Pesticides and industrial chemicals have been detected for the first time in the amniotic fluids of pregnant women, raising fears about how chemical exposure affects human development both before and after birth. A team of American and Canadian researchers, who presented their preliminary findings at a conference in San Diego yesterday, said about 30 percent of the amniotic fluid in 53 California women studied had measurable levels of DDE, a byproduct of the pesticide DDT that may affect levels of testosterone and interfere with hormonal processes. Scientists say it remains unclear how the chemicals are affecting fetuses and they hope to find out through further study.