Comparison of prevalence of ID and IDA (%, 95% confidence interval in parentheses) defined by low SF using current WHO threshold, current CDC threshold, and the thresholds identified from this physiologically based analysis in full populations of US pregnant women aged 15 to 49 years participating in the NHANES from 1999 to 2010 and 2015 to 2018
| . | n . | Current WHO threshold . | Current CDC threshold . | Physiologically based thresholds . | ΔID, % . | |||
|---|---|---|---|---|---|---|---|---|
| % ID . | % IDA . | % ID . | % IDA . | % ID . | % IDA . | |||
| First trimester | 216 | 8.1 (4.7-11.4) | 1.1 (0.5-2.6) | 8.4 (5.1-11.7) | 1.1 (0.5-2.6) | 18.0 (10.1-25.5) | 1.1 (0.5-2.6) | 9.6 |
| Second trimester | 454 | — | — | 32.8 (24.9-40.7) | 1.5 (0.1-3.0) | 41.6 (32.9-50.3) | 1.5 (0.1-3.0) | 8.8 |
| Third trimester | 415 | — | — | 56.2 (47.6-64.8) | 7.5 (3.4-11.7) | 68.3 (59.7-77.0) | 9.8 (5.1-14.5) | 12.1 |
| Unknown trimester | 325 | — | — | 30.7 (22.3-39.2) | 6.3 (3.1-9.4) | 41.6 (32.3-50.9) | 6.6 (3.5-9.8) | 10.9 |
| Total | 1410 | — | — | 33.9 (29.9-37.8) | 4.6 (3.0-6.2) | 44.3 (40.0-48.7) | 4.8 (3.2-6.5) | 10.4 |
| . | n . | Current WHO threshold . | Current CDC threshold . | Physiologically based thresholds . | ΔID, % . | |||
|---|---|---|---|---|---|---|---|---|
| % ID . | % IDA . | % ID . | % IDA . | % ID . | % IDA . | |||
| First trimester | 216 | 8.1 (4.7-11.4) | 1.1 (0.5-2.6) | 8.4 (5.1-11.7) | 1.1 (0.5-2.6) | 18.0 (10.1-25.5) | 1.1 (0.5-2.6) | 9.6 |
| Second trimester | 454 | — | — | 32.8 (24.9-40.7) | 1.5 (0.1-3.0) | 41.6 (32.9-50.3) | 1.5 (0.1-3.0) | 8.8 |
| Third trimester | 415 | — | — | 56.2 (47.6-64.8) | 7.5 (3.4-11.7) | 68.3 (59.7-77.0) | 9.8 (5.1-14.5) | 12.1 |
| Unknown trimester | 325 | — | — | 30.7 (22.3-39.2) | 6.3 (3.1-9.4) | 41.6 (32.3-50.9) | 6.6 (3.5-9.8) | 10.9 |
| Total | 1410 | — | — | 33.9 (29.9-37.8) | 4.6 (3.0-6.2) | 44.3 (40.0-48.7) | 4.8 (3.2-6.5) | 10.4 |
Unweighted n, all other analyses are weighted. Full NHANES sample with Hb and SF data were used for this analysis with no data exclusions. ID defined as follows: current WHO threshold is SF <15 μg/L for first trimester only; current CDC threshold is SF ≤15 μg/L for all trimesters; and physiologically based analysis reveals SF <25 μg/L for first trimester and SF<20 μg/L for second, third, and unknown trimesters. Anemia defined as follows: current WHO threshold is Hb <110 g/L for all trimesters; current CDC thresholds are Hb <110 g/L for first trimester, Hb <105 g/L for second trimester, Hb <110 g/L for third trimester, and Hb <110 g/L for unknown trimester.
IDA defined as both ID and anemia. Current CDC Hb thresholds were used for defining physiologically based IDA. ΔID indicates the difference between the proportion of pregnant women identified as iron deficient by using the physiologically based SF thresholds minus the CDC threshold.