Pregnancy significantly increases the risks of blood clots both in the legs and in the lungs. Sometimes just being pregnant can be enough to cause life threatening blood clots. Genetic clotting problems are one of the reasons women are at extra risk. These affect about 5% of the population but currently pregnant women are not screened for this condition. The other reasons why blood clots are more common during pregnancy is because the blood itself becomes more sticky and women often have reduced mobility especially in late pregnancy and after delivery. Other risk factors for clotting are obesity, smoking, older mothers, serious and extensive varicose veins and certain heart problems. Anyone with a previous history of thrombosis is obviously at extra risk during pregnancy.
The time when clots are most prevalent is shortly after delivery especially if this has been complicated by a caesarean section or an operative delivery. If there has been dehydration, blood loss and prolonged bed rest then these are further risk factors
As you might expect, prevention is better than cure! At your booking visit you will be assessed for possible risk of thrombosis during pregnancy and afterwards. A risk assessment will be done again if you are admitted into hospital for complications of pregnancy or more commonly when you are in labour or about to be delivered. If there are significant risk factors then there are many techniques which are useful to help prevent blood clots. Most importantly is the use of Heparin, a blood thinning treatment, which is given by a tiny needle under the skin, usually on a daily basis. This may be given throughout your pregnancy and afterwards, and is extremely safe and easy to use. Other measures include thrombo-embolism stockings, special thick, white, below-knee stockings. And in certain circumstances inflatable boots which go up to knee and keep blood circulating. Sometimes Heparin needs to be continued for up to 6 weeks after delivery. For long-term use it will be replaced by Warfarin, but only usually after delivery.
Generally Heparin is a very safe drug but can increase the amount of bruising you will get if you have had a caesarean section. If you have had a previous thrombosis you will be advised not to take the combined oral contraceptive afterwards. The mini pill is usually very safe to take.