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Taking some antibiotics may raise miscarriage risk

MiscarriageFocusA large Canadian study found that taking several classes of antibiotic – including macrolides, quinolones, tetracyclines, sulphonamides and metronidazolethe – raised the chances of having a miscarriage by between 60% and 100%. The team concluded that while there was a link between some antibiotics and an increased risk of miscarriage, 'residual confounding by severity of infection cannot be ruled out'.

The Guardian reports that the link was seen with several classes of antibiotic – including macrolides, quinolones, tetracyclines, sulphonamides and metronidazole. However, nitrofurantoin, often used to treat urinary tract infections in pregnant women, had no effect on miscarriage risk. Nor did the widely used antibiotic erythromycin.

The researchers at the faculty of pharmacy, Université de Montréal and Research Centre, Centre hospitalier universitaire (CHU) Sainte-Justine, Montréal looked at data from almost 9,000 cases of miscarriage at an average time of 14 weeks into pregnancy, involving girls and women aged between 15 and 45.

The study leader, Dr Anick Bérard, from the University of Montreal, said: “Infections are prevalent during pregnancy. 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% to two-fold increased risk.”

Women who miscarried were more likely to be older, living alone, and to have multiple health issues and infections. But all these factors were accounted for in the analysis, the report says.

Bérard added: “The increased risk was not seen for all antibiotics, which is reassuring for users, prescribers and policymakers.”

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, 8,702 (4.7%) ended with an early miscarriage.

The team concluded that there was a link between some antibiotics and an increased risk of miscarriage, but added: “However, residual confounding by severity of infection cannot be ruled out.”

Abstract
Background: Although antibiotics are widely used during pregnancy, evidence regarding their fetal safety remains limited. Our aim was to quantify the association between antibiotic exposure during pregnancy and risk of spontaneous abortion.
Methods: We conducted a nested case–control study within the Quebec Pregnancy Cohort (1998–2009). We excluded planned abortions and pregnancies exposed to fetotoxic drugs. Spontaneous abortion was defined as having a diagnosis or procedure related to spontaneous abortion before the 20th week of pregnancy. The index date was defined as the calendar date of the spontaneous abortion. Ten controls per case were randomly selected and matched by gestational age and year of pregnancy. Use of antibiotics was defined by filled prescriptions between the first day of gestation and the index date and was compared with (a) non-exposure and (b) exposure to penicillins or cephalosporins. We studied type of antibiotics separately using the same comparator groups.
Results: After adjustment for potential confounders, use of azithromycin (adjusted odds ratio [OR] 1.65, 95% confidence interval [CI] 1.34–2.02; 110 exposed cases), clarithromycin (adjusted OR 2.35, 95% CI 1.90–2.91; 111 exposed cases), metronidazole (adjusted OR 1.70, 95% CI 1.27–2.26; 53 exposed cases), sulfonamides (adjusted OR 2.01, 95% CI 1.36–2.97; 30 exposed cases), tetracyclines (adjusted OR 2.59, 95% CI 1.97–3.41; 67 exposed cases) and quinolones (adjusted OR 2.72, 95% CI 2.27–3.27; 160 exposed cases) was associated with an increased risk of spontaneous abortion. Similar results were found when we used penicillins or cephalosporins as the comparator group.
Intrpretation: After adjustment for potential confounders, use of macro-lides (excluding erythromycin), quinolones, tetracyclines, sulfonamides and metronidazole during early pregnancy was associated with an increased risk of spontaneous abortion. Our findings may be of use to policy-makers to update guidelines for the treatment of infections during pregnancy.

Authors
Flory T Muanda, Odile Sheehy, Anick Bérard

[link url="https://www.theguardian.com/society/2017/may/02/health-report-links-antibiotics-to-risk-of-miscarriage"]The Guardian report[/link]
[link url="http://www.cmaj.ca/content/189/17/E625"]Canadian Medical Association Journal abstract[/link]

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