Mild headaches can be caused by hormones and are common in pregnancy. You may also suffer from migraine in pregnancy. Paracetamol tablets taken according to the guidelines are safe for you and your baby.
If you are past 20 weeks and have a bad headache that lasts for more than two or three hours (particularly if not relieved by Acetaminophen), it could be an indication of high blood pressure, which is a symptom of pre-eclampsia. If your headache is accompanied by vision problems and bad swelling on your hands, feet, face or stomach, call your midwife immediately. If your headache is accompanied by pain while urinating or blood in the urine, you may have a urinary tract infection and need to be treated.
British Medical Association and London Royal Pharmaceutical Society, British National Formulary 62, London BMA and RPS, 2011
National Institute for Health and Care Excellence, Hypertension in pregnancy, clinical guideline 107, London NICE, 2011
Patel NB et al, Urinary tract infections in women, London BMJ Best Practice, 2013. Also available from: http://bestpractice.bmj.com/best-practice/monograph/77.html (accessed 29 April 2014)