Background: Studies suggest that preterm delivery is a risk factor for early language delays, but knowledge is scarce about the persistence of the delays and whether the association is of a linear kind. To resolve this, effects of confounding risk factors that are both shared within a family and pregnancy specific need to be distinguished from effects of preterm delivery. Our study examines the association between early gestational age and language outcomes, using a sibling-control design.
Methods: The sample comprises 22,499 siblings from the Norwegian Mother and Child Birth Cohort Study, recruited between 1999 and 2008. Mothers rated child language comprehension and production at 18 and 36 months. Analyses compared siblings discordant on gestational age group (early preterm, delivery at week 22-33; late preterm, 34-36; early term, 37-38; full term, >38) and type of onset of delivery (spontaneous; provider-initiated), and compared these findings with conventional cohort analyses.
Results: The findings revealed inverse linear relations between the gestational age groups, and persistent but diminishing language delays. Effects of preterm delivery were substantial on both language production and comprehension at 18 months. By 36 months, the effects of preterm delivery were weaker, but still extensive, in particular for language production in provider-initiated births. When comparing sibling-control with cohort analyses, preterm group was less important among spontaneous births, but remained important in provider-initiated births. Familial and pregnancy risk factors partly explained this.
Conclusions: Distinctive factors seem to underlie effects of preterm delivery across spontaneous and provider-initiated births.
Keywords: MoBa cohort study; Preterm delivery; gestational age; induced labour; language delay; provider-initiated; sibling design; spontaneous labour.
© The Author 2015; all rights reserved. Published by Oxford University Press on behalf of the International Epidemiological Association.