Original ArticleAdvanced sleep-wake rhythm in adults born prematurely: confirmation by actigraphy-based assessment in the Helsinki Study of Very Low Birth Weight Adults

- Previous studies suggest a propensity towards morningness in ex-preterm individuals.
- Sleep was measured by actigraphy in adults born preterm and in term-born controls.
- Ex-preterm adults woke up 40 min earlier, suggestive of an advanced sleep-wake rhythm.

ObjectivePrevious studies have suggested a propensity towards morningness in teenagers and adults born preterm. We set out to study sleep in a subsample from The Helsinki Study of Very Low Birth Weight Adults cohort, with emphasis on sleep timing, duration, and quality. We compared young adults who were born prematurely at very low birth weight (VLBW; <1500 g) with controls born at term.MethodsWe measured sleep by actigraphy in young adults aged 21-29 years. A total of 75 individuals (40 VLBW and 35 controls) provided adequate data. Group differences in sleep parameters were analyzed using t-test and linear regression models.ResultsVLBW adults woke up on average 40 min earlier [95% confidence interval (CI), 9-70] and reported 40 min earlier get up time (95% CI, 8-71) than did the controls. The difference remained after adjustment for confounders. We found no group difference in sleep duration or measures of sleep quality.ConclusionOur findings of earlier rising in the VLBW group are suggestive of an advanced sleep phase in that group. These results reinforce previous suggestions that chronotype may be programmed early during life.