For baby girls, higher weight and longer length at birth are linked with an increased risk of developing breast cancer.

Researchers from the London School of Hygiene and Tropical Medicine [1] have found that every 0.5 kg increase in birth weight was associated with a 7 per cent increased risk of breast cancer.

Birth length and head circumference were also linked with an increase in breast cancer risk.

This is not the first study to link birth size and breast cancer, though research results have been mixed.

Researchers believe that birth size is an indicator of the prenatal environment, which may be exposing babies to some cancer risk factors, such as the hormone estrogen.

However, these most recent findings are independent of those risk factors.

"Little is known on how the prenatal environment may affect breast cancer risk later in life," lead study author Isabel dos Santos Silva said in a statement. "Further research is needed to unravel the biological mechanisms underlying the birth size-breast cancer association."

The research included data from 32 studies of more than 600,000 women.

For accuracy, the scientists only used birth measurement data from official birth records, which are considered more accurate than information gleaned from surveys or questionnaires.