Table 3.

Risk of recurrence of pre-eclampsia between mothers who are sisters. Data from Medical Birth Registry of Norway, 1967-92, and Central Population Register of Norway

Relationship between mothers	No of pregnancies	Odds ratio (95% CI)
Full sisters*	61 186	2.2 (1.9 to 2.5)
Maternal half sisters†	3 766	1.6 (0.9 to 2.6)
Paternal half sisters‡	4 290	1.8 (1.01 to 2.9)

^*Sisters with same mother and father.  

^†Half sisters with same mother but different fathers.  

^‡Half sisters with same father but different mothers.