A total of 149 pregnant women were enrolled over the study period. Suspicion for DVT in these patients was almost always triggered by 1 or more of the following symptoms: unilateral leg swelling, pain in the leg, and discoloration of the leg. Each patient was referred from the emergency department or their primary practitioners. A total of 55, 40, 12, 36, and 6 patients were recruited, respectively, from centers 1, 2, 3, 4, and 5. Table 1 shows patient characteristics. About half of the women were 35 years of age or older, 78.5% were white, and 50% had had 1 or more children before the index pregnancy. Although most patients had singleton pregnancies (89.3%), a high proportion of pregnancies were multiple—10.7%, compared with the national average of 2.7% (23). One reason for this may be that center 1 specializes in multiple pregnancies, and that center contributed about one third of the patients. Another reason may be that women with multiple pregnancies frequently report nonthrombotic leg symptoms. Most of the women presented for investigation in their third trimester, and most reported symptoms in the left leg (Table 1).