Introduction
In light of mounting evidence regarding the importance of
maternal mental health to child health outcomes,1–5 it is
surprising that virtually all studies of maternal mental
health have restricted their focus to the perinatal period
(i.e. pregnancy and the first 12 months postpartum).6 It
has long been considered that women are at an increased
risk of depression during this time, in large part because of
the significant changes associated with the birth of a first
child.7–9 Comparatively, we know very little about the prevalence
and consequences of maternal depression after the
first 12 months postpartum. The fact that few studies
examine maternal mental health beyond the perinatal timeframe
contributes to the view that depression is most
common in pregnancy and soon after giving birth. Counter
to this, two large longitudinal mother and baby cohort
studies—one from Australia and one from Norway—report
a higher prevalence of maternal depression at 18 months
postpartum10 and 5 years postpartum11 than during the
ª 2014 Royal College of Obstetricians and Gynaecologists 1
DOI: 10.1111/1471-0528.12837
www.bjog.org
immediate postpartum period. Another US-based study
found the prevalence of depressive symptoms was highest
in the month after birth (26%), and then remained stable
at around 15% in assessments up to 36 months postpartum.
12 Interpreting the results of these studies is complicated
by the fact that they do not take into account the
timing and impact of subsequent pregnancies and births,
which may trigger episodes of ‘perinatal depression’. There
is also the probability of selective attrition over time in
longitudinal studies, where women most at risk of depression
are the most likely to be lost to follow-up, leading to
under-estimation of the true prevalence of depression in
the population, particularly at later follow-up points. Risk
factors for maternal mental health problems (such as previous
depression, intimate partner abuse, stressful life events
and socio-economic disadvantage) have also been well
examined in the perinatal period, but not in the context of
longer-term maternal mental health.6,13–16
To our knowledge, this is the first longitudinal study of
maternal mental health that takes into account the impact
of subsequent births, and the influence of selective attrition
over time. The aims of the paper are: (1) to describe the
prevalence of depressive symptoms from early pregnancy to
4 years postpartum in a nulliparous pregnancy cohort; and
(2) to assess risk factors for maternal depression at 4 years
postpartum, including subsequent pregnancies and births,
relationship transitions, intimate partner violence and
social adversity.