1, 1~2 years after renal transplantation and in good general condition; 2, stable transplanted kidney function with blood creatinine less than 180umol/L, preferably less than 125umol/L; 3, no recent signs of rejection; 4, normal blood pressure or well controlled blood pressure with medication; 5, immunosuppressants have been reduced to maintenance dose and mycophenolate esters were stopped 6 weeks before pregnancy; 6, no or only trace proteinuria; 7, ultrasound or intravenous pyelogram showed normal transplanted kidney without dilated renal pelvis or calyces.