In 2006, the average pregnancy rate per embryo transfer was 32.8 percent using in-vitro technology and 33.6 percent using a technique called intra-cytoplasmic sperm injection (ICSI), in which a single sperm is injected into an egg, they said.
In 1997, the rates were 26.1 percent for IVF and 26.4 percent for ICSI.
The figures were released in Amsterdam at the annual conference of the European Society of Human Reproduction and Embryology (ESHRE).
In a press release, ESHRE also reported a decline in multiple births using assisted reproduction.
This is important, because multiple births are strongly associated with low birthweight and poor cognitive development.
In 1997, twins, triplets and quadruplets accounted for 29.5 percent of all assisted reproduction births.
In 2006, though, only 19.9 percent were twins, 0.9 percent were triplets and, for the first time, there were no quadruplets.
The report noted that doctors in Bulgaria, Ukraine and other eastern European countries still tended to carry out multiple embryo transfers in the hope of gaining a successful birth, but then reduced the number of foetuses after the transfer succeeded.
The figures are based on data from fertility clinics in 32 countries.