Alcorn et al. (Reference Alcorn, O'Donovan, Patrick, Creedy and Devilly2010) was a prospective longitudinal study of the prevalence of post-traumatic Stress Disorder (PTSD) resulting from childbirth events. One of the features of this work was not only to estimate the absolute prevalence of PTSD, but to adjust these estimates for pre-existing PTSD symptomatology and other more common postnatal symptomatology, such as depression and anxiety. It is of course possible if not probable, that these affective expressions are co-morbid or predominantly represent the same underlying post-traumatic sequelae.
We are grateful to Matthey's (Reference Matthey2011) Letter for the opportunity to further demonstrate how robust our findings are in relation to post-traumatic stress following childbirth. Using an Edinburgh Postnatal Depression Scale (EPDS) cut-off of 14 or more we obtained PTSD rates, uncompromised by antenatal depressive symptomatology, of 3.1% at 6 months postpartum. We interpreted Matthey (Reference Matthey2004) and Murray & Cox's (Reference Murray and Cox1990) terminology in the same fashion. To be precise, as we were excluding those women with elevated depressive symptomatology, the lower cut-offs we used were more conservative in deriving adjusted PTSD rates. We did indeed use the more conservative cut-offs of 9 (possible; instead of 10) and 12 (probable; instead of 13) for postpartum depression, and 12 (possible; instead of 13) and 14 (probable; instead of 15) for antenatal depression. In fact, this interpretation of their terminology (Murray & Cox, Reference Murray and Cox1990; Matthey, Reference Matthey2004) is so widespread that Matthey and his colleagues (Reference Matthey, Henshaw, Elliot and Barnett2006) published a clarification, admitting that in previous publications even they had ‘been remiss in this respect’ (p. 309). On closer examination of Matthey's (Reference Matthey2004) paper, we do take issue with the derivation of these cut-offs [i.e. Jacobson & Truax's (Reference Jacobson and Truax1991) method was advocated, yet Matthey used unusual test–retest reliability scores and departed from their method for the clinical cut-offs]. Nonetheless, we see value in Matthey's (Reference Matthey2011) desire to apply the more conservative cut-offs for depression, which naturally make for a less conservative adjustment for PTSD.
As can be seen in Alternate Table 3, adjusting to Matthey's recommendation does not change the 3.1% figure at 6 months follow-up. It also makes only minimal difference at earlier intervals (i.e. increasing the instances of PTSD by only one person in earlier periods). PTSD at 6 months postpartum, unadjusted for antenatal anxiety and depression symptomatology, naturally stays at 5.8% as per our original Table 1 (Alcorn et al. Reference Alcorn, O'Donovan, Patrick, Creedy and Devilly2010).
Alternative Table 3. Adjusted prevalence of post-traumatic stress disorder (PTSD), partial PTSD, and PTSD-like symptoms postpartum after controlling for prior PTSD phenomenology and clinically significant depression and anxiety during pregnancy
Group 1, Group 2, and Group 3 Partial PTSD Group 1 met all PTSD criteria except for one or two of the necessary three criterion C symptoms. Group 2 met all PTSD criteria except for one of the necessary two criterion D symptoms. Group 3 met all PTSD criteria except for one or two of the necessary three criterion C symptoms, and one of the necessary two criterion D symptoms. Partial PTSD-like symptom groups met the same criteria as partial PTSD except the criteria for a traumatic birth event were not met (i.e. a non-criterion A event).
Adjusting to the higher cut-offs for postpartum depression symptomatology, we present Alternate Tables 4 and 5 here, although we only present the relevant depression sections. From Alternate Table 4 it can be seen that the new cut-offs increase the incidence of possible depression, and decrease the incidence of probable depression at 6 months postpartum. This leads to an overall difference of a decrease of possible and probable depression of only 1.8%. From Alternate Table 5, at 6 months postpartum, the new cut-offs create a small decrease of possible depression and a small decrease of probable depression. This leads to a total decrease in possible and probable depression of only 2.06%.
Alternative Table 4. Rates of clinically significant symptoms of depression and anxiety postpartum following a traumatic birth event with and without post-traumatic stress disorder (PTSD) and partial PTSD
Partial PTSD Group 1 met all PTSD criteria except for one or two of the necessary three criterion C symptoms. Group 2 met all PTSD criteria except for one of the necessary two criterion D symptoms. Group 3 met all PTSD criteria except for one or two of the necessary three criterion C symptoms, and one of the necessary two criterion D symptoms.
Alternative Table 5. Rates of clinically significant symptoms of depression postpartum following a non-traumatic birth event with and without post-traumatic stress disorder (PTSD)-like symptoms
Partial PTSD-like symptoms Group 1 met all PTSD criteria except for criteria A and one or two of the necessary three criterion C symptoms. Partial PTSD-like symptoms Group 2 met all PTSD criteria except for criteria A and one of the necessary two criterion D symptoms. Partial PTSD-like symptoms Group 3 met all PTSD criteria except for criteria A and one or two of the necessary three criterion C symptoms, and one of the necessary two criterion D symptoms.
In light of these marginal differences, our growing doubts concerning the EPDS cut-offs at a more general level, and the strong evidence in favour of PTSD following childbirth being a valid disorder; our conclusions have not changed. Indeed, on further reflection, we can find no cause to amend any of our original interpretations or recommendations.
