Kidney & Urinary System Development
Kidneys develop to filter blood and produce urine, which becomes amniotic fluid baby swallows.
Development Timeline
Weeks 5-40
Overview
Your baby's kidneys develop in stages, with three different kidney structures appearing sequentially. The final, permanent kidneys begin forming around week 5 and start producing urine by week 10-11.
Baby's urine becomes a major component of amniotic fluid. Baby swallows this fluid, which is filtered by the placenta, creating a continuous cycle. This system helps baby practice swallowing and supports lung development.
The urinary system also helps regulate amniotic fluid volume. Too little or too much amniotic fluid can indicate problems with baby's kidneys or urinary tract.
🗓️ Week-by-Week Milestones
Tap any week to open its full pregnancy guide — baby size, symptoms, and what else is developing that week.
Permanent kidneys begin forming
Kidneys move to final position in abdomen
Kidneys begin producing urine
Bladder visible on ultrasound
Baby urinating regularly into amniotic fluid
Kidneys fully formed, continue maturing
Kidneys functioning well but still immature
👀 What to Expect
- •Baby begins urinating around week 10-11
- •Urine contributes to amniotic fluid
- •Baby swallows and recycles amniotic fluid
- •Kidneys visible on anatomy scan
- •Bladder fills and empties regularly
- •Kidney function tested through amniotic fluid levels
💡 Tips for Parents
- ✓Ultrasounds check for kidney and bladder development
- ✓Low amniotic fluid may indicate kidney problems
- ✓High amniotic fluid may indicate swallowing problems
- ✓Baby peeing in amniotic fluid is normal and healthy
- ✓You swallow the amniotic fluid baby pees in (filtered by placenta)
- ✓Kidneys continue maturing after birth
🛍️ Supplements & Reads for This Development Stage
Comfort and preparation products other expecting parents find helpful at this stage. These are convenience picks, not medical advice — always follow your provider's guidance.
Prenatal Vitamins (with Folate & DHA)
Daily folate, iron and DHA support that doctors recommend before and throughout pregnancy.
Check Price on Amazon →DHA Omega-3 Supplement (Prenatal)
Doctors recommend DHA throughout pregnancy for baby's brain and eye development — especially the third trimester.
Check Price on Amazon →What to Expect When You're Expecting
The classic week-by-week guide trusted by millions of expecting parents.
Check Price on Amazon →Amazon Associates Disclosure: As an Amazon Associate, we earn from qualifying purchases at no extra cost to you. These recommendations are editorially chosen comfort and preparation products and are not medical advice.
✨ Amazing Facts
By term, baby produces about a cup of urine daily
The amniotic fluid baby swallows contains their own urine
Kidneys continue developing into childhood
Newborn kidneys can't concentrate urine well yet
Two kidneys, but humans can survive with just one
Related Development Topics
👶 Planning Ahead?
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