B. High prostaglandin level
Among the options provided, high prostaglandin levels are not typically considered a contributing factor to nausea and vomiting in early pregnancy. Prostaglandins are chemical compounds that play a role in various bodily functions, including inflammation, blood flow, and uterine contractions, but they are not commonly associated with causing nausea and vomiting during pregnancy. The other options, A, C, and D, are indeed considered contributing factors to these symptoms in early pregnancy due to the hormonal changes that occur.