43. Iron & pregnancy.
iron requirements in singleton pregnancy increase from about 2.5 mg. per day in the first trimester to about 6.5 mg. per day in the third trimester.
|b.||> 90% of anaemia in pregnancy is of the iron deficiency type.||True|
|c.||ferritin levels are the most accurate measure of iron deficiency.||True|
|d.||~ 40% of pregnant women will have side-effects on oral iron.||True|
|e.||side effects of oral iron vary according to the particular salt used.||False|
|f.||vitamin C enhances absorption of iron.||True|
|g.||intramuscular preparations of iron exist.||True|
|h.||intravenous preparations of iron no longer exist since the withdrawal of iron dextran preparations due to the risk of anaphylaxis.||False|
|i.||ferrous salts are better absorbed than ferric salts.||True|
|j.||erythropoietin has been used in extreme cases and is not contraindicated in pregnancy.||True|
(See also MCQ1, question 26, MCQ2, question 26 & MCQ7, question 22.)
Iron deficiency is common before pregnancy.
Menstruation is a significant drain on iron stores.
The Pill has reduced this problem compared with decades ago, but some women still have inadequate dietary iron intake.
Remember vegetarians whose diet adds additional difficulties.
Then pregnancy imposes a big increase in iron requirements.
The red cell mass rises by about 20% and the baby needs a load too.
The arithmetic is that iron requirements go up by a factor of 2-3 in pregnancy.
The average daily requirement is ~ 4mg.
You will recall from student days that demand outstrips the supply from a normal diet in pregnancy.
Serum ferritin levels are reckoned to be the best gauge of total-body iron stores.
Iron-deficiency anaemia is hypochromic and microcytic.
It used to be the norm for all pregnant women to be given iron supplements.
Current thinking is that this improves the blood picture, but that there is no evidence of clinical benefit.
Equally there is no evidence that the policy causes harm.
It has been argued, for example, that increasing the red cell mass thickens the blood.
This could impede placental blood flow or increase the risk of venous stasis and thrombosis.
The WHO takes an Hb of 11 gm. / dl. as the starting point for treatment, but this is not universally agreed, and the Americans take 10.5.
In this country many would not start treatment unless the Hb fell below 10, or even 9 if the woman remained symptom-free.
Nelson-Piercy in the Handbook of Obstetric Medicine says that levels < 10.5 gm. / dl. should be regarded as abnormal.
That would be a reasonable standard for the exam.
The usual treatment is oral iron.
You will remember from undergraduate pharmacology that ferrous salts are better absorbed than ferric, so are the more common.
Vitamin C increases absorption, but it is generally thought that the extra cost of preparations containing vitamin C is not justified.
All oral preparations run the risk of gut upsets.
About 30% - 40% get side-effects.
This is mainly dose-related and not dependent on which salt is prescribed.
There are slow-release preparations that seem to reduce unpleasant symptoms.
They work by releasing the active substances further down in the bowel.
However, most iron is absorbed in the upper duodenum (does this also ring undergraduate bells?).
So these preparations are much less efficient at getting iron into the patient.
If a patient fails to respond (Hb should rise by about 0.8gm. per week), you are probably dealing with failure to take the drug.
Reducing the dose may reduce the side-effects and encourage consumption.
I routinely check an MSSU in this situation as I have seen a number of patients over the years who have started to respond when asymptomatic bacteruria has been eradicated.
This is not in the books, so won’t appear in the exam.
If she still fails to respond, you need to think of other causes or additional factors: thalassaemia, folate deficiency etc.
Confirm the iron deficiency: a ferritin level < 12μg/litre is diagnostic.
Ferritin levels are reckoned to run in parallel with total body-iron stores.
The exception is that they may rise in response to:
inflammatory diseases (e.g. Rheumatoid Arthritis)
and malignancy, even when iron stores are low.
Talk to the haematologist if the response is poor.
IM and IV preparations can be used and rapidly reload depleted stores.
I.M. iron is effective and not associated with a significant level of side-effects or allergic reactions.
It has to be given by deep IM injection.
Traditional teaching is that if it leaks back into the sub-cutaneous tissues it will cause more pain and tissue staining (and this can be spectacular).
Midwives were taught to use a “Z-technique”.
The subcutaneous tissue was pulled in one direction and the needle stuck through the displaced tissue into the underlying muscle.
When the needle was removed, the subcutaneous tissue was released.
The idea was that the needle’s path through the subcutaneous tissue would be at an angle to its path through the muscle once the needle was out.
I can’t see where the “Z” came from and I have no idea if the technique does what is intended.
There are IV preparations.
They used to have a bad reputation because of allergic reactions, but the newer ones are much safer in this respect.
Folate requirements go up by a factor of at least 10.
The average diet cannot keep up with this either.
An interesting consequence is that about ¼ of pregnant women have megaloblastic changes in bone marrow.
Most of them do not show megaloblastic changes in peripheral blood.
I have used erythropoietin once.
The girl was a Jehovah’s Witness who nearly bled to death after delivery.
She dropped her haemoglobin to 2.
Remarkably, she did not die - heart failure can be expected when the Hb is < 4.
We loaded her with every haematinic we could think of and gave her erythropoietin.
The response was dramatic.
I used to see her mother from time to time around the hospital for years afterwards.
I think she may have been a pastor or regular visitor to the sick among her brethren.
It used to give me quite a jolt, remembering the terrible worry her daughter had caused.
In fact the daughter had another pregnancy with us a few years later without a hitch.
I have not used erythropoietin in pregnancy, but the books say that it is safe and effective.
There have been papers suggesting that Fe-deficiency anaemia is associated with:
intra-uterine growth retardation
and other problems.
But there is no consensus.
|Return to MCQ 1, question 26: "Physiological changes in pregnancy"|
|Return to MCQ 2, question 26: "Haemoglobin < 10gm./ dl."|
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