 He was the first doctor in North America to use the technique, which he trained other doctors to use.Dorothea Kerslake introduced the method into the United Kingdom in 1967 and published a study in the United States that further spread the technique.Harvey Karman in the United States refined the technique in the early 1970s with the development of the Karman cannula, a soft, flexible cannula that avoided the need for initial cervical dilatation and so reduced the risks of puncturing the uterus.