Steinman, whose study is being published in the September issue of the Journal of Reproductive Medicine, said the reason seems to be an insulin-like growth factor, which has been positively linked to both height and twinning.

• 斯汀曼的此项研究结果在《生殖医学》的第九期上发表，他说，这可能和类胰岛素生长因子有关，类胰岛素生长因子与身高和孪生几率呈正相关关系。