J Endocrinol Metab

Journal of Endocrinology and Metabolism, ISSN 1923-2861 print, 1923-287X online, Open Access

Article copyright, the authors; Journal compilation copyright, J Endocrinol Metab and Elmer Press Inc

Journal website http://www.jofem.org

Original Article

Volume 8, Number 6, December 2018, pages 139-143

Iron Supplementation in Non-Anemic Pregnancy and Risk of Developing Gestational Diabetes Mellitus

**Table 1.** Background Characteristics Compared Between the Early and Late Iron Supplementation Groups
Characteristics	Early iron group (n = 966)	Control group (n = 969)	P-value
A P-value < 0.05 indicates statistical significance. BMI: body mass index; GDM: gestational diabetes mellitus; SD: standard deviation.
Age (years)	28.5 ± 5.6	26.4 ± 6.5	< 0.001
Maternal age ≥ 30 years	415 (43.0)	321 (33.1)	< 0.001
Gravidity			0.871
1	385 (39.7)	370 (38.2)
2	384 (39.8)	394 (40.7)
3	145 (15.0)	148 (15.3)
4 or more	54 (5.5)	57 (5.8)
BMI (kg/m²)	22.8 ± 4.3	23.4 ± 4.3	0.002
Pre-pregnancy BMI > 25 kg/m²	230 (23.8)	288 (29.7)	0.003
First booking hemoglobin (g/dL)	12.3 ± 1.2	12.3 ± 0.8	0.308
First booking hemoglobin ≥ 13 g/dL	219 (22.7)	208 (21.5)	0.547
Previous GDM	0 (0.0)	1 (0.1)	1.000
Previous infant birth weight > 4 kg	9 (0.9)	10 (1.0)	1.000
Previous unexplained infant death	0 (0.0)	2 (0.2)	0.500
Family history of diabetes	133 (13.8)	91 (9.4)	0.003
Drug adherence ≥ 75%	689 (71.4)	668 (68.9)	0.253

Table 1. Background Characteristics Compared Between the Early and Late Iron Supplementation Groups

Characteristics

Early iron group (n = 966)

Control group (n = 969)

P-value

n (%) or mean ± SD

A P-value < 0.05 indicates statistical significance. BMI: body mass index; GDM: gestational diabetes mellitus; SD: standard deviation.

Age (years)

28.5 ± 5.6

26.4 ± 6.5

< 0.001

Maternal age ≥ 30 years

415 (43.0)

321 (33.1)

< 0.001

Gravidity

0.871

385 (39.7)

370 (38.2)

384 (39.8)

394 (40.7)

145 (15.0)

148 (15.3)

4 or more

54 (5.5)

57 (5.8)

BMI (kg/m²)

22.8 ± 4.3

23.4 ± 4.3

0.002

Pre-pregnancy BMI > 25 kg/m²

230 (23.8)

288 (29.7)

0.003

First booking hemoglobin (g/dL)

12.3 ± 1.2

12.3 ± 0.8

0.308

First booking hemoglobin ≥ 13 g/dL

219 (22.7)

208 (21.5)

0.547

Previous GDM

0 (0.0)

1 (0.1)

1.000

Previous infant birth weight > 4 kg

9 (0.9)

10 (1.0)

1.000

Previous unexplained infant death

0 (0.0)

2 (0.2)

0.500

Family history of diabetes

133 (13.8)

91 (9.4)

0.003

Drug adherence ≥ 75%

689 (71.4)

668 (68.9)

0.253

**Table 2.** The Incidence of Gestational Diabetes Mellitus Compared Between the Early and Late Iron Supplementation Groups
	Early iron group (n = 966)	Control group (n = 969)	P-value
A P-value < 0.05 indicates statistical significance. A1: subtype of gestational diabetes mellitus which does not require anti-hyperglycemic drug; A2: subtype of gestational diabetes mellitus which requires anti-hyperglycemic drug.
Gestational diabetes mellitus			< 0.001
Type A1	75 (7.8)	35 (3.6)
Type A2	19 (2.0)	19 (2.0)

Table 2. The Incidence of Gestational Diabetes Mellitus Compared Between the Early and Late Iron Supplementation Groups

Early iron group (n = 966)

Control group (n = 969)

P-value

n (%)

A P-value < 0.05 indicates statistical significance. A1: subtype of gestational diabetes mellitus which does not require anti-hyperglycemic drug; A2: subtype of gestational diabetes mellitus which requires anti-hyperglycemic drug.

