The couple admit "a lot of people" find their approach to starting a family "unusual", but Stephanie said: "We wanted the children to be blood-related.
"I'm having a boy so we are hoping Randa will have a girl. A lot people have said it's kind of like having twins."
The pair, from Galashiels, Scotland, met through the internet in 2009 and, having decided they both wanted children and to "share the experience" of pregnancy, first considering having IVF on the NHS.
But after being told they faced a wait of up to three years and would have to choose which of them would become the mother, they explored alternative means on the internet.
They found the Known Donor Registry website, which allows people hoping to become parents to see profiles of potential donors and to arrange to meet for free. Site users make their own legal arrangements about the level of contact the donor can play in rearing the children.
Randa, who has worked as a lingerie model, told The Sun: "We picked a science student who didn't smoke or drink. We thought he'd be fit enough to make it happen. We found that he had a brain... and also had the same colour hair as Stephanie. He was also willing to help, so he ticked every box."
Their first meeting with the Scots-born donor - who said he was not in a relationship and from Edinburgh - was "awkward" but Randa said: "We needed a baby."
The couple inseminated each other following visits from the donor, who was not paid for his services and lived just 35 miles away from their flat. "He was a shy guy but we could just tell he wanted to help.
"We had a cuppa and he did his thing," said Randa. Stephanie became pregnant at the second attempt in January having failed to conceive after the first time the donor visited their home last October. Randa conceived three times but miscarried in the early stages of pregnancy each time.
After Stephanie conceived, they decided Randa would take a break from trying again as they felt having a gap between the babies would be preferable so they could support each other. Randa, originally from Libya, finally conceived in April.
She revealed a strange craving for olives - at one point munching her way through two big jars in one go. "I've been craving them throughout my pregnancy and also want to eat loads of pizza," she said.
The couple, who say they have been supported by some family members and friends, plan to attend each other's respective ante-natal classes.
Randa, who said the pair also compare each other's bumps, added: "I'm going to be in holding her hand when she gives birth and recording it. Because Stephanie is three months in front of me she knows exactly what is happening with me and we can support each other.
"All our chat is about babies at the moment".
Stephanie's baby is due in October and Randa's in January. Stephanie said: "We are really looking forward to bringing them home, especially the first night when we have both together. That will be the best part."
- Daily Mail
