In the period in which the play is set, many people would have grown up with little knowledge on sex and birth control. Even among adults the subjects are unlikely to have been openly discussed.
Both the Devlins and Pedreschis are Catholic. Then as now, the Catholic Church was opposed to artificial contraception. Even if the characters had been aware of different methods of birth control they may have been against using them.
Rosinella comments of Mrs Devlin:
Eight weans! She keeps having them but she cannie even look after them right
This suggests that Mrs Devlin has no knowledge of birth control.
Abortion was not legalised in Scotland until 1967. To end a pregnancy some women resorted to illegal abortions. The abortion Bridget borrows money to pay for was therefore illegal.