LMP requirements for OB triage

I don't bill for ob, but we do sometime see pregnant patients. I believe the LMP requirement is carrier specific. Our billing software system is set up (by the corporate office) that any claim with a Z34.- dx or O00-O9A dx requires input of LMP.
Hopefully someone with more direct OB experience can weigh in to confirm or dispute.
I have a similar issue with the LMP. when the LMP is not documented in the chart note can the coder estimate the LMP using the EDD and add it to the claim without chart note documentation?

Urgent Help Needed!!!
I would not enter a LMP that is not in the documentation and is based on MY estimation. I would query the provider.