1. Clinical Overview
Clinical Overview
The newborn kidney is functionally immature: nephrogenesis finishes near term, filtration is low, concentrating ability is poor, the preterm tubule wastes salt, and acid excretion is limited — each limitation predicting a specific vulnerability. Neonatal fluid and electrolyte problems are the predictable downstream consequences of this immature kidney and a body in fluid transition. Read every disturbance through water, volume, and acid-base status: assess volume before treating a sodium number, remember potassium reflects both stores and transcellular shifts, and use the anion gap to triage metabolic acidosis. In utero the placenta does clearance while fetal urine makes amniotic fluid, linking renal anomalies to oligohydramnios and pulmonary hypoplasia.
2. Key Clinical Points
Key Clinical Points
- The neonatal kidney is immature: low GFR, poor urine concentration (dehydration/hypernatraemia risk), preterm salt-wasting (hyponatraemia), limited acid excretion (metabolic acidosis tendency).
- In utero the placenta does clearance; fetal urine makes amniotic fluid — poor output → oligohydramnios → pulmonary hypoplasia (Potter sequence). Evaluate lungs AND kidneys.
- Neonatal creatinine starts as the mother's and lags — judge injury by trend, urine output, age in days, and gestation, never a single value.
- Allow the physiologic early weight loss/diuresis; excess early fluid worsens PDA, chronic lung disease, NEC, and IVH.
- Insensible water loss through immature skin is huge and easily underestimated (raised by radiant warmers/phototherapy/low humidity; lowered by humidification and skin maturation) — unreplaced losses cause hypernatraemic dehydration.
- Hyponatraemia: distinguish dilutional (restrict free water) from depletional/renal salt-wasting (replace sodium); late hyponatraemia of prematurity emerges over weeks. Correct sodium at a measured pace.
- Non-oliguric hyperkalaemia of prematurity occurs in the first days independent of renal failure (immature K+ handling + transcellular shift); danger is cardiac — monitor ECG. Management: stabilise myocardium → shift K+ into cells → enhance elimination. Acidosis shifts K+ out of cells.
- Read a blood gas in order (pH → respiratory vs metabolic → compensation); the anion gap splits metabolic acidosis into acid gain (lactate/inborn errors/renal failure) vs bicarbonate loss (GI, RTA, immature handling). Hypochloraemic, hypokalaemic metabolic alkalosis suggests upper-GI acid loss (pyloric stenosis) or diuretics.
- A metabolic acidosis in a sick neonate is a signpost to shock, sepsis, or a duct-dependent heart — treat the cause, not the number.
- CAKUT categories: number/formation (agenesis — bilateral lethal; hypoplasia/dysplasia), cystic (multicystic dysplastic kidney, polycystic disease), obstruction/reflux (junction obstruction, VUR, posterior urethral valves).
- Posterior urethral valves = male bladder-outlet obstruction: bilateral hydronephrosis, distended bladder, poor stream, ± oligohydramnios/pulmonary hypoplasia — relieve the obstruction promptly to salvage renal function.
- Prenatal hydronephrosis: bilateral disease, distended bladder, or oligohydramnios raise concern (obstruction/lungs) and warrant prompt assessment; defer postnatal ultrasound slightly (day 1–2 shifts can mislead); most mild unilateral findings are benign.
2+. Neonatal Hypertension (Baylor Ed. 33)
Neonatal blood pressure has no single normal value — it moves with birth weight, gestational age, postnatal age and size for gestation, and the smallest, most premature infants start lowest. Hypertension is repeated measurements above the 95th percentile; repeated values above the 99th are severe.
