In what appears to be an explanation on why Planned Parenthood continues to have strong backing in the US Senate despite the uproar caused by the series of sting videos apparently showing the sale of aborted baby parts and tissues, a Fox News.com analysis has revealed that the women's health care and abortion service provider has been donating millions of dollars to Democratic politicians for the past 15 years.

Planned Parenthood workers and political action committees (PACs) have donated at least $25 million to these Democrats since 2000, the Fox News report said.

Planned Parenthood employees and affiliates also spent $12 million to lobby in support of the organisation since 2000.

"These types of contributions -- any contributions -- to public officials are important and they do sway votes," Jeanne Zaino, a political science professor at Iona College in New York, told Fox News.

A bill in the US Senate seeking to defund Planned Parenthood failed to advance last week by a vote of 53-46, falling seven votes short of the required 60 to pass the measure. Several lawmakers who voted against the measure are recipients of the organisation's PACs and supporters' donations amounting to $884,574, according to a report by the Center for Responsive Politics.

Democratic Senator Ed Markey was the largest recipient with $22,290. He voted against the Republican-sponsored bill to defund Planned Parenthood together with fellow Democratic senators Jeanne Shaheen, Al Franken and Jeff Merkley, all of whom also received donations from the organisation.

Since 2006, the biggest recipients of Planned Parenthood donations are Democratic Senators Claire McCaskill, who got $26,000; Jon Tester, $19,000; and Heidi Heitkamp, $5,300.

Among the donors, Aimee Boone Cunningham of Austin, Texas, who was the vice president of Planned Parenthood of Greater Texas, donated $233,000 to Super PAC Planned Parenthood Votes, Democratic congressional candidates and the Democratic Senatorial Campaign Committee between 2012 and 2014.

Alexandria Marcus of San Francisco worked for Planned Parenthood between 2005-2010 and gave $132,500 to the Democratic Campaign Committee, the DNC Services Corp. and Democratic candidates.

Marcus became the associate vice president of public affairs for Planned Parenthood Mar Monte, and director of Planned Parenthood Advocates Mar Monte and of two Planned Parenthood political action committees and political campaigns.

Democratic presidential bet Hillary Clinton also received donations from Planned Parenthood advocates in the amount of $18,385 between 2000 and 2006.

"Their donation priorities demonstrate that, obviously, Planned Parenthood knows who will support their agenda no matter what," said Republican Senator James Lankford.

Planned Parenthood got $528.4 million in government grants and reimbursements in 2014. Under the law, these funds cannot be used for abortion services.

Meanwhile, the Susan B. Anthony List, an anti-abortion organisation, has donated $1,990,787 to Republicans since 2000 and only $38,468 to Democrats.

Planned Parenthood has been under intense scrutiny after videos were released by anti-abortion group Center for Medical Progress that accused the organisation of selling foetal parts and tissues to medical researchers.

States get warning

Meanwhile, the US government has warned states that are aiming to defund Planned Parenthood that they may violate federal law.

The Centers for Medicare & Medicaid Services contacted officials in Louisiana and Alabama this month, according to a spokesperson of the Department of Health and Human Services (HHS), a Reuters report said.

It warned Louisiana and Alabama that their plans to defund Planned Parenthood may violate the law as it restricts access to services.

Under federal law, state Medicaid programs are required to cover family-planning services.

Medicaid is the US government's healthcare programme for the poor while Medicare is for the aged and disabled.

"It's good to hear that HHS has clarified what we already know: blocking women's access to care at Planned Parenthood is against the law," said Planned Parenthood Executive Vice President Dawn Laguens.