The statement emphasized that the law would not ban second-trimester abortions, saying it simply “ensures more humane treatment of the unborn child.”

Supporters of the law cited studies that they said demonstrated the safety of the additional procedures the law would require. However, medical officials generally oppose them. The American Congress of Obstetricians and Gynecologists has said that standard dilation-and-evacuation abortions are “evidence-based and medically preferred” in the second trimester because they cause “the fewest complications for women compared to alternative procedures.”

“We don’t really know what is the next best alternative because we haven’t had to use it as a medical community for decades,” said Dr. Bhavik Kumar, medical director of the Texas Whole Woman’s Health clinics, the main plaintiffs in the case. “There isn’t any good evidence, if any evidence, to support any of the alternatives’ being viable options.”

Before the ruling came down, Dr. Kumar said, he felt panicky thinking about having to tell patients “that this is how I normally would do the procedure if I were in any other state, but because of the new state law, I now have to provide you with care that is substandard.”

Joe Pojman, the executive director of the Texas Alliance for Life, which supports the Texas law, said in a statement that the state “should have the right to protect innocent unborn babies from dismemberment abortions, in which a doctor kills a child by tearing him or her into pieces.” The fact that courts have consistently ruled against bans on dilation-and-evacuation abortions, he argued, “shows how extremely out of touch the Supreme Court precedent is with modern science, which clearly tells us that an unborn child’’ is a living human being.

In an interview on Thursday, Dr. Daniel Grossman, a professor of obstetrics at the University of California, San Francisco, said that second-trimester abortions had increased since Texas imposed a separate set of restrictions on abortion clinics in 2013. (The Supreme Court struck those down last year.) There was a 27 percent increase in second-trimester abortions from 2013 to 2014, according to a study by Dr. Grossman, which might reflect women’s having trouble obtaining abortions in a timely manner. The increase in later-term abortions occurred even as the overall number of abortions in Texas declined.

“It’s particularly ironic that the state would then be imposing a ban on the safest and most commonly used procedure in the second trimester,” Dr. Grossman said, “when there’s some indication that previous restrictions they’ve imposed are pushing women to need this procedure more.”