Chlorination has been the major means of disinfecting drinking water in Taiwan. The use of chlorinated water has been hypothesized to lead to several adverse birth outcomes, including low birth weight and preterm delivery. We performed a study to examine the relationship between the use of chlorinated water and adverse birth outcomes in Taiwan. The study areas included 14 chlorinating municipalities (CHMs), which were defined as municipalities in which greater than 90% of the municipal population was served by chlorinated water, and 14 matched nonchlorinating municipalities (NCHMs), defined as municipalities in which less than 5% of the municipal population is served by chlorinated water. The CHMs and NCHMs were similar to one another in terms of level of urbanization and sociodemographic characteristics. The study population comprised 18,025 women residing in the 28 municipalities who had a first parity singleton birth between 1 January 1994 and 31 December 1996 and for which complete information on maternal age, education, gestational age, birth weight, and sex of the baby were available. The results of our study suggest that there was no association between consumption of chlorinated drinking water and the risk of low birth weight. Key words: chlorination, disinfection by-products, drinking water, infants, low birth weight. Environ Health Perspect 108:765-768 (2000). [Online 30 June 2000]
The economy and effectiveness of chlorine in killing waterborne organisms has made water chlorination a tremendous public health success worldwide. However, chlorination of water can produce trace amounts of by-products such as trihalomethanes (THMs), which are carcinogenic organic halogenated contaminants of water chlorination (
Recently, several epidemiologic studies have examined the associations between the consumption of chlorinated water and adverse pregnancy outcomes (
Selection of study municipalities. Taiwan is divided into 361 administrative districts, which are referred to here as municipalities. We excluded from the analysis 30 aboriginal townships and 9 islets that encompassed different lifestyles and living environments; we also excluded the 12 municipalities of the city of Taipei because of Taipei's distinctly more urban character and larger population than other municipalities in Taiwan. This elimination left 310 municipalities.
Chlorination has been the major means of disinfecting drinking water in Taiwan. Chlorine is currently added to approximately 75.8% of the nation's drinking water. The current Taiwan water system is rather simple. Residents obtain their drinking water either from the public drinking water supply systems served by the Taiwan Water Supply Corporation or from nonmunicipal sources. The major sources of municipal water supplies are almost all surface waters and are treated with chlorine. The nonmunicipal sources are mainly privately owned wells (groundwater) and are unchlorinated.
In this study, we classified an individual municipality as a chlorinating municipality (CHM) if greater than 90% of the municipal population was served by chlorinated water. In all, 156 of the 310 municipalities satisfied this criterion. A nonchlorinating municipality (NCHM) was defined as one in which less than 5% of the municipality population was served by chlorinated water (i.e., greater than 95% of the residents obtained their drinking water from unchlorinated water sources). In all, 15 municipalities satisfied this criterion. These 15 NCHMs provided a unique opportunity to investigate the issue of chlorination. To take into account the possible confounding effect resulting from differing levels of urbanization, the urbanization level of the nonchlorinating municipalities should be the same as that of the chlorinating municipalities. The assignment of urbanization levels was based on the urban-rural classification of Tzeng and Wu (
Each NCHM was matched with a CHM with the same urbanization level. Among the 15 NCHMs, one was excluded because there was no appropriate municipality for matching. If an NCHM had more than one appropriate matching CHM, we used a random sampling method to select the CHM. Details of the procedure were described by Yang et al. (
Data collection. Data on pregnancy outcomes were taken from the routine registration of births. Registration of births is required by law in Taiwan. It is the responsibility of the parents or the family to register infant births at a local household registration office within 15 days. Computerized data on live births were collected from the Household Registration System, which is managed by the Department of Interior in Taipei. The registration form, which asks for information on maternal age, education, parity, gestational age, date of delivery, infant sex, and birth weight, is completed by the physician attending the delivery. Because most deliveries in Taiwan take place in either a hospital or clinic (
There were 43,807 singleton deliveries in the study municipalities between 1 January 1994 and 31 December 1996. Of the 43,782 births with information on parity, first-parity births accounted for 43.76%. Of 19,159 first-parity singleton live births, we excluded 163 subjects who had invalid or missing information on gestational age. Among the remaining 18,996 subjects, 656 were missing birth weight data or maternal age data. Of the 18,340 first-parity births with complete information on these variables, we excluded 315 births because data were missing on at least one of three variables: maternal educational, maternal marital status, or infant birth place. These exclusions left 18,025 births for the final analysis.
