The mechanisms by which asthma may have adverse perinatal effects are not well known. Poor control of asthma leading to chronic or episodic fetal hypoxia is thought to be important. Medications used in asthma treatment may also play a role, although the limited data suggests minimal or no effects. In addition, it is possible that extrapulmonary autonomic nervous system abnormalities, such as uterine muscle hyperreactivity, could contribute to pre-term delivery or gestational hypertension independent of asthma control or therapy.