In this study, the risk factors for thromboembolism was investigated in 27 mortality due to mentioned reason. The mean gestational age was 33 weeks + 6 days and nearly half of the cases experienced premature births. This is the same reason as Simpson et al. study that reported delivery at gestational age < 36 as a risk factor for VTE (18).
The use of risk score calculator may effectively and safely determine the duration of heparin therapy (17). Darguad et al. indicated that in patients with moderate risk of VTE (score = 3–5), prescription of heparin prophylaxis in the third trimester prevent thrombosis (19). In our study, the mean score of the thromboembolism was 4.6 suggesting that these cases were a high-risk population for thromboembolic events; however only half of them with score more than 4 received heparin.
Although the age of 35 years in pregnant women is associated with an increased risk of thromboembolic events (17), in this study the average age of the cases was 33.2 years that may reveal the impact of other variables to increase the risk of thromboembolism. Although Danilenko-Dixon et al. also reported no correlation between age and VTE in pregnancy and puerperium period (20).
More than 70% of cases have embolized in first day after delivery and about one half of them deceases intrapartum. Since more than half of them did not even receive a single dose of heparin, the need to quickly and accurately identify the indications of prophylactic treatment with heparin or other preventive methods to reduce mortality in these mothers is obvious.
Available data suggests that the risk of VTE is higher after cesarean section than vaginal delivery (21). The indications for cesarean and the conditions during/after the surgery could be involved in the occurrence of thromboembolism and possibly mortality. The puerperium is the time of maximal risk of pregnancy-associated VTE and several observational studies have assessed the risk of VTE after cesarean Sect. (22–24).
Blondon et al. accounted maternal Body mass index (BMI) as an important risk factor for postpartum VTE, grading from weak in overweight women to very strong in women with class III obesity (25). However, in the other study, BMI was not related to VTE. This is similar to our result that BMI was in few patients above or equal to 30 and in none of the mortalities more than 40.
Women with inherited thrombophilia or a positive family history even with no previous episode of VTE, have a risk of developing a first VTE episode in pregnancy or postpartum period (26). The highest risks were associated with homozygosity for factor V Leiden or the prothrombin G20210A variant (27). In the present survey, one case had a history of VTE, one with an anti-phospholipid antibody syndrome, and the other with hereditary thrombophilia that all received heparin. Thromboembolism happened may be due to not receiving proper dosage of heparin.
Low molecular heparin is the preferred option for prophylaxis in most patients because of its better bioavailability, longer plasma half-life, more predictable dose response, and improved maternal safety (28, 29). Also heparin is more effective than vitamin K antagonists in preventing recurrent VTE and post-thrombotic syndrome without increasing the risk of major bleeding events (30).
In our study, the most frequent blood group of mothers was A +. The study of Mirza Aghazadeh et al. also had the highest reports of VTE associated with the A + blood group (31); Although this blood group generally has a high prevalence in Iran (32). On the other population-based study blood groups A and AB were associated with increased risk estimates for VTE in pregnancy and the puerperium either (33).
37% of mothers had more than 3 times delivery, 30% had heart disease, 21% had high blood pressure and 25% had stillbirth, it seems that these factors have a significant effect on the risk of maternal conditions.
Frequency of multiple pregnancy, severe bleeding, instrumental delivery, pregnancy by assisted reproductive techniques, prolonged delivery, sepsis, preeclampsia, and underlying illness were observed in less than 30 percent of these 27 mothers and showed that although these factors are predisposed to the occurrence of thrombotic events, but they do not contribute much to our study.
There are studies on the prevalence of risk factors and etiology of maternal mortality that explain rupture of membrane and severe bleeding are important risk factors in thromboembolism; therefore, precise follow-up and, if necessary, preventive and interventional proceedings may be effective in preventing maternal deaths.