Statistics. The outcomes of interest in this study included term low birth weight (LBW) (is greater than or equal to 37 gestational weeks and less than 2,500 g) and preterm delivery (less than 37 gestational weeks). We used an unconditional logistic regression model to estimate the effects of chlorination practice on the risk of term LBW and preterm delivery. All odds ratios (ORs) were adjusted for maternal age (less than 25 or is greater than or equal to 25 years), marital status (married or unmarried), maternal education (less than 12 or is greater than or equal to 12 years), and sex of baby. The analyses were performed using SAS software (SAS Institute Inc., Cary, NC). All statistical tests were two-sided. Values of p less than 0.05 were considered statistically significant.
Altogether, 18,025 (
The CHMs had a lower rate of term LBW than the CHMs (2.49 vs. 2.81%) but the difference was not statistically significant. Table 3 shows the ORs for term LBW and preterm delivery based on comparisons between CHMs and NCHMs using logistic regression. After controlling for possible confounders (including maternal age, marital status, maternal education, and sex of the infant), the adjusted ORs were 1.34 [95% confidence interval (CI), 1.15-1.56)] for preterm delivery and 0.90 (CI, 0.75-1.09) for term LBW, respectively, when comparing CHMs with NCHMs. Analysis using term birth weight as a continuous variable did not indicate an association between birth weight and the use of chlorinated water (data not shown).
The results of this study suggest that there is no association between the use of chlorinated drinking water and the risk of term low birth weight.
A few previous studies have looked at the relation between birth weight and preterm delivery and water chlorination (
The major difficulty in studying health effects associated with chlorination lies in assessing exposure (
THMs are common contaminants of chlorinated drinking water and are the most consistently measured contaminants in treated water. Previous studies attempted to quantify the concentration of THMs and assign exposure values to women (
Recently, Gallagher et al. (
A number of factors are known or suspected to affect birth weight, including maternal nutrition and prepregnancy weight and weight gain (
We used the extreme point contrast method to assess exposure. Nonetheless, the potential misclassification of exposure remains. Mobility between CHMs and NCHMs during pregnancy is likely to be a problem in this study. Two U.S. studies reported that approximately 25% (
In summary, the present study provides no evidence of an increased risk of term LBW related to the consumption of chlorinated water. More accurate means of exposure assessment, including quantifying individual exposure to THMs or other disinfection by-products from tap water at home, work, and elsewhere, and other water uses or use of more sophisticated modeling techniques, may help clarify the effect of water chlorination on reproduction (
Address correspondence to: C-Y. Yang, College of Health Science, Kaohsiung Medical University, 100 Shih-Chuan 1st RD, Kaohsiung, Taiwan 80708. Telephone: 886 7 3121101 ext 2141. Fax: 886 7 3110811. E-mail: chunyuh@cc.kmu.edu.tw
This study was partially supported by a grant from the National Science Council, Executive Yuan, Taiwan (NSC-89-2320-B-037-023).
Received 1 February 2000; accepted 11 April 2000.
Table 1. Some characteristics of two groups of Taiwan municipalities, grouped according to chlorination practice.
a Professional, technical, administrative, superintendents, clerical, sales, and service workers as a percentage of the total employed (is greater than or equal to 15 years of age) population.
b Producers, transportation operators, and laborers as a percentage of the total employed population. c Farmers, loggers, grazers, fisherman, hunters, and related workers as a percentage of the total employed population.
Table 2. Maternal characteristics, mean birth weight, and prevalences of term LBW and preterm delivery in first-parity singleton live births in CHMs and NCHMs.
Table 3. Adjusted ORs for term LBW and preterm delivery in first-parity singleton live births by logistic regression.
a Logistic models include all five variables in the model. b The reference group was NCHMs. c The reference groups was is greater than or equal to 25 years of age. d The reference group was married women. e The reference group was is greater than or equal to 12 years of education. f The reference group was male.
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By Chun-Yuh Yang[1]; Bi-Hua Cheng[2]; Shang-Shyue Tsai[1]; Trong-Neng Wu[1]; Meng-Chiao Lin[3] and Kuo-Cherng Lin[4]
1College of Health Science, Kaohsiung Medical University, Kaohsiung City, Taiwan; 2Department of Obstetrics and Gynecology, Kaohsiung Chang-Gung; Memorial Hospital, Kaohsiung County, Taiwan; 3Department of Health, Kaohsiung City Government, Kaohsiung City, Taiwan; 4Department of Obstetrics and Gynecology, Kaohsiung Medical University, Kaohsiung City, Taiwan