目的 探讨小于胎龄儿（SGA）生后血清Klotho和成纤维细胞生长因子23（FGF23）水平变化，并阐明其与生长发育的关系。 方法 选取35例SGA和53例适于胎龄儿（AGA）作为研究对象，分为SGA组（n=35）和AGA组（n=53），其中早产儿组51例，早产SGA组20例，早产AGA组31例；足月儿组37例，足月SGA组15例，足月AGA组22例。收集各组新生儿的临床资料，分别检测新生儿生后第7和14天血清 Klotho 和 FGF23 水平及临床生化指标，分析新生儿生后第7和14天血清Klotho及FGF23水平与新生儿体质量、身长、头围、胸围和考普氏（Kapu）指数等各项生长发育指标及钙磷代谢的相关性。 结果 与AGA组比较，SGA组新生儿出生体质量、身长、头围、胸围和 Kapu 指数均明显降低（P<0.05）。生后第7和14天，与早产儿组比较，足月儿组新生儿血清Klotho和FGF23水平均明显升高（P<0.01）；与生后第7天比较，生后第14天早产儿组和足月儿组新生儿血清 Klotho 水平均明显升高（P<0.01），FGF23 水平均明显降低（P<0.01）。与 AGA 组比较，SGA组新生儿生后第7和14天血清Klotho和FGF23水平明显降低（P<0.05或P<0.01）；与生后第7天比较，生后第14天AGA组和SGA组新生儿血清Klotho水平明显升高（P<0.01），FGF23水平明显降低（P<0.05 或 P<0.01）。 与早产 AGA 组比较， 早产 SGA 组新生儿生后第7和14天血清Klotho和FGF23水平均明显降低（P<0.05或P<0.01）。与足月AGA组比较，足月SGA组新生儿生后第7和14天血清Klotho和FGF23水平均明显降低（P<0.05 或 P<0.01）。SGA 组新生儿生后第7天血清Klotho和FGF23水平与胎龄、体质量、身长、头围、胸围和Kapu指数等生长发育指标均呈正相关关系（P<0.05 或 P<0.01）， 血清 Klotho 水平与 FGF23 水平呈正相关关系（P<0.05）。钙磷代谢方面，SGA 组新生儿生后第7天血清 Klotho 水平与血清磷水平呈正相关关系（P<0.01）；FGF23 水平与血清钙和磷水平均呈正相关关系（P<0.05或P<0.01）。 结论 Klotho 和 FGF23 蛋白与新生儿生长发育及磷酸盐代谢有密切关联。SGA 新生儿生后血清 Klotho 和 FGF23水平较低，但随着各器官发育逐渐完善，Klotho 分泌增加，而 FGF23 水平降低可能是机体的代偿性反应。

Objective To discuss the changes of serum levels of Klotho and fibroblast growth factor 23 （FGF23） in the small for gestational age （SGA） infants after birth， and to clarify their relationships with growth and development. Methods A total of 35 SGA and 53 appropriate for the gestational age（AGA） infants were selected and divided into SGA group（n=35） and AGA group（n=53）， including 51 infants in premature group， among them 20 infants in preterm SGA group and 31 infants in preterm AGA group； among them 37 infants in full-term group， 15 infants in full-term SGA group and 22 infants in full-term AGA group. The clinical materials of the infants in various groups were collected. The levels of Klotho and FGF23 in serum and clinical biochemical markers of the infants on the 7th and 14th days after birth were detected. The relationships between the levels of Klotho and FGF23 in serum on the 7th and 14th days postnatally and newborn growth indicators such as body weight， body length， head circumference， chest circumference， and Kopu index， as well as their correlations with calcium and phosphorus metabolism were analyzed. Results Compared with AGA group， the body weight， body length， head circumference， chest circumference， and Kopu index of the infants in SGA group were decreased （P<0.05）. On the 7th and 14th days after birth， compared with preterm group， the serum levels of Klotho and FGF23 of the infants in full-term group were significantly increased （P<0.01）. Compared with the 7th day after birth，the levels of serum Klotho of the infants in preterm and full-term groups on the 14th day were significantly increased （P<0.01）， and the levels of FGF23 in serum were decreased （P<0.01）. Compared with AGA group， the levels of serum Klotho and FGF23 of the infants in SGA group on the 7th and 14th days after birth were significantly decreased （P<0.05 or P<0.01）. Compared with the 7th day after birth， the levels of serum Klotho of the infants in both AGA and SGA groups on the 14th days after birth were significantly increased （P<0.01）， and the FGF23 levels were decreased （P<0.05 or P<0.01）. Compared with preterm AGA group， the levels of Klotho and FGF23 in serum of the infants in preterm SGA group on the 7th and 14th days after birth were significantly decreased （P<0.05 or P<0.01）. Compared with full-term AGA group， the levels of Klotho and FGF23 in serum of the infants in full-term SGA group on the 7th and 14th days after birth were significantly decreased （P<0.05 or P<0.01）. In SGA group，the serum levels of Klotho and FGF23 on the 7th day after birth were positively correlated with the gestational age， body weight， body length， head circumference， chest circumference， and Kopu index （P<0.05 or P<0.01）； there was a positive correlation between the serum level of Klotho and the serum level of FGF23 （P<0.05）. In terms of calcium-phosphorus metabolism， in SGA group，the serum level of Klotho on the 7th day after birth was positively correlated with serum phosphorus level （P<0.01）， and the level of serum FGF23 on the 7th day after birth was positively correlated with serum calcium and phosphorus levels （P<0.05 or P<0.01）. Conclusion Klotho and FGF23 proteins are closely associated with growth and development and phosphate metabolism of the infants. The expression levels of Klotho and FGF23 in serum of the SGA infants postnatally are lower， but the secretion of Klotho is increased with the gradul improvement of each organ， and the decrease of FGF23 may be the adaptive response.