Schizophrenia linked to fetal diuretic exposure. (Pressurized Pregnancies).

Pregnant women who take diuretic medication for high blood pressure during the third trimester substantially raise the chances that their unborn children will develop schizophrenia by age 35, according to a new study.

Schizophrenia affects 1 in 100 people. Its symptoms include hallucinations, delusions, apathy, and distorted emotional expression. Symptoms usually first appear in adolescence and young adulthood.

The new investigation is the first to link a specific treatment regimen for any medical condition during pregnancy to schizophrenia in offspring, say psychiatrist Holget J. Sorensen of the University of Copenhagen and his colleagues. However, the existence of this association doesn't demonstrate that third-trimester diuretic use directly causes schizophrenia, the researchers emphasize in the March American Journal of Psychiatry.

"There's been no prior suggestion of a link between diuretic use by hypertensive women during pregnancy and schizophrenia in their children," comments psychiatrist Daniel R. Weinberger of the National Institute of Mental Health in Bethesda, Md. "I'd be cautious about drawing conclusions from one study"

Still, the findings provide an intriguing clue in the search for factors that affect fetal-brain development and contribute to schizophrenia (SN: 7/1/00, p. 6), Sorensen's group contends. Other researchers have found that diuretic use after the first trimester of pregnancy lowers a woman's blood volume. If that effect occurs in the fetus as well, it could disrupt brain growth enough to lay the groundwork for schizophrenia, Sorensen and his coworkers theorize.

Their investigation focused on 7,866 people born in a Copenhagen hospital between 1959 and 1961. Prenatal medical information was matched with data from a registry that tracks all admissions to Danish psychiatric hospitals.

By 1994, 84 of the individuals had received a diagnosis of schizophrenia, according to a strict definition of the condition that's comparable to that now used in the United States.

Only the combination of a mother's hypertension during pregnancy and third-trimester diuretic treatment showed a strong link to the subsequent development of schizophrenia in a child. This relationship held after the researchers statistically accounted for any past diagnoses of schizophrenia among mothers, family income, mothers' ages at the time of birth, and other prescription drugs used during pregnancy.

Preeclampsia--a dangerous condition that raises blood pressure in pregnant women (SN: 3/8/03, p. 147)--didn't contribute to the schizophrenia risk, the scientists say. Neither did the prescription of diuretics during the third trimester for medical conditions other than hypertension.

Maternal hypertension and diuretic use exhibited no link to later diagnoses of any other psychiatric disorder in offspring, the scientists add.

However, they can't rule out the possibility that pregnant women with particularly high blood pressures received more diuretic prescriptions than those with slightly elevated readings. In that case, severe mammal hypertension, not third-trimester diuretic use, may explain the association with schizophrenia in offspring, Sorensen cautions.

Most researchers now assume that many relatively common human genes interact with each other and with environmental forces, such as the ones uncovered in the new study, to prime a child's brain for schizophrenia, Weinberger says.