Postnatal depression is routinely screened for and widely accepted as a serious risk to both the mother and the baby’s development. Most people don’t realize however is that depression during pregnancy is just as common. It could be caused by a serious life event such as the death of a close relative, a continuation of depressive symptoms from before pregnancy, or could occur for no apparent reason at all. It is estimated that around 30% of women experience a bout of depression whilst pregnant. That’s huge. So why don’t we know more about it? A likely explanation is because of the social pressures placed on pregnant women: they are expected to be glowing; this is supposed to be the happiest time of their life.
So why should we care more about mental health in pregnancy, it doesn’t affect the baby right? Wrong. Recent research has shown that depressed pregnant women are at increased risk of having a premature and low birth weight baby, which is linked to diabetes, obesity and heart disease in adulthood. Further, the infant is also more likely to have behavioural and emotional problems in childhood, and a psychiatric diagnosis in adulthood. This was evident when postnatal depression and genetics were accounted for, which indicates that something is going on biologically within the womb when a mum is depressed, which causes these adverse infant outcomes.
So how exactly does low mood during pregnancy affect the baby’s development? Well, that’s the million-dollar question in this field, and we currently don’t have a good enough answer. A popular theory at the moment is that depression alters the mum’s stress-response system, which is called the Hypothalamic-Pituitary-Adrenal (HPA) axis. The HPA axis is activated when a person is stressed, and results in the release of cortisol, the main stress hormone, into the blood. The current theory is that this system is over-active in depressed pregnant women, so more cortisol is released into the blood than normal. This excess cortisol then crosses the placenta, enters the fetal blood circulation and alters the development of the baby’s HPA axis so that it is permanently over-active. There is already some evidence to support this theory: infants born to mothers who were depressed whilst pregnant have over-active stress
responses. Also, infants with some behavioural and emotional problems, and adults with psychiatric disorders have
over-active stress responses. What we don’t know for certain is how, or even if, the HPA axis of depressed pregnant women is altered.
This is where my research comes in: I am attempting to fill the gap in this theory by investigating how the HPA axis of depressed pregnant women may be different from non-depressed pregnant women. I am currently recruiting depressed and non-depressed mums-to-be to take part in a study which is examining the diurnal (daily) pattern of cortisol release, and also how the HPA axis responds to mild stress. To do this, my participants watch a short video showing clips of babies crying, which induce a small amount of stress. Before and after watching this video, participants produce saliva samples, from which I measure the levels of cortisol, and see how the HPA axis may be different in the depressed and non-depressed women. Then, 2 months their babies are born, I also collect saliva samples from the infants before and after their first injections. This also allows me to see whether depressed mothers with over-active stress responses during pregnancy also give birth to infants with over-active stress responses.
Understanding how depression changes pregnancy physiology is extremely important. Depression during pregnancy somehow affects the developing baby, so understanding the underlying physiology is the first step towards identifying an effective intervention. It is estimated that 20% of the behavioural and emotional difficulties experienced by children, and a significant number of psychiatric disorders in adults, can be attributed to their mother's depression whilst pregnant. So, if we can develop a new prenatal intervention for depression (because there are also worries about prescribing antidepressants in pregnancy), we could potentially prevent the onset of these disorders in thousands of individuals, before they are even born.