President Donald Trump's controversial pick for surgeon general, Casey Means, had to postpone her Senate confirmation hearing after going into labour with her first child, a spokesperson said.

Dr Means, nominated to be the "nation's top doctor", was scheduled to appear before the Senate committee virtually because of her advanced pregnancy.

Unlike past surgeon generals, the 38-year-old Stanford-trained doctor and wellness entrepreneur does not have an active medical licence. She is known for her scepticism of conventional medicine and her promotion of wellness products instead.

It remains unclear when the confirmation hearing will be rescheduled.

But the Department of Health and Human Services (HHS) said in a statement: "Everyone is happy for Dr Means and her family. This is one of the few times in life when it's easy to ask to move a Senate hearing."

The nominee graduated from Stanford Medical School and completed most of her residency training to be a head and neck surgeon, although she quit before she finished.

"I walked out of the hospital and embarked on a journey to understand the real reasons why people get sick," she wrote in her book about leaving residency.

One of the leaders of the “Make America Healthy Again (Maha)” movement, which views pharmaceutical and food companies as corrupt and responsible for a rise in chronic disease, she is known for her book Good Energy.

The book advocates natural foods, exercise, and lifestyle changes as the foundation of good health.

Dr Means has questioned elements of the childhood vaccination schedule, and has suggested Americans not use pharmaceutical prescriptions for chronic ailments.

She has also cautioned against long-term use of hormonal birth control.

Dr Means co-founded a company called Levels, which helps people monitor their blood glucose, and has sold other wellness products - including teas and dietary supplements - on social media.

She signed an ethics agreement last month saying she would resign from her advisory position at Levels and stop posting monetised social media posts.

Her nomination has faced bipartisan criticism, including from former surgeons general.

Dr Jerome Adams, who served under Trump during his first term, said he was concerned that Dr Means lacked both a medical licence and completed residency training.

"We must acknowledge that our current healthcare system is broken and drastic change is needed," Dr Adams wrote on social media. "Yet no one would go to an unlicensed and incompletely trained doctor for a surgery or a C-section."

But the HHS said Dr Means's qualifications were not in question and pointed to her Stanford degree and years working in health research positions at the National Institute of Health and several research universities. The agency also noted she has published peer-reviewed papers in major medical journals.

"Her credentials, research background, and experience in public life give her the right insights to be the surgeon general who helps make sure America never again becomes the sickest nation on earth," said HHS press secretary Emily Hilliard.

If confirmed, Dr Means would lead the US Public Health Service, which includes more than 6,000 personnel across multiple federal agencies.

She would be responsible for issuing national health advisories and would report to Health and Human Services Secretary Robert F. Kennedy Jr.

Dr Means became the Trump administration's nominee after the White House withdrew its previous pick, Fox News host Dr Janette Nesheiwat.