The Mayo Clinic reports there was a second surgery for one of the separated twins today to relieve pressure from swelling.

The Fitterer twins continue to recoverand are listed in critical condition at Mayo Clinic. But Madysen Fitterer undergoes a second surgery this morning.

Doctor Christopher Moir says the surgery on Madysen was successful. It relieved pressure caused by swelling from yesterdays separation.

She and Abygail remain hospitalized in intensive care. Moir says doctors are optimistic that Madysen will do well.

Dr. Moir says "The first 48 hours after surgery are crucial, and we will continue to closely monitor the girls' conditions and make appropriate adjustments." Yesterday's surgery took a little over six hours.

Dr. Moir says the operation was flawless. But he says there were some tense moments as surgeons separated the girls' chests and then fit their hearts back into their bodies.

Moir won't predict when the girls might go home from the hospital.

But he expects them to spend at least a few weeks in intensive care.

Moir also led the team that separated conjoined twin girls Abbigail and Isabelle Carlsen of Fargo last May.

Mayo experts say conjoined twins may develop in as many as one in 50-thousand pregnancies, but they account for only one in about 250-thousand live births. watch the video | save this article / add to your favorites list