With my 2nd son I had to abstain as well. Tho the act itself wouldnt cause a miscarriage, the stimulation could possible cause contractions, ranging from Braxton Hicks to severe ones that could cause your uterus to open. So if your doctor thinks it's best I would defiantly follow his advise. How far along are you? Even when it comes to (oral) some doctors suggest it not be done during a certain trimester.
Nope it just sounds like he wants no penetrations for the reasons he said. Orgasming doesnt cause miscarriages. Best of luck to you!