The Association Between Air Pollution and Low Birth Weight and Preterm Labor in Ahvaz, Iran

Figures & data

Table 1 Descriptive Indexes of Hospital Admissions Due to Low Birth Weight and Preterm Labor, Air Pollutant Concentrations and Meteorological Parameters in Ahvaz During 2008–2018

Variable (Mean per Day)	N	Mean	SD	Min	Max	Q1	Median	Q3
Low Birth Weight	863	0.2	0.6	0.0	5.0	0.0	0.0	0.0
Premature Birth	5776	1.6	1.9	0.0	12.0	0.0	1.0	2.0
O3 (µg/m^3)	–	70.5	188.6	0.04	6520.0	26.4	42.7	64.6
PM2.5 (µg/m^3)	–	85.7	150.4	0.57	3938	35.9	52.7	81.2
PM10 (µg/m^3)	–	216.9	278.3	1.8	4324.2	105.8	149.2	222.4
NO2 (µg/m^3)	–	46.4	43.1	1.5	443.8	17.8	35.6	60.7
NO (µg/m^3)	–	29.1	31.0	0.12	608.7	9.1	19.6	38.2
CO (µg/m^3)	–	1.5	2.1	0.1	70.4	0.6	1.13	2.0
SO2 (µg/m^3)	–	48.8	57.0	0.0	907.4	19.3	35.9	59.3
Temperature (° C)	–	27.0	9.4	1.4	47.8	18.4	27.7	36.0
Relative Humidity (%)	–	42.3	17.9	7.0	96.0	27.5	40.0	54.5

Abbreviations: O₃, ozone; SO₂, sulfur dioxide; NO, nitrogen monoxide; NO₂, nitrogen dioxide; CO, carbon monoxide; PM₁₀, particulate matter 10 micrometers or less in diameter; PM_2.5, particulate matter 2.5 micrometers or less in diameter.

Table 2 The Results of the Modified GAM of the Relationship Between Air Pollutants and Low Birth Weight of Ahvaz (Increasing the Cases of Daily Low Birth Weight per Increasing 10 Units in a Daily Average of the Pollutant)

Lag	Pollutant	edf	Risk Ratio	95% CI	P-value*
Lag 0	O3	8.578	0.988	0.978–0.997	0.014^†
	NO2	6.073	0.872	0.848–0.896	<0.001^†
	NO	5.790	0.869	0.839–0.900	<0.001^†
	SO2	8.399	1.010	0.999–1.020	0.067
	CO	6.152	0.616	0.369–1.028	0.064
	PM10	4.322	1.003	1.001–1.004	0.002^†
	PM2.5	6.559	1.000	0.996–1.005	0.906
Lag 1	O3	8.286	0.983	0.973–0.994	0.002^†
	NO2	5.960	0.874	0.850–0.898	<0.001^†
	NO	5.880	0.883	0.853–0.914	<0.001^†
	SO2	6.076	1.008	0.997–1.018	0.143
	CO	4.605	0.597	0.358–0.996	0.048^†
	PM10	3.776	1.002	1.000–1.004	0.029^†
	PM2.5	4.282	0.999	0.993–1.004	0.640
Lag 2	O3	7.344	0.983	0.972–0.993	0.002^†
	NO2	5.690	0.879	0.856–0.902	<0.001^†
	NO	7.683	0.897	0.868–0.927	<0.001^†
	SO2	6.952	1.014	1.004–1.023	0.005^†
	CO	5.568	0.884	0.602–1.296	0.526
	PM10	3.818	1.003	1.002–1.005	<0.001^†
	PM2.5	4.257	1.001	0.997–1.006	0.589
Lag 3	O3	8.263	0.990	0.981–0.999	0.027^†
	NO2	5.304	0.865	0.841–0.890	<0.001^†
	NO	8.194	0.857	0.827–0.889	<0.001^†
	SO2	8.341	1.012	1.002–1.022	0.016^†
	CO	5.550	0.978	0.711–1.346	0.893
	PM10	3.657	1.004	1.002–1.005	<0.001^†
	PM2.5	4.021	1.002	0.997–1.006	0.480
Lag 4	O3	8.192	0.992	0.984–1.000	0.057
	NO2	2.020	0.887	0.864–0.910	<0.001^†
	NO	6.926	0.894	0.865–0.925	<0.001^†
	SO2	6.887	1.006	0.996–1.016	0.212
	CO	4.652	0.757	0.480–1.192	0.229
	PM10	4.256	1.002	1.001–1.004	0.006^†
	PM2.5	5.052	0.998	0.993–1.004	0.588
Lag 5	O3	8.386	0.974	0.962–0.987	<0.001^†
	NO2	7.819	0.893	0.870–0.916	<0.001^†
	NO	7.481	0.906	0.878–0.936	<0.001^†
	SO2	4.571	1.005	0.994–1.016	0.376
	CO	7.240	0.828	0.551–1.242	0.360
	PM10	4.112	1.003	1.001–1.005	0.001^†
	PM2.5	4.692	1.000	0.995–1.005	0.917
Lag 6	O3	8.638	0.975	0.963–0.988	<0.001^†
	NO2	6.078	0.877	0.855–0.900	<0.001^†
	NO	8.757	0.902	0.873–0.932	<0.001^†
	SO2	4.461	1.009	0.999–1.019	0.088
	CO	6.236	0.926	0.639–1.343	0.687
	PM10	4.031	1.004	1.003–1.006	<0.001^†
	PM2.5	4.526	1.002	0.999–1.006	0.222

Notes: ^†Statistically significant. *Adjusted for trend, seasonality, temperature, relative humidity and weekdays.