| Average BP by gestational age — day of life | <28 weeks (S / D / M) | 29–32 weeks | 33–36 weeks | >37 weeks |
|---|
| Day 1 | 42 / 26 / 31 | 48 / 32 / 37 | 56 / 36 / 44 | 63 / 40 / 47 |
| Day 3 | 44 / 28 / 34 | 53 / 35 / 42 | 59 / 38 / 46 | 65 / 42 / 50 |
| Day 5 | 46 / 33 / 37 | 57 / 37 / 45 | 62 / 40 / 48 | 67 / 44 / 52 |
| Day 7 | 49 / 35 / 41 | 59 / 40 / 47 | 65 / 41 / 49 | 71 / 46 / 54 |
| Day 30 | 62 / 42 / 48 | 71 / 47 / 56 | 73 / 50 / 56 | 76 / 50 / 59 |
Baylor Table 11-6 (Pejovic 2007), systolic / diastolic / mean in mmHg. After about 2 weeks the transitional changes slow and blood pressure is better read against postmenstrual age — Table 11-7 below.
| Postmenstrual age | Systolic 50th / 95th / 99th | Mean 50th / 95th / 99th | Diastolic 50th / 95th / 99th |
|---|
| 44 weeks | 88 / 105 / 110 | 63 / 80 / 85 | 50 / 68 / 73 |
| 42 weeks | 85 / 98 / 102 | 62 / 76 / 81 | 50 / 65 / 70 |
| 40 weeks | 80 / 95 / 100 | 60 / 75 / 80 | 50 / 65 / 70 |
| 38 weeks | 77 / 92 / 97 | 59 / 74 / 79 | 50 / 65 / 70 |
| 36 weeks | 72 / 87 / 92 | 57 / 72 / 77 | 50 / 65 / 70 |
| 34 weeks | 70 / 85 / 90 | 50 / 65 / 70 | 40 / 55 / 60 |
| 32 weeks | 68 / 83 / 88 | 49 / 64 / 69 | 40 / 55 / 60 |
| 30 weeks | 65 / 80 / 85 | 48 / 63 / 68 | 40 / 55 / 60 |
| 28 weeks | 60 / 75 / 80 | 45 / 58 / 63 | 38 / 50 / 54 |
| 26 weeks | 55 / 72 / 77 | 38 / 57 / 63 | 30 / 50 / 56 |
Baylor Table 11-7 (Dionne 2012), mmHg, for infants beyond 2 weeks of age.
Measuring it properly, and what causes it
- Intra-arterial monitoring is the gold standard. Oscillometric readings are usable when trended, with a cuff width to arm circumference ratio of 0.45–0.55, and an awareness that devices differ between manufacturers.
- Technique decides the number: crying, feeding and even non-nutritive sucking raise it. Document the infant's activity at the time. Let the infant rest 15 minutes after the cuff is placed, measure in the right upper limb, lying down, at least 1.5 hours after a procedure or feed. The more severe the elevation, the fewer confirmatory readings are needed.
- The three commonest causes are umbilical artery catheter-associated thromboembolism, chronic lung disease and kidney disease. Beyond those: IVH, subdural haematoma, pain, seizures, birth asphyxia, neural crest tumour; post-PDA-ligation, ductal aneurysm, coarctation; BPD and pneumothorax; congenital adrenal hyperplasia, hyperaldosteronism, adrenal haemorrhage or tumour, phaeochromocytoma; obstructive uropathy, polycystic and multicystic dysplastic kidney disease, congenital nephrotic syndrome, Wilms tumour; renal artery or vein thrombosis, renal artery stenosis; hypercalcaemia, fluid overload, parenteral nutrition, maternal cocaine or heroin, vitamin D toxicity, steroids, inotropes and methylxanthines.
- Workup: urinalysis with or without culture, CBC with platelets, electrolytes, BUN and creatinine, chest radiograph, and renal ultrasound with Doppler. Add thyroid studies, aldosterone, renin, cortisol, urine VMA and HVA, echocardiography, abdominal and pelvic ultrasound, VCUG, arteriography or a nuclear scan as indicated. Four-extremity pressures screen for coarctation but an echocardiogram is needed to confirm it. Doppler cannot exclude renal artery stenosis — with high suspicion, follow a negative study with CT or MR angiography.
