Dr Colin Smyth said he was disappointed there was no replacement in situ before he left, but 35 years of being on call was long enough.
He said the WA Country Health Service (WACHS) had 10 months� notice of his intention to quit and he had delayed his departure.
The GP obstetrician had intended to leave at the end of June.
�We did have someone but it fell through at the last moment,� Dr Smyth said.
Sixty mums-to-be are without a local obstetrician.
Dr Smyth said he had spoken on video link with several doctors appointed to share the position but for reasons unknown they did not go on to start the job.
�It is certainly not ideal from the patients� point of view,� Dr Smyth said.
The Northam doctor has been involved in the safe arrival of thousands of babies at the hospital over the years, on occasion delivering up to 100 a year.
�There needs to be a qualified (obstetrics) doctor available to the hospital in the best interests of the mother and her baby,� Dr Smyth said.
Swan District Hospital in Midland is the nearest obstetrics service until the new St John of God Hospital public and private facilities opens on November 24 in Yelverton Drive, near the Midland Railway Workshops.
WACHS acting regional director Sean Conlan said Dr Smyth had stopped practising obstetrics at Northam Hospital after 30 years of dedicated service to the town and the surrounding districts.
�We have been working hard to recruit salaried GP obstetricians to Northam Hospital and to attract other GP obstetricians to establish a private practice in Northam. To date these efforts have been unsuccessful,� he said.
Mr Conlan said earlier this year a new community midwifery program had engaged with a significant number of women in Northam and the surrounding area.
�These midwives work collaboratively with local GPs and metropolitan birthing hospitals to provide high-quality, safe antenatal care and education closer to home,� he said.
He said low-risk pregnancy referrals went to Swan District Hospital and other metropolitan hospitals, while patients at high risk were directed to King Edward Memorial Hospital in Subiaco.
There were 47 births at Northam Hospital in 2013-14 and to date there have been 15 deliveries for 2014-15.
Dr Smyth said he would continue in general practice at Grey Street Surgery.