Psychosocial factors and preterm birth : national register-based studies

Every year, approximately fifteen million infants are born preterm, defined as prior to 37 gestational weeks. Preterm birth is the number one cause of neonatal mortality, which kills more than one million babies every year globally. However, its aetiology remains largely unclear, hindering effective preventions. Besides genetic predisposition, the most commonly studied factors are maternal behavioural or clinical indicators measured shortly before or during pregnancy. Meanwhile, as a population health indicator in itself, preterm birth rates vary to a large extent both within and between countries, even among high-income countries. The mechanisms and processes generating unequal preterm birth rates await elucidation and action.

With an ecological perspective and a focus on the psychosocial mechanism of human disease, this thesis considers the causes of preterm birth as being embedded in the mother’s living circumstances across her lifespan. To better understand the pathogenesis of preterm birth, this thesis aims to address the relationship between a mother’s adverse social environment and the preterm birth of her offspring, by investigating several indicators of her living situation at different life stages. For all studies included in this thesis, this is made possible by linking data from various Swedish National Registers through the use of the personal identification number and obtaining information on all parents of infants born between 1987 and 2012.

Study I showed that severe early life adverse experience, marked by being placed in out-of-home care, was associated with preterm delivery later in life, independent of a woman’s genetic or prenatal predisposition to delivering preterm. Multiple social and behavioural trajectories are hypothetically involved, including the priming of her stress response system. The partner (expecting father of the infant) was investigated in Studies II and III, as an integral part of the psychosocial environment later in life. Depression (marked by specialized hospital care or filled prescriptions of antidepressant) and aggression (marked by convicted violent crimes) of the partner were both associated with an increased risk of preterm birth. Extensive adjustment for potential maternal confounding factors did not appreciably account for these associations. Study IV investigated the risk of preterm birth with larger contextual changes experienced by refugee women. Migration, especially as an asylum seeker fleeing from one’s homeland, is a considerable stressor that has a potentially long-lasting impact on the maternal hormonal profile. Compared to babies born in the second year of residence, those born sooner after settlement were more likely to be preterm. In summary, the risk of offspring preterm birth was associated with psychosocial adversities on individual, interpersonal, and macro-social levels at various stages across the life-course. Early life, both of the woman and of her offspring, was highlighted as being sensitive to psychosocial adversities. Meanwhile, chronic strain in day-to-day life, especially with the significant other, was suggested to impact the risk of preterm birth significantly.

Overall, the findings of these studies highlight how social disadvantages can ‘get under the skin’, taking their toll on both the affected individual and on future generations. Given this, a psychosocial approach with an extended preconception lifecourse may shed light onto future explorations of the aetiology of preterm birth. Moreover, the interdependence and interactions with other key individuals in one’s life need to be incorporated into future research agendas. Understanding the maternal and child health in a cohesive framework incorporating social, biological, and time perspectives may help to integrate a continuum of maternal and child care. Healthcare providers are encouraged to consider a family-centred approach, which acknowledges and treats the mother, father and the infant as a triad.

List of scientific papers

I. Liu C, Vinnerljung B, Östberg V, Gauffin K, Juarez S, Cnattingius S, Hjern A. Out of home care in childhood and preterm delivery: a Swedish national intergenerational cohort study. [Submitted]

II. Liu C, Cnattingius S, Bergström M, Östberg V, Hjern A. Prenatal parental depression and preterm birth: a national cohort study. BJOG. 2016 Nov;123(12):1973–82.
https://doi.org/10.1111/1471-0528.13891

III. Liu C, Långström N, Ekéus C, Frisell T, Cnattingius S, Hjern A. Paternal violent criminality and preterm birth: a Swedish national cohort study. [Manuscript]

IV. Liu C, Urquia M, Cnattingius S, Hjern A. Migration and preterm birth in war refugees: a Swedish cohort study. Eur J Epidemiol. 2014 Feb;29(2):141–3.
https://doi.org/10.1007/s10654-013-9877-9