| Drug | Class / route | Dose | Comment |
|---|
| Severe, symptomatic hypertension — a continuous infusion is preferred so the fall can be titrated; a rapid drop risks cerebral ischaemia and haemorrhage, and the preterm periventricular circulation is especially vulnerable |
| Nicardipine | Calcium channel blocker, IV infusion | 0.5–2 mcg/kg/min | Usually needs a large infusion volume |
| Labetalol | α and β blocker, IV infusion or bolus | Infusion 0.25–3 mg/kg/h; bolus 0.2–1 mg/kg every 4–6 h | Caution in BPD or heart failure |
| Esmolol | β blocker, IV infusion | May start at 50–75 mcg/kg/min | Shorter half-life than labetalol |
| Sodium nitroprusside | Direct vasodilator, IV infusion | 0.5–10 mcg/kg/min | Thiocyanate toxicity beyond 72 hours or in renal failure |
| Hydralazine | Direct vasodilator, IV bolus | 0.25–1 mg/kg every 4–6 h | — |
| Asymptomatic hypertension — oral agents first line, chosen around the cause and comorbidity |
| Amlodipine | Calcium channel blocker, oral | 0.05–0.3 mg/kg/day divided twice daily | Generally a safe first-line oral agent; may cause reflex tachycardia or peripheral oedema |
| Propranolol | β blocker, oral | 0.25–1 mg/kg every 8 h; maximum 8–10 mg/kg/day | Avoid in BPD; monitor heart rate |
| Labetalol | α and β blocker, oral | 0.5–1 mg/kg two to three times daily; maximum 10 mg/kg/day | Avoid in heart failure and BPD |
| Hydralazine | Direct vasodilator, oral | 0.25–1 mg/kg every 6–8 h; maximum 7 mg/kg/day | May cause tachycardia |
| Lisinopril | ACE inhibitor, oral | 0.07–0.6 mg/kg/day divided twice daily | Monitor creatinine and potassium. Avoid until at least 44 weeks corrected postmenstrual age — nephrogenesis completes at 34–36 weeks but maturation continues. Captopril is the preferred ACE inhibitor under 6 months because of its shorter half-life, and its first dose can drop the pressure sharply |
| Enalapril | ACE inhibitor, oral | 0.08–0.6 mg/kg/day divided twice daily |
| Captopril | ACE inhibitor, oral | Under 3 months 0.01–0.5 mg/kg three times daily, maximum 2 mg/kg/day; over 3 months 0.15–0.3 mg/kg three times daily, maximum 6 mg/kg/day |
| Clonidine | Central α agonist, oral | 5–10 mcg/kg/day divided three times daily; maximum 25 mcg/kg/day | May cause mild sedation |
Baylor Table 11-10. Diuretics may suit an infant with chronic lung disease — controlling pressure and improving the lungs at once — where β-blockers should be avoided. Procedural intervention for coarctation or renal artery stenosis is rarely needed; endovascular treatment may be precluded by size, and nephrectomy is a last resort.
2++. Renal Tubular Acidosis, Nephrocalcinosis and the Genetic Renal Disorders (Baylor Ed. 33)
Why almost every very preterm infant is a little acidotic
The bicarbonate reabsorption threshold rises with maturity: about 14 mEq/L in the extremely premature infant, 18 in the preterm, and 21 in the term infant — a consequence of immature Na⁺/H⁺ exchange, H⁺-ATPase, Na-K-ATPase and carbonic anhydrase type 4. The more premature the infant, the more bicarbonate is wasted in the urine. A Japanese chart review found 80% of infants below 30 weeks developed transient RTA in the first 7 days, and most infants can acidify their urine by 6 weeks. All transient forms resolve with tubular maturation.
