Table 1 Number and distribution of two cohorts of singleton births in Sweden, with mean and standard deviation (SD) of birthweight, birth length, and Apgar score by infant sex and gestational age, before and after the implementation of ultrasound for pregnancy dating

Gestational age

N

%

N

%

N

%

N

%

35–40 weeks

187,163

100.0

170,375

100.0

479,118

100.0

477,946

100.0

35–36 weeks

8,737

4.7

6,733

4.0

20,527

4.3

18,095

3.8

37–38 weeks

41,434

22.1

33,746

19.8

122,074

25.5

121,500

25.4

39–40 weeks

136,992

73.2

129,896

76.2

336,517

70.2

338,351

70.8

Gestational age

Infant characteristics

Mean

SD

Mean

SD

Mean

SD

Mean

SD

35–36 weeks

Birthweight (g)

2,850

499

2,749

503

2,846

452

2,778

461

Birth length (cm)

47.9

2.5

47.3

2.4

47.6

2.2

47.0

2.2

Apgar score

9.2

1.3

9.2

1.3

9.5

1.0

9.6

1.0

37–38 weeks

Birthweight (g)

3,284

472

3,159

465

3,349

460

3,254

450

Birth length (cm)

49.7

2.1

48.9

2.1

49.6

2.0

48.9

2.0

Apgar score

9.5

0.9

9.5

0.9

9.8

0.7

9.8

0.6

39–40 weeks

Birthweight (g)

3,591

463

3,451

446

3,665

451

3,544

437

Birth length (cm)

51.0

2.0

50.1

2.0

51.0

1.9

50.2

1.8

Apgar score

9.6

0.8

9.6

0.7

9.8

0.7

9.8

0.6