The young British woman was travelling with her family to Birmingham when she felt dizzy and then fell unconscious.
Emergency services were called but the woman, who was between three and four months pregnant, died at the scene, Spain's ABC newspaper reported on Wednesday.
The cause of death is not yet known, but Spain's large UGT union is now considering investigating the death.
An ambulance took 14 minutes to arrive at the scene, which operators described as "within standard" time frames.
But Girona–Costa Brava airport closed its 24-hour medical facilities a year ago, a decision made because of falling passenger numbers at the facility, according to El País newspaper.
The UGT's Secretary General of Transport Joan Muntada, told Spanish news agency Efe the union had requested information about the incident.
They will now "analyze events to see if they could lead to charges".