TABLE 1.

Baseline characteristics of the two study populations

	Routine ultrasound population (A) n = 99 265		Ultrasound on indication population (B) n = 24 868		p value a
	n	%	n	%
Maternal age (years)					0.068
<20	1946	2.0	428	1.7
20–24	13 319	13.4	3329	13.4
25–29	30 760	31.0	7851	31.6
30–34	34 926	35.2	8754	35.2
35–39	15 527	15.6	3794	15.3
40+	2787	2.8	712	2.9
Parity					<0.001
Parity 0	48 143	48.5	11 653	46.9
Parity 1	32 883	33.1	8680	34.9
Parity 2+	18 239	18.4	4535	18.2
Maternal smoking					<0.001
Yes	10 506	10.6	3076	12.4
No	84 175	84.8	20 870	83.9
Not known	4584	4.6	922	3.7
Maternal body mass index (kg/m2)					0.38
<18.5	2460	2.5	645	2.6
18.5–24.9	56 617	57.0	14 472	58.2
25–29.9	21 178	21.3	5412	21.8
30+	8533	8.6	2275	9.1
Not known	10 477	10.6	2064	8.3
Maternal height (cm)					<0.001
<155	3326	3.4	787	3.2
155–164	33 138	33.4	7922	31.9
165–174	48 577	48.9	12 515	50.3
175+	10 017	10.1	2412	9.7
Not known	4207	4.2	1232	5.0

^a p‐values obtained by chi‐squared test.