Dads-to-be who are in poor health have been linked to an increased risk of ectopic pregnancies and pregnancy loss, a new study by Stanford University has found.
Researchers looked at close to one million pregnancies in the United States conceived between 2009 and 2016, assessing the health of the father-to-be for each.
Published in the Human Reproduction journal, the study found pregnancies where fathers had three or more medical conditions such as obesity, high cholesterol or high blood pressure, as well as poor general health, were at higher risk of loss.
Of these, more than a quarter of pregnancies were found to be linked to ectopic, miscarriage or stillbirth.
Comparing dads-to-be in poor health with those who did not have any metabolic syndromes, they found the risk was increased by 10 per cent for men with one syndrome, 15 per cent for two and 19 per cent for three or more.
The father's age was also found to be a contributing factor.
The data was taken from US insurance claims for 958,804 pregnancies. Other diseases which were also looked at included chronic obstructive pulmonary disease, depression and heart disease.
Factors affecting the mums, including age, weight, health and the smoking status of both parents were also taken into account.
Stanford University School of Medicine Associate Professor Michael Eisenberg said it showed the health of a pregnancy was not only tied to maternal health.
"It's been known for some time that the health of mothers has an impact on the developing foetus and events at the time of birth," he said.
"This is the first study to suggest that pregnancies sired by men with increasing numbers of medical conditions are at higher risk of ending in miscarriage, ectopic pregnancy or stillbirth."
"In the group of men we studied, the risk of losing the pregnancy was 17 pe cent in couples where the father had no components of the metabolic syndrome but increased to 21 per cent in couples where the father has one metabolic syndrome component, 23 per cent where he has two, and 27 pe cent where he has three or more."
Eisenberg continued to say the study can't prove a dad to be's poor health caused pregnancy loss, it did show a link.
"We hypothesise that the father's health and lifestyle could adversely affect the genetic make-up and expression in the sperm, and that this may alter how well the placenta functions," he continued.
"If the placenta isn't working properly then this could lead to the pregnancy losses that we observed; for instance, we know already that paternal smoking and diet can affect sperm quality."
Researchers said more studies would need to be undertaken to better understand the possible associations, and that pre-conception counselling should also include dads-to-be.