I'm 20 weeks pregnant and had a fever for 4 days. started taking antibiotics for uti after 2 days of fever. can fever of that duration harm the fetus?

OK if lowgrade/mild: Mild fever for a few days should not do harm to your unborn child. High fever in pregnant mom for brief period also has not been shown to do harm to the baby. So, if your fever was of mild degree and you are doing better now, i would not worry. If high fever >102-103 range still now, consult doc for eval and treatment. Good luck and congrats on the pregnancy!

If preterm labor.: If your infection/fever cause preterm labor, then sure you can have a bad pregnancy outcome. I hope you have received intravenous Rocephin (ceftriaxone) for what sounds like pyelonephritis! a maternal-fetal medicine specialist should be following you at this time!