Diagnosis is a normal-anion-gap metabolic acidosis with normal renal function and no diarrhoea. Baylor calculates the gap here as Na⁺ + K⁺ − (Cl⁻ + HCO₃⁻), normal 12–20. The urinary anion gap is not used in neonates — tubular immaturity makes it inaccurate.
| Feature | Type 1 (distal) | Type 2 (proximal) | Type 4 (hyperkalaemic) |
|---|
| Mechanism | Impaired H⁺ excretion distally (reduced H⁺-ATPase) | Bicarbonate wasting proximally | Impaired H⁺ and K⁺ excretion distally from aldosterone deficiency or resistance |
| Serum HCO₃ | Low, below 10 mEq/L | Low-normal, 10–20 | Almost normal, 18–22 |
| Potassium | Low — urinary losses | Low-normal | High |
| Urine pH | Alkaline, above 5.3 | Acidic | Acidic, below 5.5 |
| Nephrocalcinosis | Present | No | No |
| Bone disease | Yes — rickets | Yes | No |
| Alkali requirement | 1–3 mEq/kg/day | 10 mEq/kg/day divided every 4–6 hours | Bicarbonate plus treatment of the cause |
| Other | Sensorineural hearing loss in the recessive form; renal stones | Global proximal dysfunction — wasting sodium, potassium, phosphate, glucose and protein (Fanconi) | Look for urinary obstruction, UTI, adrenal insufficiency, CAH, pseudohypoaldosteronism; drugs — ACE inhibitors, NSAIDs, ketoconazole, spironolactone |
Treating it
- Bicarbonate deficit = (target HCO₃ − serum HCO₃) × weight in kg × 0.4. Oral route preferred where possible.
- In type 1 RTA, correct the hypokalaemia before the acidosis — correcting the pH drives potassium intracellularly and the hypokalaemia will worsen.
- Alkali therapy is not only about pH: it reduces proximal citrate reabsorption, delivering more citrate downstream, which reverses hypercalciuria, slows stone formation and prevents or improves nephrocalcinosis.
- Fanconi syndrome brings severe hypophosphataemia and vitamin D deficiency with an ongoing need for both supplements. Type 4 needs the hyperkalaemia managed alongside the underlying obstruction, UTI or adrenal insufficiency.
Nephrocalcinosis
- Reported in 7% to as much as 64% of infants below 32 weeks or 1.5 kg — usually asymptomatic and found incidentally. Ultrasound or plain radiography is sufficient to diagnose it; screen high-risk infants — VLBW, haematuria, chronic loop diuretics, BPD.
- Mechanism: hypercalciuria. Paracellular calcium absorption in the thick ascending limb depends on sodium reabsorption through the furosemide-sensitive NKCC2 cotransporter — which is precisely why chronic furosemide in BPD causes it. Acidosis compounds it three ways: less protein-bound calcium so more is filtered, calcium released from bone as buffer, and reduced urinary citrate, the natural stone inhibitor.
- Also contributing: glucocorticoids, caffeine and theophylline, and supplemental vitamin D, calcium or sodium. Consider a monogenic cause in a term infant, or in a preterm infant without these risk factors.
- Workup: creatinine, electrolytes, calcium, magnesium, phosphate; if hypercalcaemic add 25-OH and 1,25-(OH)₂ vitamin D and PTH; urine calcium-to-creatinine ratio (normal under 6 months is below 0.8 mg/mg); urine pH and electrolytes; urinary and plasma oxalate.
- Management: reduce or stop the loop diuretic where possible, or combine it with a thiazide; reduce dietary calcium and phosphate, especially on PN; alkali for distal RTA; thiazides for hypercalciuria. Repeat the ultrasound in 1–2 months. Most diuretic-associated cases resolve after the drug stops; genetic and tubulopathy-related cases need periodic monitoring, and untreated cases progress to chronic kidney disease.
ARPKD and congenital nephrotic syndrome
- Autosomal recessive polycystic kidney disease occurs in 1:10,000 to 1:40,000 live births. Presumptive antenatal diagnosis after 24 weeks rests on markedly enlarged echogenic kidneys with poor corticomedullary differentiation plus oligo- or anhydramnios; discrete cysts above 10 mm are unusual and should raise dominant polycystic disease or multicystic dysplasia instead. Scan both parents — cysts in a parent point to the dominant form. 30% die in the neonatal period or first year from respiratory insufficiency, but long-term survival now exceeds 80%. Confirm with PKHD1 (rarely DZIP1L) testing. Management is respiratory stabilization, uni- or bilateral nephrectomy if the kidneys impair diaphragmatic excursion, peritoneal dialysis where urine output demands it, and attention to the biliary disease — malabsorption of fat-soluble vitamins and the risk of ascending cholangitis, with portosystemic shunting or combined liver-kidney transplantation in severe cases.