Gestational diabetes mellitus

< 0.001

Type A1

75 (7.8)

35 (3.6)

Type A2

19 (2.0)

**Table 3.** Univariable and Multivariable Analysis of Association Between Early Antenatal Iron Supplementation and GDM
	Binomial regression	Multinomial regression
A P-value < 0.05 indicates statistical significance. ^aType A1 compared to no gestational diabetes mellitus. ^bType A2 compared to no gestational diabetes mellitus. Factor 1: maternal age, pre-pregnancy BMI, history of DM in first-degree relatives; Factor 2: maternal age ≥ 30 years, pre-pregnancy BMI ≥ 25 kg/m², history of DM in first-degree relatives; Factor 3: maternal age ≥ 30 years, pre-pregnancy BMI ≥ 25 kg/m², history of DM in first-degree relatives, previous GDM, previous infant birth weight > 4 kg; Factor 4: maternal age ≥ 30 years, pre-pregnancy BMI ≥ 25 kg/m², history of DM in first-degree relatives, previous GDM, previous infant birth weight > 4 kg, drug adherence, first hemoglobin level result. BMI: body mass index; CI: confidence interval; DM: diabetes mellitus; GDM: gestational diabetes mellitus; RR: relative risk.
Univariable analysis	1.83 (1.29, 2.59); 0.001	2.25 (1.49, 3.39); < 0.001^a 1.05 (0.55, 2.00); 0.883^b
Multivariable analysis adjusted for
Factor 1	1.65 (1.15, 2.39); 0.007	1.98 (1.29, 3.03); 0.002^a
Factor 2	1.68 (1.17, 2.41); 0.005	2.01 (1.32, 3.06); 0.001^a
Factor 3	1.57 (1.10, 2.25); 0.014	2.00 (1.31, 3.05); 0.001^a
Factor 4	1.56 (1.09, 2.24); 0.016	1.98 (1.29, 3.02); 0.002^a

Table 3. Univariable and Multivariable Analysis of Association Between Early Antenatal Iron Supplementation and GDM

Binomial regression

Multinomial regression

RR (95% CI); P-value

A P-value < 0.05 indicates statistical significance. ^aType A1 compared to no gestational diabetes mellitus. ^bType A2 compared to no gestational diabetes mellitus. Factor 1: maternal age, pre-pregnancy BMI, history of DM in first-degree relatives; Factor 2: maternal age ≥ 30 years, pre-pregnancy BMI ≥ 25 kg/m², history of DM in first-degree relatives; Factor 3: maternal age ≥ 30 years, pre-pregnancy BMI ≥ 25 kg/m², history of DM in first-degree relatives, previous GDM, previous infant birth weight > 4 kg; Factor 4: maternal age ≥ 30 years, pre-pregnancy BMI ≥ 25 kg/m², history of DM in first-degree relatives, previous GDM, previous infant birth weight > 4 kg, drug adherence, first hemoglobin level result. BMI: body mass index; CI: confidence interval; DM: diabetes mellitus; GDM: gestational diabetes mellitus; RR: relative risk.

Univariable analysis

1.83 (1.29, 2.59); 0.001

2.25 (1.49, 3.39); < 0.001^a
1.05 (0.55, 2.00); 0.883^b

Multivariable analysis adjusted for

Factor 1

1.65 (1.15, 2.39); 0.007

1.98 (1.29, 3.03); 0.002^a

Factor 2

1.68 (1.17, 2.41); 0.005

2.01 (1.32, 3.06); 0.001^a

Factor 3

1.57 (1.10, 2.25); 0.014

2.00 (1.31, 3.05); 0.001^a

Factor 4

1.56 (1.09, 2.24); 0.016

1.98 (1.29, 3.02); 0.002^a

**Table 4.** Birth Outcomes Compared Between the Early and Late Iron Supplementation Groups
	Early iron group (n = 966)	Control group (n = 969)	P-value
A P-value < 0.05 indicates statistical significance. ^aHemoglobin level < 11 g/dL. SD: standard deviation.
Gestational age at birth	38.3 ± 1.4	38.3 ± 1.4	0.962
Infant birth weight (g)	3,134.8 ± 431.7	3,096.6 ± 436.2	0.053
Maternal hemoglobin level at delivery (g/dL)	12.4 ± 1.2	12.3 ± 1.1	0.521
Maternal anemia at delivery^a	48 (12.0)	40 (11.1)	0.734

Table 4. Birth Outcomes Compared Between the Early and Late Iron Supplementation Groups

Early iron group (n = 966)

Control group (n = 969)

P-value

n (%) or mean ± SD

A P-value < 0.05 indicates statistical significance. ^aHemoglobin level < 11 g/dL. SD: standard deviation.

Gestational age at birth

38.3 ± 1.4

0.962

Infant birth weight (g)

3,134.8 ± 431.7

3,096.6 ± 436.2

0.053

Maternal hemoglobin level at delivery (g/dL)

12.4 ± 1.2

12.3 ± 1.1

0.521

Maternal anemia at delivery^a

48 (12.0)

40 (11.1)

0.734