From the Prologue of Ochrid, July 12th:
THE HOLY MARTYRS THEODORE AND JOHN (+983)
Theodore and John were father and son, and by descent Varangians (Vikings) who were baptized and then settled in the pagan city of Kiev. The enraged pagans destroyed their home with them in it and, thus, both suffered for Christ. Their relics repose in the monastery of the Caves of Anthony in Kiev. Those without children and those who miscarry invoke their intercession.
I have been unable to find out why they are asked to intercede on behalf of those who miscarry, but that part of the story may have been lost in the last 1,000 years. Interesting notes: (1) Their martyrdom predates the conversion of Russia by 5 years. (2) They were Vikings, specifically from the area which is now Sweden.
Portion of their lives from the OCA site:
"Among the Kievans," reports St Nestor the Chronicler, "lived a Varangian by the name of Theodore, who was in military service at Constantinople long before this, and was baptized there. His pagan name, preserved in the term "Turov pagan temple," was Tur (Scandinavian Thor) or Utor (Scandinavian Ottar), and this other signature is also found in the old manuscripts. Theodore had a son John, a devout and handsome youth, confessing Christianity like his father."
"And the elders and boyars said: let us cast lots upon the boys and girls. Upon whichever one it falls, that one we shall slaughter in sacrifice to the gods." The lots thrown by the pagan priests, evidently not by chance, fell upon the Christian John.
When the messengers told Theodore that his son "had been chosen by the gods themselves to be sacrificed to them," the old warrior decisively answered: "This is not a god, but wood. Today it is, and tomorrow it rots. They do not eat, nor drink nor speak, but are crafted by human hands from wood. God however is One, and the Greeks serve and worship Him. He created heaven and earth, the stars and the moon, the sun and man, and foreordained him to live upon the earth. But these gods, what have they created? They themselves are made. I shall not give my son over to devils."
This was a direct challenge by the Christian to the customs and beliefs of the pagans. An enraged crowd of pagans rushed at Theodore, smashed up his courtyard, and surrounded the house. Theodore, in the words of the chronicler, "stood at the entrance way with his son," and with weapon in hand he bravely met the enemy. (The entrance way in old Russian houses as mentioned was set up on posts of a roofed gallery of the second storey, which was reached by a ladder). He calmly gazed upon the demon-possessed pagans and said: "If they are gods, let them send one of the gods to take my son." Seeing that the brave and seasoned warriors Theodore and John could not be beaten in a fair fight, the besiegers knocked down the gallery posts. When they were broken, the crowd rushed upon the confessors and murdered them.
Already during the time of St Nestor, less than a hundred years after the confessor's deed of the Varangians, the Russian Orthodox Church numbered them among the Saints. Theodore and John became the first martyrs for the holy Orthodox Faith in the Russian land. They were called the first "Russian citizens of the heavenly city" by the transcriber of the Kiev Caves Paterikon, the holy Bishop Simon of Suzdal (May 10). The last of the bloody pagan sacrifices at Kiev became the first holy Christian sacrifice with a co-suffering for Christ. The pathway "from the Varangians to the Greeks" became for Rus the pathway from paganism to Orthodoxy, from darkness to light.
On the place of the martyrdom of the Varangians, St Vladimir later built the Desyatin Church of the Dormition of the Most Holy Theotokos, consecrated on May 12, 996. The relics of St Olga were transferred into it in the year 1007.
Wondrous is God in His saints! Time does not spare stones and bronze, but the lower framework of the wooden house of the holy Varangrian martyrs, burned a thousand years before, has been preserved to our day. It was discovered in the year 1908 during the excavation of the altar of the Desyatin church at Kiev.
Sts Theodore and John are invoked by women who have miscarried.