Table 1 Characteristic of subjects

Age, years

30.14 ± 4.39

Maternal height, cm

158.4 ± 5.20

Maternal pre-pregnancy weight, kg

51.57 ± 7.51

Paternal height, cm

171.2 ± 5.40

Paternal weight, kg

67.95 ± 10.37

Gestational age, gestational weeks

39.03 ± 1.47

Measurement time of iron-related indicators, gestational weeks

10.63 ± 1.56

Measurement time of femur length, gestational weeks

38.15 ± 1.91

Gravidity, times

2.13 ± 1.21

Parity, times

1.50 ± 0.61

Maternal education

Senior high school or below

362 (39.6)

Junior college

301 (32.9)

Bachelor or above

251 (27.5)

Household income, Yuan per month

≤ 5000

353 (38.6)

5000–10,000

398 (43.5)

> 10,000

163 (17.8)

Neonatal s

Boy

476 (52.1)

Girl

438 (47.9)

Delivery mode

Natural labour, n (%)

498 (54.5)

Caesarean section, n (%)

416 (45.5)

Iron or multivitamin supplements (before pregnancy)

Yes

46 (5.0)

No

868 (95.0)