WASHINGTON — The share of female troops in the U.S. military increased only slightly over 14 years, consistently representing less than a fifth of service members, and women remain more likely to leave the military than male troops, a government watchdog report shows.

Women cited an array of challenges in deciding to end military careers at higher rates than men, including sexual assault and difficulty reconciling pregnancies and parenthood with career advancement, according to the study by the nonpartisan Government Accountability Office.

The GAO’s analysis stems from concerns raised by lawmakers in recent years that disproportionate female attrition may harm Defense Department readiness and take an economic toll on the military.

The report comes as the Pentagon seeks to modernize its force and reorient toward China after two decades of counterinsurgent operations. In recent years, the military has sought to prepare for high-tech conflicts by buying sophisticated weaponry and growing its digital capability as the Trump administration has promoted increased defense spending.

But the GAO found that the military has failed over multiple administrations to adequately plan for and track the integration of women across the force, including into ground combat roles. More recently, the department — whose senior leaders remain predominantly male — has not established clear plans and metrics to ensure it can create a more diverse force, the watchdog found.

In fiscal 2018, women represented 16.5 percent of the active-duty force, compared with 15.1 percent in fiscal 2004, making up a small share of the more than 1 million active-duty troops. In the most recent year examined, the Air Force and Navy had the highest number of female personnel, both around 20 percent, while the Marine Corps had the lowest, at less than 9 percent, the GAO said.

“Without DOD guidance and service plans with goals, performance measures, and time frames to monitor female recruitment and retention efforts, DOD may continue to miss opportunities to recruit and retain a valuable segment for its active-duty force,” the report stated.

While the GAO found that the gap between the rate of male and female departures from the military has narrowed, women continue to leave at higher annual rates than men. Losing troops trained at great cost represents a persistent challenge for the military.

In fiscal 2004, the attrition rate for men was 22.7 percent and 33.1 percent for women. In fiscal 2018, it was 6.1 percent for men and 8.6 percent for women. A statistical model based on historical data compiled by the GAO, meanwhile, showed that women are 28 percent more likely to leave the force than men.

The analysis also found that the share of women decreases after the 10-year service mark, “meaning a smaller pool of female service members being available for leadership opportunities.”

According to the GAO modeling, attrition rates vary among troops based on a variety of factors, including race, marital status and whether they have children.

Women in the Navy who are married and have children, for example, are 17 percent more likely to leave than their single female counterparts without children. But the converse is true for men: Married men in the Navy who have children are 28 percent less likely to leave than single male Navy personnel without children.

The study found that black and Hispanic female troops in every service are less likely to leave the military than white female troops.

Women reported several factors influencing their decisions to leave the military, including deployments; long or unpredictable work schedules that decrease family time; child-care issues; an organizational culture that some described as dominated by men and characterized by sexism; a desire for family planning in a way that does not damage career prospects; and sexual assault.

“Female service members also discussed how having leaders who are not supportive or understanding of family needs can contribute to a negative or toxic work environment,” the report stated.

The GAO presented a more mixed picture regarding promotions, saying that women are less likely to be promoted overall, but that female commissioned officers have consistently been more likely to be promoted than their male counterparts. Female enlisted troops were also less likely to be promoted than men over the entire period studied but surpassed men in promotions slightly between 2015 and 2018.

However, women remain far outnumbered, especially in the military’s higher echelons.

For 2018, the GAO found that the percentage of women among commissioned officers declined by nearly three-quarters from lowest to highest rank, from 21 percent to 5.4 percent. Among enlisted personnel, the share of women declined by nearly half, from 16.6 percent at the lowest rank to 9.1 percent at the highest.