Despite the high burden of anaemia in pregnancy in low resource setting and effectiveness of antenatal iron supplementation, we found that only 12% of participants adhered to iron supplements. Similarly very low adherence to iron supplements has been shown in the Scandinavia of 27% . Conversely, higher levels of adherence to iron supplements has been reported in Nigeria and Senegal of 88 and 58% respectively [5, 7]. The adherence to iron supplements in this study was very low compared to that reported in other African countries. It is possible that the adherence levels seen in Senegal were due to the fact that a lower cut off (70%) was used to assess adherence. The differences in levels of adherence can be explained by the different methods used in data collection and definition of adherence in the studies. It has been suggested adherence to medication should be defined as a patients taking 90% or more of prescribed medicine . The general weakness of most studies assessing adherence is the use of self reports in measurement of adherence. The challenge with self reports is that patients tend to overestimate their adherence [9,10,11]. For example in a study done in Iran, 80% of the pregnant women reported taking their iron supplements but this could only be confirmed in 21% of participants after examining the stool samples .
Using the visual analogue scale, about 12% of participants adhered to their iron supplements in this study. VAS is a tool used in data collection of adherence where the participant judges herself/himself on a given scale in absence of the interviewer has been suggested to be reliable and cheap. Previous studies done to assess adherence to ARVs, anti-TB drugs and pain assessment have identified the VAS as a reliable method of assessing adherence in resource limited settings [10, 13]. Other methods like pill count have been used but it is time consuming.
One of the main findings in our study was that mothers were not getting enough iron supplements to last them till the next visit were less likely to adhere to the supplements as prescribed. Galloway et al.  in a systemic review identified supplies as the main reason that women don’t comply to their iron supplements. In a study done in Vietnam, supplies were identified as the most important factor affecting adherence . Most women, if provided with adequate iron supplements, whether pills or syrup are likely to take them [14, 16]. The burden of insufficient supplies of iron supplements is still reflected in the USAID cross country report across 33 developing countries with less than 50% of pregnant women having bought or received iron supplements in the preceding pregnancy in the eight African countries studied .
Another factor that was independently associated with adherence was providing women with information on importance of iron supplements through health talks. Previous studies have shown that providing mothers with information is one of the ways to improve the effectiveness of iron supplementation programmes [17, 18]. Patients who know why they are taking their medication and how to deal with the possible complications that may arise are likely to adhere to their medications [14, 18, 19]. Health talks during pregnancy are a very good avenue for conveying massages to the pregnant women.
Pregnant women who had attended the antenatal clinic four or more times were more likely to adhere to their iron supplements than their counterparts after controlling all factors. In a cross country survey carried out in 33 developing countries in Africa, Asia and Latin America, there was no statistically significant correlation between the median number of ANC visits that a mother had and the number of days women consumed their iron tablets . Prior studies have shown that the number of antenatal visits had no added advantage to maternal welfare when compared to the four ANC visits recommended by WHO provided there were no maternal complications . The possible explanation is that, women who attended more than four times are likely to have had a complicated pregnancy and therefore adherence issue discussed with physician.
From our study, side effects were one of the main reasons that mothers gave for failing to adhere to their iron supplements. There’s conflicting evidence regarding the impact of side effects on adherence to iron supplements. While some studies show that side effects are actually the main reason why some mothers stop taking their drugs, others argue otherwise. In a study by Nir Melamed to assess the effect of side effects on compliance, it was found that although 45% of the participants reported at least one side effect, only 18.3% attributed discontinuation of therapy to side effects . Different studies that have reviewed iron supplementation programmes show that the proportion of pregnant women who stop taking drugs due to side effects are actually low [14, 16, 18, 21, 22]. In Norway, women receiving a placebo complied as well as those on iron supplements, suggesting that side effects may actually not be important . In Tanzania, women who were taking the conventional iron supplements complied less than those who were on a gastric delivery system, indicating that side effects actually did affect compliance .
We were surprised to find that formal employment was associated with non adherence, considering the fact that these are usually women of higher education status and better socio-economic status. We would ideally expect these mothers to be better informed about the supplements and be in a better position to buy more drugs in case stocks run out. While our findings are in agreement with those of Nordeng , they are contradictory to those of Muture in his study of adherence to anti- TB drugs [11, 24]. It is possible that mothers in formal employment are very busy and would frequently forget to take the iron supplements. We found no association between age, parity, marital status and adherence.
This study used the visual analogue scale which allows patients to score their adherence in a range of 0–100 without being observed. This may have led to over estimation of adherence to iron supplements. This study assessed adherence for over 30 days yet in some cases the participants were received a supply of less than that in the hospital pharmacy. The patients are usually given a prescription by the attending clinician and asked to buy from private pharmacy when supply is inadequate. We feel this may not have had a very big impact since a month’s supply of antenatal iron supplements cost less than a dollar which is usually affordable by most mothers.
Assessing adherence by measuring serum concentrations of radiologically labeled iron supplements would have been a more objective way of measuring adherence. However this is very costly and may not feasible in studies with large number of participants.