UTI and Kidney Infection in Pregnancy

Why pregnancy changes the whole approach

Outside pregnancy, a lower urinary tract infection is often managed with a back-up prescription or with self-care first. In pregnancy, that option disappears.

NICE guideline NG109, recommendation 1.1.5: "Offer an immediate antibiotic prescription to pregnant women and men with lower UTI." Compare that with recommendation 1.1.3 for women who are not pregnant, where NICE says to "consider a back-up antibiotic prescription... or an immediate antibiotic prescription", noting that the evidence for back-up prescriptions "was only in non-pregnant women with lower UTI where immediate antibiotic treatment was not considered necessary".

The reason is anatomical and hormonal. Progesterone relaxes the ureters and the bladder wall, urine drains more slowly, and the enlarging uterus presses on the ureters. Bacteria that would be flushed out in a non-pregnant bladder have time to ascend to the kidneys, and kidney infection in pregnancy is associated with preterm labour and with serious maternal illness.

The urine sample that has to go to the lab

NG109 recommendation 1.1.6: "Obtain a midstream urine sample from pregnant women and men before antibiotics are taken, and send for culture and susceptibility testing."

Recommendation 1.1.7 explains why it matters: "For pregnant women with lower UTI: review the choice of antibiotic when microbiological results are available, and change the antibiotic according to susceptibility results if the bacteria are resistant, using a narrow-spectrum antibiotic wherever possible."

Note the difference from men, where recommendation 1.1.8 only changes the antibiotic if the bacteria are resistant "and symptoms are not already improving". In pregnancy, resistance triggers a change even if you feel better. Feeling better is not the same as the infection being cleared, and the point is protecting the kidneys.

Infection with no symptoms at all

This is the part that surprises people. Bacteria in the urine without any symptoms — asymptomatic bacteriuria — is not treated outside pregnancy in most circumstances. In pregnancy it is.

NICE Clinical Knowledge Summaries sets out the pathway: "In women who are assessed as being as having an intermediate or high risk category pregnancy, a midstream urine sample (MSU) should be taken and sent for culture and sensitivity at their booking appointment." Where the culture shows asymptomatic bacteriuria, CKS advises prescribing "an immediate antibiotic, taking into account recent urine culture and susceptibility testing results, any recent antibiotic use, local antimicrobial resistance patterns, and any contraindications".

Antibiotic choice and duration are set by that guidance and by your prescriber; we do not publish doses. What is worth knowing is that some antibiotics used for UTI are avoided at particular stages of pregnancy, so what you were given last time may not be what you are given now.

One further detail from the same source matters for your birth: "If group B streptococcal bacteriuria is identified on urine culture, ensure the woman's midwife and obstetric team are also made aware, as intrapartum intravenous antibiotic prophylaxis should be offered in labour." Group B strep found in urine at any point in pregnancy changes your labour plan, so check it has been recorded.

Recognising a kidney infection

The NHS lists the symptoms of a kidney infection as "a high temperature; feeling or being sick; pain in your lower back or side; diarrhoea; aching muscles and flu-like symptoms; pain, burning or stinging when you pee; needing to pee more often and urgently than usual; pee that's dark or cloudy".

Pregnancy appears explicitly in the NHS urgent-advice list: seek an urgent GP appointment or help from NHS 111 if you think you may have a kidney infection and "have a very high temperature, or feel hot, cold or shivery... have pain in the lower tummy or in the back, just under the ribs... are feeling or being sick... you are pregnant". The page adds that "a kidney infection can be serious if it's not treated as it can cause sepsis".

The distinguishing features from a bladder infection are the fever, the shivering and the loin or back pain. A bladder infection generally does not make you feverish; a kidney infection does.

Why hospital is often recommended

NICE guideline NG111 on acute pyelonephritis asks clinicians to "consider referring or seeking specialist advice for people aged 16 years and over with acute pyelonephritis if they... are pregnant".

NG111 also directs prescribers to a separate antibiotic table specifically for "pregnant women aged 12 years and over", which is a reminder that the antibiotic choices differ in pregnancy rather than being the standard ones at a different dose.

In practice, pyelonephritis in pregnancy often means admission for intravenous antibiotics and fluids, at least initially, because vomiting makes oral antibiotics unreliable and because dehydration and fever can provoke contractions. Being admitted is not a sign that something has gone badly wrong; it is the standard response.

Preventing the next one

Drinking enough, not delaying when you need to pass urine, and emptying your bladder after sex are the usual general measures. None of them replaces getting a symptomatic infection treated promptly.

If you have had more than one UTI in this pregnancy, ask whether repeat urine cultures are planned and whether you should be seen by an obstetric team. Recurrent infection sometimes points to an underlying problem worth investigating after birth. Your routine antenatal schedule under NICE guideline NG201 continues alongside any of this.

Finally, do not use leftover antibiotics or someone else's. NG109 asks for treatment guided by culture and by local resistance patterns, and the antibiotic that suited a friend may be one avoided at your stage of pregnancy.