According to his analysis, modern women do fewer arduous tasks, and their muscles are less flexible. Because of such factors as marrying older and giving birth later in life, difficulties and impediments in giving birth are increased.
他分析，除了因現代婦女勞動量減少，以致肌肉彈性較差；晚婚、高齡生育的趨勢等因素，提高自然產的困難度或難產的比例之外，其他大多可歸類為心理因素。