Risk factors for venous thromboembolism in 1.3 million pregnancies: a nationwide prospective cohort.
OBJECTIVE
To quantify risk factors for venous thromboembolism during pregnancy and the puerperal period.


METHODS
In a nationwide prospective cohort study we followed pregnant and puerperal women in Denmark from 1995 to 2009 for venous thromboembolism. Information on risk factors and confounders was retrieved from national registries. The diagnosis of venous thromboembolism was confirmed through medical charts. We calculated adjusted incidence rates per 10,000 women years and used Poisson regression to estimate effects during pregnancy and the puerperal period.


RESULTS
We studied 1,297,037 pregnancies and related puerperal periods, during which there were 748 venous thromboembolisms. The incidence rate for venous thromboembolism during a pregnancy with and without hospitalization for hyperemesis was 15.2/10,000 yr and 6.3/10,000 yr, respectively, (adjusted rate ratio: 2.5 (95%-confidence interval; 1.4-4.5)). The incidence rate among women with multiple pregnancies was 18.2/10,000 yr and 6.3/10,000 yr in singletons (adjusted rate ratio: 2.8 (1.9-4.2)). Increased risk was found with hospitalization during pregnancy or the puerperal period with incidence rates of 42.1/10.000 and 54.7/10.000, respectively, (rate ratios: 12.2 (8.7-17) and 5.9 (4.0-8.8)). Women hospitalized with infections during pregnancy had incidence rates of 25.9/10,000 yr and 29.3/10,000 yr during pregnancy and the puerperal period, respectively, and of 62.7/10,000 yr if hospitalized with infection in the puerperal period. Puerperal venous thromboembolism was associated with hospitalization for preeclampsia and intrauterine growth restriction/fetal death with incidence rates of 45.8/10,000 yr and 18.3/10,000 yr, respectively (rate ratio: 5.0 (3.1-7.8) and 1.9 (0.9-4.4)). Additionally puerperal venous thromboembolism was associated with obesity, elective and acute caesarean sections and major postpartum bleeding with incidence rates of 25.5/10,000 yr, 23.2/10,000 yr, 34.0/10,000 yr and 20.3/10,000 yr, respectively (rate ratios 1.7 (1.1-2.7), 2.1 (1.4-3.1), 3.0 (2.3-4.0) and 1.4 (1.0-2.1)).


CONCLUSIONS
Important risk factors for venous thromboembolism during pregnancy or the puerperal period were hospitalization, infection, hyperemesis, multiple pregnancies, preeclampsia, obesity, caesarean section, major postpartum bleeding, and intrauterine growth restriction or fetal death.
Department of Obstetrics & Gynecology, Hillerød Hospital, University of Copenhagen, Hillerød, Denmark.
Rie Adser
RA
Virkus
Department of Obstetrics & Gynecology, Hillerød Hospital, University of Copenhagen, Hillerød, Denmark.
Ellen
E
Løkkegaard
Gynecological Clinic, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark.
Øjvind
Ø
Lidegaard
Obstetrical Clinic, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark.
Jens
J
Langhoff-Roos
Gynecological Clinic, Rigshospitalet, University of Copenhagen, Copenhagen, Denmark.
Anne Kristine
AK
Nielsen
Research Triangle Institute, Research Triangle Park, North Carolina, United States of America.
Kenneth J
KJ
Rothman
Department of Obstetrics & Gynecology, Hillerød Hospital, University of Copenhagen, Hillerød, Denmark.
Thomas
T
Bergholt
D000293:Adolescent; D000328:Adult; D002585:Cesarean Section / Q000009:adverse effects; D003718:Denmark / Q000453:epidemiology; D005260:Female; D005313:Fetal Death; D005317:Fetal Growth Retardation; D006760:Hospitalization; D006801:Humans; D015994:Incidence; D007239:Infections / Q000150:complications; D008875:Middle Aged; D009765:Obesity / Q000150:complications; D049590:Postpartum Period / Q000097:blood; D011247:Pregnancy; D011250:Pregnancy Complications, Hematologic / Q000453:epidemiology* / Q000209:etiology; D011272:Pregnancy, Multiple; D015995:Prevalence; D011446:Prospective Studies; D012042:Registries / Q000706:statistics & numerical data*; D012189:Retrospective Studies; D012307:Risk Factors; D054556:Venous Thromboembolism / Q000453:epidemiology* / Q000209:etiology; D055815:Young Adult