- Congenital nephrotic syndrome — nephrotic syndrome at birth or within 3 months — occurs in 1–3 per 100,000 children, with about 80% monogenic. Defined by proteinuria above 2000 mg/L, albumin below 2.5 g/dL, oedema and hyperlipidaemia; severe hypoalbuminaemia below 1.5 g/dL is common. A raised maternal serum alpha-fetoprotein on second-trimester screening is the antenatal clue, and generalized oedema appears in the first week in 70–80%. The genetic forms do not respond to steroids or other immunosuppression. Treatment is salt and fluid restriction with diuretics, often with daily IV 25% albumin to hold the albumin above 2.5 g/dL, a high-calorie high-protein diet, thyroid replacement, and an ACE inhibitor with or without indomethacin for the proteinuria. Watch for hypogammaglobulinaemia, hypothyroidism and a hypercoagulable state from urinary losses. Most undergo nephrectomy in early childhood and move to renal replacement therapy pending transplantation.
- CAKUT numbers worth carrying: horseshoe kidney is the commonest fusion anomaly at 1 in 400; malrotation 1 in 500; crossed fused ectopia 1 in 2000; ureteropelvic junction obstruction 1 in 500 live births, usually unilateral and partial, with only 20–25% needing surgery; posterior urethral valves 1 in 5000–8000 male births, about 10% of antenatal hydronephrosis, with the "keyhole" sign at the bladder neck effectively pathognomonic; vesicoureteral reflux explains 10–20% of antenatal hydronephrosis — and a normal postnatal ultrasound does not exclude it. Hydronephrosis appears in 1–5% of all pregnancies and 44–88% resolve. Timing of the postnatal scan: severe or bilateral hydronephrosis, or bilateral parenchymal anomalies, within 24–48 hours; a unilateral anomaly or solitary kidney after the first 48 hours, within the first week or before discharge. Bilateral hydroureteronephrosis means a Foley catheter first to drain the bladder, with daily chemistries — these infants develop polyuria with renal salt wasting from tubular damage.
Feeding an infant with renal failure (Baylor Table 11-12)
| Nutrient | AKI without kidney replacement | Continuous KRT | Haemodialysis | Peritoneal dialysis |
|---|
| Protein | Minimum 1.5 g/kg/day; limit time on any restriction | At least 2.5 g/kg/day — BUN is not expected to be low or normal | DRI + 0.2 g/kg/day | DRI + 0.7 g/kg/day |
| Sodium | 1–3 mEq/kg/day depending on blood pressure, with supplementation as levels demand — unrestricted on CKRT |
| Potassium | Tightly limited — may need to go as low as 1 mEq/kg/day | 1–3 mEq/kg/day |
| Phosphorus | Below 100% of the DRI for age | Adjust to laboratory values |
| Micronutrients | Avoid vitamin A supplementation | Water-soluble vitamins; levocarnitine 20 mg/kg/day; 25-OH vitamin D titrated; trace elements need not be limited; extra selenium may be needed | Water-soluble vitamins; levocarnitine 10–20 mg/kg per treatment when dialysing at least 4 times a week, with monthly plasma carnitine | Water-soluble vitamins; vitamin D titrated |
- Targets: potassium 3.5–5.5 mg/dL and phosphorus 5–7.5 mg/dL (venous). Expressed or donor human milk is the preferred low-potassium feed; dilution may be needed with badly reduced function, but not long term, and protein modular then becomes necessary. Potassium exchange resin must not be used below 37 weeks postmenstrual age and exchanges 1 mEq of potassium for 1 mEq of sodium per gram.
