早产是导致早产儿近远期并发症的主要因素，尽管某些流行病学的高危因素是早产的主要诱因，但仅有10%的孕妇在妊娠34周之前发生早产。无论是单胎妊娠还是双胎妊娠，在妊娠18～24周常规经阴道超声测量子宫颈长度，以25mm作为截断值，可以起到预测早产的作用。

Preterm labor is the leading cause of neonatal severe short-term and long-term complications.Although some epidemiological high-risk factors are the main cause，preterm labor occurs in only 10% of women who deliver before 34 weeks of gestation.Whether it is singleton or twin pregnancy，the measurement of cervical length can be performed routinely by transvaginal ultrasonography at 18 to 24 weeks of gestation，and cervical length ≤25mm can be used an a cut-off value to predict preterm labor.