Water Consumption in Early Pregnancy and Risk of Spontaneous Abortion
Trihalomethanes (chloroform, bromoform, bromodichloromethane, and chlorodibromomethane) are common contaminants of chlorinated drinking water. They form when chlorine reacts with decomposing plant material, which is often found in water from surface sources.
Although animal data suggest some of the trihalomethanes may interfere with reproduction at high doses, little information exists on the relationship between trihalomethane exposure and miscarriage (spontaneous abortion) in humans.
We examined exposure to trihalomethanes in relation to miscarriage in a study of 5,144 pregnant women living in three areas of California (centered in Santa Clara, Walnut Creek and Fontana). These women were interviewed early in pregnancy about their water consumption and a variety of other factors that may influence pregnancy outcome. (That study is discussed in further detail in Swan et al, an analysis conducted on the same data).
Eighty-five drinking water utilities served the pregnant womens homes. These utilities provided records of distribution system measurements of total trihalomethanes (TTHM) and, where available, the four individual trihalomethanes. The TTHM level in a participants home tap water was estimated by averaging all measurements taken by her utility during her first trimester. Tap water levels of the individual trihalomethanes (chloroform, bromoform, etc.) were estimated in the same manner.
Women who drank five or more glasses per day of cold home tap water containing at least 75 ug per liter of TTHM had a miscarriage rate of 15.7%. Among other women (those who drank less than 5 glasses per day and/or had tap water containing less than 75 µg per liter of TTHM) the miscarriage rate was 9.5% (Adjusted odds ratio for miscarriage of 1.8, 95% confidence interval 1.1-3.0).
Of the four individual trihalomethanes, only high bromodichloromethane exposure (drinking 5 or more glasses per day of cold home tap water containing >18 µg/L bromodichloromethane) was associated with miscarriage both alone and after adjustment for the other trihalomethanes (adjusted odds ratio for miscarriage of 3.0, 95% confidence interval 1.4-6.6).
Given the widespread exposure to trihalomethanes, we recommend that additional research be conducted to replicate our findings.
Questions and Answers
Q: What are trihalomethanes?
A:Trihalomethanes (chloroform, bromoform, bromodichloromethane, and chlorodibromomethane) are common contaminants of drinking water that has been chlorinated or chloraminated. Trihalomethanes form when chlorine reacts with certain acids that come from decomposing plant material. Trihalomethanes are found mainly in water that originally came from surface sources, such as rivers and lakes. The amount of trihalomethanes in drinking water can change a lot from day to day, depending on the temperature, the amount of plant material in the water, the amount of chlorine added, and a variety of other factors.
Q: What did your study find?
A: Women with high personal exposure to total trihalomethanes (TTHM) during their first trimester of pregnancy had a miscarriage rate of 15.7%, compared to a miscarriage rate of 9.5% among women with low TTHM exposure (adjusted odds ratio (OR) = 1.8, 95% confidence interval 1.1-3.0). When we looked at the individual trihalomethanes, only high personal exposure to bromodichloromethane (BDCM) was associated with miscarriage after adjusting for the other trihalomethanes (adjusted OR = 3.0, 95% confidence interval 1.4-6.6).
high personal TTHM exposure: drinking five or more glasses per day of cold home tap water containing at least 75 µg per liter of TTHM
low personal TTHM exposure: drinking less than 5 glasses per day of cold home tap water or having home tap water containing less than 75 µg per liter of TTHM
high personal BDCM exposure: drinking five or more glasses per day of cold home tap water containing at least 18 µg per liter of BDCM
low personal BDCM exposure: drinking less than 5 glasses per day of cold home tap water or having home tap water containing less than 18 µg per liter of BDCM
Q: Why was this study done?
A: Some trihalomethanes have been associated with poor reproductive outcomes in animals at high levels of exposure. Two studies in humans have seen a relationship between trihalomethane exposure and less-than-expected fetal weight gain, although another study did not see such an effect. Only one previous study has looked at miscarriage and trihalomethanes and it did not find a clear-cut effect. Since we already had collected a lot of water information from a group of pregnant women (this study is described in our companion report by Swan et al., 1998), the U.S. Environmental Protection Agency gave us funding to obtain additional information about trihalomethanes in the pregnant womens drinking water.
Q: Who was in this study?
A: We studied 5,144 pregnant women living in three areas of California. They were recruited from the Santa Clara area (recruitment at Kaiser Santa Clara), the Fontana area in southern California (recruitment at Kaiser Fontana) or the Walnut Creek area (recruitment at Walnut Creek, Martinez, Antioch and Pleasanton). The women were all members of the Kaiser Permanente Medical Care Program and were offered a chance to participate in the study when they called to arrange their first prenatal visit. This study looked at the same women, and the same pregnancies, as the study described in Swan et al., but for this study we obtained additional water quality information from the womens drinking water utilities so that trihalomethanes could be examined.
Q: How did you do this study?
A: Most drinking water utilities are required by state and federal regulations to measure the amount of TTHM in their system every three months. We found out which utilities served the women in our study and, with the utilities full cooperation, obtained the records of the trihalomethane measurements taken during the time our study participants were pregnant. The TTHM level in a participants home tap water was estimated by averaging all the water distribution system measurements taken by her utility during her first three months of pregnancy. This first trimester TTHM level was then examined together with the amount of tap water she reported drinking to create a personal TTHM exposure level. Personal exposure levels of the individual trihalomethanes (chloroform, bromoform, etc.) were estimated in the same manner. We did not measure the actual trihalomethanes levels in the home tap water.
