"Stressed mothers-to-be face an increased risk of giving birth to a child who will develop ADHD or heart disease later in life," the Mail Online reports.
However, the new study it is reporting on did not look at long-term outcomes in children, such as attention deficit hyperactivity disorder (ADHD), only at stress hormone levels during pregnancy.
This Swiss study involved 34 healthy pregnant women. Levels of stress hormones were measured from their saliva and the amniotic fluid around the baby during an amniocentesis – a test for genetic conditions.
Women who reported being under stress had higher levels of stress hormones in the amniotic fluid. Higher levels of stress hormones in the amniotic fluid were associated with lighter and smaller babies, but they then grew faster so that there was no difference by the time they were born.
It is difficult to draw any firm conclusions from this small study. It certainly does not show that stress during pregnancy causes ADHD.
The Mail Online provides a useful list of things you can do to reduce stress during pregnancy, and maybe "avoid reading baseless health scare news stories" should be added to that list.
The study was carried out by researchers from the University of Zurich and was funded by the Swiss National Science Foundation. The study was published in the peer-reviewed medical journal Stress.
The Mail Online reported the study at length but did not explain the numerous limitations of this type of research.
Also, its headline was both inaccurate and needlessly stress-inducing. The study does not contain a single mention of ADHD or heart disease.
The researchers wanted to see if acute or chronic levels of maternal stress affected the development of the foetus.
Using the amniotic fluid samples, the researchers were also able to measure the levels of stress hormones such as corticotropin-releasing hormone (CRH). They also took saliva samples and used questionnaires.
Unfortunately the tests on amniotic fluid were only taken once which is a major limiting factor when analysing the results.
We don't know if the levels of stress hormones in the amniotic fluid changed over time – either in response to acute stress, as measured with the maternal saliva results, or with stress over a longer period, as reported in the maternal questionnaire.
At best this type of study can show associations between factors. But it cannot prove that stress hormone levels affect development or birth weight as it does not take into account all the other potential influences such as genetic make-up.
It also cannot prove that stress hormone levels during pregnancy cause ADHD.
The researchers recruited 34 healthy pregnant women in their second trimester aged between 18 and 45. All were having an amniocentesis and were paid 200 Swiss Francs and given a gift set of skincare products for participating in the study.
Women were excluded from the study if they had become pregnant through IVF, had any medical or psychiatric conditions, took medication, smoked or drank more than one unit of alcohol per week during pregnancy or had a restrictive diet such as being vegetarian or vegan.
On the day of the amniocentesis, an ultrasound scan was also performed to determine the gestational age of the baby and to estimate weight and size.
Acute stress was measured using repeat testing of saliva samples for stress hormone levels one minute before the procedure and then, 10, 20, 30, 45 and 60 minutes after it. The women were also interviewed by clinical psychologists who asked them to rate their anxiety levels 40 minutes before, 10 minutes before and 20 minutes after the amniocentesis.
After the women had received the results of the amniocentesis, they were asked to fill out a questionnaire to determine their chronic level of stress in the previous three months according to their amount of "social overload". This measures the amount of time the women spent looking after excessive demands from others, such as:
The researchers then received information about the size and weight of the babies when they were born. They analysed the results to take into account the gestational age at amniocentesis and birth, number of weeks between the procedure and birth and the mother's body mass index (BMI).
All 34 women had a normal amniocentesis result and gave birth to a healthy child.
The saliva samples showed stress hormones increased around the time of the procedure and then reduced afterwards in accordance with reported maternal stress.
For chronic stress, women who scored higher for social overload had higher levels of stress hormones in the amniotic fluid.
Higher levels of stress hormones in the amniotic fluid were associated with a smaller and lighter foetus than average when measured at the amniocentesis.
But there was no association between the level of stress hormones in the amniotic fluid and weight, size or gestational age at birth.
The researchers concluded that their results "suggest that chronic, but not acute maternal stress affects fetoplacental CRH." They also say that they "confirm recent assumptions that CRH plays a complex and dynamic role in the mechanisms of fetal growth."
Despite the media headlines and scaremongering, ADHD is never mentioned in the study.
The researchers cite animal studies which suggest increased levels of the stress hormone cortisol may speed up development before birth. They say this may prevent proper maturation of the organs and so could cause any "mental or physical illness" occurring later in life, such as ADHD.
However, for ethical reasons, the levels of stress hormones in the amniotic fluid were only measured once in this study. This means we are unable to tell whether they changed during periods of maternal stress or during the pregnancy.
Though the researchers say that the levels were higher in women who reported higher social overload, this was based on such a small sample of women that we cannot say for sure this effect would be seen in all pregnant women. We also have no information on whether any of the babies who were healthy at birth developed any problems during childhood, such as ADHD.
Other limitations of the study include the fact that measures of chronic maternal stress relied on accuracy of reporting in the questionnaire and only looked at stress due to caring for other people. This would not have taken into account many other types of stress which women may experience during pregnancy. The average age of women in the study was 37 and it may also be that the findings may apply to younger pregnant women.
In conclusion, this study does not show a link between stress during pregnancy and ADHD.
It's not uncommon for women to feel anxious or stressed at some points in pregnancy. If feeling stressed is affecting your everyday life, mention it to your midwife.
Read more about feelings and emotions during pregnancy.