Hunt Carl E
Uniformed Services University of the Health Sciences, Bethesda, MD 20892, USA.
Semin Perinatol. 2006 Apr;30(2):73-6. doi: 10.1053/j.semperi.2006.02.005.
Late preterm infants (34-37 weeks postmenstrual age at birth) are intermediate between less mature preterm infants and infants born at 38 weeks or more in regard to autonomic brain stem maturation. Ventilatory responses to CO(2) in preterm infants born at 33 to 36 week are significantly higher than in infants born at 29 to 32 weeks both at 3 to 4 and 10 to 14 days postnatal age, but do not differ from full-term reference levels. The ventilatory response to hypoxia in preterm infants is biphasic; initial transient hyperventilation is followed by a return to baseline and then a decrease below baseline. In infants born at 32 to 37 weeks, parasympathetic maturation appears significantly less than in full-term infants based on diminished increases in high frequency heart rate variability in quiet sleep, suggesting that late preterm infants are still more susceptible to bradycardia than full-term infants. Both the presence and severity of apnea of prematurity progressively decrease the higher the postmenstrual age. Late preterm infants, however, are still at risk, with prevalence rates as high as 10% compared with about 60% in infants born at <1500 g. The incidence of apparent life-threatening events is more common in preterm infants (8-10%) than full-term infants (1% or less). In the Collaborative Home Infant Monitoring Evaluation studies, the frequency of conventional and extreme events in near term infants is intermediate between preterm infants <34 weeks at birth and full-term infants. The relative risk for at least one extreme event in late preterm infants is increased (5.6 and 7.6, respectively, P < 0.008) compared with full-term infants and remains higher until 43 weeks postmenstrual age. The rate for Sudden Infant Death Syndrome in preterm infants born at 33 to 36 weeks is 1.37/1000 live births compared with 0.69 in infants born full term. Affected late preterm infants die at a older mean postmenstrual age compared with less mature infants (48 and 46 weeks, respectively), but die at a younger postmenstrual age than full-term infants (53 weeks, P < 0.05).
晚期早产儿（出生时孕龄为34 - 37周）在自主脑干成熟度方面介于不太成熟的早产儿和孕38周及以上出生的婴儿之间。孕33至36周出生的早产儿在出生后3至4天和10至14天时对二氧化碳的通气反应显著高于孕29至32周出生的婴儿，但与足月儿参考水平无差异。早产儿对低氧的通气反应呈双相性；最初短暂的过度通气之后是恢复到基线水平，然后低于基线水平。基于安静睡眠时高频心率变异性增加减少，孕32至37周出生的婴儿副交感神经成熟度明显低于足月儿，这表明晚期早产儿仍比足月儿更容易发生心动过缓。早产呼吸暂停的发生率和严重程度随着孕龄增加而逐渐降低。然而，晚期早产儿仍有风险，患病率高达10%，而出生体重<1500 g的婴儿患病率约为60%。明显危及生命事件的发生率在早产儿（8 - 10%）中比足月儿（1%或更低）更常见。在“家庭婴儿协作监测评估”研究中，近足月儿中常规和极端事件的发生频率介于出生时<34周的早产儿和足月儿之间。与足月儿相比，晚期早产儿至少发生一次极端事件的相对风险增加（分别为5.6和7.6，P < 0.008），并且在孕43周之前一直较高。孕33至36周出生的早产儿的婴儿猝死综合征发生率为1.37/1000活产，而足月儿为0.69/1000活产。与不太成熟的婴儿相比（分别为48周和46周），受影响的晚期早产儿死亡时的平均孕龄更大，但比足月儿死亡时的孕龄小（53周，P < 0.05）。
