(CNN)"Nobody could tell us why we couldn't have children, but we've been trying at this point for about 12 years," said Elizabeth Prior, 49, of Buckinghamshire.
She and her husband tried in-vitro fertilization and adoption for several months but were advised against taking any of the children they met. They looked into fostering too, but Prior felt that nothing worked, "so we went down the surrogacy route."
They are among an increasing number of British couples who chose to pursue surrogacy, when one woman carries a child for another.
But UK law has many restrictive elements, which in addition to high cost and a shortage of surrogates in the UK makes many couples feel that going abroad is the only option.
Prior and her husband chose to carry out the process in the United States. "It was just so straightforward compared to how it could have been in the UK," she said of her experience.
The UK's legal limitations were highlighted in a recent study published in the journal Human Fertility that suggested the need for reforms. Of the 132 parents who completed surrogacy and were surveyed for the study, 92 underwent the process abroad, the researchers found.
"Surrogacy is legal, but it's restricted," said Natalie Gamble, who co-authored the study. Gamble runs a family law firm, NGA Law, and a not-for-profit surrogacy agency, Brilliant Beginnings. NGA Law claims to have helped over 1,000 families created through surrogacy.
The practice has been on the rise over the past couple of years, according to the study.
There are no statistics on surrogacy births, but the study suggests deriving an estimate from parental orders, when would-be parents apply to become the legal family of their child born through surrogacy.
These orders can be granted to couples only when one or both partners is the genetic parent of the child and one or both partners live in the UK; this rules out many family structures. The consent of the surrogate and her spouse are also required.
In 2007, 51 post-birth parental orders were issued. By 2016, that number rose to 316, according to Gamble.
This aspect of UK law leaves the possibility open that the surrogate could her mind about the process, as was the case in a 2015 lawsuit in England. The surrogate, who had entered an informal arrangement, refused to give the baby to its biological father and his partner. After a 15-month legal battle, the court ruled that it would be in the child's best interest to live with her biological father and his partner.
For Prior, the lack of legal security was her chief consideration in deciding to go abroad: the fact that there was a chance "that somebody would change their mind and keep the child that was destined for us."