Bryan trained as a paediatrician at York Hospital and at London's Hammersmith Hospital. She returned to York in 1975 to work as a senior clinical medical officer. She first became interested in twins in 1973, after assisting in the delivery of a set of twins: as a result of twin-twin transfusion syndrome, one was large and red while the other was small and pale. Inspired by this encounter, she gained an MD in 1977 with her thesis on "Serum Immunoglobulins in Twin Pregnancy with Particular Reference to the Fetofetal Transfusion Syndrome". In 1978, she co-founded the Twins and Multiple Births Association and published guidelines for healthcare workers on managing multiple births. She moved back to London in 1979, becoming a consultant paediatrician at Queen Charlotte's and Chelsea Hospital. She was a senior research fellow and later a senior lecturer at the Royal Postgraduate Medical School, where she taught until 1995. From 1987, she established specialised clinics for twins in London, York and Birmingham. In response to the rise in multiple births caused by the increasing popularity of in vitro fertilisation, she founded the Multiple Births Foundation, a charity that provides support to twins' families, in 1988. She also campaigned for IVF providers to reduce the number of embryos they implanted, to decrease the incidence of multiple births. Throughout her career, Bryan encountered over 100 sets of twins, and when she married in 1978, 25 pairs of twins attended her wedding. She and her husband, Ronald Higgins, an ecologist and diplomat, wrote a book titled Infertility: New Choices, New Dilemmas about their failed experience with IVF and other attempts to become pregnant. With her 1995 book Twins, Triplets and More, she was one of the first to write about the unique psychology of being a twin or triplet. She was also among the first people to study the grief felt by a twin when the other dies, and established a clinic for bereaved twins. Bryan was president of the Twins and Multiple Births Association from 1978 until 1984, and was a trustee until 1991. She directed the Multiple Births Foundation from its founding in 1988 until 1998. She was elected president of the International Society for Twin Studies in 1998 and held the position until 2001. She was elected Fellow of the Royal College of Physicians in 1989 and was a reader in paediatrics at Imperial College School of Medicine from 1995 until her retirement in 2005.
Bryan discovered in 1975 that she carried the BRCA1gene mutation, which predisposes carriers to ovarian and breast cancer. One of her sisters died from ovarian cancer, while the other developed breast cancer; as a precaution, Bryan had her ovaries removed in 1992 and a double mastectomy in 1992. She was eventually diagnosed with terminal pancreatic cancer in 2005, and underwent surgery and chemotherapy. In 2007, she published a book, Singing the Life: The Story of a Family in the Shadow of Cancer, about her family's experience with cancer. She died a year later, on 21 February 2008.
