- Design
- longitudinal nationwide cohort study using laboratory values interpreted against trimester-specific standards
- Population
- commercially insured individuals in the United States who gave birth between 2018 and 2023, with routine screening laboratory values
- Primary outcome
- prevalence of anaemia during pregnancy
- Effect
- 25.6% (95% CI 25.3-25.9) overall; 4.3% (4.1-4.4) at 4 to under 14 weeks and 24.5% (24.2-24.8) at 22 to under 30 weeks
Anaemia in pregnancy is usually estimated from diagnosis codes, which capture only what was recorded, or from selected samples. This study took a different route: laboratory haemoglobin and haematocrit values, interpreted against trimester-specific standards, in a nationwide longitudinal cohort of commercially insured people who gave birth between 2018 and 2023, restricted to values drawn at routine screening windows.
Over the course of pregnancy, 25.6% (95% CI 25.3-25.9) met criteria for anaemia at some point. At the first screen, between 4 and 14 weeks, 4.3% were anaemic. By the 22 to 30 week screen the figure was 24.5%.
The jump between the two screens is the useful part, and it is largely physiological dilution meeting an inadequate iron supply. The population studied is commercially insured Americans — among the best-resourced pregnant populations in the world — which is what makes a quarter striking, and which makes the Indian figure, where anaemia in pregnancy has long run above 50% by NFHS estimates, the more sobering comparison. The practical implication is the same in both settings: a normal booking haemoglobin does not predict the second-trimester value, so the mid-pregnancy screen has to be done and acted on, and iron started on the basis of that result rather than the first one.
- Do not let a normal booking haemoglobin substitute for the mid-pregnancy screen
- Check ferritin where available: depleted stores precede a fall in haemoglobin
- Use trimester-specific thresholds rather than a single cut-off across pregnancy
- Address adherence and gastrointestinal side effects before escalating to intravenous iron
- Indian prevalence is roughly double this figure — treat prophylactic iron and folate as a floor, not a plan
The statistics, in plain English
A prevalence of 25.6% with an interval from 25.3% to 25.9% is precise because the cohort is very large; precision says nothing about generalisability, and a commercially insured US population is not representative of anyone else. Restricting to people with laboratory values drawn in the defined windows excludes those with irregular or absent antenatal care, who are likelier to be anaemic, so this is probably an underestimate even within that population. Using trimester-specific standards rather than diagnosis codes is the methodological improvement here and is why the figure is higher than code-based estimates.
Read the rest in the app
You have read your two free briefings this month. The app carries all 27 specialties, every morning, free — and this finding is waiting in it.
Scan to keep reading on your phone. No account needed to start.
Tomorrow morning, before your first patient
One edition a day for obstetrics & gynaecology, written by the desk, every claim tied to its paper. Six minutes.
Get the app — free