Urine Colour Changes in Pregnancy: What to Watch For
Updated April 2026
Summary: Bright yellow from prenatal vitamins is normal. Pale straw remains the hydration target. Cloudy with burning needs same-day assessment (UTI in pregnancy always needs treatment). Foamy urine plus swelling is urgent - possible preeclampsia.
How Pregnancy Changes Urine
Pregnancy produces significant physiological changes that affect kidney function and urine composition. Blood volume increases by 40-50% during pregnancy, which increases blood flow to the kidneys and raises the glomerular filtration rate (GFR) by 50%. This means the kidneys filter more blood and produce more urine - pregnant women typically urinate more frequently from early pregnancy onward, particularly in the first and third trimesters.
Increased fluid needs during pregnancy also tend to produce naturally paler urine. Combined with prenatal vitamin B complex (which brightens urine to yellow or fluorescent yellow regardless of hydration), most pregnant women see a range from pale to bright yellow - both of which are reassuring.
The colours that require prompt attention during pregnancy are cloudy, pink, red, foamy, or brown - all for the same reasons as in non-pregnancy, but with lower thresholds for action.
Key Urine Changes in Pregnancy
Bright yellow - Reassuring (prenatal vitamins)
Nearly all prenatal vitamins contain riboflavin (B2), which produces bright or fluorescent yellow urine within 2-4 hours of taking the supplement. This is completely harmless and expected. Many women are startled by it during early pregnancy when they first start prenatal vitamins. It is not a sign of dehydration or liver problems.
Cloudy with burning - Urgent (UTI)
Urinary tract infections are more common during pregnancy due to changes in the urinary tract anatomy (the growing uterus compresses the ureters) and hormonal changes that reduce urinary tract muscle tone. UTIs in pregnancy carry higher risks than in non-pregnant individuals - including preterm labour and kidney infection - and always require same-day treatment with pregnancy-safe antibiotics. Do not delay assessment.
Foamy with swelling - Urgent (possible preeclampsia)
Preeclampsia is a serious pregnancy complication (typically after 20 weeks) characterised by high blood pressure and protein in the urine (proteinuria). Foamy urine is a visible sign of proteinuria. Combined with swelling of feet, ankles, hands, or face, and headaches or visual disturbances, foamy urine in pregnancy is an obstetric emergency. Contact your midwife or obstetric triage unit immediately - do not wait for a GP appointment.
Dark yellow / amber - Dehydration risk
Pregnant women have higher fluid needs (approximately 300ml per day more than non-pregnant baseline). Morning sickness can make adequate fluid intake difficult. Dark yellow or amber urine during pregnancy should prompt increased fluid intake. Severe dehydration from morning sickness (if you cannot keep fluids down) may require hospital IV fluids.
Pink or red - Always assess
Pink or red urine in pregnancy should always be assessed by your midwife or GP, even if you ate beetroot. The differential includes UTI with haematuria, kidney stones (more common in pregnancy), and placental or vaginal bleeding mixing with urine. Same-day assessment is appropriate.
Asymptomatic Bacteriuria in Pregnancy
Asymptomatic bacteriuria - bacteria in urine without symptoms - is present in approximately 2-7% of pregnant women and is significant because, untreated, it progresses to symptomatic UTI or pyelonephritis in 20-40% of cases. This is why urine cultures are routinely performed at the first antenatal appointment in most health systems. A positive culture is treated even if you have no symptoms.
This is different from the general population, where asymptomatic bacteriuria in healthy adults is typically not treated (the evidence does not support antibiotic treatment in non-pregnant adults). In pregnancy, treatment is recommended and effective.
Gestational Diabetes and Urine
Gestational diabetes mellitus (GDM) can produce glucose (glycosuria) in urine, detectable on a dipstick. Some degree of glycosuria is actually normal in pregnancy - the renal threshold for glucose is lower during pregnancy - so a single positive dipstick for glucose does not diagnose GDM. Formal diagnosis requires an oral glucose tolerance test (OGTT). If you have persistent glycosuria or are at risk for GDM (overweight, family history, prior GDM), discuss screening with your midwife.
Ketones in urine (ketonuria) during first-trimester morning sickness indicate the body is breaking down fat for energy in the absence of adequate carbohydrate intake. Mild ketonuria in morning sickness is common. Severe ketonuria with inability to eat or drink requires medical assessment for hyperemesis gravidarum.
When to Seek Care in Pregnancy
Obstetric emergency: Foamy urine plus swelling, headache, or visual disturbance after 20 weeks (preeclampsia). Call your midwife or obstetric triage immediately.
Same day: Cloudy with burning (UTI); pink or red urine; inability to keep fluids down for 24+ hours (dehydration risk).
Contact midwife: Dark amber urine despite drinking water; any unusual urine change without obvious explanation.
Monitor: Bright yellow from prenatal vitamins - completely normal, no action needed.
Sources: NICE Guidelines on UTI in adults (including pregnancy); WHO preeclampsia guidance; Mayo Clinic pregnancy content; Royal College of Obstetricians and Gynaecologists (RCOG).