In this analysis of women during pregnancy and postpartum we determined that pre-screening with the 2-item PHQ generally had good sensitivity and specificity for identifying women with positive scores ≥13 on the Edinburgh Postnatal Depression Scale. The addition of a question regarding history of depression improved the sensitivity, at the expense of specificity, and the PPV of this screening. Out of 100 unselected cases seen at 15 weeks, the PHQ-2 alone would help correctly detect 16 out of 17 depressed patients (missing only one patient) and correctly reassure 62 out of 83 patients, falsely diagnosing 21. Similarly, out of 100 unselected patients seen postpartum, the PHQ-2 alone would help correctly identify 4 out of 5 depressed patients (the prevalence is 5% in this case) and correctly reassure 81 out of 95 patients, misidentifying 13. This demonstrates that when the PHQ-2 is negative it has a 97% to 99% chance of accurately ruling out depression with very few false negatives. Thus, this rapid screening procedure may be useful as part of a multistage case finding strategy to rule out women who would otherwise require further time-consuming assessment for the presence of maternal depression.
Based on the rate of positive 2-item screens in the current study, 60% to 80% of the women being assessed (depending on the particular point in pregnancy and postpartum) can be ruled out with high certainty of not having depression. When the history of depression item is added, the number of women quickly ruled out is slightly higher but at a cost of approximately 10% in case-finding accuracy. It is important to keep in mind that even when the PHQ-2 is negative and the NPV is 90% or higher, it is possible that these women actually have major depression. For this reason we suggest that a negative screen should not overrule clinical concern and that anyone judged to be symptomatic clinically but with a negative pre-screen or screen for depression should have a further concurrent or follow-up examination. It may be somewhat surprising that adding history of depression questions did not substantially improve the performance of prescreening, particularly given the recognition that depression is a recurrent episodic disorder.39
One explanation is that the women in our sample were young enough that they were still experiencing their first episode of depression. A second reason might be that the PHQ-2 alone has reached a ceiling regarding rule-out accuracy. A third possible reason questions the validity of simple self-report questions for assessing history without a basis for explaining the questions or probing the responses that an interview provides, a finding that has been reported elsewhere.40
Importantly, we have shown that the modified PHQ-2 used here functions well as a first pre-screening step in early and late pregnancy and postpartum. By efficiently ruling out those who do not have depression, resources can be targeted at the women at highest risk of a major depressive disorder. However, the value of this strategy depends on diagnostic follow-up of the women registering positive with both the pre-screening and the EPDS. A positive score on the EPDS is by itself an inadequate basis for clinical decision making and, if used as such, scarce resources might be used on the treatment of women who are not truly depressed and in need of help. There is some evidence that busy primary care clinicians are inclined not to follow up on the results of screening questionnaires, instead accepting a positive score on a screening questionnaire as a sufficient basis for diagnosis.41
It would be unfortunate if the introduction of a pre-screen further encouraged this practice; before recommending this pre-screening strategy clinically it would be important to determine that it would not be used inappropriately.
Although we assessed the PHQ-2 as a pre-screen it has been recommended for use alone as a screening instrument in general primary care practice.10
It is possible that this instrument, without the use of the EPDS, has sufficient accuracy to identify women at risk (or those not at risk) for depression during pregnancy and postpartum. Currently, the EPDS is well validated and highly accepted in perinatal settings, but little work has justified the use of the PHQ-2 to date. A 3-question approach (essentially the PHQ-2 plus a help question) has been recommended by the British health system’s National Institute for Clinical Excellence guidelines but has never been formally evaluated in perinatal settings.12
In one study, Olson et al42
found that 17% of 1398 mothers answered positively to at least one question of the PHQ-2, although validity was not reported. Recently, Dubowitz et al43
adapted the PHQ-2 into the “Parent Screening Questionnaire.” The authors evaluated this questionnaire among 216 mothers in a primary care clinic compared with the Beck Depression Inventory II completed 2 months later. When a positive response to either
of the 2 questions was considered, the sensitivity was 74%, the specificity was 80%, and the NPV was 95%, but the PPV was only 36%.
An unresolved issue is how many of those who screen positive actually are willing to accept professional help. In one study,44
only 30% of those who screened positive agreed to be contacted for further help. In a second study,45
only 23% of high scorers on the Beck Depression Inventory took up the offer for psychological therapy and 10% agreed to medication. This highlights that screening alone is rarely sufficient for improvements in quality of care, and enhanced detection should be paired with enhanced treatment and follow-up.46
A number of limitations of the current study should be reviewed. First, we use as a criterion measure the EPDS screening instrument rather than the clinical diagnosis of depression. However, the goal of the current analysis was to reduce the burden of screening for depression through a pre-screen step, not to diagnose major depressive disorder. Because the formal diagnosis of depression requires significant diagnostic expertise and the investment of valuable clinical time, the rapid identification of women at risk for depression (and not at risk) is critical to the efficient delivery of maternal care. Another limitation of the current study is that the women included were primarily low income as indicated by the high rate of Medicaid insurance. The findings from this study may not be generalizable to higher-income and other less vulnerable populations. However, women with low incomes have higher risk for depressive symptomatology and are less likely to receive mental health services and so are a particularly important group to target for screening.4,47
One recent study48
found that the sensitivity of the PHQ-2 for a positive EPDS score was lower for women with a high school education or less than for those who went on beyond high school. We did not find any difference in sensitivity across levels of educational attainment in our sample. This difference may be because of our use of a simpler dichotomous yes/no response choice for the PHQ-2 and a follow-up oral review of the items, which reduces concerns of low education- and literacy-related inaccuracy of a written and more complex instrument.11
Finally, although we had complete data for more than 50% of the women eligible for analysis at each of the time points, it is possible that missing data were related to depression risk status. For example, women with more obvious symptoms may have been either more or less likely to have both the pre-screen (PHQ-2) and screening (EPDS) conducted (both were required to be included in the analysis). Because of the protocol-driven system of data collection in this study, we believe that it is unlikely that any such bias was widespread enough to greatly influence our findings.
Based on the results of these analyses it is reasonable for maternal care providers who are currently using or are planning to use the EPDS to use the PHQ-2 pre-screen, with simplified response items (yes/no), as an initial component of a multistep case-finding strategy for depression during pregnancy and postpartum. Although this approach should not overrule clinical concern, women who answer “no” to both of the questions in the PHQ-2 can, with high confidence, avoid the longer EPDS and a diagnostic clinical interview. Women who answer “yes” to either of these items should proceed to the EPDS, followed by an in-depth clinical interview for women who have a positive EPDS (≥13). Although further research is needed, we recommend that the screening process make use of a direct oral interview rather than relying entirely on a written questionnaire to elicit or review screening questions to avoid error caused by low education and literacy.