In some cases of spontaneous abortion, surgery is required to remove retained contents of conception. Prophylactic antibiotics have shown positive outcomes in reducing the risk of pelvic infection (a miscarriage surgery complication), but its efficacy is not well-studied. The objective of this study is to determine the safety and efficacy of prophylactic antibiotics in reducing the complications of miscarriage surgery. 

This is a double-blind, placebo-controlled, randomized trial that included a total of 3,412 patients with spontaneous abortion who were scheduled to undergo miscarriage surgery. The participants were randomly assigned to a single preoperative dose of 400 mg of oral doxycycline plus 400 mg of oral metronidazole or to identical placebos. The primary outcome of the study was pelvic infection within 14 days of surgery.

Out of 3,412 patients, 1,705 were assigned to antibiotics and 1,707 to placebo. The risk of pelvic infection was reported to be 4.1% in the antibiotics group and 5.3% in the placebo group. The original strict criteria resulted in 2.6% and 1.5% risk of pelvic infection, respectively.

The research concluded that prophylactic antibiotics before miscarriage surgery in case of spontaneous abortion did not result in a significantly lower risk of pelvic infection than a placebo treatment.