Table 1 Characteristics of the 22,812 pregnancies screened

From: Prenatal reflex DNA screening for trisomies 21, 18, and 13

Median age (years) at estimated date of delivery (IQR) 31 (28–35)
Median maternal weight (kg) (IQR) 64 (57–73)
Median gestational age (weeks + days) at blood sample (IQR) 12 + 5 (12 + 2–13 + 1)
Ethnicity
 Caucasian 11,939 (52%)
 Black 1,858 (8.1%)
 South Asian 6,484 (28.4%)
 Oriental (East or South East Asian) 962 (4.2%)
 Other 1,569 (6.9%)
Insulin-dependent diabetes 87 (0.4%)
In vitro fertilization 791 (3.5%)
Twins 381 (1.7%)
Monochorionic 80 (21%)
Dichorionic 295 (77%)
Unknown chorionicity 6 (1.6%)
Smoker 1,222 (5.4%)
Trisomy 21 (prevalence) 73 (0.32%)
Trisomy 18 (prevalence) 25 (0.11%)
Trisomy 13 (prevalence) 8 (0.04%)
All affected (prevalence) 106 (0.46%)
  1. IQR, interquartile range.