Table 4

 Time to first event of pulmonary embolism during trimesters in pregnant women after in vitro fertilisation (IVF) and women with natural pregnancies matched on age and calendar period of delivery. Values are numbers (percentages) unless stated otherwise

Variables IVF pregnancies (n=23 498)Natural pregnancies (n=116 960)Proportional hazard regression (95% CI)
First trimester (weeks 1-12)7 (0.03)5 (0.004)6.97 (2.21 to 21.96)
Second trimester (weeks 13-25)5 (0.02)13 (0.01)0.42 (0.05 to 3.20)
Third trimester (week 26 to <3 days before birth)6 (0.03)18 (0.02)0.40 (0.10 to 1.68)
≤3 days before to 42 days after birth11 (0.05)49 (0.04)1.79 (0.86 to 3.74)
P value for test of difference*0.0034
Test of equal effect in all time periods†0.0092

*Wald χ2 for difference between IVF and no IVF.

†Wald χ2 test.