The rate of babies being conceived in the United States through in vitro fertilization is on the rise, a report says.

The assisted reproductive technique, in which eggs and sperm are combined in a laboratory and a resulting embryo is then placed in a woman's uterus, saw 2,000 more babies born in 2013 than in the previous year, researchers have reported.

Almost 175,000 in vitro fertilization attempts resulted in the birth of slightly more than 63,000 babies; in 2012 it was slightly fewer than 62,000 babies from 165,000 IVF attempts, according to a report from the Society for Assisted Reproductive Technology.

Around 1.5 percent of children born each year in the United States are conceived by means of some form of fertility treatment, the society says.

Because IVF is a complex and expensive procedure -- the average price of an IVF cycle in the U.S. is $12,400 -- it is requested by only around 5 percent of infertile couples, but it has still resulted in more than 200,000 babies since its introduction in the U.S. in 1981.

IVF dates to 1978 when Louise Brown, dubbed a "test tube baby" and the first to be conceived outside of her mother's womb, was born in England.

Since the introduction of IVF in the Unites States, many women have chosen to have multiple embryos implanted to increase the chances of a successful full-term pregnancy, but the latest statistics show that's becoming less popular, with more women, regardless of age, requesting a single embryo be implanted in an effort to avoid multiple births.

"We are extremely encouraged to see the number of embryos transferred per cycle continue to go down and that more and more patients are choosing single embryo transfer," says society president Dr. James Toner.

The increase in the number of women choosing single embryo implantation was greatest in women under 35, the society said, with 22.5 percent of that age group making that choice compared to around 15 percent in 2012.

"The goal of reducing the incidence of multiple pregnancies is extremely important, and patients can see from the data that fewer embryos transferred do not mean a lower chance of pregnancy," Toner says.

There has been an overall reduction in multiple births; twin births following IVF treatment dropped from 12,436 in 2012 to 12,085 in 2013, while the number of triplets fell from 411 to 376, the society's report shows.