Study population
Women with a diagnosis of DVT or PE, which combined VTE in pregnancy or
in the first 6 postnatal weeks were identified by search for selected
ICD-9 or 10 codes in the Hospital Information System. 192 women were
registered with a diagnosis of VTE in 129443 pregnancies. We excluded 3
cases wrongly diagnosed with VTE in index and subsequent pregnancies, 3
cases with thrombotic events in association with miscarriage, induced
abortion, or ectopic pregnancy terminated before gestational week 28. In
addition, we excluded possible cases with a diagnosis of amniotic fluid
embolism (n=7). Further exclusions were applied to women who started
antenatal care after 18 week’s gestation (n=2) and women with missing
data for pre-pregnancy, delivery weight and height information (n=26).
Finally, we excluded 3 cases with server heart/liver/kidney disease,
malignancy or history of VTE. The eligible case population comprised 151
women (Figure 1).
The Hospital Information System selected first two women without VTE in
pregnancy or the first 6 weeks following delivery, who gave birth at
Shanghai First Maternity and Infant Hospital at the same time as the
case, as possible controls. If these women did not meet the criterions
above, we included the 3rd or 4th selection as controls. In total 302
controls were identified.