The centre, a private scanning clinic that offers ultrasound scans for pregnancy and gynaecology, previously handled PR in house.
The ultrasound clinic claims to be the largest in London in terms of qualified staff and is also only one of two in the UK to boast four-dimensional scanning of unborn children.
Wimbledon-based Say will use a multi-channel comms approach to raise awareness of the centre's pregnancy services and, more specifically, its new premature birth screening service.
The London Ultrasound Centre is run by co-founder Dr Darryl Maxwell, senior foetal medicine specialist in the Foetal Medicine Unit at Guy's and St Thomas' Hospital and a renowned specialist in ultrasound diagnostics for pregnancy and gynaecology.
Maxwell is also credited with being the first doctor in the UK to develop chorionic villus sampling, a technique that can diagnose genetic disorders in the womb.
The pregnancy expert said he wanted to attract a wider audience to the clinic, near London's Harley Street.
'Many people believe that only the rich and famous use private scans during pregnancy, but we want to let women know that they too can enjoy the highest quality of care. Say was the natural choice to help us do this,' he added.
Say MD Stefi Rucci said: 'The centre offers state-of-the-art diagnostic services and we look forward to working with leading lights at the forefront of foetal medicine.'