Table 3.
Included studies assessing maternal zinc status and sPTB.
| Author, Country | Sample Size | Zinc Measure | Outcome of the Study |
|---|---|---|---|
| (1) Sample Type | |||
| (2) Time at Which Gestation Diet Was Assessed or Sample Collected | |||
| (3) Method of Analysis | |||
| [44] Scholl, United States a | 115 with zinc intake ≤6 mg/day 699 with zinc intake ˃6 mg/day |
Dietary zinc intake 28 and 36 weeks 24 h dietary recall |
2-fold ↓ risk of delivering a preterm infant with dietary zinc intake ˃6 mg/day. OR (LMP): 1.85, 95% CI: 1.09–3.12, OR (OE): 2.13, 95% CI: 1.20–3.79 2.75 to 3.44-fold ↓ risk of delivering a very preterm infant with dietary zinc intake ˃9 mg/day. OR (LMP): 2.75, 95% Cl: 1.31–5.77, OR (OE): 3.44, 95% Cl: 1.39–8.55 |
| [94] Carmichael, United States a,b | 413 preterm and 58 early preterm 5267 term |
Dietary zinc intake Harvard food frequency questionnaires |
2-fold ↓ for preterm birth <32 weeks with zinc intake ˃ 8.0 mg/day compared to 8.0–14.2 mg/day. OR: 2.3, 95% CI: 1.2–4.5 |
| [45] Neggers, United States a | 238 preterm 1160 term |
Dietary zinc intake 18 and 30 weeks 24 h dietary recall using the nutrient database developed by the University of Minnesota |
NS association between low dietary zinc intake (less than median) and risk of PTB. OR: 1.1, 95% CI: 0.7–1.7 |
| [95] Hsu, Taiwan c | 28 preterm 423 term |
Dietary zinc intake Each trimester 24 h dietary recall |
NS in dietary zinc intake between each of the trimesters and in those who delivered preterm versus term. Preterm: 9.6–10.8 mg/day vs. term: 8.90–10.9 mg/day |
| Inadequate dietary zinc intake estimated to affect <17% of the studied population | |||
| [96] Wang, China a | 169 preterm 2912 uncomplicated |
Fasting serum zinc First and second trimester Flame AAS |
↑ risk of preterm birth with serum zinc <767 μg/L and serum zinc between 767 and 996 μg/L. aOR: 2.41, 95% CI: 1.57, 3.70; aOR: 1.97, 95% CI: 1.27, 3.05, p < 0.001 for both, respectively |
| [50] Bro, Denmark c | 34 preterm 220 uncomplicated |
Serum zinc Collected at delivery Flame AAS |
NS mean (SD) serum zinc levels in women who delivered preterm compared to term women. Preterm: 666.7 (104.6) vs. term: 679.7 (98) μg/L |
| [54] Tamura, United States c | 505 preterm and 136 early preterm 2038 uncomplicated |
Non-fasting heparin plasma zinc Collected at first prenatal visit (6 to 34 weeks) Flame AAS |
NS in the prevalence or n (%) of PTB measured between the lowest quartile and upper three quartiles of zinc. Highest: 373 (14.5) vs. lowest: 132 (15.3) NS in the prevalence (n (%)) of early PTB measured between the lowest quartile and upper three quartiles of zinc. Highest: 107 (4.2) vs. lowest: 29 (3.4) |
| Inadequate dietary zinc intake estimated to affect ≥17% of the studied population | |||
| [66] Jeswani, India c | 25 preterm 25 term |
Serum zinc Collected at 28–40 weeks AAS |
↑ mean (SD) serum zinc in women who delivered preterm women compared to term. Preterm: 1154.4 (154.1) vs. uncomplicated: 962.8 (194.8) µg/L, p ˂ 0.01 |
| [64] Goel, India d | 20 preterm 25 term |
Heparin plasma zinc Collected at delivery AAS |
↑ mean (SD) plasma zinc in mothers who delivered preterm compared to term mothers. Preterm: 842 (43) vs. term: 744 (51) μg/L, p ˂ 0.001 |
| [60] Bahl, India a | 10 preterm 97 term |
Serum zinc Collected at delivery Flame AAS |
NS mean (SD) in women who delivered Preterm that were an appropriate weight for date compared to uncomplicated. Preterm: 627 (212) vs. uncomplicated: 670 (96) µg/L |
| [65] Srivastava, India c | 26 preterm 23 term |
Heparin plasma zinc Collected at delivery Flame AAS |
NS mean (SD) plasma zinc between preterm and term mothers. Preterm: 6350 (2640) vs. term: 6310 (5090) μg/L |
a PTB defined as ˂37 weeks gestation; b Early PTB defined as ˂32 weeks gestation; c PTB defined as ≤37 weeks gestation; d PTB not defined. Bold print signifies results that were significantly different. Abbreviations: AAS: atomic absorption spectrometry; aOR: adjusted odds ratio; CI: confidence interval; LMP: last menstrual period; OE: obstetric estimate; PTB: preterm birth; SD: standard deviation.