Table 1.

Physiological iron balance in menstruating and pregnant females by gestation

Iron fate	Menstruating females (28 days)	First trimester (weeks 0–13; 13 weeks total)	Second trimester (weeks 14–26; 13 weeks total)	Third trimester (weeks 27–40; 14 weeks total)	Pregnancy sum (weeks 0–40; 40 weeks total)
Basal iron losses	23 mg (0.8 mg/day)^a	73 mg (0.8 mg/day)^a	73 mg (0.8 mg/day)^a	78 mg (0.8 mg/day)^a	224 mg
Menstruation	13 mg^a	NA	NA	NA	NA
Placental iron	NA	NA	16 mg (0.2 mg/day)^d,e	30 mg (0.3 mg/day)^b,d,f	46 mg
Fetal iron	NA	NA	60 mg (0.7 mg/day)^b,c	210 mg (2.1 mg/day)^b,c	270 mg
Expansion of maternal RBC mass	NA	NA	112 mg (1.2 mg/day)^g,h	338 mg (3.5 mg/day)^g,h	450 mg^h
Total iron needs	36 mg (1.3 mg/day)	73 mg (0.8 mg/day)	261 mg (2.9 mg/day)	656 (6.7 mg/day)	990 mg
Delivery blood loss	NA	NA	NA	NA	150 mg^g
RBC mass contraction after delivery	NA	NA	NA	NA	−450 mg^g
Net iron loss	NA	NA	NA	NA	690 mg

On the basis of data reported by ^aHallberg & Rossander-Hulten (58), ^bWiddowson & Spray (139), ^cAlexander et al. (2), ^dBarad et al. (8), ^eHecht et al. (61), ^fHayward et al. (60), ^gBothwell (13), and ^hHytten (69), assuming a 55-kg woman.

Menstruation calculation (58): Hb, 135 g/L blood; Fe,3.34 mg/g Hb.

Fetal iron: iron content/g fetus weight (139); average fetal weights in second trimester (2, 110) and third trimester (2).

Placental iron: iron content/g placenta weight (71.1 μg/g) (8); average placenta weight in second trimester (61) and third trimester (8, 60, 139).

Maternal RBC expansion: total iron required (13); second and third trimesters area under curve calculation assuming a linear increase in requirement (69). Abbreviations: Hb, hemoglobin; NA, not applicable; RBC, red blood cell.