WASHINGTON — The bipartisan criminal justice reform legislation known as the "First Step Act" put in place improvements in the care of pregnant inmates, but advocates say it was a baby step and are calling for more to be done.

The new law bans restraining federal inmates during pregnancy, labor and postpartum recovery unless the inmate is considered a flight risk or an immediate threat to themselves or others.

For many years, pregnant inmates have been subjected to restraints as a security measure, despite the American College of Obstetricians and Gynecologists and others warning that using restraints can put the mother and baby at risk. While the Federal Bureau of Prisons changed its policy in 2008 to bar the use of restraints on pregnant women, the "First Step Act" codified that into law.

"For too long, our criminal justice system has treated incarcerated women as an afterthought," First Step Act co-sponsor and 2020 Democratic contender Sen. Elizabeth Warren, D-Mass., told NBC News of the bill signed into law by President Donald Trump in December.

With data sparse, the measure also requires the Federal Bureau of Prisons to count the number of pregnant inmates, as well as keep track of the outcomes of the pregnancies, whether it is a live birth, miscarriage or abortion.

"The lack of data speaks to the fact that nobody really seems to care about what happens to pregnant women behind bars," said Carolyn Sufrin, an OB-GYN and medical anthropologist at the Johns Hopkins University School of Medicine.

Former inmate Kimberly Haven, of the Reproductive Justice Inside coalition, said of the First Step Act, "It opened up the national dialogue and brought likely and unlikely allies to the same space to have substantive conversations around criminal justice, mass incarceration, racial disparities and gender injustices."

Sufrin and a team of researchers recently published a study in The American Journal of Public Health finding that 3.8 percent of women newly admitted to federal facilities were pregnant, while there were 753 live births, 46 miscarriages, four stillbirths and 11 abortions in the span of a year.

Sufrin and others say the bill only skims the surface when meeting the needs of pregnant inmates.

The ban on restraining pregnant prisoners — advocates call it shackling — only addresses women in federal prisons, leaving out a large share of the female population behind bars.

While there isn't an up-to-date number on the total number of pregnant inmates, the nonprofit The Sentencing Project says the majority of incarcerated women are in state and local facilities, not federal prison.

More than 20 states have passed laws limiting the use of restraints and including a variety of safeguards, such as barring pregnant inmates from being restrained during transportation, childbirth, and immediately after. Utah and at least three other states also are looking at banning the practice, according to The Associated Press.

Amy Fettig, deputy director of the National Prison Project of the American Civil Liberties Union, expressed concern that correctional facilities often fall short when putting the requirements of new legislation into place.

"We've gotten these laws passed and then three years later, we find that no one has implemented it," Fettig said, adding that a general lack of oversight makes it difficult to hold jails and prisons accountable.

In addition, there is no required national standard in prenatal and postpartum care for pregnant inmates.

The National Commission on Correctional Health Care (NCCHC), the American Congress of Obstetricians and Gynecologists (ACOG) and others have established minimum standards for pregnancy-related health care for correctional facilities to follow but they are voluntary.

"The (Supreme) Court doesn't set policy in the sense of saying what those standards are or how agencies should comply with the law," Maya Wiley, a legal analyst for NBC News and MSNBC, said.

Sufrin said an onsite or offsite health care provider can range from a certified midwife to a trained nurse practitioner to someone with no experience. As a result, complications can arise such as inadequate nutrition and the lack of screening tests or the inability to troubleshoot acute issues.

One point of varying postpartum care that is gaining attention is pumping. In 2017, Monique Hidalgo successfully filed a lawsuit against New Mexico's Corrections Department over her right to breastfeed after a judge ruled it was a violation of the state constitution to keep incarcerated mothers from breastfeeding their babies.

Sufrin said breast milk provides important nutrients for babies and allows mothers to bond with their newborns. Denying mothers access also can lead to postpartum depression or breast inflammation from milk buildup.

"I think that a lot of jails and prisons have just categorically dismissed the possibility of postpartum women being able to provide their babies with breast milk," Sufrin said.

Advocates cite the example of Maryland, which has taken steps to prioritize inmate's reproductive health care. Lawmakers required all correctional facilities in the state to provide free menstrual hygiene products and have written policies on medical care for pregnant inmates. The policies range from including access to prenatal and postpartum care to miscarriage counseling that must be provided to inmates once a pregnancy is confirmed.

Diana Philip, executive director of NARAL Pro-Choice Maryland, said the state is the first in the nation to ensure correctional facilities statewide establish guidelines on how to care for pregnant inmates, and she hopes other states will follow.

"The First Step Act only addresses shackling and that's the tip of the iceberg when it comes to treating women behind bars," Sufrin said.