I have a thick septate hymen (hole is big enough for sex) & want a baby. should i get the hymen cut prior to getting pregnant, whilst pregnant or during birth? would there be any complications with each option, e.g. anaesthetic, scar tissue, tearing?

Although the "thick septate hymen" may tear during a vaginal delivery, this can be easily repaired after the delivery, but it may stretch significantly enough not to affect delivery or start bleeding, so it is perfectly safe to wait until delivery. If there is concern by your GYN physician, it can easily be remedied by incision under local anesthesia if that is his/her recommendation.