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Table 2 Maternal, delivery and infant characteristics as risk factors for preterm birth—overall and site-specific risk ratios with 95% confidence intervals and p values

From: Rates and risk factors for preterm birth and low birthweight in the global network sites in six low- and low middle-income countries

Characteristic Relative risk (95% CI), p-value
Overall, all sites DRC Zambia Kenya Guatemala Belagavi Nagpur Pakistan
Maternal age (20–35) 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
 < 20 1.31 (1.26,1.37), < .0001 1.45 (1.30, 1.63), < .0001 1.36 (1.28, 1.44), < .0001 1.51 (1.40, 1.62), < .0001 1.30 (1.22, 1.38), < .0001 1.09 (0.99, 1.20), 0.0880 1.25 (1.07, 1.47), 0.0061 1.05 (0.93, 1.20), 0.4115
 > 35 1.07 (1.02,1.12), 0.0078 1.08 (1.00, 1.18), 0.0636 1.13 (1.02, 1.25), 0.0196 1.05 (0.93, 1.19), 0.3893 1.13 (1.02, 1.24), 0.0151 2.22 (1.56, 3.16), < .0001 1.00 (0.68, 1.49), 0.9847 0.94 (0.86, 1.03), 0.1647
Maternal education (University+) 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
 No formal education 1.32 (1.23,1.41), < .0001 2.30 (1.01, 5.25), 0.0474 1.77 (1.46, 2.14), < .0001 1.48 (1.04, 2.09), 0.0294 1.18 (0.97, 1.44), 0.0969 1.29 (1.11, 1.48), 0.0006 1.50 (1.27, 1.77), < .0001 1.13 (0.94, 1.35), 0.1895
 Primary/secondary 1.17 (1.11,1.23), < .0001 2.20 (0.94, 5.14), 0.0684 1.57 (1.26, 1.95), < .0001 1.23 (1.08, 1.40), 0.0013 1.07 (0.91, 1.25), 0.4209 1.01 (0.92, 1.12), 0.7693 1.39 (1.27, 1.52), < .0001 1.01 (0.86, 1.18), 0.9492
Parity (1–2) 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
 0 1.12 (1.07, 1.16), < .0001 1.49 (1.37, 1.62), < .0001 1.13 (1.05, 1.23), 0.0018 1.39 (1.25, 1.55), < .0001 1.00 (0.94, 1.06), 0.9133 1.10 (0.98, 1.24), 0.0944 1.05 (0.98, 1.12), 0.1429 0.98 (0.92, 1.05), 0.5708
 > 2 0.93 (0.89, 0.97), 0.0002 0.95 (0.88, 1.02), 0.1329 0.95 (0.88, 1.03), 0.2046 1.11 (1.03, 1.19), 0.0045 0.94 (0.87, 1.02), 0.1227 1.07 (0.96, 1.19), 0.2446 1.31 (1.04, 1.65), 0.0243 0.87 (0.82, 0.92), < .0001
Consumption of vitamins/calcium/iron 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
 Not consumed 1.18 (1.11, 1.25), < .0001 1.33 (1.20, 1.47), < .0001 1.24 (0.59, 2.61), 0.5700 1.46 (1.07, 2.00), 0.0178 1.10 (0.98, 1.23), 0.1168 1.78 (1.53, 2.08), < .0001 1.29 (0.86, 1.93), 0.2139 1.06 (1.03, 1.10), 0.0006
Received tetanus toxoid immunization 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
 Did not receive 1.08 (1.02, 1.14), 0.0050 1.15 (0.99, 1.32), 0.0656 0.90 (0.75, 1.07), 0.2436 1.10 (0.96, 1.27), 0.1796 0.96 (0.88, 1.05), 0.3776 0.89 (0.30,2.64), 0.8286 1.39 (0.98,1.97), 0.0680 1.12 (1.07,1.18), < .0001
Number of ANC visits (4+) 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
 0 1.66 (1.46, 1.88), < .0001 2.42 (1.90, 3.07), < .0001 3.97 (1.61, 9.77), 0.0027 3.28 (2.58, 4.15), < .0001 1.17 (1.02, 1.34), 0.0217 2.33 (0.89, 6.14), 0.0856 0.42 (0.17, 1.03), 0.0590 1.30 (1.14, 1.47), < .0001
 1–3 1.65 (1.54, 1.78), < .0001 2.14 (1.85, 2.47), < .0001 2.48 (2.05, 3.00), < .0001 2.04 (1.85, 2.24), < .0001 1.52 (1.43, 1.63), < .0001 1.83 (1.61, 2.08), < .0001 1.30 (1.08, 1.56), 0.0050 1.16 (1.11, 1.21), < .0001
No obstructive labor 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
