More evidence is emerging that babies conceived in test tubes might be just as healthy as those conceived naturally, researchers said Tuesday.

Two studies presented at a meeting of the European Society of Human Reproduction and Embryology found that in-vitro fertilization and the freezing of embryos did not significantly increase the babies' chances of medical problems.

"These procedures are relatively safe and patients shouldn't be overly concerned," said Dr. Christopher Barratt, a professor of reproductive medicine at the University of Dundee in Britain.

Barratt, who was not connected to the research, said the studies were encouraging but more information was still needed.

About one percent of babies born in developed countries are conceived using techniques like in-vitro fertilization. Yet Dutch experts studying children born after in-vitro fertilization concluded that the invasive procedure is not dangerous for babies' early physical and neurological development.

"This is important in reassuring people worried about the risks of these techniques," said Dr. Sue Avery, director of The Assisted Conception Unit at Birmingham Women's Hospital in Britain. "There's naturally a fear when you start doing things like sticking needles into eggs." She was also not connected to the Dutch study.

Previous studies have shown that babies produced from artificial reproduction techniques are more likely to have major birth defects and to be underweight at birth. That is thought to be linked to factors in the parents, like the older age of mothers having infertility treatment, lifestyle or genetic factors.

Doctors have also worried that low birth weight of babies born following in-vitro fertilization could lead to disorders like cerebral palsy.

Dr. Karin Middelburg, of the University Medical Center Groningen in the Netherlands and colleagues examined more than 120 babies born after in-vitro fertilization. Those children were compared to 90 babies born to parents with fertility problems who spontaneously conceived while waiting for fertility treatment and to 450 babies conceived naturally.

Middelburg and colleagues assessed the babies' brain development when they were several months old by observing how they waved their hands, made a fist, or kicked their feet.

"When a child is wired right in the brain, he is able to show a wide range of different movements," Middelburg said.

They found that the test-tube babies moved as well as babies spontaneously born to parents waiting for infertility treatment. That showed that artificial reproduction techniques are not to blame for any early developmental problems, Middelburg said.

When those babies were compared to babies naturally conceived in the general population, researchers did not find a difference in abnormal movements.

Another study presented Tuesday concluded that children born from frozen embryos weighed more at birth than those born after a fresh embryo transfer.

Embryos are sometimes kept at minus 196 degrees Celsius for up to five years before being thawed and implanted into women. Doctors are increasingly freezing embryos across Europe as a standard part of fertility treatment, and some have wondered if the procedure might be riskier than using a fresh embryo.

"With this study, we can be very encouraged that the data seem to point to the conclusion that these techniques are very safe," Barratt said.

Experts said one reason why frozen embryos resulted in heavier and healthier babies could be that women who produced enough eggs to freeze were probably healthier than women who only had enough embryos for a fresh transfer.