The women, aged 38 and 33, made the revelation during two hours of questioning by Pol Col Decha Promsuwan at the Lumpini police station on Saturday.
The officer said the women identified Dr Pisit Tantiwatanakul, owner of the All IVF clinic on Witthayu Road, as the person who arranged the surrogacy services.
One of the women was quoted as saying that she was hired last year and gave birth to male and female twins at a hospital in Bangkok last September. The other said she bore a baby girl in January at the same hospital. Each was hired for between 300,000 and 400,000 baht.
Pol Col Decha said staff of the Ministry of Social Development and Human Security were now caring for the three infants.
He said he planned to interview five other women on Monday to collect evidence for further legal action.
The officer is also seeking to question Dr Pisit but the latter's lawyer has sought a postponement until Sept 6. Pol Col Decha said that was too long a delay and if the two sides can't agree on an earlier date, and arrest warrant could be issued.
The babies born to both of the women questioned on Saturday had been brought to The Niche ID condominium in Bang Kapi district, where authorities later found many babies and nannies reportedly hired by Mitsutoki Shigeta, a 24-year-old Japanese man.
The two women said they returned to their home provinces shortly after the babies were brought to the condo.
Pol Maj Gen Thitirat Nonghanpitak, the Bangkok deputy police chief, said that Dr Pisit was now the key to helping unravel the surrogacy case. If he did not cooperate, he would face actions including a request for the revocation of his specialty licence, said Pol Maj Gen Thitirat.
Police are also trying to gather more information about Mr Shitega, he added. The Japanese man left Thailand earlier this month as reports emerged that linked him to as many as 16 babies born in Thailand.
Interpol has launched a multinational investigation into what has become known as the "baby factory" case and into reports that Mr Shitega intended to father hundreds more children.
"I've never seen a case like this," said Apichart Suribunya, the Interpol director for Thailand. "We are trying to understand what kind of person makes this many babies."
Pol Maj Gen Apichart said regional Interpol offices in Japan, Cambodia, Hong Kong and India had been asked to probe Mr Shigeta's background. Police say he appears to have registered businesses or apartments in those countries and has frequently travelled there.
"We are looking into two motives. One is human trafficking and the other is exploitation of children," said Kokiat Wongvorachart, the local lead investigator in the case. He said Mr Shigeta made 41 trips to Thailand since 2010. On many occasions he travelled to Cambodia, where he brought four of his babies.
Mr Shigeta has not yet been charged with any crime.