(Reuters) - A Texas mother had a one-in-70-million kind of Valentine's Day this year when she gave birth to two sets of identical twin boys, a Houston hospital announced on Monday.

The four brothers were delivered at 31 weeks to Tressa Montalvo, 36, via Cesarean section at The Woman's Hospital of Texas in Houston, according to a news release from the hospital.

Tressa and Manuel Montalvo Jr. were not using any fertility drugs and had just hoped for a little brother or sister for their 2-year-old son, Memphis, according to the release.

"We planned the pregnancy - I guess we just succeeded a little too much!" said Tressa Montalvo, quoted in the release.

When Montalvo was 10 weeks pregnant, her physician told her she was having twins, and on a subsequent visit, the doctor detected a third heartbeat. The Montalvos were later informed they were having four babies - not quadruplets but two sets of twins.

The odds of delivering two sets of naturally occurring identical twins is somewhere in the range of 1 in 70 million, according to the hospital. Two boys shared one placenta and the two other boys shared another placenta.

Ace and Blaine were born at 8:51 a.m. on February 14 and weighed 3 pounds, 10 ounces (1.64 kg), and 3 pounds, 15 ounces (1.79 kg), respectively. Cash and Dylan followed a minute later, weighing 2 pounds, 15 ounces (1.33 kg), and 3 pounds, 6 ounces (1.53 kg), respectively.

"We tried to stick to the A-B-C-D theme when naming them," Tressa Montalvo said. "We didn't expect it, we were trying for just one and we were blessed with four."

Manuel Montalvo said in the release that they're not done yet - he still wants a girl.