 Had obstructive labor 0.77 (0.72, 0.82), < .0001 0.88 (0.77, 1.00), 0.0417 0.97 (0.77, 1.20), 0.7559 0.82 (0.68, 0.99), 0.0405 0.67 (0.53, 0.83), 0.0004 0.80 (0.65, 0.97), 0.0255 0.70 (0.60, 0.81), < .0001 0.75 (0.68, 0.83),< .0001
No severe antepartum hemorrhage 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
 Had severe antepartum hemorrhage 2.81 (2.49, 3.18), < .0001 2.54 (1.94, 3.32),< .0001 2.89 (1.99, 4.21), < .0001 1.97 (1.50, 2.57), < .0001 4.66 (3.80, 5.72), < .0001 5.63 (4.80, 6.60), < .0001 5.19 (4.17, 6.45), < .0001 1.92 (1.76, 2.09), < .0001
No severe postpartum hemorrhage 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
 Had severe postpartum hemorrhage 0.93 (0.84, 1.02), 0.1369 0.91 (0.65, 1.27), 0.5680 1.01 (0.69, 1.47), 0.9742 1.11 (0.93, 1.34), 0.2493 1.24 (0.93, 1.67), 0.1460 0.96 (0.78, 1.18), 0.6729 1.52 (0.83, 2.77), 0.1721 0.81 (0.74, 0.89), < .0001
No hypertensive disorders 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
 Had hypertensive disorders 1.81 (1.68, 1.95), < .0001 2.12 (1.43, 3.15), 0.0002 1.79 (1.18, 2.72), 0.0062 1.95 (1.32, 2.87), 0.0008 1.95 (1.76, 2.17), < .0001 2.52 (2.30,2.77), < .0001 2.30 (2.05,2.57), < .0001 1.19 (1.05,1.35), 0.0075
No fetal malpresentation 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
 Had fetal malpresentation 1.35 (1.26, 1.45), < .0001 1.31 (0.81, 2.09), 0.2679 1.53 (1.20, 1.97), 0.0007 1.11 (0.81, 1.53), 0.5165 1.44 (1.28, 1.62), < .0001 1.65 (1.26,2.15), 0.0002 0.99 (0.81,1.22), 0.9594 1.34 (1.20,1.50), < .0001
BMI, kg/m2 (18.5–24.9) 1.0 1.0 1.0   1.0 1.0 1.0 1.0
 < 18.5 1.18 (1.15, 1.22), < .0001 1.20 (1.12, 1.28), < .0001 1.19 (1.03, 1.39), 0.0213 □ 1.22 (0.98, 1.53), 0.0779 1.26 (1.16, 1.37), < .0001 1.18 (1.10, 1.26), < .0001 1.18 (1.11, 1.25), < .0001
 ≥ 25.0 0.80 (0.77, 0.83), < .0001 0.73 (0.63, 0.84), < .0001 0.79 (0.73, 0.85), < .0001 □ 0.78 (0.73, 0.83), < .0001 1.14 (1.00, 1.29), 0.0529 0.82 (0.68, 0.98), 0.0336 0.78 (0.72, 0.85), < .0001
Hemoglobin (≥ 11 g/dL) 1.0      1.0 1.0  
 10.0–10.9 g/dL (mild) 0.97 (0.90, 1.04), 0.3626 ░ ░ ░ ░ 0.92 (0.82, 1.02), 0.1119 1.04 (0.97, 1.12), 0.2950 ░
 < 10.0 g/dL (moderate/severe) 1.10 (1.04, 1.17), 0.0013 ░ ░ ░ ░ 1.04 (0.97, 1.12), 0.3015 1.20 (1.10, 1.30), < .0001 ░
Sex of the baby (male) 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
 Female 1.03 (1.01, 1.06), 0.0055 1.14 (1.08, 1.20), < .0001 1.16 (1.11, 1.21), < .0001 1.10 (1.05, 1.15), < .0001 0.94 (0.92, 0.97), < .0001 0.87 (0.82, 0.92), < .0001 1.00 (0.95, 1.06), 0.9464 1.03 (1.00, 1.07), 0.0812
  1. □—BMI not calculated for Kenya because maternal height was not recorded before 2017
  2. ░—maternal hemoglobin not consistently collected at all GN sites except Belagavi, India and Nagpur, India
  3. Generalized linear models were used to evaluate the relationship of potential factors and prematurity and to develop point and interval estimates of relative risk associated with these factors. Generalized estimating equations were used to account for the correlation of outcomes within cluster to develop appropriate confidence intervals. The reference group is indicated by 1.0 in the Risk Ratio column
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Reproductive Health

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