Suboptimal iron deficiency screening in pregnancy and the impact of socioeconomic status in a high-resource setting

Abstract

Iron deficiency (ID) anemia in pregnancy is associated with poor maternal and childhood outcomes, yet ferritin testing, the standard test for ID, is not considered part of routine prenatal bloodwork in Canada. We conducted a retrospective cohort study of 44 552 pregnant patients with prenatal testing at community laboratories in Ontario, Canada, to determine the prevalence of ferritin testing over 5 years. Secondary objectives were to determine the prevalence and severity of ID and to identify clinical and demographic variables that influence the likelihood of ID screening. A total of 59.4% of patients had a ferritin checked during pregnancy; 71.4% were ordered in the first trimester, when the risk of ID is lowest. Excluding patients with abnormally elevated ferritins, 25.2% were iron insufficient (30-44 µg/L) and 52.8% were iron deficient (≤29 µg/L) at least once in pregnancy. A total of 8.3% were anemic (hemoglobin <105 g/L). The proportion of anemic patients with a subsequent ferritin test in pregnancy ranged from 22% to 67% in the lowest and highest anemia severity categories, respectively. Lower annual household income was negatively associated with the odds of a ferritin test; compared with those in the fifth (ie, highest) income quintile, the odds of ferritin testing for patients in the first, second, and fourth quintiles were 0.83 (95% confidence interval [CI], 0.74-0.91), 0.82 (95% CI, 0.74-0.91), and 0.86 (95% CI, 0.77-0.97), respectively. These data highlight gaps in prenatal care and issues of health equity that warrant harmonization of obstetrical guidelines to recommend routine ferritin testing in pregnancy.

Graphical abstract

Figure 1.

Laboratory definition of pregnancy based on prenatal testing guidelines. The “index date” is the date of the ABO/Rh and the Rubella tests, or if they occur on separate dates but within 28 days of each other, the earlier of the two. The GBS swab must occur at least 4 months and no greater than 8 months following the index date. Weeks refer to gestational age. Timeline is not to scale.

Figure 2.

STROBE flow diagram of participants screened for eligibility in the final cohort. “Records” refer to discrete laboratory tests. STROBE, strengthening the reporting of observational studies in epidemiology.

Figure 3.

Histogram of ferritin values for 26 419 patients with a ferritin test. Of the 26 469 with a ferritin test ordered, 50 were missing results. Mean ferritin was 47 µg/L, median 36 µg/L. Inlay shows the data for higher ferritin values on an amplified y-axis.

Figure 4.

Proportion of all ferritin tests ordered per 4-week interval relative to index date. Trimesters are estimated based on an assumed gestational age of 8 to 12 weeks at the index date (first prenatal visit). Areas where the gray bars overlap indicate lower confidence in the estimated trimester.

Figure 5.

Odds of a ferritin test based on income quintile. The highest quintile (Q5) is the reference group. Annual household income was estimated using the patient’s postal code. Income quintiles were derived from provincial census data.