Despite advances in understanding the causes of major depression, the predictors of antenatal and postpartum depressive symptoms remain poorly understood. Major depression in women is associated with poor social support, marital conflict, adverse life events, and low maternal education.⁶ Poverty is a powerful predictor of major depression, with incidence rates two to three times higher among lowest socioeconomic groups.^7,8 Several stressors associated with major depression also predict depression during the childbearing year. Primary among these are adverse life events and poor social support.^9,10,11,12

There is more debate, and less data, with regard to sociodemographic risk factors for antenatal and postpartum depression. Although several studies report no association of socioeconomic position with antenatal and postpartum depression,^{13,14,15,16,17,18} others conducted in impoverished areas report depression rates as high as 25% during pregnancy and 20% or more postpartum.^11,19,20 Large epidemiological surveys have shown that white persons and Hispanics may be more vulnerable to major depression uncomplicated by other illness, while black persons are especially prone to comorbid depression.^21,22,23 Almost no studies, however, have examined how antenatal and postpartum depression vary across racial and ethnic groups, and the extent to which such variation is explained by socioeconomic position. We determined to investigate sociodemographic predictors of antenatal and postpartum depressive symptoms in a large obstetrics practice.

Of 2128 Project Viva participants who delivered a live infant, 1662 (78%) completed a mid‐pregnancy questionnaire that assessed history of depression as well as current depressive symptoms with a 10 item Edinburgh postpartum depressive symptoms scale (EPDS).²⁶ At six months postpartum, 1278 respondents (77% of the cohort that completed the mid‐pregnancy questionnaire) completed a second EPDS.

We chose the EPDS because it has been validated for both antenatal and postpartum use.^26,27,28 The EPDS focuses on cognitive and affective symptoms, avoiding the inflation of prevalence by physical symptoms (such as fatigue and physical discomfort) typical of normal pregnancy and the postpartum.^9,29 An EPDS score above 12 indicates probable depression.^29,30,31 Validation of the EPDS against diagnostic clinical interviews indicated a specificity of 78% and a sensitivity of 86%.²⁶ While a score of more than 12 on the EPDS does not confirm depression, factors that predict an EPDS score above this threshold probably predict clinically significant depression.

We measured history of depressive symptoms before pregnancy with the question, “Before this pregnancy, was there ever a period of time when you were feeling depressed or down or when you lost interest in pleasurable activities most of the day, nearly every day, for at least 2 weeks?” There were 309 women (19%) who endorsed this question. A history of depression required an endorsement of the symptom question plus either an indication that she saw a health care professional who said she was depressed or an indication that a health care professional had prescribed her a medication for depression. By this definition, 185 (11%) women had a history of depression. Concerned that women with lower socioeconomic status might be less likely to receive professional diagnosis or treatment of depression, we also considered history of depressive symptoms without treatment or diagnosis.

We measured by interview and questionnaire risk factors for depression. Maternal age, race/ethnicity, immigrant status, household income, education, maternal employment status, cigarette smoking, pre‐pregnant body mass index (kg/m²), partnership status, and pregnancy intention/wantedness were recorded at enrolment, typically in the first trimester. Pregnancy intention/wantedness was assessed with the question: “Regarding this pregnancy: (a) I was actively trying to become pregnant; (b) I was not actively trying, but I was glad to become pregnant; (c) I wanted to be pregnant someday, but not now; or (d) I did not want to be pregnant now or at any time in the future”. Because of small numbers, we collapsed both “not now” responses into one category that represented 5% of respondents. As teen motherhood and childbearing before the typical age of college graduation were rare in this cohort, we considered as the youngest age group mothers under the age of 23 years (74 participants, or 4% of the cohort). We chose this age cut off point because it represented the age at which a woman might bear a child after having completed four years of post‐high school education. Social support was recorded at mid‐pregnancy, using short questionnaire scales that measured emotional and material support from a partner and, separately, from family or friends.³² Offspring birth weight was extracted from hospital delivery records. At six months postpartum, when the EPDS was readministered, we again recorded partnership status, body mass index, cigarette smoking, household income, financial hardship, maternal employment, as well as resumption of menstrual cycles, breast feeding, social support, postpartum physical symptoms, and quantity of maternal and infant sleep. Postpartum financial hardship was defined as a “no” response to any of the following items, “Since your baby was born, have you always had enough money to: (a) buy infant formula; (b) buy baby food; (c) buy nappies (diapers); (d) buy food; (e) pay rent or mortgage.” We used multiple imputation to account for missing independent variables.³³ This study was approved by the human subjects committee of Harvard Pilgrim Health Care.

