Suboptimal Screening for Iron Deficiency in Pregnancy in a High Resource Setting

Background: Iron deficiency (ID) and ID anemia (IDA) are common in pregnancy. ID, even without anemia is associated with poor outcomes including maternal and childhood neurocognitive dysfunction, low birth weight, prematurity, and childhood anemia. In spite of this, major obstetrical guidelines do not recommend routine screening for ID in pregnancy. To date, the rates of ferritin testing among these women have not been reported.

Aims: The primary objective was to determine the point prevalence of ferritin testing over a five-year period among pregnant women with prenatal testing at outpatient private laboratories in Ontario, Canada. Secondary objectives were to determine the point prevalence and severity of ID, and to identify clinical and demographic variables that influence the likelihood of ID screening in this population.

Methods: We conducted a retrospective cohort study of pregnant women ages 13-54 years in Ontario, Canada. Out-patient laboratory data was provided by Dynacare, a large laboratory company representing approximately 30% of all non-hospital outpatient testing in the province. Tests ordered between January, 2013 and June, 2018 were retrieved. A pregnancy taken to term was inferred from the co-occurrence of a Rubella test and a blood group/Rh test (the “index date”) followed by a Group B Streptococcus (GBS) vaginal swab ≥ 4 months and ≤ 8 months later (Figure 1). The duration of pregnancy was defined as 4 weeks prior to and 32 weeks following the index date. Multiple pregnancies per patient were included, provided a minimum of 365 days elapsed between pregnancies. Women were excluded if ordering providers were not physicians, nurse practitioners or midwives. Normal iron stores, mild ID, moderate ID and severe ID were defined as ferritin levels of 45-150 µg/L, 30-44.9 µg/L, 15-29.9 µg/L and <15 µg/L, respectively. Annual household income was estimated using the patient’s postal code and Statistics Canada census data. Research ethics board approval was obtained. Dynacare was not involved in the design of the study nor in its analysis.

Results: 4,291,442 laboratory records were retrieved from the Dynacare database. 44,552 women representing 47,590 pregnancies were eligible for inclusion (Figure 2), 3,003 of whom had >1 eligible pregnancy. Of these 44,552 women, 26,469 (59.4%, 95%CI 59.0%-59.9%) had a ferritin checked during pregnancy. 16,525 (62.4%) had a single ferritin test, while 9,944 (37.6%) had ≥2 ferritin tests. The mean ferritin value was 47 µg/L (SD 40) with a median of 36 µg/L (IQR 21-61 µg/L). After excluding women with abnormally elevated ferritins (>150), 45.6% had normal iron stores, 25.2% mild ID, 36.3% moderate ID and 22.9% severe ID on at least one occasion in pregnancy. Only 30.2% of women had never been iron deficient (all ferritin levels 50-150 µg/L). 71.4% of ferritin tests were ordered at the index date (Figure 3). General practitioners and obstetrician/gynecologists ordered the majority of ferritin tests (48.1% and 32.1%, respectively), while physicians from other specialties, midwives and nurse practitioners ordered 7.7%, 11.7% and 2.3% of all ferritin tests, respectively. Compared to women in the fifth (i.e. highest) income quintile, the odds of any ferritin test for women in the first (lowest), second, and fourth income quintiles were 0.83 (95%CI 0.74-0.91), 0.82 (95%CI 0.74-0.91), and 0.86 (95%CI 0.77-0.97), respectively (Table 1). Among the 34,034 women who had at least one hemoglobin check in pregnancy, 8.3% were anemic (hemoglobin <105 g/L) on at least one occasion. The proportion of anemic women with a subsequent ferritin test in pregnancy increased with anemia severity, ranging from 22% to 67% of women in the lowest and highest anemia severity categories, respectively (Table 2).

Conclusion: ID affects more than half of pregnancies in Ontario, with 1 in 4 pregnancies complicated by severe ID. Despite this, 1 in 3 pregnant women are not screened with a ferritin. The vast majority of ID screening occurs in the first trimester, when the risk of ID is lowest. Anemia affected 8% of pregnancies, yet the underlying etiology was rarely investigated unless severe. Annual household income was significantly associated with the odds of a ferritin check. These important gap in care should be addressed by revising obstetrical guidelines to recommend routine ferritin testing in pregnancy.