PAIN AND PERINATAL FACTORS Association of preterm birth and low birth weight with long-term chronic pain and experimental pain sensitivity
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Adverse early life factors may be associated with long-term alterations in health and disease susceptibility. Low birth weight, an indicator of reduced fetal growth or preterm birth, may be associated with altered brain development and early programming of stress-response systems. Neonatal pain may cause developmental changes in pain pathways. This may ultimately manifest as increased pain sensitivity and possibly an increased vulnerability towards developing chronic pain. Aims The main aims of this thesis were: To investigate whether chronic pain in adolescence is associated with perinatal factors To investigate self-reported chronic pain among two well-defined low birth weight cohorts in young adulthood To investigate potential alterations in thermal and pain sensitivity among young adults with low birth weight Methods First, we linked data on self-reported pain from a large health survey conducted among youth (Young-HUNT) to the Medical Birth Registry of Norway. We investigated the association of birth weight, standardized birth weight, gestational age and 5-minute Apgar score with three chronic pain definitions of increasing strictness. Secondly, we investigated self-reported chronic pain as part of a prospective long-term follow-up study of two low birth weight cohorts: preterm very low birth weight (VLBW; birth weight ≤1500 grams) and term small for gestational age (SGA; birth weight <10th percentile) individuals, together with a term-born, normal birth weight control group at 26 years. Finally, in a subsequent sub-study at mean age 28 years, we used quantitative sensory testing to investigate thermal detection and pain thresholds, pressure pain thresholds and the sensitivity to prolonged supra-threshold heat among the same study groups. Results We found no material associations of preterm birth or low birth weight with chronic non-specific pain in adolescence, with a possible exception for chronic daily pain in boys. Post-term birth seemed to be associated with chronic daily pain in boys, and a low 5-minute Apgar score was associated with chronic multisite and chronic daily pain in girls. Preterm VLBW and term SGA young adults reported more pain than the controls at 26 years. Adjustments for potential confounders and anxiety and depression symptoms attenuated the results, but some effect of low birth weight remained, particularly in the term SGA group. Pain reports seemed to increase from 19 to 26 years in the term SGA group. We did not find substantially altered thermal detection thresholds, thermal pain thresholds, pressure pain thresholds or increased sensitivity to prolonged supra-threshold heat among either VLBW or term SGA participants compared to controls. The VLBW group tended to report more chronic pain at 28 years. Conclusions Our findings indicate that perinatal factors do not contribute substantially to the prevalence of chronic pain in adolescence at the population level. Preterm VLBW or term SGA birth may be associated with increased pain reports in young adulthood. We found no substantial changes in thermal perception or pain sensitivity among young adults with low birth weight.