WASHINGTON, Jan. 24 (Xinhua) -- A large international trial has been launched to find the best HIV treatment for pregnant women and their infants, the U.S. National Institutes of Health (NIH) announced Wednesday.

The study will "compare the safety and efficacy of three antiretroviral treatment regimens for pregnant women living with HIV and the safety of these regimens for their infants," the NIH said in a statement.

One is the current preferred first-line regimen for pregnant women recommended by the World Health Organization, which comprises of efavirenz (EFV), lamivudine (3TC) or emtricitabine (FTC), and tenofovir disoproxil fumarate (TDF).

The other two contain newer antiretroviral drugs that are becoming more widely used: dolutegravir (DTG), and either tenofovir lafenamide (TAF), an alternative formulation of tenofovir, or TDF.

According to the NIH, EFV has been linked to neuropsychiatric symptoms, including suicidal thoughts, as well as liver problems.

TDF can cause kidney problems and loss of bone mineral density in adults, and some evidence suggests that prenatal exposure to TDF could cause bone loss in infants.

"Women should have access to the best available HIV medications throughout their lives," said Anthony Fauci, director of NIH's National Institute of Allergy and Infectious Diseases.

"Our priority is to evaluate newer, improved antiretroviral drugs during pregnancy to identify the optimal regimens for women living with HIV and their infants."

The first participants in the new clinical trial have begun receiving treatment at research sites in Zimbabwe, the NIH said.

Clinical trial sites in the United States and Zimbabwe are now open for enrollment, with additional sites in Botswana, Brazil, Haiti, India, Malawi, South Africa, Tanzania, Thailand and Uganda expected to open in the coming months.

The study, known as IMPAACT 2010 or VESTED, aims to enroll 639 women who are 14 to 28 weeks into their pregnancies, are living with HIV and are not currently on antiretroviral treatment.

The women will be randomly assigned to treatment with EFV/FTC/TDF, DTG/FTC/TAF or DTG/FTC/TDF.

The investigators will monitor both mother and infant for 50 weeks after delivery.

The study is expected to last for approximately three years.

Currently, an estimated 1.5 million women living with HIV give birth each year worldwide.