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Personal Health Jane Brody on health and aging.

The thalidomide disaster of the early 1960s left thousands of babies with deformed limbs because their mothers innocently took a sleeping pill thought to be safe during pregnancy,

In its well-publicized wake, countless pregnant women avoided all medications, fearing that any drug they took could jeopardize their babies’ development.

I was terrified in December 1968 when, during the first weeks of my pregnancy, I developed double pneumonia and was treated with antibiotics and codeine. Before swallowing a single dose, I called my obstetrician, who told me to take what was prescribed, “reassuring” me that if I died of pneumonia I wouldn’t have a baby at all.

In the decades that followed, pregnancy-related hazards were linked to many medicinal substances: prescription and over-the-counter drugs and herbal remedies, as well as abused drugs and even some vitamins.

Now, however, the latest findings about drug use during pregnancy have ignited new concerns among experts who monitor the effects of medications on the developing fetus and pregnancy itself.

During the last 30 years, use of prescription drugs during the first trimester of pregnancy, when fetal organs are forming, has grown by more than 60 percent.

About 90 percent of pregnant women take at least one medication, and 70 percent take at least one prescription drug, according to the Centers for Disease Control and Prevention.

Since the late 1970s, the proportion of pregnant women taking four or more medications has more than doubled.

Nearly one woman in 10 takes an herbal remedy during the first trimester.

A growing number of pregnant women, naïvely assuming safety, self-medicate with over-the-counter drugs that were once sold only by prescription.

While many commonly taken medications are considered safe for unborn babies, the Food and Drug Administration estimates that 10 percent or more of birth defects result from medications taken during pregnancy. “We seem to have forgotten as a society that drugs pose risks,” Dr. Allen A. Mitchell, professor of epidemiology and pediatrics at Boston University Schools of Public Health and Medicine, said in an interview. “Many over-the-counter drugs were grandfathered in with no studies of their possible effects during pregnancy.”

Medical progress has contributed to the rising use of medications during pregnancy, Dr. Mitchell said. Various conditions, like depression, are now recognized as diseases that warrant treatment; drugs have been developed to treat conditions for which no treatment was previously available, and some conditions, like Type 2 diabetes and hypertension, have become more prevalent.

Misled by the Web

Now a new concern has surfaced: Bypassing their doctors, more and more women are using the Internet to determine whether the medication they are taking or are about to take is safe for an unborn baby.

A study, published online last month in Pharmacoepidemiology and Drug Safety, of so-called “safe lists for medications in pregnancy” found at 25 Web sites revealed glaring inconsistencies and sometimes false reassurances or alarms based on “inadequate evidence.”

The report was prepared by Cheryl S. Broussard of the Centers for Disease Control and Prevention with co-authors from Emory, Georgia State University, the University of British Columbia and the Food and Drug Administration.

“Among medications approved for use in the U.S.A. from 2000 to 2010, over 79% had no published human data on which to assess teratogenic risk (potential to cause birth defects), and 98% had insufficient published data to characterize such risk,” the authors wrote.

But that did not stop the 25 Web sites from characterizing 245 medications as “safe” for use by pregnant women, which “might encourage use of medications during pregnancy even when they are not necessary,” the authors suggested.

Furthermore, the information found online was sometimes contradictory. “Twenty-two of the products listed as safe by one or more sites were stated not to be safe by one or more of the other sites,” the study found.

The question of timing was often ignored. A drug that could interfere with fetal organ development might be safe to take later in pregnancy. Or one (for example, ibuprofen) that is safe early in pregnancy could become a hazard later if it raises the risk of excessive bleeding or premature delivery.

Fewer than half the sites advised taking medication only when necessary, and only 13 sites encouraged pregnant women to consult their doctors before stopping or starting a medication.

Doctors, too, are often poorly informed about pregnancy-related hazards of various medications, the authors noted. One woman I know was advised to wean off an antidepressant before she became pregnant, but another was told to continue taking the same drug throughout her pregnancy.

“In many instances the best bet is for mom to stay on her medication,” said Dr. Siobhan M. Dolan, an obstetrician and geneticist at Albert Einstein College of Medicine. She said that if a woman is depressed during pregnancy, her risk of postpartum depression is greater and she may have difficulty bonding with her baby.

Dr. Dolan, who is author, with Alice Lesch Kelly, of the March of Dimes’ newest book, “Healthy Mom Healthy Baby,” emphasized the importance of weighing benefits and risks in deciding whether to take medication during pregnancy and which drugs to take.

“In anticipation of pregnancy, a woman taking more than one drug to treat her condition should try to get down to a single agent,” Dr. Dolan said in an interview. “Of the various medications available to treat a condition, is there a best choice — one least likely to cause a problem for either the baby or the mother?”

She cautioned against sharing medications prescribed for someone else and assuming that a remedy labeled “natural” or “herbal” is safe. Virtually none have been tested for safety in pregnancy.

Among medications a woman should be certain to avoid, in some cases starting three months before becoming pregnant, are isotretinoin (Accutane and others) for acne; valproic acid for seizure disorders; lithium for bipolar disorder; tetracycline for infections, and angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor antagonists for hypertension, Dr. Dolan said.

“Many medications that are not recommended during pregnancy can be replaced with low-risk alternatives,” she wrote.

Dr. Broussard, who did the “safe lists” study, said in an interview, “We’ve heard about women seeing medications on these lists and deciding on their own that it’s O.K. to take them. “Women who are pregnant or even thinking about getting pregnant should talk directly to their doctors before taking anything. They should be sure they’re taking only what’s necessary for their health condition.”

A reliable online resource for both women and their doctors, Dr. Mitchell said, are fact sheets prepared by OTIS, the Organization of Teratology Information Specialists, which are continually updated as new facts become available: //www.otispregnancy.org.