By Tom Balmforth

CHERNIHIV, Ukraine (Reuters) -When gaunt Ukrainian soldiers dismount from buses as part of prisoner swaps with Russia, Mariia Pylnyk tries to find out anything she can about her missing husband from the freed men, and hopes, just maybe, that he will be among them.

Holding up a photograph of Dmytro Pylnyk, lost in action in early 2023, she has many questions. What happened to his unit when it was ambushed by Russian forces? Was he captured by Russia? Could he eventually be released?

The mass prisoner swap last month was an opportunity for people like her to ask troops just out of Russian captivity about missing loved ones who they believe, or simply hope, are prisoners of war. The alternative is unthinkable.

"I hold out great hope that someone has heard something, seen something," Pylnyk, 29, told Reuters at a recent exchange in May, flanked by other relatives of those missing in action.

"My son and I are waiting for (his) dad to come home. Hope dies last. God willing, it'll all be okay and dad will come back."

Precise numbers for soldiers missing in action are not made public.

For Ukrainians, and for Russians on the other side of the conflict, it can be hard to find out even basic information. Pylnyk says she has written to government agencies and Russian authorities and learned almost nothing.

Ukrainian officials say more than 70,000 Ukrainians have been registered missing since 2022, when Russia launched its full-scale invasion. The majority are from the military but the figure also includes civilians.

Another 12,000 have been removed from the list after being identified among the dead or returned in exchanges.

Petro Yatsenko, a spokesman for the Coordination Council that arranges prisoner swaps from the Ukrainian side, said Russia had never notified Kyiv which soldiers it is holding prisoner. Ukraine collects that data by other means as best it can, he said.

Pylnyk and others like her share information in online chat groups and use it to try to piece together what happened.

"Misfortune brought us together," she said. "After two years of this, we're like a family."

LAST PHONE CALL

Dmytro Pylnyk, an electrician by trade, was drafted into the army in late 2022. He phoned home often so that his wife did not worry but last called on their son Artem's third birthday on Feb. 27, 2023.

He was deployed from Kharkiv region towards Bakhmut, a small city that later fell to Russian forces after fierce fighting.

His unit's convoy was caught in a Russian ambush, Mariia Pylnyk said she had learned.

"The guys ran any which way," she said, citing conversations with commanders who told her 41 soldiers were missing in action.

Two were captured and have since been released. One, who was freed in an exchange at Easter and had lost both his arms, was unable to share any valuable information, she said.

The second refused to talk.

The pace of prisoner swaps has increased in the last month.

Ukraine and Russia each released 1,000 prisoners in a three-day exchange last month, the only tangible outcome of direct talks in Istanbul.

A prisoner swap of under-25s on Monday was the first in a series of exchanges also expected to include each side repatriating the remains of thousands.

Mariia Pylnyk has given her son's DNA to the authorities so that if Dmytro is confirmed killed in action they will be notified.

"We all understand that this is war and anything is possible. But to this day, I don't believe it and I don't feel that he is dead. I feel like he's alive and God willing he'll return," she said.

NO SIGNAL TO CALL

She lives with Artem, now five, in Pakul, a village in the northern Chernihiv region that was briefly occupied by Russians. She has not told Artem his father is missing in action.

"He knows that dad is a soldier, dad is a good man, dad is at work and just doesn't have any signal to call," she said.

She takes comfort from seeing families reunited and never allows herself to cry in front of her son.

She used to work in a shop, but Artem has often been ill. The angst of the last two years have taken their toll on her health too. She receives state support.

Pylnyk has vowed to find her husband but has often not had time to attend prisoner swaps while looking after their son.

"Only a weakling can give up, you know, throw up their hands and say that's it, he's not there," she said, adding that she was very emotional when she attended last month's big exchange.

"When I was there, the fighting spirit awoke in me that I needed. I have to do this. Who else will do it but me?"

(Editing by Mike Collett-White and Timothy Heritage)