Table 1.

Estimated incidence of a first episode of venous thrombosis in carriers of various thrombophilic defects

	Antithrombin, protein C, or protein S deficiency [18, 23, 24, 26, 27]	Factor V Leiden, heterozygous [23, 27–29]	Prothrombin 20210A mutation [31, 32]	Factor V Leiden, homozygous [30, 35–37]
Overall (%/year, 95% CI)	1.5 (0.7–2.8)	0.5 (0.1–1.3)	0.4 (0.1–1.1)	1.8 (0.1–4.0)a
Surgery, trauma, or immobilization (%/episode, 95% CI)	8.1 (4.5–13.2)	1.8 (0.7–4.0)	1.6 (0.5–3.8)	–
Pregnancy (%/pregnancy, 95% CI)	4.1 (1.7–8.3)	2.1 (0.7–4.9)	2.3 (0.8–5.3)	16.3b
During pregnancy, %, 95% CI	1.2 (0.3–4.2)	0.4 (0.1–2.4)	0.5 (0.1–2.6)	7.0b
Postpartum period, %, 95% CI	3.0 (1.3–6.7)	1.7 (0.7–4.3)	1.9 (0.7–4.7)	9.3b
Oral contraceptive use (%/year of use, 95% CI)	4.3 (1.4–9.7)	0.5 (0.1–1.4)	0.2 (0.0–0.9)	–

Data apply to individuals with at least one symptomatic first-degree relative

^a Based on pooled OR of 18 [8–40] and an incidence of 0.1% in non-carriers

^b Data from family studies, risk estimates lower in other settings