- On CKRT, hypophosphataemia and hypomagnesaemia are the expected derangements — supplement phosphate intravenously in the PN, since peripheral and enteral routes usually cannot keep up. Calcium is not required in the PN when citrate anticoagulation is running, and the citrate solution's 2.45% dextrose raises the effective glucose infusion rate. The CARPEDIEM ultrafiltration limit is 2 litres per day including anticoagulation.
- On peritoneal dialysis, expect higher sodium and protein losses, more liberal fluid allowances while urine output persists, and very common reflux — fill volumes compete for abdominal space and uraemic gastroparesis adds to it. Respond with smaller, more concentrated, continuous rather than bolus feeds, reflux precautions, post-pyloric feeding or a prokinetic.
- Lipid: above 1000 g, SMOFlipid at a full 3 g/kg/day; where fluid restriction forces a lower lipid dose, use Intralipid at a minimum of 0.5 g/kg/day to prevent essential fatty acid deficiency — limiting SMOFlipid below 3 g/kg/day causes it and is strongly discouraged.
- Base everything on estimated dry weight, re-evaluated weekly with the renal team, and judge it from daily weight against intake and output, blood pressure, examination, growth trends and laboratory values together. Do not restrict protein to delay dialysis in an infant who is otherwise ready for it.
Newborn Urology: Single Umbilical Artery, Urinary Tract Dilation and the Genital Exam (Baylor Ed. 33)
Single umbilical artery
- Occurs in 0.7–1% of singletons and 3–7% of multiples, less often in Black infants, and more often with aneuploidy or other malformations. Cardiac anomalies occur in 7% and renal anomalies in 5%, and growth restriction is twice as likely, but associated anomalies follow no single organ pattern.
- Investigate only when another major anomaly is suspected. Isolated single umbilical artery carries outcomes similar to unaffected infants.
| Normal renal pelvis AP diameter (Baylor Table 13-5) | <28 weeks' gestation | >28 weeks' gestation | Postnatal |
|---|
| APRPD | <4 mm | <7 mm | <10 mm |
Antenatal urinary tract dilation (formerly "antenatal hydronephrosis")
- Seen in 1–4.5% of pregnancies. Causes, from commonest: transient collecting-system dilation, UPJ obstruction, vesicoureteral reflux, UVJ obstruction, multicystic dysplastic kidney, posterior urethral valves, then ureterocele, duplication and cysts.
- Findings that raise the risk of real uropathy: abnormal APRPD, calyceal dilation, abnormal parenchymal thickness or appearance, ureteral dilation, abnormal bladder, and unexplained oligohydramnios.
- Who needs postnatal imaging: every infant with third-trimester dilation. Not needed if dilation seen earlier had resolved by the third-trimester (or latest) scan.
- Two ultrasounds, even if the first is normal: the first at more than 48 hours and before 4 weeks, because low urine output in the first days underestimates dilation; the second at 1–6 months. Scan before 48 hours when antenatal findings suggest obstruction (for example bladder outlet or urethral obstruction), or when outpatient follow-up cannot be assured — paediatric urology can guide the plan.
- Prophylaxis: no randomized trials exist. Antibiotics are reasonable for high-risk postnatal dilation; for low- and intermediate-risk dilation, amoxicillin 10 mg/kg once daily is decided case by case.
Circumcision
- AAP position: benefits (fewer UTIs, less penile cancer, reduced transmission of some STIs including HIV) outweigh the risks, and justify access for families who choose it — but they are not great enough to recommend routine circumcision. Complication rates are much lower in the newborn period. Always give analgesia: Baylor uses a ring block or dorsal penile nerve block with 1% lidocaine without epinephrine, plus oral 24% sucrose.
- Contraindications: medical instability; genital anomalies (hypospadias, significant webbing, chordee); a family history of bleeding disorders until screening tests are done; parental refusal of vitamin K (in some units). Consider delaying with bilateral cryptorchidism; in preterm infants, wait until close to discharge. Urinary tract dilation is not a contraindication.
