In Gombe, Nigeria, and its environs, most prenatal care is provided collectively by the Federal Medical Centre, a tertiary-care centre, and the Specialist Hospital which serves patients from a broad range of socioeconomic levels. The goals of this study were to determine the prevalence of anaemia and to examine the contributions of iron, folate and vitamin B12 status to anaemia in pregnant women residing in this region. Our main finding was that 30% of the pregnant women were anaemic, using the WHO cut-off haemoglobin concentration of 105 g/L. The most common deficiency relating to anaemia in these women was iron.
This finding was not unexpected, since the diets of the population in the region are heavily reliant on grains, such as millet and sorghum, that contain large amounts of phytates which are known to interfere with the intestinal uptake of iron and other trace minerals, such as zinc and calcium. Requirements of iron during pregnancy are high, and it is difficult to meet the requirements through diet alone. Therefore, maintaining iron balance during pregnancy is dependent on maternal iron stores.
To better understand the aetiology of anaemia in our study population, we determined the proportion of anaemic and non-anaemic women who were deficient in iron (ferritin <30 ng/mL), folate (<7.7 nmol/L), or vitamin B12 (<148 pmol/L). The greatest distinction between the anaemic and the non-anaemic subjects was in the serum ferritin level: 27% of the anaemic women had serum ferritin concentrations of <10 ng/mL compared to 16.4% of the non-anaemic women. On the other hand, the incidence of vitamin B12 deficiency was similar in the anaemic (7.8%) and non-anaemic groups (10.9%), and the numbers of subjects with folate deficiency were comparable in both the groups (). Malaria was not common in women who were classified as anaemic; only 4 of the 44 anaemic women had malaria at the time of the study.
These results are similar to those reported for anaemic pregnant women in Malawi where van den Broek and Letsky (15
) reported that 23% of anaemic pregnant women in the southern part of the country were deficient in iron. One-third of anaemic subjects in that study were also deficient in vitamin B12, while another one-third were deficient in folate. Malaria and hookworm infections were found in 8% and 6% of their subjects respectively.
The most common screening test for assessing an individual's vitamin B12 status is the serum concentration of vitamin B12. Serum vitamin B12 concentrations have been shown to lack sensitivity in detecting vitamin B12 deficiency. Assays for vitamin B12, such as competitive protein-binding immunoassay used in this study, detect all forms of vitamin B12 in serum, including physiologically-inactive analogues. On the other hand, excretion of increased amounts of methylmalonic acid in urine is an early indicator of vitamin B12 deficiency. In a study of elderly individuals in the USA, 10–40% of the subjects had elevated methylmalonic acid in their urine, while their serum concentration of vitamin B12 was in the low-normal to normal range (16
). Although the vitamin B12 concentration in the sera of most women in this study was above 148 pmol/L, the lower end of the reference range, the serum concentrations we observed in this study, may not reflect the physio-logically-active amount of vitamin B12 in our subjects studied.
The second important finding of the study was the high percentage of pregnant women with an elevated serum concentration of homocysteine. The mean homocysteine level (14.1 μmol/L) of pregnant women in Gombe exceeded the upper limit of normal (i.e. 12.0 μmol/L) (16
). Since both folate and vitamin B12 are involved in a single-carbon transfer reaction that converts homocysteine to methionine, a deficiency of either vitamin can cause the serum concentration of homocysteine to be elevated. An elevated homocysteine level during pregnancy is associated with several adverse outcomes, including increased habitual spontaneous abortions, placental abruption, and preeclampsia (17
). Several of our previous studies with adolescent girls and adults of both genders have shown that moderate hyperhomo-cysteinaemia was prevalent in Nigerian populations (12
). We also reported that Nigerian women with pre-eclampsia had significantly higher serum concentrations of homocysteine than their healthy counterparts (10.1 vs 8.4 μmol/L), and their homocysteine concentrations were inversely correlated with high-density lipoprotein concentrations (21
). In the present study, serum concentrations of homocysteine correlated inversely with both folate and vitamin B12 levels ( and ). Of particular interest was the marked increase in the serum concentrations of homocysteine when the vitamin B12 levels fell below 250 pmol/L.
Few women in the present study had a serum folate level indicative of folate deficiency. However, a sub-optimal vitamin B12 status may elevate serum concentration of folate. In order for folate to be retained by cells, folate must be converted from its monoglutamate form to its polyglutamate form. The preferred substrate for the enzyme that catalyzes this reaction is the tetrahydrofolate form of folic acid (22
). Therefore, in vitamin B12 deficiency, if methyltetrahydrofolate cannot be converted to tetrahydrofolate, folate will not be retained by the cell. This condition results in high serum concentrations of folate in the face of low tissue folate levels.
There were several limitations in our study. The first was that the folate status was determined using serum samples as opposed to determining the red blood cell concentration of folate which would have provided a better indication of tissue folate status. Other nutrients, such as vitamin A and vitamin B6 that are associated with anaemia, were not measured. Subjects were also not tested for hookworm or other parasitic diseases besides malaria—a potential cause of anaemia due to intestinal blood loss. Although a comprehensive assessment of parasitic infections was not conducted in the study, such infections are common in pregnant women in Nigeria. Egwunyenga and co-workers (23
) studied more than 2,000 pregnant women in Plateau State in north-central Nigeria and found that approximately 40% and 48% of the women were infected with malaria parasites and intestinal helminths respectively.
We conclude that a high percentage of the pregnant women we studied in Nigeria were anaemic. The main contributing factor to anaemia in these women was iron deficiency. Secondly, suboptimal vitamin B12 status may contribute to elevated concentrations of homocysteine, a risk factor for neural tube defects and pre-eclampsia. Once identified, either or both of these nutritional deficiencies could be corrected by food assistance programmes or supplementation of vulnerable groups in a population. An effective method for ensuring widespread correction of specific nutritional deficiencies could be accomplished by fortification of foods similar to the fortification with folate that is common in developed countries for the prevention of neural tube defects. Because of the importance of iron stores in maintaining iron balance during pregnancy, efforts should also be directed to improving the iron stores of young women prior to pregnancy.