How many lumbar punctures can a baby have to check for ivh before it gets dangerous?

Unknown: Sounds like there is misunderstanding or miscommunication. Transfontanelle cranial ultrasonography (sonogram through soft spot) and ct scanning are the diagnostic methods of choice for the detection of ivh.

LP not IVH diagnosis: I think there may be some confusion, and you should speak with you neonatologist. Ultrasound is generally used for ivh diagnosis. Lp's can sometimes be used to reduced hydrocephalus (fluid on the brain) caused by ivh, this is generally done until a shunt can be placed to drain the fluid somewhere else, generally the belly. Lp can be done for a week or two, however it is not terribly effective.