Although our study is one of the first to report a higher prevalence of antenatal depressive symptoms among minority and young mothers, these associations were largely explained by differences in income, partnership status, and pregnancy intention. We saw a roughly 30% higher prevalence of antenatal depressive symptoms among women with household incomes below $40000, although this did not reach statistical significance. However, the higher risk is consistent with several studies^20,35,37 that have reported high prevalence of antenatal depression among women of lower socioeconomic position. We also found a twofold increased risk of antenatal depressive symptoms with unwanted pregnancy, which we believe has not been previously examined. By far the most powerful risk factor for depressive symptoms during pregnancy was a history of prior depression, which conferred a fourfold increased risk of antenatal depressive symptoms, similar to that reported in a small study of Norwegian mothers.¹

Few studies have examined race/ethnicity as a risk factor for postpartum depression. As with antenatal depression, the higher prevalence of postpartum depressive symptoms that we saw among minority mothers was explained by financial hardship. Although some studies report no associations of postpartum depression with socioeconomic position,^11,39 others have found that financial difficulties,^19,29 unemployment,^11,38 or low education³⁶ are more prevalent among women with postpartum depression. We saw a nearly threefold increased risk of postpartum depression among mothers who had low birthweight infants. One study reported increased risk of postpartum depression with poor infant health,³⁶ but another found reduced risk of depression among women who had delivered before term.²⁹ The single strongest risk factor for postpartum depressive symptoms was depressive symptoms during pregnancy, as has been seen consistently.^34,40

To the extent that depressive symptoms before, during, and after pregnancy represent a consistent underlying depressive syndrome, it is possible that depressive symptoms preceding pregnancy might increase social and economic risk (such as unemployment or lack of a partner); if this were the case, these social and economic risks might seem as spurious “predictors” of antenatal and postpartum depression. To our knowledge, no study has examined whether these risk factors predict depressive symptoms among women with no history of depressive symptoms. Lack of a partner and unwanted pregnancy remained associated with antenatal depressive symptoms among women with no history of depressive symptoms, suggesting that the risks associated with partnership status and pregnancy intention are not spurious artefacts of an antecedent depressive symptoms. For postpartum depressive symptoms, financial hardship was a risk factor whether or not women had experienced prior depressive symptoms, suggesting that poverty precedes postpartum depression, rather than the alternative that depression leads to poverty.

This study had several limitations. Chief among these is our reliance on a self reported screen of depressive symptoms, rather than clinician diagnosis. Although the EPDS has been validated in a broad range of populations,⁴¹ it remains possible that cultural and/or economic factors may have caused women to over‐report or under‐report depressive symptoms. Social desirability bias may particularly affect minority⁴² and lower socioeconomic participants,⁴³ leading them to under‐report symptoms of depression,⁴² and us to underestimate associations between these factors and depressive symptoms. The timing of exposures and the onset of depressive symptoms is not established for every exposure; in particular, the examination of social support and depression is effectively cross sectional and should be interpreted with caution (as in most other studies). While 23% of the cohort who responded to the mid‐pregnancy questionnaire did not return the postpartum questionnaire, the proportion responding was similar among those with (75%) and without (77%) depression mid‐pregnancy. This suggests that non‐response neither substantially reduced our estimate of the prevalence of depression, nor created bias in ascertaining predictors of depression. If anything, the higher loss to follow up among minority and disadvantaged mothers might have caused us to slightly underestimate associations between lower socioeconomic status and depressive symptoms.