Construct validity and factor structure of the Pittsburgh Sleep Quality Index among pregnant women in a Pacific-Northwest cohort

Poor sleep quality during pregnancy is associated with adverse obstetric and neuropsychiatric outcomes. Despite its routine use as a sleep quality assessment scale among men and non-pregnant women, the psychometric properties of the Pittsburgh Sleep Quality Index (PSQI) have not been assessed among US pregnant women. We sought to evaluate the construct validity and factor structure of the PSQI among 1488 pregnant women. A structured interview was used to collect information about demographics and sleep characteristics in early pregnancy. The Patient Health Questionnaire-9 (PHQ-9) and the Depression, Anxiety, and Stress Scale-21 (DASS-21) were used to assess symptoms of depression, anxiety, and stress. Consistency indices, exploratory and confirmatory factor analyses (EFA and CFA), correlations, and logistic regression procedures were used. The reliability coefficient, Cronbach's alpha for the PSQI items was 0.74. Results of the EFA showed that a rotated factor solution for the PSQI contained two factors with eigenvalues > 1.0 accounting for 52.8 % of the variance. The PSQI was significantly positively correlated with the PHQ-9 (r (s) = 0.48) and DASS-21 (r (s) = 0.42) total scores. Poor sleepers (PSQI global score > 5) had increased odds of experiencing depression (OR = 6.47; 95 % CI = 4.56-9.18), anxiety (OR = 3.59; 95 % CI = 2.45-5.26), and stress (OR = 4.37; 95 % CI = 2.88-6.65) demonstrating evidence of good construct validity. CFA results corroborated the two-factor structure finding from the EFA and yielded reassuring measures indicating goodness of fit (comparative fit index = 0.975) and accuracy (root mean square error of approximation = 0.035). The PSQI has good construct validity and reliability for assessing sleep quality among pregnant women.