U.S. obstetricians are getting more precise about exactly what determines a full-term pregnancy.

On average, a pregnancy lasts 40 weeks, counting from the first day of the woman's last menstrual period. That's how a due date is estimated.

The Missouri Department of Corrections said Tuesday it is switching to a new lethal injection drug, less than two weeks after the governor halted executions until it could find a replacement for the anesthetic propofol.

The Corrections Department said in a news release that it will use the sedative pentobarbital. Death Penalty Information Center director Richard Dieter said 13 states use the drug for executions. He said every execution but one over the past two years in the U.S. used pentobarbital.

A woman who received a donor windpipe seeded with her own stem cells in groundbreaking surgery five years ago is healthy, said a report Wednesday, hailing progress in tissue engineering.

Donor windpipes are often rejected by the recipient's immune system, while patients also suffer the uncontrolled die-off of cells, called necrosis, and bleeding.

Niger has made the most progress worldwide on reducing child mortality since 1990, according to a study out Wednesday.

Also among the top 10 nations that have made the greatest strides in tackling such deaths are Liberia, Rwanda, Indonesia, Madagascar, India, China, Egypt, Tanzania and Mozambique, Save the Children found.

Argentine farmworker Fabian Tomasi was never trained to handle pesticides. His job was to keep the crop-dusters flying by filling their tanks as quickly as possible, although it often meant getting drenched in poison.

Now, at 47, he's a living skeleton, so weak he can hardly swallow or go to the bathroom on his own.

More than 15,000 people in Japan have been left with skin blotches caused by a chemical contained in popular skin-whitening creams, the maker of the products said Tuesday.

Japanese cosmetics giant Kanebo said it had received 15,192 complaints from Japan from users of 54 products containing the whitening chemical "Rhododenol", in what has become an escalating public relations nightmare for the company.

Regular exercise boosts teenagers' school grades -- and particularly helps girls in science, a British study said Tuesday.

The more physically active they were, the better children performed in school, according to findings published online in the British Journal of Sports Medicine.

A new experiment to regrow hair by cloning follicles and using discarded infant foreskins to graft them has shown some early success in lab mice, researchers said Monday.

The process generated new human hair in five of the seven animals on which it was tested, according to the study published in the Proceedings of the National Academy of Sciences.

Asia-Pacific countries face serious challenges from "lifestyle" diseases and ageing populations even as they overcome more traditional illnesses, the World Health Organization's regional director said Monday.

Western Pacific WHO director Shin Young-soo said such ailments, often arising from a change in diets and less exercise, were sharply rising in Asian nations.

Cholera has killed 50 people in northwest Nigeria in the past week, health officials said Monday, in the latest outbreak of the disease which has claimed thousands of lives across the country since 2010.

The latest infections struck Zamfara state where residents began drinking water directly from streams and untreated wells after a main water pipeline was forced to shut.