Characteristics Mean ± SD
Age (years) 34.6 ± 5.3
Body mass index (kg/m2) 22.3 ± 3.6
N. (%)
Ethnicity White Asian Black 152 (91.6) 9 (5.4) 5 (3.0)
Nulliparous 97 (58.4)
Parous 69 (41.6)
History of preterm birth 23 (13.9)
Singleton pregnancy Multiple pregnancy: Twin pregnancies
Triplet pregnancies
118 (71%) 48 (28.9) 43 (25.9) 5 (3.0)
Spontaneous preterm birth <34 weeks in the index pregnancy: Singleton pregnancy Twin pregnancies Triplet pregnancies 26/118 (22.0%) 16/43 (37.2%) 4/5 (80.0%)