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A new study suggests that guidelines for antibiotic use during early pregnancy might need to be reviewed, after finding that some common classes of the drug could double the risk of miscarriage.

Miscarriage, also known as spontaneous abortion and pregnancy loss, is the natural death of an embryo or fetus before it is able to survive independently.Avoiding drugs and alcohol, infectious diseases, and radiation may prevent miscarriage

A major review involving more than 95,000 women has found five common classes of the drug were associated with an increased risk, while two others were shown to be safe.

According to the Eunice Kennedy Shriver National Institute of Child Health and Human Development, miscarriage occurs in around 15 to 20 percent of women who are aware of their pregnancy, and it is most common among women aged 35 or older.

Over half of all miscarriages are caused by abnormalities in the chromosomes of the fetus. Other factors that may raise the risk of miscarriage include diabetes, polycystic ovary syndrome,obesity,and infection.

Experts say the major risk highlighted by the study is for women prescribed antibiotics who do not yet know they are pregnant, as UK doctors are generally cautious in prescribing the medicines when they know conception has occurred.

Published in the Canadian Medical Association Journal, the investigation found a heightened chance of miscarriage was associated with commonly used antibiotics known as macrolides, quinolones, tetracyclines, sulfonamides and metronidazole.

But the scientists also found Erythromycin and nitrofurantoin, often used to treat urinary tract infections in pregnant women, were not associated with an increased risk.

Dr Nicola Davies, a GP and former trustee of the association, said: “The main risk this research throws up is for those women who don’t know they are pregnant.

“Most of these drugs are drugs you wouldn’t prescribe if you knew a woman was pregnant.”

Macrolides are commonly prescribed for respiratory infections, as well as some intestinal infections and skin infections, especially for those resistant to penicillin.

Meanwhile tetracyclines can be prescribed for people suffering from acne.

She said the data indicating that nitrofurantoin was safe was not associated with an increased risk of miscarriage was to be welcomed as until recently its safety had been in doubt.

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Age is one of the most significant factors connected with the risk of miscarriage, with chances ranging from one in 10 for pregnant women under the age of 30 to 50 per cent in those above the age of 45.

“Although antibiotic use to treat infections has been linked to a decreased risk of prematurity and low birth weight in other studies, our investigation shows that certain types of antibiotics are increasing the risk of spontaneous abortion, with a 60 percent to two-fold increased risk,” said Anick Berard from Universite de Montreal.

“Given that the baseline risk of spontaneous abortion can go as high as 30 percent, this is significant,” Berard said.

The researchers identified a total of 182,369 pregnancies from the Quebec Pregnancy Cohort, a large population group from the province providing data for ongoing studies.

Of these, 8702 (4.7%) ended with an early miscarriage.

Berard and her team looked at data from the Quebec Pregnancy Cohort between 1998 and 2009.

Writing in the journal, the team concluded: “Use of macrolides (excluding erythromycin), quinolones, tetracyclines, sulphonamides and metronidazole during early pregnancy was associated with an increased risk of spontaneous abortion.

The study was published in the Canadian Medical Association Journal.

While the association between antibiotics and adverse pregnancy outcomes isn’t new, evidence related to spontaneous abortion hasn’t been as robust, explained Norwitz, chairman of obstetrics and gynecology at Tufts University School of Medicine in Boston.

“I think the consensus is that there probably isn’t an association, but this study suggests that maybe there is,” he said.

“Overall, it [the study] was quite well done,” Norwitz added.

Norfloxacin, a type of quinolone, was associated with more than a fourfold increased risk, the study showed.

The study’s biggest deficiency, in Norwitz’s view, is that it did not address underlying genetic problems, which he said account for the vast majority of miscarriages.

The researchers also couldn’t rule out that the severity of women’s infections may have influenced the results. But they don’t think such differences fully explain their findings.

So what’s a woman to do if she’s pregnant and has a bacterial infection?

The best approach is to aim for the “lowest effective dose” using the most appropriate antibiotic, Norwitz said.



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