Twenty years ago.
D000698:Analgesia / Q000266:history*; D000700:Analgesics / Q000008:administration & dosage; D000769:Anesthesia, Inhalation; D000773:Anesthesia, Obstetrical / Q000266:history*; D002725:Chloroform / Q000266:history; D004739:England; D005260:Female; D049673:History, 20th Century; D006801:Humans; D009609:Nitrous Oxide; D011247:Pregnancy; D012651:Self Medication; D014241:Trichloroethylene
D000700:Analgesics; D014241:Trichloroethylene; D002725:Chloroform; D009609:Nitrous Oxide