author(s).