Q: Were the trihalomethane results similar in all three areas?
A: With respect to TTHM, the association was somewhat stronger among women in the Santa Clara area than among women in the Walnut Creek area. Most women in the Fontana area received ground water, so there were very few women there with high TTHM levels. When we compared the composition of TTHM between the three study areas, there was a higher proportion of BDCM in the Santa Clara-area womens water than in the Walnut Creek-area womens water. The association between miscarriage and BDCM was similar in all areas.
Q: How did the risk of miscarriage vary with water intake and trihalomethane level?
A: For TTHM, the highest risk was seen in the 121 women who drank at least five glasses per day of cold tap water containing high levels of TTHM (at least 75 µg per liter). These women, who made up only 2% of the whole study group, had a miscarriage rate of 15.7%. Women whose home tap water contained high levels of TTHM but who drank less than 5 glasses of tap water per day had a miscarriage rate of 10.8%. Women who drank less than 5 glasses of tap water per day of water with low TTHM levels had a miscarriage rate of 9.2%, and women who drank 5 or more glasses of tap water per day of water with low TTHM levels had a miscarriage rate of 8.5%. When we looked specifically at BDCM levels, the differences were more pronounced. Of women who drank at least five glasses per day of cold tap water, those whose water contained high levels of BDCM (at least 18 µg per liter) had a miscarriage rate of 16.4%, whereas those with lower levels of BDCM had a miscarriage rate of 6.1%. Women who drank less than 5 glasses of tap water per day had miscarriage rates of 9.4% and 10.2% (high and low levels of BDCM, respectively).
Q: Did you take water consumed at work and other places into account?
A: No, we only had information about exposure to trihalomethanes via home tap water. However, to see what sort of effect not having this information might have had on our results, we looked at miscarriage rates by employment status. We thought that our estimate of TTHM exposure for women who were not employed outside the home might be more accurate than for women who were employed. As it turned out, the association between high personal TTHM exposure and miscarriage was twice as strong among women not employed outside the home compared to employed women.
Q: Do the children born to women with high personal exposure to TTHM have more birth defects or other problems?
A: We didnt have a big enough study to look at birth defects. Since about 3% of all babies are born with birth defects, in the 121 women with high personal exposure we would expect only 3-4 birth defects in all. We are currently analyzing our data to see if trihalomethanes are associated with poor fetal weight gain or premature delivery, but we dont have any results about this yet.
Q: Why is drinking water chlorinated?
A: Drinking water is often chlorinated (or chloraminated) to kill bacteria and viruses that could cause serious illnesses. Overall, chlorination of drinking water has benefited the public health enormously. There are other methods of disinfecting public drinking water, but they are often more expensive, and the potential health effects of using these other methods are in general less well understood.
Q: How common is it for drinking water to contain high levels of TTHM?
A: TTHM concentrations in tap water can vary greatly from place to place, and from time to time, depending on the source of the water, how it is treated, and other factors. In our study, 18% of the participants received water during their first trimester which we estimated contained at least 75 µg of TTHM per liter, and 13% had water with at least 90 µg per liter.
Q: Is there a regulatory standard for these chemicals in drinking water?
A: Drinking water utilities that use chlorination are required by law to sample water throughout their distribution system at least once a quarter, average the TTHM measurements, and report the results to the state. The Maximum Contaminant Level (MCL) permissible for TTHM in drinking water by State and federal law is currently an average of 100 µg per liter over four consecutive quarters. In other words, a utility has not violated the standard unless the average of the system-wide averages over the past year is over 100 µg per liter. The water in the three study areas met all State and federal drinking water standards for TTHM. There are no standards for the individual trihalomethanes.
Q: I am pregnant. Should I stop drinking my tap water?
A: First of all remember that it is important to drink lots of liquids during pregnancy. Keep following the advice which your physician or midwife has given you. This study presents a new finding which should be confirmed by other studies before any firm recommendations can be made. In the meantime, if you are concerned about your tap water you can ask your water utility (or look at your annual water quality statement) to see if your tap water is frequently high in TTHMs. If it is and this concerns you, you have several options you can consider, although our study did not prove that miscarriage rates were lower in women making these choices.
You can boil your water for one minute and then let it stand in an open container in the refrigerator for several hours before drinking it. Some studies suggest that this may lower TTHM levels, although this is not yet established. Boiling water for more than a minute may concentrate metals if they are present and may affect taste.
You can use a carbon-activated filter, which should remove most trihalomethanes as long as you follow the manufacturers recommendations to change the filter regularly.
You may choose to drink bottled water. Bottled waters tend to be low in TTHM, although they can vary widely.
Q: What is the California Department of Health Services doing next to look at the issue of trihalomethanes in drinking water?
A: The EPA is funding additional studies which will improve our understanding of chlorination by-products as well as improve our estimates of individual exposures.
For More Information About:
Study Water quality
Call Dr. Kirsten Waller Call Dr. Shanna Swan Call David Spath
(301) 620-9551 (510) 450-3818 (916) 322-2308, or your local water utility