Discussion
Our analyses leveraged longitudinal data to examine associations between
maternal psychological functioning and respiratory outcomes in
childhood. Our findings suggest that exposure to postpartum and
recurrent maternal depression are associated with higher risk of wheeze
and asthma in childhood. The observed associations remained significant
after adjustment for a number of important potential confounders and
covariates. We also found that child sex modified the association
between maternal depression and respiratory outcomes; the association
between postpartum and recurrent depression and higher risk of current
wheeze was stronger in females when compared to males.
Prospective birth cohorts examining maternal depression at different
time points in relation to wheeze and asthma development in childhood
have produced mixed results5, 9, 12. A Canadian
population based birth cohort study found that continued exposure to
maternal anxiety or depression from birth into early childhood was
associated with a twofold increase in the risk of asthma at age 7
years5. This is fairly consistent with the results our
study although we observed an association earlier at 48 months (4 years
of age)5. Also in line with our results, Ramratnam et
al. assessed the associations between maternal stress and depression
during pregnancy and early life, and recurrent wheezing utilizing the
Urban Environment and Childhood Asthma (URECA) birth
cohort12 and found an association between cumulative
maternal depression in the first 3 years of life and recurrent
wheezing12. However, we did not find any associations
between prenatal depression and any of our outcomes like previous
studies have reported9, 11. Differences in our
findings may be attributable to our classification of depression (e.g.,
limited only to the prenatal period), the prevalence of our outcome and
sample size.
The assessment of maternal mental health in the first postnatal year
signifies an important critical window as the biological systems of
children are rapidly maturing within the first two years of life, and
may be compromised by exposure to more severe and enduring maternal
mental health problems beyond the first postnatal
year25. A potential mechanism for the observed
relationships between postpartum and recurrent maternal depression and
respiratory outcomes in our study may be through dysfunction of the
hypothalamic pituitary adrenal (HPA) axis. McLearn et al reported
that depressed women had reduced odds of playing or talking with their
infants 4, 26 and animal studies have reported that
decreased maternal attention enhanced hypothalamic-pituitary-adrenal
(HPA) axis stress response in their offspring4, 27,
28. These interactions could be associated with symptoms of distress
and raised cortisol levels in infants4, 29 and
recurrent infections and asthma in preschool children4,
30. Additionally, previous studies have reported that maternal
postnatal depression and anxiety strongly correlate with infant cortisol
levels31, 32. HPA dysregulation and the production of
proinflammatory cytokines could increase children’s susceptibility and
sensitivity to persistent maternal distress and other co-occurring
sources of chronic stress throughout the early childhood
period32, 33. As a result, this could manifest as high
allostatic load or a blunted cortisol response, increasing children’s
vulnerability for the development of asthma5, 34, 35.
There is also growing evidence that the effects of maternal mental
health on children’s health outcomes may differ by sex. Previous studies
have shown that the prenatal environment seems to impact males more than
females whereas, females may be more susceptible to the postnatal
environment. Lee et al. examined the associations between pre- and/ or
postnatal stress and children’s asthma, along with their effect
modification by sex in a prospective cohort study utilizing the Asthma
Coalition on Community, Environment, and Social Stress (ACCESS)
project10. Increased maternal stress during the
postnatal period was more strongly associated with higher odds of asthma
in females10, which is in line with our study
findings. Previous studies have also shown that females may be more
adaptive in utero, though at a cost of adverse health effects later in
life10, 36. As a result, the usual increase in stress
reactivity in females exposed to in utero stress could explain their
greater vulnerability to stress- induced health effects after
birth10, 36. Alton et al concluded that wheeze at 3
years of age was nearly 5 times more likely in girls of mothers who
experienced postpartum depression, which is fairly similar to the
results seen in this paper4.
Utilizing the PROGRESS cohort in Mexico City is an important
contribution to this growing body of work as the prevalence of postnatal
and recurrent depression varies widely across cultures and geographic
regions10. This study has several strengths, which
include a prospective study design, large urban population and sample
size of participants, and validated methods for measuring maternal
depression and childhood respiratory health outcomes. Additionally, we
had the ability to adjust for important environmental factors, including
prenatal and early life exposure to PM2.5.
Our study also had some limitations. Asthma and wheeze outcomes are
based on caregiver report which might be subject to recall bias.
However, given the logistical and technical complexity of objectively
recording asthma and wheeze in children, caregiver-reported wheeze and
asthma is commonly utilized in moderate- to larger-sized population
level studies. The ISAAC survey has been validated internationally and
in Spanish-Speaking populations37. Future work should
examine more objective respiratory outcomes, such as lung function as
these children continue to be followed. As with any observational study,
we cannot rule out residual confounding due to unmeasured factors that
may influence depression and wheezing/asthma in childhood. PROGRESS is
composed of urban, low-income families and our results may translate to
other populations who face similar rates of depression. Research into
the respiratory childhood health risks of maternal depression may be
particularly clinically relevant in countries with high maternal
depression such as the United States where 1/8 women experience symptoms
of postpartum depression23.