New research at the Coombe Women and Infants University Hospital has revealed that the father's weight can have a significant bearing on a baby's health.
It found that one in six fathers-to-be were obese and half were overweight.
Consultant obstetrician and gynaecologist Prof Michael Turner said that obese fathers are two to four times more likely to have obese children and he said fathers should take better care of their health.
The research shows that both paternal and maternal obesity are associated with a higher birth weight for the offspring.
Up to now, the focus has been on the mother's weight and its implications.
According to the research, just 22% of couples were in the normal weight category, only one in three fathers had a normal body mass index and one in six was already obese, increasing lifetime risks for diabetes and heart disease.
Doctors accurately measured maternal and paternal weight, instead of relying on women and men self-reporting their weight and height.
Women tend to underestimate their weight and men tend to overestimate their height.
Obesity in men increases the lifetime risk for diabetes which may affect a man's ability to support the family.
Obesity in men also affected their fertility.
Previous studies show that maternal obesity has serious implications for mother and baby due to much higher risk of complications including higher induction rate, pregnancy induced hypertension, higher Caesarean rates and an increased risk of diabetes.