Kidney Infection in Pregnancy

A kidney infection, or pyelonephritis, is a serious urinary tract infection reaching the upper urinary system. In pregnancy, changes to the urinary tract make this more likely, and it can become severe quickly. This page explains the symptoms, why pregnancy raises the risk, and how kidney infections are treated in the UK.

Why pregnancy raises risk

Pregnancy hormones relax the muscles of the urinary tract, and the growing womb can press on the ureters. This slows urine flow and increases the chance that a bladder infection ascends to the kidneys. Asymptomatic bacteriuria, found on routine urine tests, is treated in pregnancy precisely to prevent this progression. If you have had one kidney infection in pregnancy, your team may recommend a low dose of preventative antibiotics for the rest of the pregnancy. This is standard practice and reduces the risk of recurrence.

Symptoms to take seriously

Fever, chills, back or flank pain, nausea, vomiting, and pain on urinating are the hallmarks. The pain is usually on one side, in the back below the ribs. In pregnancy, any of these symptoms warrant urgent assessment, because pyelonephritis can progress rapidly and has been linked to premature birth and sepsis. Drink plenty of water throughout pregnancy to help flush the urinary system. Urinating regularly and not holding on can also reduce the risk of infection ascending to the kidneys.

Diagnosis

Urine dipstick and culture, blood tests, and sometimes ultrasound of the kidneys are used. The ultrasound checks for obstruction or stones. Your team may also monitor foetal wellbeing, because high fever can affect the baby. Admission to hospital is common, especially if you are unwell, pregnant with multiples, or past 20 weeks. If you are admitted to hospital with a kidney infection, you can expect to stay for a few days until the infection is controlled and you are well enough for oral antibiotics. Your baby will be monitored during your stay.

Treatment

Intravenous antibiotics are standard, usually switched to oral once you improve. Common choices in UK practice are guided by culture results and pregnancy safety profiles. Pain relief and fluids are given as needed. Most women recover fully with prompt treatment. Your team will arrange follow-up urine cultures, because recurrence in pregnancy is common and may warrant preventative antibiotics. After recovery, your team will arrange regular urine checks for the rest of the pregnancy. If bacteria are found again, even without symptoms, they will be treated to prevent another kidney infection from developing.

This page is for general information only and does not replace advice from your UK maternity or mental health team. If you are worried about your physical or mental health in pregnancy, contact your midwife, GP, or call 111. In an emergency, call 999.