Normative data suggests that, before 30 weeks, accelerations of 10 bpm sustained for 10 seconds are oberserved more commonly than accelerations of meeting the 15bpm, 15 second-criteria.

• 依据标准数据，对于孕不到30周的胎儿，更常见的做法是按每10秒增加10次心跳的标准进行观察，而不是按每15秒心跳增加15次为标准。