Transabdominal ultrasound of rectal diameter in healthy infants: a prospective cohort study during the first year of life

Transabdominal rectal ultrasound (TRU) is used to measure transverse rectal diameter (TRD) in order to diagnose functional constipation (FC) and megarectum, and to evaluate treatment. The proposed cut-off value is 3.0 cm. Currently, no standardised values exist for children below the age of 4. We used repeated TRUs to establish reference TRD values in healthy infants and to describe rectal diameter in infants with FC.This prospective observational cohort study enrolled healthy term babies from a maternity department. TRD measurements were taken at 2 and 12 months of age, and questionnaires completed in interviews helped diagnose FC according to Rome III criteria.Two hundred TRUs were performed on 110 infants (62 males). In infants without FC anytime, the mean TRD at 2 months was 1.56 (SD 0.32) cm and at 12 months 1.78 (0.47) cm, while the 95th percentiles were 2.26 and 2.64 cm, respectively. In 77 infants with two TRUs, the mean increase was 0.21 cm (95% confidence interval: 0.099-0.318). Thirteen infants were diagnosed with FC during the study period. At 2 and 12 months of age, there was no difference in TRD between infants with and without FC.TRD increased from 2 to 12 months. We suggest 2.3 cm as an upper limit for normal TRD at 2 months and 2.6 cm at 12 months. Infants diagnosed with FC did not have a greater TRD than infants without, either before or after treatment. Further studies are needed to evaluate the usefulness of TRU in infants with FC or megarectum.