Table 2.
Meta‐analysis of association between high maternal Hb and child outcomes
| LBW OR (95% CI) | PTB OR (95% CI) | SGA OR (95% CI) | Stillbirth OR (95% CI) | |
|---|---|---|---|---|
| Timing: high maternal Hb (>130 g/L) by timing | ||||
| Preconception | 1.04 (0.93−1.16)* | 1.06 (1.00−1.13)* | 1.03 (0.97−1.10)* | 0.83 (0.52−1.33)* |
| First trimester | 1.34 (0.52−3.46)* | 0.93 (0.84−1.03) | 1.12 (0.99−1.27) | 1.28 (0.96−1.70)* |
| Second trimester | 1.40 (1.02−1.93) * | 1.07 (0.83−1.39) | 1.54 (1.31−1.81) * | |
| Third trimester | 0.58 (0.45−0.74) * | 0.92 (0.55−1.56)* | 1.08 (0.92−1.27)* | 2.31 (1.30−4.10) * |
| Cutoff: high maternal Hb at any time during pregnancy by cutoff | ||||
| ≥120 g/L** | 1.41 (0.94−2.13) | 1.16 (0.97−1.38) | 1.19 (1.08−1.31) | 1.38 (1.11−1.73) |
| ≥130 g/L | 1.61 (0.82−3.16) | 1.14 (0.95−1.37) | 1.22 (1.10−1.35) | 1.59 (1.14−2.22) |
| ≥140 g/L | 1.37 (0.44−4.23) | 1.10 (0.84−1.46) | 1.18 (0.97−1.42) | 2.30 (1.38−3.85) |
| ≥150 g/L | 0.78 (0.19−3.18)* | 1.01 (0.55−1.85) | 0.92 (0.55−1.56)* | |
| ≥160 g/L | 0.78 (0.19−3.18)* | 0.42 (0.14−1.29)* | 0.61 (0.22−1.56)* | |
| Overall estimate*** >130 g/L | 1.80 (0.86−3.77) | 1.17 (0.94−1.45) | 1.22 (1.08−1.37) | 1.88 (1.21−2.91) |
notes: The sample size for individual studies is provided in Table S2 (online only), and the total number of studies included in each Hb cut‐off effect estimate and timing are specified in Table S8 (online only). A number of studies included for an overall estimate (>130): LBW (5), PTB (10), SGA (4), and stillbirth (4). Reference groups for individual studies included in the meta‐analysis were highly variable, with some providing a range (e.g., 110−119 g/L) and others a cut off (≥110), with little consensus on what represents a “healthy” reference value. Reference groups for all studies included in meta‐analyses can be found in Figures S1−S4 (online only). Categories are cumulative; for example, the ≥140 g/L category includes studies using the ≥140 g/L cutoff or any subset where all Hb values were ≥140 g/L. Definitions: LBW, low birth weight (<2500 g); PTB, preterm birth (birth at <37 weeks gestation); SGA, small‐for‐gestational‐age (birth weight below the 10th percentile for gestational age or as defined by study authors); stillbirth (as defined by study authors); perinatal mortality (defined as the sum of fetal deaths (28 weeks or more gestation) and infant deaths occurring less than 7 days after birth); first trimester: ≤13 weeks; second trimester: 1–26 weeks; third trimester: ≥27 weeks. Bold values are statically significant with P < 0.05.
*Summary estimates from meta‐analyses of <3 studies.
**Summary estimates for ≥120 g/L presented, but high Hb defined as ≥130 g/L for inclusion in meta‐analysis summary estimates.
***Overall estimates using Hb concentrations measured at any point during pregnancy.