You're right that anaemia can affect milk production, and may be a concern if a mum has had a big blood loss after birth.
However, anaemia in preganacy... it's a bit of a minefield. Essentially, the use of Hb levels as an indicator of anaemia in late pregnancy is very dubious. Late in pregnancy there are well documented physiological changes to the blood volume. These are incredibly often mis-interpreted as anaemia.
The following is an extract from the Primal Health Research newsletter vol 7 no 4 written by Michel Odent and including references:
"When a woman has a haemoglobin concentration in the region of 9.0 or 9.5 at the end of her pregnancy, there are two possibilities. More often than not she will meet a practitioner (doctor or midwife) who is not interested in epidemiological studies and who thinks that iron deficiency in pregnancy can be detected via the haemoglobin concentration. She will be told that she is anaemic and she will be given iron tablets. She will understand that there is something wrong in her body that needs to be corrected.
It can happen, on the other hand, that a pregnant woman with a similar haemoglobin concentration meets a practitioner who is aware of the most significant epidemiological studies and who is interested in placental physiology. This practitioner has digested the huge and authoritative study by a London team about the relation between maternal haemoglobin concentration and birth outcomes (1). Birth outcomes of 153 602 pregnancies were analysed (the haemoglobulin measurement used in the study was the lowest recorded during pregnancy). They found that the highest average birth weight was in the group of women who had a haemoglobin concentration between 8.5 and 9.5. Their main conclusion was that "the magnitude of the fall in haemogloblin concentration is related to birth weight".A similar pattern occurred in all ethnic groups. Furthermore it appeared that when the haemoglobin concentration fails to fall below 10.5, there is an increased risk of low birth weight and preterm delivery. Similar conclusions have been reached by other - yet smaller - epidemiological studies (2,3). This sort of practitioner is also probably aware of the many studies that fail to demonstrate that iron supplementation may improve birth outcomes (4). When such a practitioner suspects anaemia, he (she) prescribes specific tests such as erythrocyte protoporphyrin, transferrine saturation or serum ferritin.
References
-1- Steer P, Alam MA, Wadsworth J, Welch A. Relation between maternal haemoglobin concentration and birth weight in different ethnic groups. BMJ 1995; 310:489-91
-2- Koller O, Sandvei R, Sagen N. High hemoglobin levels during pregnancy and fetal risk. Int J Gynaecol Obstet 1980; 18:53-56.
-3- Garn SM, et al. Maternal hematologic levels and pregnancy outcome. Semin Perinatol 1981; 5:155-62.
-4- Hemminki E, Starfield B. Routine administration of iron and vitamins during pregnancy. Br J Obst Gynaecol 1978; 85: 404-410."