A five-month pregnant woman was thrown to the floor and her necklace ripped off by a robber in a "cowardly attack", police have said.
The 34-year-old was at Beckenham Tram stop in south-east London and was taken to hospital suffering from neck pain. She was later given the all-clear.
British Transport Police are appealing for witnesses to the incident.
Det Sgt Don Thompson said the incident was very rare but it was "a cowardly attack on a vulnerable woman".
He added: "It is extremely fortunate that the victim and her baby were unharmed. The incident left her shocked and extremely upset and we are determined to track down the culprit."