Quadruplets were born at the Ljubljana maternity hospital last weekend in a rare event that previously happened there nearly ten years ago, the hospital announced on Facebook on 15 January.

The last time quadruplets were delivered at the hospital was in 2015, its head Gorazd Kavšek said.

The four boys, Matej, Luka, Marko and Jovan, who each weighed from 1,030 to 1,450 grams, were born by caesarean section in week 31 of pregnancy. Quads are almost always born prematurely.

Their mother currently lives in Slovenia, but she hails from Banjaluka in Bosnia and Herzegovina, where the event has been described as a true miracle.

"The chance of having quadruplets is extremely slim: they occur in approximately 500,000 deliveries or fewer. This means that such an event in Slovenia would occur once every 15 to 20 years," Kavšek said as quoted in the Facebook post.

The latest birth of quads was a case of spontaneous conception, which is all the more rare.