Mothers who have had higher levels of the male hormone testosterone while they were pregnant find it hard to breastfeed newborns, suggests a new Norwegian study.
The research also questions the health benefits of breast milk over formula.
Researchers at the Norwegian University of Science and Technology studied 180 pregnant women to come up with their findings.
The group examined included women who were likely to give birth to small babies due to high levels of testosterone.
Even after considering factors like age, education and smoking, researchers found a direct relationship between low breastfeeding rates at three and six months and higher testosterone levels.
Reasons for high testosterone levels during pregnancy can be numerous after the placenta, the site of hormone production, comes into action.
And according to scientists testosterone may hamper the development of glandular tissue in the breast, thereby affecting breastfeeding ability.
"Basically a mother who finds she has difficulty shouldn't feel guilty - it probably is just the way it is, and her baby will not suffer for being fed formula milk," the BBC quoted lead researcher Professor Sven Carlsen, as saying.
"A mother should do what makes her happy."
Taking about the benefits of breast milk and formula milk he said: "These health differences are really not so significant in any event.
"When you look at the epidemiological studies and try to strip away the other factors, it is really hard to find any substantial benefits among children who were breastfed as babies."
The study has been published in Acta Obstetricia and Gynacologica Scandinavica.