It has not only been observed in infants and in newborns, but also in fetuses of 12-14 weeks' gestational age.
不仅婴儿和新生儿有呵欠行为，就连12 - 14周的胎儿也会打呵欠。
The crown-rump length becomes less accurate after 12 weeks in determining gestational age because the fetus begins to curve.
孕12周后，因胎儿身体屈曲，以胎儿顶臀径推算孕龄已不够准确。
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