Initial - acetaminophen 1000mg PO, and may add:
Metoclopramide 10mg IM/IV or PO
Other options
Sumatriptan 100mg PO or 4-6mg SQ
Diphenhydramine 25 - 50mg PO
Promethazine 12.5 - 25mg PO
Ondansetron 4 - 8mg IV for severe nausea/vomiting
Ensure no hypokalemia, hypomagnesemia, hypocalcemia for prolonged QT
Consider recent conflicting studies on risk of birth defects
Refractory migraine option 1:
IV hydration
Pre-treatment diphenhydramine 25mg for EPS
Antiemetics
Codeine 30mg PO
IV opioid
Refractory migraine option 2:
Triptan
Droperidol 2.5mg IV q30 min up to 3 doses
Consider peripheral nerve blocks
Consider steroids in intractable migraines
Prednisone 20mg PO QID x2 days or methylprednisolone 4mg PO, 21 tablets over 6 days
Avoid dexamethasone and betamethasone
Avoid steroids in 1st trimester
No benefit of IV magnesium in meta-analysis
Metoclopramide 10mg IM/IV or PO
Sumatriptan 100mg PO or 4-6mg SQ
Diphenhydramine 25 - 50mg PO
Promethazine 12.5 - 25mg PO
Ondansetron 4 - 8mg IV for severe nausea/vomiting
Ensure no hypokalemia, hypomagnesemia, hypocalcemia for prolonged QT
Consider recent conflicting studies on risk of birth defects
Ensure no hypokalemia, hypomagnesemia, hypocalcemia for prolonged QT
Consider recent conflicting studies on risk of birth defects
IV hydration
Pre-treatment diphenhydramine 25mg for EPS
Antiemetics
Codeine 30mg PO
IV opioid
Triptan
Droperidol 2.5mg IV q30 min up to 3 doses
Prednisone 20mg PO QID x2 days or methylprednisolone 4mg PO, 21 tablets over 6 days
Avoid dexamethasone and betamethasone
Avoid steroids in 1st trimester
Class B - acetaminophen, caffeine, metoclopramide, promethazine
Class C - prochlorperazine (not enough human data but studies suggest safety), prednisolone, droperidol, ketorolac, 5-HT1 agonists (triptans), gabapentin, topiramate, calcium-channel blockers, TCAs
Class D - valproate
Class D in 3rd trimester - aspirin, ibuprofen, naproxen
Class D at term or prolonged use - codeine, morphine, beta-blockers
Class X - dihydroergotamine, ergotamine
Breastfeeding compatible - aspirin, caffeine, ibuprofen, naproxen, codeine, morphine, prednisolone, triptans (likely compatible), beta-blockers
Breastfeeding contraindicated - dihydroergotamine, ergotamine
Headache during pregnancy
Consider usual differential for headaches
Cardiac arrest in pregnancy
Also consider preeclampsia/eclampsia 
Abdominal pain in pregnancy
New onset of severe headache in no history of migraines → maintain high suspicion of[1]:
Vaginal bleeding in pregnancy 
ICH