Table 3. Comparison of some index between two groups.

	Early onset group(cases)	Late onset group(cases)	P value
Birth weight (kg)	3.19±0.47(97)	3.25±0.43(198)	0.233
length of pyloric muscle (cm)	2.00±0.37(89)	2.12±0.38(179)	0.026
thickness of pyloric muscle (mm)	5.08±0.95(89)	5.53±1.06(179)	0.001
PO2 (kpa)	10.76±4.27(76)	8.86±4.24(163)	0.001
PCO2 (kpa)	4.20±1.27(76)	5.20±1.54(163)	1.62×10−6
HCO3 − (mmol/L)	26.75±6.66(76)	34.99±10.59(163)	2.13×10−9
Serum chloride (mmol/L)	93.89±11.12(63)	86.69±12.78(138)	0.000158
Serum potassium (mmol/L)	4.07±0.65(75)	3.60±0.83(164)	2.34×10−5
serum sodium (mmol/L)	134.69±5.76(76)	133.06±6.27(165)	0.056
serum pH	7.54±0.10(76)	7.56±0.11(163)	0.182

Notes: detailed data not recorded in some medical records.