According to new research, a stressful pregnancy could damage the unborn child's health for years to come.
The study of pregnant English woman found that going through a major upheaval, such as a bereavement or separation, dramatically raised the odds of their baby suffering ill health by the time the infant turned four.
The link with chronic conditions was particularly strong, with two bouts of severe stress in pregnancy raising the odds five-fold.
The researchers, from the Institute of Psychiatry at King's College London, said it was crucial for the unborn babies' health that pregnant women are supported through stressful events.
The scientists asked more than 150 mothers-to-be who were early in their pregnancy and again just a few weeks before giving birth about any stressful events affecting them, such as a family bereavement, separation, sudden unemployment and a difficult pregnancy.
Four years later, the women were interviewed regarding their children's health, including any illnesses that had led to them visiting their doctor or being admitted to hospital.
This showed a clear link with stress in pregnancy and ill health, with trauma early in pregnancy particularly likely to be linked to asthma or infections such as tummy bugs, the British Association for Psychopharmacology's annual conference heard.
As the babies were not affected by the problems in the mother's life post-birth, researchers believe the health of the baby in the womb is the key factor.
Possible reasons include changes in the mother's hormones or immune system affecting the development of the child's immune defences.
Researcher Jasmin Wertz said that the finding "suggests the stress experienced during pregnancy induces biological changes in the unborn child that render it susceptible to the development of illness later in life," the Daily Mail reported.
With the study also showing high levels of depression among the stressed-out mothers-to-be, Wertz's supervisor, psychiatrist Carmine Pariante said it was important pregnant women got the support they needed.
"Everybody expects you to be happy because you are pregnant - it's very, very difficult to go and say you are depressed. But a pregnant woman who is depressed actually attracts a lot of empathy and sympathy," he added.