Ashley Adams, 24, and her husband, Andy, discovered in March she was pregnant with quadruplets, a result of fertility treatments, CNN reported Thursday.
Four months into the pregnancy, an ultrasound revealed she had stage 1 thyroid cancer, which had spread into her lymph nodes.
"Ashley has probably had that cancer for several years, and it went undiagnosed, probably because with her young age," said Julie Scott, a high-risk obstetrician at the University of Colorado Hospital in Aurora. "The doctors missed the warning signs."
The mother and her doctors waited until after the babies -- one boy and three girls, two of them identical twins -- were born Aug. 26 to proceed with surgery for the cancer, CNN reported.
"In cancer -- which is always unfortunate -- Ashley is fortunate that she had a form of cancer that was slow-growing and wasn't going to be altered by the course of pregnancy and could be managed," Scott said.
Doctors performed a thyroidectomy and lymph node removal in a 7-hour surgery.
The parents said they expect to bring son Wyatt home from the hospital this week. The three girls -- Rylie and identical twins Samantha and Braelynn -- should be home before Thanksgiving, CNN reported.