An increasing amount of female same-sex couples are undergoing a new IVF procedure which allows both women to share the biological role when having a child.

This “two-mom” approach involves one woman’s eggs being mixed in a lab dish with donated sperm and then implanted into the other woman, who carries the pregnancy.

A New York doctor described 18 such cases at a fertility conference in Boston on Tuesday. The conference, a meeting of 50 fertility societies from around the world, also featured other research on how to let same-sex couples have children.

Dr Alan Copperman, who works at a New York City clinic that offers the procedure, told the Associated Press: “The modern family is created in a way that would be humbled by traditional fertility treatments. We’re seeing more and more couples come in and want to share the parenting experience”.

New York couple Sarah Marshall and Maggie Leigh Marshall now have an 18 month old daughter thanks to the approach, and both women are listed as parents on the birth certificate.

Sarah, who carried the pregnancy, said: “It allowed us both to participate, I had to mentally and psychologically give up the idea of, is she going to look like me or my family. But from the time I started carrying her up to now, she is definitely mine”.

Maggie, whose eggs were used to make the embryo, said that she had had no interest in being pregnant: “Sarah really wanted to have the experience. We also thought it would be a great way to bond with a kid that ultimately would look a lot like me”.

As with all IVF treatments however, the procedure is expensive. Sarah and Maggie spent nearly $100,000 on failed attempts.

In the UK, the Human Fertilisation and Embryology Act 2008 and the Civil Partnership Act 2004 have made it easier for lesbian couples to secure parental rights for any children they conceive through artificial insemination.