A contemporary proposed definition of anaemia advocated by Munoz and colleagues is Hb < 130 g/L (Munoz et al., 2017). Using this definition, we demonstrated a high prevalence of iron deficiency anaemia perioperatively in women undergoing caesarean section in a high-income country. Over one in three women were iron deficient at their first hospital appointment, and nearly one in two women with anaemia had iron deficiency. Despite these large numbers, only 68 (46%) women received treatment; 57 (84%) receiving oral iron, and 11 (16%) receiving iron infusions.
Using a Hb threshold of 130 g/L, our findings demonstrate that at all timepoints in pregnancy the prevalence of anaemia was at least 50%. In the postpartum period on discharge from hospital, the prevalence was over 40%. Importantly, nearly one in three women who were anaemic by WHO standards on discharge from hospital were iron deficient at their first hospital appointment. This finding suggests that more aggressive treatment of iron deficiency in the antenatal period is needed to reduce significant postoperative anaemia after caesarean section.
Haemoglobin values decreased and anaemia prevalence increased with gestation. A small rise in haemoglobin concentration and a small fall in anaemia prevalence was noted preoperatively. This may be explained by the known reduction in dilutional anaemia at term (Milman et al., 2007), and possibly by preoperative fasting. Preoperatively, two out of every three women were anaemic. Postoperatively, almost all women were anaemic using a threshold of < 130 g/L, and over half of the women had a discharge haemoglobin less than 110 g/L. Similarly, only a few women with postoperative anaemia received treatment with intravenous iron. Our data also demonstrated a 6.4% rate of moderate postoperative anaemia (Hb < 90 g/L) and this was consistent with previously published data reporting severe anaemia in 7% of women after caesarean section (Butwick et al., 2017). We have also shown that postoperative anaemia after caesarean section is a significant issue. WHO classifies anaemia prevalence cut-off values for public health significance as < 5% no public health problem; 5–19% mild public health problem; 20–39% moderate public health problem; ≥ 40% severe public health problem. In this study we have shown the prevalence of postoperative anaemia in women having had a caesarean section, to be at least 25% of the total cohort. This represents a moderate public health problem. As women who are discharged from the hospital after caesarean section are no longer pregnant, non-pregnant Hb reference ranges should apply to them. With such a high prevalence of postoperative anaemia, future studies should serially measure Hb levels in the weeks to months after caesarean section to determine changes in haemoglobin in this population (World Health Organization, 2022b).
Caesarean section is a moderate-to-high blood-loss open abdominal surgery, with an average blood loss of 440 mL to 800 mL (Stafford et al., 2008; Larsson et al., 2006), and associated transfusion rates of 2 to 4% (Hammad et al., 2014; Ferguson & Dennis, 2019). A physiologic dilutional anaemia of pregnancy occurs during the second trimester and the haemoglobin drop associated with elevated plasma volume has recently been demonstrated to be greater than previously reported (14 g/L compared to 5 g/L) (Churchill et al., 2019; World Health Organisation, 2011). This may contribute to perioperative anaemia if pre-pregnancy haemoglobin concentrations are in the anaemic range.
Antenatal anaemia is common. According to WHO, anaemia is present in 38% of pregnant women globally (Stevens et al., 2013). 39% of all women undergoing caesarean section in a large healthcare network in the USA (Butwick et al., 2017) were found to be anaemic. Among women receiving routine iron supplementation during pregnancy, the mean haemoglobin concentration at term ranges from 124 g/L to 129 g/L (Milman et al., 2007; Centers for Disease Control and Prevention (CDC), 1989; Milman et al., 2000).
The antenatal period therefore represents an important window of opportunity for haemoglobin optimisation (Wilson et al., 2018; Munoz et al., 2018a). Australian and UK guidelines recommend measuring haemoglobin concentration at the first hospital appointment and at 28 weeks gestation (Royal Australian and New Zealand College of Obstetricians and Gynaecologists, 2022; Royal College of Obstetricians and Gynaecologists, 2015). These time-points provide convenient windows for an initial trial of oral iron during the first trimester, and intravenous iron if anaemia persists at 28 weeks. Oral iron supplementation reduces the incidence of maternal anaemia at term by approximately 50 to 70% (Haider et al., 2013; Pena-Rosas et al., 2015), and increases haemoglobin concentration values by 8.9 g/L at term and 7.6 g/L at 6 weeks postpartum (Pena-Rosas et al., 2015). There are also trends towards a reduced incidence of low birthweight and preterm birth (Haider et al., 2013; Pena-Rosas et al., 2015). Antenatal haemoglobin optimisation may also reduce transfusion rates after caesarean and vaginal delivery (Flores et al., 2017).
