Only a small fraction of contraceptives donated in Puerto Rico to prevent Zika-related birth defects are expected to get to the women who need them this month, public health officials told Reuters.

The donations - tens of thousands of intrauterine devices and birth control pill packs - came from major healthcare companies as the virus spreads rapidly through the island.

The delivery delays illustrate the struggles of Puerto Rico's healthcare system, which is faltering amid the commonwealth's financial crisis.

Hundreds of thousands of residents are expected to be infected in the coming months by the mosquito-borne Zika virus.

Infections in pregnant women can cause microcephaly, a rare birth defect that can lead to severe developmental problems.

Many local doctors do not have the expertise to insert IUDs, and have not stocked them because of their high cost to patients.

The CDC Foundation, the US public health agency's philanthropic arm that received the donations, said it needs $20 million for training and follow-up services to get the contraceptives to women.

"We have people who would love to have them available," said Dr Carmen D. Zorrilla, professor of obstetrics and gynecology at the University of Puerto Rico School of Medicine. She is encouraging patients to wait at least a year to get pregnant.

As many as 138,000 women on the island are at risk of unintended pregnancy, based on historical trends and a lack of access to contraceptives, according to the U.S. Centers for Disease Control and Prevention.

Many could be infected

Bayer AG, Allergan, Medicines360, Upstream USA and Merck have together contributed about 60,000 IUDs and 80,000 packs of birth control pills in recent weeks. The CDC estimates that about a quarter of Puerto Rico's 3.5 million people could be infected with the virus.

Doctor Judith Monroe, president and CEO of the CDC Foundation, said the organization has trained about two dozen doctors and raised about $1.7 million in cash, enough to provide 700 women free services starting in June. It needs to raise an additional $20 million to train and pay medical professionals who will provide the services.

In the meantime, the companies are still holding the donated devices and pills while the CDC Foundation lines up a licensed distributor in Puerto Rico.

At the behest of the CDC, the nonprofit in February began soliciting private sector donations for Puerto Rico, Monroe said.