Kate's morning sickness can distress women for six months after birth
Research to be presented at a conference on hyperemesis gravidarum (HG) will highlight how women suffering from the condition feel acute distress throughout pregnancy and half a year after giving birth.
But the effects seem to pass by 18 months postpartum, according to the study, published in Archives of Women's Mental Health.
The authors wrote: "Women with HG were more likely to report emotional distress compared to women without HG during pregnancy and six months postpartum, but the difference between the groups disappeared 18 months after birth.
"The results suggest that the increased risk of developing emotional distress may primarily be a consequence of HG."
Kate, who is expecting her third child, is again suffering from HG which plagued her during the early stages of her pregnancies when she was carrying Prince George and Princess Charlotte.
The conference on the condition, organised by Pregnancy Sickness Support (PSS) and the British Pregnancy Advisory Service (bpas), will examine the latest reserach into HG and available treatments.
According to PSS, 53% of sufferers have difficulty accessing treatment for their condition, which can lead to dehydration, malnutrition, and hospitalisation.
PSS chairwoman Caitlin Dean said: "Care and treatment options for HG have improved massively in the last few years and research into the condition is finally attracting attention and tentative funding.
"Research to be presented today demonstrates the mental health effect of this condition can be profound and doesn't always end when the baby is born but can persist for years after."
Clare Murphy, director of external affairs at bpas, added: "HG can be an extremely serious condition, and for far too long women were expected to simply 'put up' with their debilitating symptoms.
"Women should have access to the full range of treatments available and above all be trusted and believed when they describe a level of nausea and vomiting affecting their ability to get on with their everyday lives."