Q: How and why do you think that the stress experienced by mothers during pregnancy can affect the unborn child?
A: We found two possible mechanisms by which maternal stress during pregnancy could affect the development of the baby. One is if the mother is very anxious or stressed while she's pregnant, there's reduced blood flow to the baby through the uterine arteries, the main source of blood and nutrition for the baby, and this could explain why the baby doesn't grow as well and also set up a secondary stress response in the fetus. Second, we have shown that if the mother has high levels of cortisol, the main stress hormone, so does the fetus. It seems that enough cortisol crosses the placenta from the mother to the fetus to actually affect fetal levels. So if the mother is stressed, her cortisol goes up, so does the cortisol level in the fetus. This in turn could well affect the development of the brain and the future stress responses of the baby.
Q: In what ways could a mother's cortisol levels affect the baby?
A: We're realising now that the development of the brain is sensitive to the hormones that are around it, and particularly cortisol, just as it is to alcohol, smoking or other drugs. And that the cortisol level that the fetus experiences will set a number of brain receptors to cortisol and this in turn will set later responses. It's very important that we learn to understand what's the optimal development here because it's much easier to change things while they're being made than to try and change them later. If, for example, it turns out that high levels of maternal stress—or even different methods of delivery, really have adverse affects on the development of the baby's brain, it's important to understand more about this and address it at this period, than have children with behavioral problems more difficult to resolve later.
Q: What effect does different methods of delivery have on a newborn's stress response?
A: The most stressful thing that happens to any baby is being born, compared to anything else that goes on. We're very concerned about the experience of the mother during pregnancy and her pain and a lot's done for the mother but very little attention is paid to the baby. But we now know from looking at cortisol levels in the umbilical cord immediately after birth that birth is very distressful for the baby and different types of delivery induce different levels of stress. We've found that babies born by elective cesarean had the lowest response. Those born by normal vaginal birth had an intermediate response. And those born by assisted delivery, such as with forceps or suction, had the biggest response.
We then looked at eight-week-old babies who'd been born by these different methods and looked at their stress responses to a vaccination by measuring saliva cortisol. This showed that, at least for the first eight weeks, delivery method affects the behavior, the stress response of the baby. And it may well have a much more long-term effect, so that's the next thing we need to study.
But we can't assume that the least stressful delivery is the best for the child. I think it's likely that a normal vaginal delivery is actually best. Because we know that babies born by elective caesarean, for example, don't breathe so well just after they're born. It's likely that the amount of stress associated with a normal vaginal delivery does get the baby best adjusted to the outside world. But what I think we can be concerned about is that some assisted deliveries put a very high level of stress on the baby and this may be damaging.
Q: What are you looking at with your current research?
A: Well all the evidence we have so far suggests that the very early period is important for the long-term stress responses. But we need much more evidence to actually pinpoint what is exactly going on; when during pregnancy does stress matter, what degree of stress becomes harmful and so on. Our current research is to try and find out more about the long term affects of stress in pregnancy on the behavior of a child, and we're using about ten thousand women who've been followed through pregnancy to actually determine properly whether pre-natal stress as opposed to post-natal does have an effect on the child. We also intend to follow up children who've been born by different methods up to the age of one or two and see how long the different types of delivery actually affect their stress responses. We know it affects up to eight weeks, but does it carry on for one year, two years or for life?
Q: Many women feel the need to return to work as soon as possible after having a baby, even working at home. What effects might the stress of juggling work and early motherhood have?
A: We don't know enough in terms of our changing lifestyles and their effect on the future generation. But I think we do need to do a lot of research to actually find out what our changing lifestyles are doing to us and particularly to our children.
It's clear that from birth, babies are very sensitive to their mother's feelings. If the mother is stressed or depressed, the baby picks up on it, can cry more, [and] you get a bad interaction. We know that if mothers are depressed in the very early weeks or months, this often has an effect on the interaction with the child. And this in turn has long term harmful effects on the development of the child. The children have more behavioral problems, more cognitive problems, the boys may have a lower IQ. So the very early mother-baby interaction is very important for the later development of the child. And a very stressed mother can interfere with this. Alternatively, the good news is that very good mothering early on can actually help to undo some of the possible damage that might have been caused during the fetal period. So that the whole system is very plastic both for benefit and harm in this very early period.
I think that all our research is making us more aware that very early mothering is absolutely crucial. And that perhaps women should take a bit of time off work, certainly in the early months, to make sure that they get a good relationship going with their baby. I think that this has implications for society as a whole and governments, that we need to give women time to establish the relationship with their child, help them to be in as good an emotional state as possible, while they have a new baby. And then go back to work later. I think that politicians maybe have a role to play here, that they ought to be aware that for the sake of the emotional health of future generations, encouraging mothering and parenting is very important.