Table 1.

Sir Bradford Hill criteria and their application to SDB and preeclampsia [17••, 26••, 27, 54••, 73, 74••, 75–78]

	Pros	Cons
Strength	Two-three-fold increased risk
Consistency	Association across study designs and populations
Specificity	Some markers associated with OSA but not snoring	Minimal data
Temporality	SDB at 6–15 weeks associated with later development of PEC	Unclear if SDB preceded biological changes associated with PEC and not just clinical changes since PEC is usually determined in early pregnancy
Biological gradient	Severity of SDB associated with higher risk of PEC
Biological plausibility	Explained by shared mechanisms and placental involvement
Coherence		Minimal laboratory-based data exist
Experiment	Recent experimental data of gestational intermittent hypoxia demonstrate changes in mechanistic pathways linked to PEC
Analogy	High altitude model of chronic hypoxia	Mechanisms for chronic vs. intermittent hypoxia may be different
Reversibility	Data mainly on hemodynamic improvement- ongoing trials pending

PEC: preeclampsia; SDB: sleep disordered breathing; OSA: obstructive sleep apnea