Breathing spells and bradys . how long will last with a preemie baby ?

34 weeks: Every baby is different, but most stop having apnea and bradycardia events (stopping breathing and low heart rates) around 34 weeks corrected gestational age, however sometimes this can be delayed. Gastric reflux can contribute to continued bradycardia and desaturations beyond this point.

Prematurity: Apnea (breathing spells) are signs of prematurity, bradycardia is usually secondary to the apnea. Usually once the baby above 2500 grams in weight (>34 weeks of gestation age) will stop the apnea. Some will have the apnea seconday to other problems like bleeding in the brain (which can happen in prematures) or secondary to some meds.

? till due date: If you mean stopping breathing/ apnea and low heart rate it could last close to term gestation which is 37 to 40 weeks.