Venous thromboembolism in pregnancy

Causes and risk

The pregnancy states that carry a raised risk of thromboembolism are named one by one rather than by a general rule. Twin and other multiple pregnancy is one of them: thromboembolism sits among the maternal antenatal complications of twin pregnancy, alongside preeclampsia, gestational HTN, cholestasis, pulmonary edema, acute fatty liver, IDA and hyperemesis gravidarum. Antiphospholipid syndrome is named as well, and is treated before pregnancy in its own right. In mitral stenosis in pregnancy the arrhythmias, AF in particular, bring their own risk of thromboembolism.

The risk factors are counted one by one. The pre-existing ones carry:

• Previous history of VTE, except a single event provoked by major surgery: 4.
• Previous history of VTE provoked by major surgery: 3.
• Thrombophilia: 3. The heritable ones are antithrombin deficiency, protein C and protein S deficiency, factor V Leiden and the prothrombin gene mutation; the acquired ones are antiphospholipid syndrome, persistent lupus anticoagulant, persistent moderate or high titre anti cardiolipin antibodies, and persistent beta 2 glycoprotein antibodies.
• Medical co-morbidities: 3. Named are cancer, heart failure, active SLE, inflammatory poly arthropathy or inflammatory bowel disease, nephrotic syndrome, type I diabetes with nephropathy, sickle cell disease, and current intravenous drug use.
• Family history of unprovoked or oestrogen provoked VTE in a first degree relative: 1.
• Low risk thrombophilia: 1.
• Age over 35 years: 1.
• Obesity with a BMI from 30-39 kg/m2 at booking: 1; a BMI of 40 kg/m2 or more at booking: 2.
• Parity of 3 or more: 1. Smoking: 1. Paraplegia: 1. Gross varicose veins: 1.

The obstetric risk factors in the current pregnancy are pre-eclampsia, ART or IVF, that is assisted reproductive technology or in vitro fertilisation, and multiple pregnancy, each scoring 1, and emergency caesarean section, scoring 2. Elective caesarean section, mid cavity or rotational operative delivery, prolonged labour over 24 hours, PPH over 1 litre, preterm birth under 37 weeks and stillbirth each score 1 as well.

The new onset and transient risk factors in the current pregnancy score more than the obstetric ones. Any surgical procedure in pregnancy or the puerperium scores 3, and hyperemesis with dehydration scores 3. Ovarian hyperstimulation syndrome, first trimester only, scores 4, the same score the table gives a previous VTE that was not a single event provoked by major surgery. Immobility, current systemic infection and long hours of travel over 4 hours each score 1.