Goodbye is always the worst moment for a parent hovering over a child enroute to the operating room, and the nurses at Children's National Medical Center have mastered the art of the quick but gentle nudge-away. Kevin and Melissa Buckles give each twin daughter a kiss on the cheek before Jade and Erin disappear behind the big, swinging doors, leaving their fretful parents behind to wait.

Waiting is an art the Woodbridge couple is slowly learning to master 10 weeks after their girls beat tremendous odds to become one of only 700 or so sets of conjoined twins born alive. Delivered by Dr. Christian Macedonia at the National Naval Medical Center in Bethesda on Feb. 26, Jade and Erin are fused at the chest and abdomen, sharing a liver and diaphragm.

After undergoing a test a week earlier to confirm their doctors' belief that their hearts were completely separate , the twins returned to Children's last Saturday for the first crucial step in preparing them for separation next month.

Pediatric surgeon Gary Hartman and plastic surgeon Michael Boyajian lead the medical team this time, making four tiny incisions near the bridge where the girls are fused face-to-face from breast bone to navel. They then slip devices that resemble deflated balloons with nickel-sized valves just beneath the skin. These tissue expanders will be gradually filled with a saline solution during the next five weeks, causing the girls' delicate skin to stretch and grow. The extra tissue is vital to their successful separation: surgeons will need it to close the massive wound created by essentially amputating one human being from another. The Buckles absorb the medical details without apparent squeamishness. Melissa is a high school English teach on indefinite leave, but spent her first year of college as premed. Kevin, a Marine gunnery sergeant in the renowned Drum and Bugle Corps, never goes to an appointment without a list of questions.

"For me, it's just information, really," Kevin explains the night before the procedure. "Give it to me as you see it, line it all up, don't be afraid to tell me. Melissa likes the information also, but the closer it gets . . . " The stress is like a low-grade fever that never breaks, exacerbated by exhaustion from caring for the girls. Melissa, at the kitchen table coaxing 2-year-old daughter Taylor to finish her chicken nuggets, nods in agreement.

"Kevin is just really calm," she explains. "I kind of do the what-ifs once in awhile even though I know I shouldn't. I try not to think about the separation surgery, but I'm a pretty emotional person." The night before, she admits, "I kind of broke down."

What triggered it, Kevin explains, was an episode of "ER" on TV. The plot centered around a woman whose baby died in the womb. The small body was left in the hospital room for the parents to say goodbye.

"I could see all the connections going on in her head," Kevin says of his wife, "but by then it was too late to change the channel. We were up until 1, talking and crying."

Earlier that same day, Kevin had gone alone to Children's to be briefed by the surgical team about the upcoming procedure. Melissa stayed home with the girls and Taylor, who was sick with diarrhea and a fever -- a development that had everyone nervous. The babies would have to be monitored closely -- any sign of illness would mean postponing the tissue expanders. And that, in turn, would mean pushing back the surgery to separate them, tentatively scheduled for June 12.

Kevin listened to the clinical discussion about anesthetizing the girls and figuring out exactly where, on the limited body surface available, the extenders would best serve their critical purpose. He remembers thanking the doctors for all their analysis, their troubleshooting, the contingency planning. And he remembers how surprised they looked when he said, in his polite, precise, military way: "When all is said and done, though, we realize that it's not in your hands." Whether Jade and Erin survive, both parents believe, is up to God alone.

Saturday morning dawns sunny and bright, a beautiful day the Buckles will miss entirely as they spend the day waiting for the babies to emerge from surgery. The hospital gives them a big dayroom to themselves; Saturdays are quiet here. Kevin plays checkers with Kevin Jr., his 11-year-old son from a previous relationship. A hospital volunteer takes Taylor off her parents' hands, spiriting the toddler down to the lobby atrium to blow bubbles. Melissa tries to read, or fiddles with the family Web page she's created on her laptop computer.

The plastic surgeon strides into the dayroom just before 3:30 p.m., smiling. "So listen, we're all done," Michael Boyajian announces, adding, "they're tough little kids." He tells the Buckles how to spot signs of rejection or infection with the implants, which initially will resemble large spider bites. If the skin turns white, it might be breaking down. Red, warm patches around the inserts could signal infection. The girls will spend the night in the Neo-Natal Intensive Care Unit, and then go home the following morning.

Kevin cajoles a reluctant Melissa into going home. They both need the rest. The babies are fine, and the nurses will take care of them. There's nothing more they can do for now. In the intensive care unit, they hover again over their small, medical rarities. They lean in past the IV poles and beeping monitors to kiss identical cheeks and offer a finger to tiny hands that reach out and clasp tightly.