We found that the two case-finding questions endorsed by the National Institute for Health and Clinical Excellence offered a brief, simple and precise approach for identifying perinatal depression. Negative responses to both questions showed acceptable accuracy for ruling out perinatal depression. For positive responses, the use of an additional question about the need for help improved specificity and the ability to rule in perinatal depression.
This approach has important implications for clinical practice. Use of the case-finding questions should be considered in the context of a triage test, rather than as a replacement test to existing methods of assessment.32
Triage tests are simple and noninvasive, have no wait time and do not aim to improve the diagnostic pathway; instead, they reduce the number of patients who need further assessment. The benefit of using the brief case-finding approach in clinical settings where routine perinatal care takes place is not necessarily to diagnose perinatal depression per se. It would, however, reduce the number of women who need extensive clinical assessment or evaluation with much longer questionnaires, such as the Edinburgh Postnatal Depression Scale6
or the Patient Health Questionnaire-9,33
by more than 50%. The use of good psychometric instruments with acceptable discriminative properties is a necessary but not sufficient step for use in routine practice in larger population-based screening strategies, and the adoption of screening for disorders such as postnatal depression should be based on evidence of benefit derived from randomized trials. In other areas, this has not been shown to be an effective strategy, and screening should therefore not be considered without a wider consideration of the policy implications, costs and benefits.34
The sensitivity of the two case-finding questions in our antenatal and postnatal validation study (100%) was the same as that in a previous postnatal validation study,20
providing further evidence of a simple approach to rule out perinatal depression. The number of false-positive responses to the two questions was substantial in the previous postnatal study and in our study.
Our results should be considered alongside the results of a similar validation study in a primary care population.13
The increased specificity of an additional question about the need for help effectively discriminated between positive screens. In our study, the added question resulted in the number of false-positive responses in the postnatal phase dropping to zero.
Increased specificity compromises sensitivity, however, and increases the risk of depression being missed (false negative). Arroll and colleagues13
reported increased specificity and unchanged sensitivity (96%) when respondents answered either “yes” or “yes, but not today” or “no” to the additional question about the need for help. They identified 12 false-negative cases but did not refer to this issue in their discussion. In our study, the answer to the additional question was dichotomized as “yes” or “no”; sensitivity was reduced, and the number of false-negative cases was 7 in the antenatal phase and 11 in the postnatal phase. Poor discrimination between true-negative and false-negative cases in practice may mean that patients with depression are effectively lost to follow-up. The benefit of the additional question about the need for help was therefore not conclusive in our perinatal sample.
Twenty-six women in the antenatal phase did not complete the diagnostic telephone interview. However, these women did not differ significantly from the 126 who were interviewed in terms of age and ethnic background.
In the postnatal phase, the 52 women who did not respond to postnatal contact were significantly younger, less educated and less likely to be employed than those who returned the questionnaire. This is an important limitation in our sample. In terms of age, it may reflect difficulties surrounding the competing demands associated with the transition to motherhood for younger mothers. In addition, some women may not have responded because of postnatal depressive symptoms.
Implications for future research
Further studies are warranted because our study was limited to the third trimester and first three postnatal months. Studies that involve other perinatal populations, include other trimesters and have longer postnatal follow-up are required. Specific strategies to retain nonrespondents, especially those who are younger and less educated, might be considered. Validation of the case-finding approach among pregnant women who do not speak English and those who are less than 18 years old is needed. Finally, the effect of the questions on outcomes of perinatal care warrants evaluation.
The brevity of the case-finding questions has substantial appeal for the identification of perinatal depression in frontline health care services. In our study, the use of specific case-finding questions had acceptable validity in the perinatal setting. The ability to rule out depression would help to substantially reduce the number of women needing more extensive evaluation of their antenatal and postnatal mental health issues. Identification of perinatal depression is important but represents only the first step. It must be followed by confirmation of the diagnosis and appropriate treatment or referral. Ultimately, the findings of our study may assist the utility of clinical guidelines that advocate the brief case-finding approach for the identification of perinatal depression.