OMGP registered midwife Robyn Hart said about 100 mothers and children who had been helped by the service over the years plus seven midwives attended the celebration last week.

"There were mums from over the past six years who had their babies [using the service]," she said.

"We had lots of five year olds and three year olds."

Mrs Hart said it was the second time they had celebrated their anniversary with an event in Cook Park.

She said the OMGP is part of the service provided by the Western NSW Local Health District at the Orange hospital for expectant parents.

"We offer a continuity of care program. Each mum-to-be has their own midwife," she said.

The Know Your Midwife program provides care by the midwife during pregnancy, labour, birth and during the postnatal period.

Mrs Hart said the midwives were on call to assist the parents.

She said the OMGP program concentrated on "low-risk births."