Twenty-two percent of participants had a positive PHQ-9 score from 0–9 months postpartum, a finding that is comparable to Gaynes et al.'s 22% 12-month period prevalence of major (postpartum) depression.2
The point prevalence of positive PHQ-9s was greatest at 0–1 month postpartum (12.5%), then fell to lower levels (5–7%) at 2–6 months postpartum, and rose again to 10.2% at 9 months. This secondary peak at 9 months was unexpected and could not be explained by certain discretionary factors, such as length of maternity leave, currently working at a job, infant cared for outside of home, or 9-month breastfeeding status. It is possible that we did not have adequate power to detect such associations, given that only 22 women changed from a negative PHQ-9 score at 6 months to a positive score at 9 months. Previous research has found PPD to be associated with prenatal depression and anxiety, other history of depression, child care stress, life stress, lower levels of social support (including partner support), marital dissatisfaction, infant temperament, maternity blues, poor self-esteem, lower socioeconomic status, single status, younger age, and unplanned/unwanted pregnancy.12–14
We did not include social support variables in this study, so it is not known if changes in social support may have contributed to the 9-month increase in depressive symptoms.
In looking at specific PHQ-9 items in this postpartum population, we found that most of the PHQ-9 items—mood, pleasure, self-esteem, difficulty concentrating, psychomotor agitation/retardation, and suicidal ideation—discriminated very well between depressed and nondepressed women, with most likelihood ratios being >20. Three somewhat less discriminating symptoms—abnormal sleep, appetite/eating, and fatigue—still differentiated reasonably well between cases and noncases, with likelihood ratios of approximately 5–17. Our PHQ-9 item analysis results are quantitatively different from but qualitatively similar to those of Weobong et al.,8
on 160 postpartum women from Ghana, 18 of whom had PPD. Here, likelihood ratios were lower overall, ranging from 1.82 to 5.74, and symptoms with the lowest likelihood ratios (≤3.1) included sleep problems, feeling depressed, little interest, poor appetite, and feeling tired. Three of these symptoms corresponded to our less discriminating symptom group (sleep, appetite, and fatigue).8
The fact that the symptoms of abnormal sleep, poor appetite, and fatigue did not differentiate between cases and noncases as well as other symptoms does not lessen their importance. In fact, abnormal sleep/appetite and fatigue were the most prevalent of symptoms among our cases (women with positive PHQ-9 scores), with >70% of cases acknowledging these symptoms at nearly every observed interval. Both fatigue and sleep loss are commonly considered a normal part of the postpartum experience because of the process of mothers' postpartum recovery and newborns' needs for continuous care, yet it is possible that these so-called normal symptoms could be precursors to depression, particularly when they are intense or prolonged or when the mother is otherwise susceptible to depression. One study found that maternal fatigue as early as 7 days postpartum was predictive of depression on day 28.15
Another study found that mothers with high EPDS scores (>12) at 4 and 8 weeks postpartum reported that their babies cried often, did not sleep well, woke them up three or more times a night, and did not allow them to get a reasonable amount of sleep (<6 hours of sleep in a 24-hour period).16
Given this apparent relationship between poor infant and maternal sleep and maternal mood disorders, additional research on sleep interventions and sleep education, particularly in the setting of PPD, may be useful. Some experts question the use of a PPD screen that includes symptoms that overlap with the normative postpartum experience, such as fatigue and sleep loss. We would argue that abnormal sleep and fatigue are just as important, and perhaps moreso for women with PPD than for women with nonpostpartum depression, and should be recognized in both the diagnosis and treatment of PPD.
Strengths of the study include its prospective, longitudinal design, use of the PHQ-9 depression screen, which contains the 9 criteria for depression diagnosis, performance of PHQ-9 item analysis in a postpartum sample, and the diversity of study participants in factors of maternal race, education, earnings, and marital status. Although our dropout rate over 9 months was respectable at 6.7%, dropouts (vs. study completers) were more likely to have positive PHQ-9 screens (21% vs. 6% at 0–1 month), suggesting that selection bias that may have caused us to underestimate actual depression prevalence rates at later postpartum intervals. Other limitations include our modest response rate, our inability to compare participants with nonparticipants (we did not collect data on nonparticipants), and our inability to show why depressive symptoms increased from 6 to 9 months postpartum or to examine social support systems as a possible predictor of this change. We did not include additional popular PPD screens, such as the EPDS, so we do not have comparative data on the prevalence of depressive symptoms with those instruments. Future studies of similar populations may consider having dedicated research assistants at each study site to ensure that all eligible women are invited to participate.
In conclusion, results from this study revealed a bimodal peak in depressive symptoms at 0–1 month and 9 months postpartum, which suggests the need for repeat screening for PPD during the first postpartum year. We also found that most PHQ-9 items discriminate well between depressed and nondepressed mothers, which supports the use of the PHQ-9 for identifying PPD. Given that the PHQ-9 is becoming increasingly popular in general depression care as an easy to administer diagnostic survey, we hope that the growing evidence of its applicability to PPD will help improve screening and detection of depression in the postpartum period.