- Refer to paediatric surgery or urology if the infant is ≥44 weeks PMA, over 4.5 kg (10 lb), or would need a 1.6 Gomco clamp.
- Aftercare: watch for bleeding for 1–2 hours; parents check the site every 8 hours for the first day. Use petroleum jelly liberally for 3–5 days after Gomco or Mogen clamps (Plastibell needs routine hygiene only). Gently reduce adhesions at diaper changes. A white-yellow exudate is normal healing, not infection. The Plastibell falls off in 3–7 days; a retained or malpositioned ring may need a ring cutter. Infants usually void within 8 hours — do not delay discharge waiting for urine.
- Uncircumcised boys: clean like the rest of the diaper area. Never forcibly retract the foreskin — it stays adherent for months to years.
Testes, hernias, hydroceles and hypospadias
- Cryptorchidism — the commonest male genital anomaly, unilateral in 75–90%, more often on the right, and commoner in preterm infants and with a family history. Distinguish a retractile testis, which can be milked into the scrotum. Confirm by serial examination; when bilateral, ultrasound helps locate abdominal testes and confirm male sex (think DSD — chapter 4.9). Follow monthly after discharge. Descent after 6 months is extremely unlikely, and surgery is ideally done by 1 year. Risks include malignancy, infertility, torsion and hernia.
- Inguinal hernia — commonest in males and preterm infants, rarely present at birth; risk of entrapment and strangulation. Reduce gently at every exam and refer to paediatric surgery before or after discharge. Almost all are indirect; incidence rises to 16–25% below 28 weeks, and 31% of incarcerations occur under 2 months. Risk rises with chronic lung disease, raised abdominal pressure (ascites, abdominal wall repair, VP shunt, peritoneal dialysis), bladder exstrophy and connective tissue disorders. A hernia never resolves on its own; pain, vomiting, irritability and an irreducible mass mean incarceration — call surgery immediately. Infant hydroceles usually resolve by 12–18 months. Hydrocele — transilluminates; present to some degree in 15–20% of newborn boys and usually resolves within weeks to months.
- Hypospadias — 3–8 per 1000 live births, the second commonest male genital anomaly: 87% glanular or coronal, 10% penile, 3% scrotal or perineal. It is associated with cryptorchidism in 8–10% and inguinal hernia in 8%. Mild, isolated hypospadias needs no work-up. Severe (scrotal or perineal) hypospadias, or any hypospadias with cryptorchidism, raises endocrinopathy, DSD or a chromosomal cause. Take a maternal progestin/oestrogen and family history, examine carefully (meatus, chordee, scrotal folds), use ultrasound for gonads and uterus, image the kidneys when severe, and measure stretched penile length. Repair is ideally late in the first year — no circumcision beforehand.
- Testicular torsion — mostly in cryptorchid testes, and often prenatal: a well baby with a firm scrotal mass and red-blue skin, or an abdominal mass and intermittent irritability when the testis is impalpable. Damage becomes irreversible within about 6 hours, and salvage is almost unheard of because torsion so often happens before birth. Still treat it as a urological emergency: STAT scrotal Doppler ultrasound and immediate urology consultation, with transfer if needed.
Check the cryptorchidism figure
Baylor quotes an incidence of 1 in 125 male infants (0.8%). That matches prevalence at about 1 year of age; commonly cited rates at birth in term boys are higher, a few per cent, because many testes descend in the first months. Treat 1:125 as an under-estimate for the newborn exam.
3. References to Verify
- 1.The Neonatal Bedside, Part IX — Kidney, Fluids & Electrolytes (Ch. 46–50).
- 2.Jetton JG, et al. Neonatal AKI and the neonatal modified KDIGO definition.
- 3.Guignard JP, et al. Neonatal renal physiology and fluid/electrolyte management.
- 4.Elder JS. Congenital anomalies of the kidney and urinary tract (CAKUT) and posterior urethral valves.