Table 2:
Adjusted risk differences and adjusted absolute risks for each adverse birth outcome by supplementation strategy
| Folic acid supplementation only (n=1133) | Iron supplementation only (n=36 334) | Iron and folic acid supplementation (n=23 101) | Multiple micronutrient supplementation (n=31 588) | |
|---|---|---|---|---|
| Stillbirth | ||||
| Risk difference | 1·71% (−0·83 to 4·26) | 0·56% (0·31 to 0·81) | 0·00 (ref) | −0·06% (−0·32 to 0·19) |
| Risk | 3·51% | 2·36% | 1·80% | 1·74% |
| Preterm birth (<37 weeks) | ||||
| Risk difference | 5·75% (1·38 to 10·13) | 2·39% (1·78 to 3·00) | 0·00 (ref) | −1·06% (−1·69 to −0·42) |
| Risk | 18·43% | 15·07% | 12·68% | 11·63% |
| Very preterm birth (<32 weeks) | ||||
| Risk difference | 0·93% (−0·37 to 2·24) | 0·92% (0·63 to 1·21) | 0·00 (ref) | −0·50% (−0·77 to −0·23) |
| Risk | 3·32% | 3·31% | 2·39% | 1·89% |
| Small for gestational age (<10th percentile) | ||||
| Risk difference | −0·66% (−4·69 to 3·36) | −0·05% (−0·69 to 0·59) | 0·00 (ref) | 0·53% (−0·17 to 1·24) |
| Risk | 14·78% | 15·39% | 15·44% | 15·97% |
| Very small for gestational age (<3rd percentile) | ||||
| Risk difference | 0·16% (−3·01 to 3·34) | 0·20% (−0·21 to 0·61) | 0·00 (ref) | 0·39% (−0·06 to 0·84) |
| Risk | 5·75% | 5·79% | 5·59% | 5·98% |
| Neonatal death (in hospital ≤28 days) * | ||||
| Risk difference | 0·77% (−0·80 to 2·34) | 0·22% (0·04 to 0·40) | 0·00 (ref) | −0·09% (−0·27 to 0·09) |
| Risk | 1·71% | 1·16% | 0·94% | 0·86% |
| Stillbirth or neonatal death * | ||||
| Risk difference | 2·43% (−0·48 to 5·34) | 0·77% (0·47 to 1·08) | 0·00 (ref) | −0·15% (−0·46 to 0·16) |
| Risk | 5·16% | 3·51% | 2·73% | 2·58% |
| Low birthweight (<2500 g) | ||||
| Risk difference | 5·46% (1·09 to 9·83) | 1·24% (0·66 to 1·82) | 0·00 (ref) | −0·99% (−1·59 to −0·38) |
| Risk | 16·92% | 12·70% | 11·46% | 10·48% |
| Very low birthweight (<2000 g) | ||||
| Risk difference | 3·08% (−0·04 to 6·20) | 1·00% (0·63 to 1·38) | 0·00 (ref) | −0·56% (−0·94 to −0·19) |
| Risk | 7·36% | 5·29% | 4·28% | 3·72% |
| 3rd trimester anaemia (haemoglobin <11g/dL) | ||||
| Risk difference | 7·23% (1·27 to 13·18) | −0·95% (−3·51 to 1·62) | 0·00 (ref) | −0·71% (−2·43 to 1·00) |
| Risk | 38·67% | 30·50% | 31·44% | 30·73% |
| Caesarean | ||||
| Risk difference | 3·25% (−1·89 to 8·39) | −0·69% (−1·43 to 0·05) | 0·00 (ref) | −2·67% (−3·47 to −1·87) |
| Risk | 26·94% | 23·00% | 23·69% | 21·02% |
| Short length-for-age (<10th percentile) | ||||
| Risk difference | −0·24% (−3·30 to 2·81) | 0·60% (0·06 to 1·13) | 0·00 (ref) | 0·46% (−0·12 to 1·04) |
| Risk | 9·30% | 10·14% | 9·55% | 10·00% |
Data are risk (%) or risk difference (95% CI). Risk differences are adjusted for HIV status (positive or negative), first haemoglobin concentration in pregnancy (restricted cubic splines with five knots at 9·5 g/dL, 10·2 g/dL, 11·9 g/dL, 13·4 g/dL, and 13·8 g/dL), first weight in pregnancy (restricted cubic splines with five knots at 47·9 kg, 53·5 kg, 62·0 kg, 73·5 kg, and 86·0 kg), region of first antenatal care visit, age (restricted cubic splines with three knots at 19, 27, and 36 years), year of booking (2014–16, 2017–18, and 2019–20), trimester of booking (first [<12 weeks’ gestation] or second [12–24 weeks’ gestation]), employment (salaried, other, or unknown), education (secondary or higher, primary or lower, or missing), parity (first or missing, and second and more), season (dry [April–October], rainy [November–March]), smoking (yes, no, or missing), and alcohol (yes, no, or missing) via inverse probability weighting. The models for each outcome are additionally adjusted for first haemoglobin concentration in pregnancy (modelled linearly). We used log-binomial models to estimate risk ratios and linear probability models (fit by specifying an identity link and binomial distribution) to estimate risk differences. Models did not converge for third trimester anaemia so in this case Poisson models with robust variance were used. Absolute risks are adjusted for the same set of variables and are calculated by standardising the inverse probability weighted risk estimates to the distribution of the first haemoglobin in pregnancy. The mean stabilised inverse probability weight was 1·01 (99th percentile 3·19).
Restricted to liveborn infants (98% of births).