Figure 1 Risk ratio (95% confidence interval) of low birth weight associated with a 10-unit increase in air pollutant levels for different lags of lag 0–6 days.

Table 3 The Results of the Modified GAM of the Relationship Between Air Pollutants and Preterm Labor of Ahvaz (Increasing the Cases of Daily Low Birth Weight per Increasing 10 Units in a Daily Average of the Pollutant)

Lag	Pollutant	edf	Risk Ratio	95% CI	P-value*
Lag 0	O3	8.887	0.996	0.994–0.999	0.004^†
	NO2	8.643	1.031	1.025–1.037	<0.001^†
	NO	6.196	1.055	1.049–1.061	<0.001^†
	SO2	4.827	0.966	0.958–0.973	<0.001^†
	CO	8.679	1.457	1.369–1.551	<0.001^†
	PM10	7.605	1.000	0.999–1.001	0.971
	PM2.5	7.109	1.004	1.003–1.005	<0.001^†
Lag 1	O3	8.790	0.996	0.993–0.999	0.004^†
	NO2	6.338	1.031	1.025–1.037	<0.001^†
	NO	8.703	1.055	1.049–1.061	<0.001^†
	SO2	4.138	0.962	0.954–0.969	<0.001^†
	CO	8.051	1.448	1.358–1.544	<0.001^†
	PM10	8.716	1.000	0.999–1.001	0.381
	PM2.5	8.477	1.004	1.003–1.005	<0.001^†
Lag 2	O3	8.880	0.994	0.991–0.997	<0.001^†
	NO2	8.592	1.037	1.031–1.043	<0.001^†
	No	7.224	1.056	1.051–1.062	<0.001^†
	SO2	8.259	0.962	0.955–0.970	<0.001^†
	CO	8.799	1.451	1.365–1.542	<0.001^†
	PM10	7.124	0.999	0.997–1.000	0.006^†
	PM2.5	8.375	1.004	1.003–1.005	<0.001^†
Lag 3	O3	8.873	0.997	0.995–1.000	0.022^†
	NO2	7.969	1.037	1.031–1.043	<0.001^†
	NO	6.001	1.057	1.051–1.062	<0.001^†
	SO2	5.211	0.959	0.952–0.967	<0.001^†
	CO	8.491	1.471	1.387–1.560	<0.001^†
	PM10	7.394	0.999	0.998–1.000	0.022^†
	PM2.5	8.739	1.004	1.003–1.005	<0.001^†
Lag4	O3	8.803	0.997	0.995–1.000	0.021^†
	NO2	7.333	1.039	1.033–1.045	<0.001^†
	NO	8.738	1.057	1.051–1.062	<0.001^†
	SO2	4.224	0.963	0.956–0.971	<0.001^†
	CO	8.357	1.472	1.388–1.562	<0.001^†
	PM10	8.059	0.998	0.997–0.999	<0.001^†
	PM2.5	8.862	1.003	1.002–1.005	<0.001^†
Lag 5	O3	8.766	0.995	0.992–0.998	<0.001^†
	NO2	7.987	1.039	1.033–1.045	<0.001^†
	NO	8.562	1.057	1.052–1.063	<0.001^†
	SO2	4.968	0.959	0.952–0.967	<0.001^†
	CO	8.366	1.455	1.369–1.546	<0.001^†
	PM10	6.915	0.997	0.996–0.998	<0.001^†
	PM2.5	6.536	1.003	1.001–1.004	<0.001^†
Lag 6	O3	8.856	0.995	0.992–0.998	<0.001^†
	NO2	6.366	1.038	1.032–1.044	<0.001^†
	NO	7.450	1.057	1.051–1.062	<0.001^†
	SO2	3.975	0.959	0.951–0.966	<0.001^†
	CO	8.304	1.492	1.404–1.585	<0.001^†
	PM10	8.193	0.998	0.997–0.999	<0.001^†
	PM2.5	8.744	1.004	1.002–1.005	<0.001^†

Notes: ^†Statistically significant. *Adjusted for trend, seasonality, temperature, relative humidity and weekdays.

Figure 2 Risk ratio (95% confidence interval) of preterm labor associated with a 10-unit increase in air pollutant levels for different lags of lag 0–6 days.