Ay hindi na talaga magbabago ang gender, mama, what they see at 20 weeks is already very accurate, so you're safe for the surprise reveal! Two weeks lang din ang gap, so even if mag-ultrasound ka ulit sa 22 weeks, it's the same baby, the same gender na makikita mo. A few of us planned gender reveals din around that time and walang issues, so go ahead with your sis-in-law's surprise, your hubby will be so excited na!