. Author manuscript; available in PMC: 2016 Aug 10.

Published in final edited form as: Eur J Clin Nutr. 2016 Jan 27;70(8):918–924. doi: 10.1038/ejcn.2015.229

Table 1.

Sample characteristics and iron status measures by body mass index.

	Body mass index (kg m⁻²)
Maternal characteristics at enrollment (mid-pregnancy)	Underweight (<18.5)	Normal weight (≥18.5 and <25)	Overweight (≥25 and <30)	Obese (≥30)	Test statistic
n	219	1,084	233	77
Age (y)	24 (3.0)^a	25 (3.5)^b	26 (4.3)^c	25 (3.6)^b,c	14^***
Height (cm)	162 (4.6)	161 (4.4)	161 (4.5)	161 (5.2)	1.3
Gave birth previously (%)	14^a	21^a	29^b,c	24^a,c	15^**
High school education or greater (%)	40	33	28	32	17
Week of gestation	16 (2.0)	16 (1.9)	16 (2.1)	16 (1.9)	2.4
Pregnancy and birth outcomes

Weight gain (kg)	18.5 (5.2)^a	18.3 (5.8)^a	16.0 (6.0)^b,d	15.6 (6.1)^c,d	13^***
Excessive weight gain (%)^§	47^a	65^b	79^c,d	92^d	78^***
Gestational age at birth (wk)	39.8 (1.1)	39.7 (1.1)	39.6 (1.0)	39.5 (1.2)	1.1
Birthweight (g)	3 227 (362)^a	3 358 (375)^b	3 475 (398)^c	3 431 (433)^b,c	17^***
Macrosomic birth (birthweight > 4000 g) (%)	1.8^a	3.6^a	8.2^b,c	6.5^a,c	14^**
Maternal mid-pregnancy iron and anemia status

Hemoglobin (g/L)	120 (9.8)^a	122 (9.2)^b	124 (8.5)^c,d	124 (8.7)^b,d	10^***
Anemia (Hb<110 g/L) (%)	9.1	9.2	4.7	6.5	5.6
Serum ferritin (SF) (μg/L)	43 (36)	41 (35)	44 (36)	37 (28)	1.3
Iron depletion (SF<15 μg/L) (%)	18	20	17	22	1.9
Transferrin receptor (sTfR) (nmol/L)	14 (4.5)^a	15 (4.7)^a	16 (5.3)^b,c	17 (6.2)^c	9.1^***
Zinc protoporphyrin/heme (ZPP/H) (μmol/mol heme)	53 (27)	56 (25)	57 (27)	57 (27)	1.2
Body iron (BI) (mg/kg)	5.7 (3.5)	5.2 (3.5)	5.3 (3.4)	4.7 (3.3)	1.8
hsCRP (mg/L)	2.6 (4.6)^a	3.4 (5.3)^a	5.6 (5.7)^b	5.7 (7.3)^b	18^***
High hsCRP (>5 mg/L) (%)	12^a	18^a	45^b	40^b	104^***
Neonatal iron and anemia status (cord blood)

Hemoglobin (g/L)	152 (15)	152 (16)	152 (15)	151 (14)	0.35
Anemia (Hb<130 g/L) (%)	6.4	5.7	5.2	5.2	0.36
Serum ferritin (SF) (μg/L)	139 (86)	127 (86)	118 (87)	123 (84)	2.5
Low SF (SF<75 μg/L)	21^a	26^a,b	33^b	31^a,b	9.2^*

Mean (SD) or proportion are shown; “Test statistic” refers to F-value for means and Chi-square statistic for proportions;

^***

P<0.001

^**

P<0.01

P<0.05.

^§

Excessive gestational weight gain was defined according to IOM recommendations based on the difference in weight pre-pregnancy and at or near term (28).

Means or proportions with: 1) different superscript letters correspond to groups wherein pair-wise differences are not consistent with random variation (i.e., P<0.05); 2) identical superscript letters correspond to groups wherein pair-wise differences are consistent with random variation (i.e., P>0.05); and 3) no superscripts correspond to groups wherein all pair-wise differences are consistent with random variation (i.e., P>0.05).