Background: The epidemiological profile of infants failing to thrive is unclear. The aim of this study is to investigate the prenatal and socioeconomic factors associated with these infants using standardized weight gain conditional on previous weight.
Methods: In a large UK population cohort study, 11 718 infants born at term in 1991-1992 with no major congenital abnormalities were identified. Using a weight gain criterion conditional on initial weight from birth to 6-8 weeks, 6-8 weeks to 9 months, and birth to 9 months, the slowest gaining 5% were identified.
Results: None of the prenatal factors was associated with failure to thrive in the multivariable analysis nor were traditional markers of socioeconomic deprivation such as poor parental education or low occupational status. Parental height was significantly correlated with slow infant weight gain in both separate periods and from birth to 9 months (Pearson's r = +0.20, P < 0.001). Eight times as many infants born to shorter parents (8.7%, 95% CI: 6.6, 11.3) showed slow weight gain as infants born to taller parents (1.1%, 95% CI: 0.5, 2.5). Higher parity was also related to slow infant weight gain; infants born in the fourth or subsequent pregnancy were twice as likely to fail to thrive from birth to 9 months (8.3%, 95% CI: 6.4, 10.6) as first-born infants (3.4%, 95% CI: 2.9, 10.6).
Conclusions: Future studies need to take account of parental height when calculating growth standards and look at why failure to thrive is more common, not in poorer families but in larger families.