Doubly blessed: Two sisters act as surrogates for sibling Tanya Ratcliff burst into tears as she left her fertility doctor's office. She'd just been told that though she could conceive, she'd never be able to carry a baby. Without a surrogate there would be no hope of producing a child from any of those the picture perfect embryos formed when her eggs united in the test tube with her husband Dan's sperm. But as Tanya sat weeping in her car in the fertility clinic's parking lot, her sisters, Tara Schamel and Cassie Ripp offered one of the most precious gifts a sibling could: they would carry the babies she could not. Today both sisters are pregnant with Tanya and Dan's babies. Tara is expected to give birth to a baby girl in April, while Cassie is due to deliver a baby boy in July. "Every day my husband and I will just stop and say, wait, I just can't believe this is happening," Tanya told NBC's Janet Shamlian. To be able to have two children with all the limitations I had just blows my mind. Tanya and Dan Ratcliff had planned to start a family right after they married. But after months and months passed with no pregnancy, they turned to a fertility clinic for help. At first the news was good. The couple's sperm and eggs were healthy enough to produce 14 embryos. The problem was, Tanya's womb didn't respond properly to the hormone treatments designed to plump up its lining. Doctors told the couple the embryos wouldn't survive if they were transferred to Tanya's uterus. That's when the sisters stepped in. Tara, 35, has twin 9-year-olds and a 6-year-old daughter. Cassie, 26, is a single mother with a 3-year-old daughter. Tanya remembers her emotions when her sisters" offered their gift. "I was crying," she told TODAY's Ann Curry. "It was raining outside and we were sitting in the car at the fertility clinic and she said to me, "somebody in this car will be pregnant with one of your babies by the end of this year." Tara said she and Cassie were delighted to be able to help their sister. "Cassie and I had been talking about it behind the scenes and I had been talking about it with my husband, and the little wheels in my head were turning, and I knew this was something that we could do if we were physically able to," Tara told Curry. It would be a great gift. The plan they suggested was to have embryos transferred to both of them in order to raise the likelihood that at least one would become pregnant. The process wasn't easy for either sister. To get Tara and Cassie ready for the embryos, doctors first treated them with medications that stopped them from ovulating and in essence shot them temporarily into a menopause-like state. Then the sisters were given large doses of estrogen to ready their wombs for the embryos. After embryos were transferred to both women's wombs, the waiting began. Two weeks later they learned that Tara had become pregnant, but Cassie had not. After discussing the situation with Tanya, Cassie decided she wanted to keep trying and on the third attempt - with the last of Dan and Tanya's frozen embryos - she became pregnant, too. Tanya explained on her blog why she and Cassie agreed to keep trying. "Dan and I have always wanted several children," she wrote. Of course we would prefer them two or three years apart like most people, but we don't have the same options as most people. For us to have more children, we need help from other people. Tara will be shutting up shop after this pregnancy, and I could never ask her to make this sacrifice again. Cassie wants to get married and have more children of her own down the road. So this is our window of time to have that family we always wanted - however crazy and strange it may seem to some. Now, as the couple waits for the birth of their two children, Dan is still amazed at the huge gift that his wife's sisters have bestowed on them. "It was unbelievable," he told Curry. To give up your body for a whole year for us. It's just unbelievable. Cassie, with a smile, reminded Dan that her job would be over with the delivery but his and Tanya's would be just starting. "I think being pregnant is the easy part," she told Curry. With a laugh she added, "Raising the children is the tougher part. I'm glad I'll be able to see the children being raised. Linda Carroll is a regular contributor to msnbc.com and TODAY.com. She is co-author of the new book "The Concussion Crisis: Anatomy of a Silent Epidemic" Also on Today Health: C-sections aren't always the best for preterm babies