The study shows mums who pile on the pounds during pregnancy are no more likely to give birth to a baby that develops heart problems in later life than those who remain a healthy weight.
Previous research has reported children whose mothers who were obese or overweight in pregnancy were at greater risk of death or heart-related health problems.
However until now no study has had adequate follow up time to assess the effects on cardiovascular events, such as heart attacks, and mortality in adulthood.
The first study of its kind, published in the journal Heart, found that mothers' weight gain in pregnancy is not linked to increased risk of premature death in their adult children.
Only a very extreme rate of weight gain was associated with increased risk of strokes in the offspring. In these cases adult health and lifestyle factors could mitigate the risk.
Dr Sohinee Bhattacharya and colleagues used data from the Aberdeen Children of the 1950's Birth Cohort to follow-up children whose mothers' weight gain during pregnancy was recorded.
This meant that the impact of lifestyle factors in adulthood could also be accounted for.
Dr Bhattacharya said: "These findings are quite startling because what they show is that there is basically no relationship between mother's weight gain in pregnancy and heart disease, or premature death in adulthood.
"Only in very extreme cases, where the mother had an exceptionally high weight gain, we found a higher risk of stroke in the adult offspring - however once we took the adults' lifestyle factors into account - such as BMI and smoking status, this difference disappeared.
"So this study provides a very important public health message. You can't do very much about your mother's weight gain in pregnancy, but if you lead a healthy life - you can mitigate any effects of this on your risk of having heart disease or dying prematurely.
"How might this impact on clinical practice? Well for the first time, this large scale cohort study was able to show that adult health and lifestyle factors and not early life risk factors played the most important role in determining cardiovascular mortality and morbidity.
"Modifying these risk factors (obesity, smoking, diabetes) would constitute effective preventive strategy irrespective of maternal or early life factors."
Women often say during pregnancy that they are 'eating for two' which has been linked with giving their offspring health problems in later life including heart disease, type 2 diabetes and stroke.
One previous study found overweight mothers had babies with shorter telomeres - which are protective 'caps' on DNA.
Having shorter telomeres is associated with higher risk of disease and a shorter lifespan.