. 2023 Jul 5;102(9):1147–1158. doi: 10.1111/aogs.14607

TABLE 2.

Summary of results: Maternal and infant primary outcomes.

Outcomes	Anticipated absolute effects ^a (95% CI)		Relative effect (95% CI)	No. of participants (studies)	Certainty of the evidence (GRADE)
Outcomes	Risk with no oral iron supplements	Risk with oral iron supplements	Relative effect (95% CI)	No. of participants (studies)	Certainty of the evidence (GRADE)
Maternal iron deficiency anemia at term (37 weeks' gestation or more)	177 per 1.000	90 per 1.000 (67–124)	RR 0.51 (0.38–0.70)	1670 (4 RCTs) ^b	⨁⨁⨁◯ MODERATE ^c
Maternal iron deficiency at term (37 weeks' gestation or more)	672 per 1.000	497 per 1.000 (403–618)	RR 0.74 (0.60–0.92)	1663 (4 RCTs) ^b	⨁⨁◯◯ LOW ^c ^, ^d
Maternal high Hb concentrations during pregnancy (more than 130 g/L)	106 per 1.000	100 per 1.000 (10–1.000)	RR 0.94 (0.09–10.07)	1346 (3 RCTs) ^e	⨁◯◯◯ VERY LOW ^c ^, ^f ^, ^g ^, ^h
Small for gestational age	177 per 1.000	69 per 1.000 (30–152)	RR 0.39 (0.17–0.86)	213 (1 RCT) ⁱ	⨁⨁◯◯ LOW ^j ^, ^k
Low birthweight (less than 2500 g)	121 per 1.000	36 per 1.000 (16–82)	RR 0.30 (0.13–0.68)	361 (2 RCTs) ^l	⨁⨁⨁◯ MODERATE ^m
Preterm birth (before 37 weeks' gestation)	98 per 1.000	88 per 1.000 (46–167)	RR 0.90 (0.47–1.71)	361 (2 RCTs) ^l	⨁⨁◯◯ LOW ^g ^, ^m

Note: GRADE Working Group grades of evidence. High certainty: We are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: We are moderately confident in the effect estimate: The true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: Our confidence in the effect estimate is limited: The true effect may be substantially different from the estimate of the effect. Very low certainty: We have very little confidence in the effect estimate: The true effect is likely to be substantially different from the estimate of effect. Maternal elevated iron status and congenital anomalies are not included in the table as no trials reported these outcomes.

Abbreviations: CI, confidence interval; Hb, hemoglobin; RCTs, randomized clinical trials; RR, risk ratio.

^{^a}

The risk in the intervention group (and its 95% CI) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI).

^{^b}

Tura et al. (1989), ¹⁴ Cogswell et al. (2003), ¹⁶ Falahi et al. (2011), ¹⁹ Zhao et al. (2015). ²⁰

^{^c}

Several trials contributing data had design limitations.

^{^d}

Moderate/high heterogeneity: I ² = 58%.

^{^e}

Cogswell et al. (2003), ¹⁶ Zhao et al. (2015),²⁰ Alizadeh & Salehi (2016). ²¹

^{^f}

High heterogeneity: I ² = 83%.

^{^g}

Wide 95% CI.

^{^h}

Cogswell et al. ¹⁶ reported higher incidence of elevated Hb concentration at term in the placebo group. However, the incidence of elevated Hb at 28 weeks' gestation was similar between groups, whereas the conflicting estimate from term was affected by substantial loss to follow‐up. Excluding the trial from the meta‐analysis gave the following result: RR: 2.19, 95% CI: 1.64–2.93, I ² 0%; 2 RCTs, 1194 women; moderate‐certainty evidence.

^ⁱ

Cogswell et al. (2003). ¹⁶

^{^j}

The trial contributing data had design limitations.

^{^k}

Small sample size.

^{^l}

Cogswell et al. (2003), ¹⁶ Falahi et al. (2011). ¹⁹

^{^m}

Both trials contributing data had design limitations.