Serum ferritin levels below approximately 100 μg/L represent iron stores that are inadequate for postoperative haematopoiesis (Munoz et al., 2018b). Additionally, 75 to 80% of pregnant women have absent postpartum bone marrow iron stores without iron supplementation (Puolakka et al., 1980; De Leeuw et al., 1966) due to the high net additional iron requirement of pregnancy and delivery (approximately 1000 mg) (Puolakka et al., 1980). Postoperatively, hepcidin is upregulated; consequently, oral iron is poorly absorbed (Munoz et al., 2018b). Therefore, postpartum anaemia after caesarean section will likely persist in the absence of postoperative treatment with intravenous iron. Despite this, only 13.1% of patients in our study received oral iron postoperatively, and only 1.2% received a postoperative iron infusion. Postpartum anaemia has important effects on maternal quality of life including being associated with a higher burden of depressive symptoms (Corwin et al., 2003) and adverse mother-infant interactions (Perez et al., 2005).
Specifically related to anaemia, perioperative anaemia in women undergoing caesarean section represents an important global health issue, particularly in low-income countries where iron deficiency anaemia is prevalent and caesarean section accounts for almost one-third of all operations performed.
Beyond the emphasis on caesarean section as an alternative mode of birth, there is an urgent need to raise the profile of caesarean section as a moderate risk surgery associated with the significant risk of blood loss (Dennis & Sheridan, 2019). There is a critical need to identify, classify, and treat anaemia in the early antenatal period (first hospital appointment) to decrease the prevalence of preoperative, and postoperative anaemia. The key to increasing awareness is the acceptance and acknowledgement of all individuals involved in the care of pregnant women. Also, women must be made aware that iron deficiency anaemia is highly prevalent after caesarean section and can occur in one in three pregnant women. Society can then begin to have informed discussions that consider the antenatal period as an essential time for not only preparing for the birth and care of a baby, but a time for the preparation of women for major surgery. Furthermore, essential data must be collected that includes the measurement of haemoglobin concentration and ferritin in the perioperative period including at the first hospital appointment, during third trimester, preoperatively and postoperatively. Additional iron studies including transferrin saturation, vitamin B12 and folate should be collected to determine the cause of non-iron deficiency anaemia. Despite numerous studies surrounding anaemia, there is still significant uncertainty as to what the appropriate reference range for haemoglobin should be in healthy pregnant women. This uncertainty arises because pregnancy is a unique situation compared to all other abdominal surgeries, in that the body is physiologically prepared to accommodate some level of blood loss in the healthy pregnant woman. Munoz and colleagues have recommended a preoperative Hb of 130 g/L or more in all patients. However, additional well-designed studies are needed to determine whether this is an appropriate level in the healthy pregnant woman with or without iron deficiency. Serial studies well into the postpartum period are also needed to observe the changes in haemoglobin concentration after recovery from pregnancy.
There is also a need to develop and use more precise measurements of intraoperative blood loss, such as quantitative assessment measures which use gravimetric (weight-based), volumetric (volume-based), and colorimetric (image analysis of surgical sponges and cannisters) approaches.
Our study has several limitations. These include the retrospective nature of data collection and missing data, the lack of follow up beyond discharge from hospital (which may have shown a stabilisation and perhaps increase in haemoglobin concentration), and some imprecision in the reported data (such as estimated blood loss). In addition, the use of a retrospective study design increases the possibility of unmeasured confounders, and the use of a single institution limits the generalisability of our findings to the general patient population. Not all women had a haemoglobin concentration measured at each time point, and this limits the conclusions that can be drawn regarding postoperative anaemia prevalence, as only 202 women (41%) had a discharge haemoglobin measurement. However, even if the remaining non-sampled women all had normal haemoglobin concentration values, this still leaves almost half of all women anaemic on discharge postoperatively.
Importantly, we do not present outcome data. There is, however, some evidence in the literature that anaemia in pregnancy is related to poorer outcomes in both the woman and neonate. Future studies should explore the relationship between anaemia and patient centred outcome measures in this population. Outcomes such as blood transfusion rate, postoperative infection, postoperative hypertension, depression, fatigue, bonding with baby, and breastfeeding, would be important to correlate with haemoglobin concentrations.