Iron Deficiency In Pregnancy Calculator

How does the iron deficiency in pregnancy calculator work?

This health tool can help in estimating the iron deficit and can be used for pregnancy iron deficiency calculations. It requires the pregnancy weight of the mother at the time of testing, a target and actual hemoglobin levels and also the size of the iron stores in miligrams.

The weight can be input in either kilograms or pounds while hemoglobin values are measured in g/dL, g/L or mmol/L.

The iron store size is recommended to be input as 500 mg for all weights over 35 kilograms.

The hemoglobin threshold values for anemia in each of the three trimesters of pregnancy are as follows:

■ Less than 11 g/dL Hb during first trimester;

■ Less than 10.5 g/dL Hb during second trimester;

■ Less than 10 g/dL Hb during third trimester.

Hemoglobin levels are influenced by the state of dehydration or hyperhydration.

The pregnancy iron deficiency calculator uses the Ganzoni formula:

Total iron deficit (mg) = Weight in kg x (Target Hb - Actual Hb in g/dL) x 2.4 + Iron stores           

According to the weight, the calculator also computes the prenatal iron deficit per kilogram. This is the amount of iron which needs to be replaced so the actual hemoglobin level reaches the target value.

Iron in pregnancy

The most common deficiency remains the iron one and its addressing, especially in pregnancy remains primordial to avoid adverse outcomes such as need for RBC transfusion.

Pregnant women are advised to undergo at least two full blood count tests with one of them scheduled at 28 weeks.

Pregnant women need to receive nutritional advice in order to maximize iron intake but not all countries recommend iron supplements as routine unlike the prescription of prenatal vitamins. In case of established diagnosis of IDA, iron deficiency anemia, 100 to 200 mg of daily elemental iron is prescribed.

Parenteral iron is only considered from the second trimester in case of oral iron intolerance or lack of response.

The main cause of anemia during pregnancy regards the fact that during this time, the volume of blood in the body increases by almost 50% which in turn decreases hemoglobin concentration. When iron stores are not increased, they cannot support the new requirement of hemoglobin for the new red blood cells.

Less common causes include B12 vitamin deficiency, kidney disease, sickle cell anemia or blood loss.

Symptoms of anemia with low iron may include excessive tiredness, general feeling of weakness, dizziness, shortness of breath, low body temperature, pale skin or rapid heartbeat.

Example of a calculation

Taking the case of a patient weighing 70 kg (154.3 lbs) with a target hemoglobin value of 13 g/dL (130 g/L or 8.07 mmol/L), an actual hemoglobin of 11 g/dL (110 g/L or 6.83 mmol/L) and iron stores of 500 mg, the iron deficit is:

■ Iron deficit = 70 x (13 – 11) x 2.4 + 500 = 836 mg.

■ Iron deficit / kg body weight = 12 mg.

Since this is less than the threshold of 20 mg/kg, the deficit can be eliminated with a single infusion.

References

1) Ganzoni AM. (1970) Intravenous iron-dextran: therapeutic and experimental possibilities. Schweiz Med Wochenschr; 100(7):301-3.

2) Pavord S, Myers B, Robinson S, Allard S, Strong J, Oppenheimer C. (2011) UK guidelines on the management of iron deficiency in pregnancy. British Committee for Standards in Haematology.

3) Bayoumeu F, Subiran-Buisset C, Baka NE, Legagneur H, Monnier-Barbarino P, Laxenaire MC. (2002) Iron therapy in iron deficiency anemia in pregnancy: intravenous route versus oral route. Am J Obstet Gynecol; 186(3):518-22.

4) Litton E, Xiao J, Ho KM. (2013) Safety and efficacy of intravenous iron therapy in reducing requirement for allogeneic blood transfusion: systematic review and meta-analysis of randomised clinical trials. BMJ; 347: f4822.

5) Shafi D, Purandare SV, Sathe AV. (2012) Iron Deficiency Anemia in Pregnancy: Intravenous Versus Oral Route. J Obstet Gynaecol India; 62(3): 317–321.