Estimated Gestational Age From Infant's Foot Length in Japanese

Aim In developed countries including Japan, gestational age (GA) is predicted by the last menstrual period (LMP) and/or fetal ultrasound. In some developing countries, GA is predicted by infant's foot length (FL). Pregnant women who did not have pregnancy check-up is not infrequent in Japan, therefore there are sometimes opportunities to estimate the GA from infants after the delivery. The aim of this study is to determine the estimated GA formula from infant's FL in Japanese. Methods This study was a prospective cohort study. Infants between May 2021 and August 2021 at Iizuka Hospital and Tagawa Hospital or transferred from other hospitals within 24 hours of birth were collected. GA was determined using LMP and/or fetal ultrasound. The infant's FL was measured with a digital caliper within 24 hours of birth. The relationship between FL and GA was analyzed by simple regression analysis to determine the coefficient of determination (R²). The infant's FL of males and females, infant's FL of preterm and term, and infant's FL of low birth weight and appropriate weight infants were performed by the t-test as independent samples. A statistically significant difference was p < 0.05. Statistical analysis was performed using JMP Pro 16 (SAS Institute Japan Co., Ltd., Minato-ku, Tokyo). Results Ninety of the 135 infants were enrolled. The average GA was 38.2 ± 1.8 weeks, the average infant's FL was 7.230 ± 0.411 centimeter (cm), and the range of the infant's FL was 5.385 to 8.089 cm. The estimated GA formula, GA = 18.49 + 0.27 x infant's FL (R² = 0.39), was determined. Conclusions We determined the estimated GA formula from the infant's FL. There are some limitations and care should be taken in the use.