Study Links Women in Agricultural Counties With Severe Birth Defects

Women living in California counties high in agricultural production and pesticide use have a heightened incidence of bearing babies with birth defects, including missing and malformed arms and legs--conditions similar to those associated with the banned drug thalidomide, a study has found.

The research at the University of Washington in Seattle also suggests--though less definitively--that there may also be a relationship between a mother working in agriculture and what are technically called “limb reduction” birth defects.

Causes Little Notice

A report of the research was published, virtually unnoticed, in the American Journal of Public Health last month. It is the second study by the same University of Washington expert and joins two other papers published in recent months in other countries suggesting the same relationship between pesticide exposure and crippling birth defects in which fetal extremities are missing or severely deformed.

The study appeared to raise serious questions about potential dangers of pesticide exposure--particularly among female farm workers in busy agricultural districts. The researcher who headed the study urged caution in interpreting it, however, emphasizing that the results are preliminary and that the study team was unable to assess other factors--such as maternal drug use--that could have played a role in the birth defects.

Dr. Lowell Sever, a top birth defects expert at the federal government’s Centers for Disease Control in Atlanta, said he has not fully evaluated the methods used in the new University of Washington study, but he termed the possible pesticide-limb reduction defect link an “intriguing possibility” that warrants further scrutiny.

Sever said the appearance of four studies from three different countries suggesting the relationship makes the possibility that limb reduction defects and pesticide exposure may be linked a compelling theory.

But Dr. John Harris, chief of the California Birth Defects Monitoring Program, criticized the research for relying on birth certificate information, which he said is unreliable because birth certificates may miss many defect cases and that data they contain on a child’s parents are of questionable reliability.

The study was conducted by a team headed by Dr. David Schwartz, who in 1986 tentatively suggested a link between parental employment in agriculture and birth defects in farm communities.

In the new study, Schwartz tested the theory by identifying every limb-reduction case reported on California birth certificates between Jan. 1, 1982 and Dec. 31, 1984. The defects are extremely rare with records showing just 237 cases statewide in the period.

Schwartz compared occupational and residential characteristics of the mothers to the economic base and pesticide use in the counties in which the women resided. Women whose children had defects were compared at random with 475 other women who gave birth at about the same time of each year.

Double the Risk

Schwartz found that living in a county high in pesticide use carried 1.9 times--or nearly double--the normal risk for giving birth to a child with a limb reduction defect. Living in an intensely agricultural county was associated with a risk 1.7 times normal. Twelve counties were identified by the University of Washington team as being both high in agricultural production and pesticide use--Colusa, Fresno, Imperial, Kern, Kings, Merced, Monterey, San Joaquin, Stanislaus, Sutter, Yolo and Yuba.

The researchers found the association between parental occupation in agriculture and limb reduction defects less clear cut--with farm employment associated with a slightly lower risk. However, Schwartz found that agricultural employment was associated with 1.6 times the risk of having a child with both a limb reduction defect and some other type of deformity. Multiple deformity cases had an even stronger relationship with living in an agricultural county or one with a high pesticide use.

“Our findings indicate that (a mother living) in an agricultural community is a risk factor,” Schwartz concluded. “The apparent (defect-producing) effect of this environmental exposure is most pronounced among infants with limb reduction defects and at least one additional anomaly. The smaller association between parental involvement in agricultural work may be an underestimate based on misclassification of maternal occupation.”

But Schwartz noted that factors including maternal use of prescription or other drugs had not been explored and that drug use in pregnancy, in particular, or other unaccountable factors “may be responsible for our findings.”

Schwartz said researchers found that fully 50% of the birth certificates for babies born with the deformities classified their mothers only as “homemakers.” But he said researchers suspect--but cannot prove--that a significant proportion of women so classified actually had been employed as farm workers during pregnancy. He and other experts said it is difficult to isolate what--if any--single pesticide may be to blame since it is difficult to know precisely when during their pregnancies the women in question may have been exposed.

In a telephone interview, Schwartz urged caution in interpretation of the results. “One piece of work does not establish a causal relationship,” he emphasized. “You’d like to see studies that confirm (ours) and understand the precise exposures that are responsible for the association.”

Harris, who was extremely critical of Schwartz’s initial 1986 research, said the new study had not satisfactorily addressed his objections. He said that, in particular, reliance on birth certificate information--until recently the only type of such mass data available to researchers--has significant risks. He said a new California data base is being established to identify birth defect incidents far more thoroughly than existing reporting programs permit.

“I don’t think (Schwartz’s) data, in a scientific world, is very strong,” Harris said. “You’re saying pesticide-applying counties, but you don’t really know if the people in that county are (actually) exposed. You don’t know whether the people actually exposed are the ones having the birth defects.

“This is an ecological fallacy. You’re assuming that people, just because they live in a county, are exposed to pesticides. The birth certificate is both extremely inaccurate and very incomplete vis-a-vis anything about these anomalies except whether (in gross terms) they exist.”

Dr. Marian Moses, a medical adviser to the United Farm Workers Union, said the new findings are in concert with claims by the union, which has contended that workers in the grape industry, in particular, experience an abnormally high birth defect rate. The parents of one such child recently reached an out-of-court settlement in Kern County Superior Court with seven chemical companies after alleging that their son had been born with arm defects after maternal pesticide exposure.

The settlement contained a stipulation that neither the family nor their attorneys could publicly discuss the case or its resolution. Dolores Huerta, a union vice president, said a second case is under investigation but no litigation has been filed.