The newly emerged IEEE 802.15.6 standard provides a multiple priority-based services for Wireless Body Area Networks (WBAN). Categorizing a node as high/low priority device leads to be assigned a relatively larger/smaller contention probability (CP), respectively. In contention-based protocols, halving the maximum CP value (CP max ) the way down to its minimum value (CP min ) has no consideration to the device's awaiting packets in the buffer. Moreover, this halving process shrunken the device's chance to contend to the current time slot which affects the throughput and the average packet service time. In this paper, we propose an amendment to the IEEE 802.15.6 standard introducing novel CP dynamism based on the device's queue length. The numerical results show an improvement of the proposed dynamism over the conventional in terms of throughput, delay and data packet dropping rate. In addition, the proposed scheme showed a stability in a realistic channel condition.