Sciatica pain is due to compression sciatic nerve In pregnancy this can be caused by the pressure of the gravid uterus and in advanced pregnancy of the baby on the sciatic nerve. I once had a gynaecology patient who had severe sciatica and a large fibroid uterus filling her pelvis. I cured her sciatica by doing a hysterectomy.
If the sciatica pain is due to pregnancy changes then it is likely to be self-limiting and end once the baby is delivered. But for the same reason, it could get worse while pregnant.
A pre-pregnancy back problem can be exacerbated in pregnancy and may predispose to sciatica in pregnancy So if this is a back issue then this should be assessed and appropriate measures taken before embarking on pregnancy. Also, if overweight, then weight loss pre-pregnancy can help.
Care with posture, lifting, bending, avoiding high heel shoes and rest all can help. Appropriate back mobility and muscle strengthening exercises (usually with an appropriately qualified personal trainer), remedial massage, chiropractor, osteopath, physiotherapist, acupuncture, wheat packs heated (but not too hot so as to cause a burn) all can help. Try to keep oral analgesics to a minimum, as it is likely that the problem will persist while pregnant.
Sciatica can be due to circumstances peculiar to that pregnancy such as how big the baby is, how the baby’s head is turned, how low in the pelvis the baby’s head is, etc. So it may not recur next pregnancy.