'a check' here is something that limits, restrains, holds back or even stops. Preventive means something that is intended to act as an obstacle or deterent. So in fact the word 'preventive' only serves to make the meaning of 'check' clearer as 'check' can also mean an inspection or test.

Hi. In this sentence it means that a couple is forced to limit the size of their family due to government housing restrictions.

check = brake When you check yourself, you stop what you are doing.