In the study, pregnant rats given caffeine had offspring with lower birth weights, altered growth and stress hormone levels and impaired liver development.

Published in the Journal Of Endocrinology, the findings indicate the equivalent of two to three cups of coffee may alter stress and growth hormone levels.

It suggests this is done in a manner that can impair growth and development and increase the risk of liver disease in adulthood.

The researchers point to previous studies that suggest prenatal caffeine intake of 300mg a day or more in women, about two to three cups of coffee, can result in lower birth weights.

Animal studies have further suggested prenatal caffeine consumption may have long-term effects on liver development with an increased susceptibility to non-alcoholic fatty liver disease.

Researchers say the underlying link between prenatal caffeine exposure and impaired liver development remains poorly understood.

Professor Hui Wang and colleagues at Wuhan University in China, investigated the effects of low doses, the equivalent of two to three cups of coffee, and high doses, the equivalent of six to nine cups of coffee, of caffeine, given to pregnant.

They found the offspring exposed to prenatal caffeine had lower levels of a liver hormone, insulin-like growth factor (IGF-1), and higher levels of the stress hormone corticosteroid at birth.

Dr Michelle Bellingham, member of Britain's Society for Endocrinology, said: "While this is an interesting and extensive study which attempts to increase our understanding of how caffeine can affect foetal development ... We must bear in mind that these results are in rats, in which caffeine may not have exactly the same effects as in humans due to inherent species differences."

Australian Associated Press