“There is significant national momentum, and the pace of change is quickening,’’ said Jeanne Smoot, senior counsel for public policy and strategy at Tahirih Justice Center, a nonprofit advocacy group that favors tighter limits. “States are realizing that so long as laws remain on their books that may actually facilitate the forced marriage of a child, they need to consider themselves accountable.’’

Data that the group collected from public records in 41 states showed that between 2000 and 2015, more than 200,000 minors were married.

Experts on family law and advocates for women say that early marriage imposes social, educational and financial burdens on teenage girls. Because as minors they may lack the legal standing to file for divorce, experts say, many find themselves trapped in abusive relationships. The testimony of several survivors of child marriages has helped galvanize the movement to close marriage-law loopholes.

But some legislators and religious groups have argued that the stricter marriage laws infringe on religious freedom and parents’ rights. Some have argued that in the case of a pregnancy, a teenage mother would benefit from being married. Last year, Chris Christie, a Republican who was governor of New Jersey, conditionally vetoed a bill that would have banned marriage for children under 18, on the ground that it did not “comport with the sensibilities” or “religious customs” of some residents.

In addition to banning anyone under 16 from marrying, the bill pending in Missouri would prohibit 16- or 17-year-olds from marrying anyone over 21. Girls are often wed to older men in marriages that are arranged by families.