ST. LOUIS — A $100 million settlement involving NuvaRing, a birth-control device linked to sometimes-fatal side effects, will stand now that the vast majority of claimants have chosen to opt into the agreement, those involved in the lawsuits said Thursday.

U.S. District Judge Rodney Sippel of St. Louis approved the settlement in February, but NuvaRing maker Merck had the right to abandon the deal if less than 95 percent of eligible claimants opted in.

The lead attorney for the claimants, St. Louis lawyer Roger Denton, said the 95 percent threshold has been reached, and the deal is final. Merck confirmed that the agreement is final.

Denton said about 3,800 claimants will share in the settlement.

NuvaRing is a hormonal contraceptive inside a flexible ring that slowly releases two hormones. Severe side effects connected to Nuva­Ring include blood clots, strokes and heart attacks, high blood pressure and heart disease, and cancer of the reproductive organs and breast. Denton said 83 wrongful-death claims were part of the lawsuits.