Table 2.

Risk of recurrence of pre-eclampsia in mother’s second pregnancy considering her own previous pregnancy or another woman’s pregnancy with same father. Data from Medical Birth Registry of Norway, 1967-92

Pre-eclampsia in 1st pregnancy	No at risk	No of cases of pre-eclampsia in 2nd pregnancy	Risk (%)	Unadjusted odds ratio (95% CI)	P value*
Same mother and same father
Yes	12 437	1635	13.1	11.8 (11.1 to 12.6)	< 0.0001
No	351 321	4443	1.3
Same mother and different fathers
Yes	432	51	11.8	8.2 (5.9 to 11.3)	< 0.0001
No	13 834	223	1.6
Different mothers and same father
Yes	989	29	2.9	1.8 (1.2 to 2.6)	0.005
No	25 163	418	1.7

^*Exact two sided P value testing difference of odds ratio from 1.