Whether it is a tihetuka or a dvihetuka human bhava is determined at the cuti-patisandhi moment that initiates the human bhava, and then it lasts to the end of that human bhava. Therefore, all human births (jati) are within that bhava.
So, in a way, practicing Dhamma is as important if one has a dvihetuka bhava. One could make conditions for the next bhava to be tihetuka.
Of course, it is not possible to determine whether a given person has a dvihetuka or tihetuka bhava.