Giving birth in water is becoming more popular, particularly among women seeking an alternative to a medicated or hospital birth experience. But a new review finds little evidence on whether this option is good for babies.

Researchers analyzed data from 29 previously published studies and found no significant differences between water births and other delivery methods in terms of complications, infant mortality or admissions to intensive care. Most of these studies were small, however, and didn’t show any advantages of water births, either.

“The notion that it is safe to have the baby under water has not been shown as safe or unsafe in our review,” said senior study author Dr. Alastair Sutcliffe, a pediatrics researcher at University College of London Hospitals in the U.K.

“Whilst it is a good plan to try labor in water, my advice is to wait until there is more convincing evidence of safety before having the actual delivery in water,” Sutcliffe added by email.

For mothers, laboring in a pool of warm water can help ease pain, lower the need for anesthesia and potentially speed up the early stages of labor before the cervix is fully dilated and the baby is ready to emerge. Once it’s time to push, however, the benefits are unclear.

About 9 percent of babies in the U.K. were delivered under water last year, Sutcliffe and colleagues note in the Archives of Disease in Childhood – Fetal and Neonatal Edition.

In the U.S., however, the American College of Obstetricians and Gynecologists and the American Academy of Pediatrics recommend against underwater deliveries due to potential complications for babies such as infections, breathing difficulties and drowning 

To assess the risks and benefits for babies, Sutcliffe and colleagues looked at data from studies that, combined, included about 39,000 births.

All of these studies were done in hospitals or birthing centers. Most were small observational studies with brief follow-up periods, and many were limited to women with uncomplicated, low-risk pregnancies.

The studies did point to one possible advantage of underwater delivery – slightly higher newborn Apgar scores, which measure heart rate, breathing, muscle tone, reflexes and skin tone.

But because most studies didn’t randomly assign some women to water births and others to more traditional deliveries, it’s impossible to conclude that water births cause higher Apgar scores.

“There is no evidence that delivering underwater has any benefits and the authors of this study fail to acknowledge a benefit other than to mention that whales and dolphins give birth under water,” said Dr. Amos Grunebaum, director of obstetrics at New York Weill Cornell Medicine.

“Just because something is popular does not mean it’s safe or has any benefits,” Grunebaum, who wasn’t involved in the study, added by email. “In fact, there is plenty of evidence to suggest harm like infections, seizures and pneumonia in the (infant).”