The 37-year-old American achieved her victory over sister Venus in the final two years ago while eight weeks pregnant with her daughter Alexis Olympia.
There is still only a median 25 percent probability no agreement is reached before Britain is due to leave the EU on March 29, unchanged from a November poll.
Trump, via Twitter, held out the possibility of an extension of the ceasefire but warned tariffs would be back on the table if the talks failed to bear fruit.
The Islamic Republic's government has ruled out negotiations with Washington over its military capabilities, particularly its missile program, which is run by the Revolutionary Guards.
US has become sensitive to criticisms after President Donald Trump has imposed tariffs not only on $250 billion of Chinese goods but also on steel and aluminum imports
The two-day summit discussed issues such as the future of work, infrastructure for development, financial stability, climate sustainability and international trade, among others.
Immigration was a major issue in the 2016 vote to leave the European Union and May has promised to end the free movement of EU citizens to live in Britain.
China is the world's largest and fast-growing market for new-energy vehicles (NEVs), a category comprising electric battery cars and plug-in electric hybrids.