What are the risks of pregnancy with a single kidney?

Risks of Pregnancy with a Single Kidney

Women with a single kidney face increased risks during pregnancy, particularly a 35% chance of developing preeclampsia, gestational hypertension, or proteinuria, and a 50% risk of urinary tract infections. 1

Maternal Risks

Hypertensive Disorders

• Women with a solitary kidney have significantly higher rates of:
  • Preeclampsia
  • Gestational hypertension
  • Gestational proteinuria 1
• These risks are similar to those seen in women with mild chronic kidney disease (CKD)
• Blood pressure typically falls during the first half of pregnancy but may become more difficult to control later 2

Urinary Tract Infections

• 50% of pregnancies in women with a single kidney are complicated by urinary tract infections 1
• Monthly urinalysis is recommended, with prompt treatment of positive cultures even when asymptomatic 2

Renal Function

• Pregnancy creates increased physiological demands on the remaining kidney
• Risk of temporary worsening of renal function during pregnancy
• Women with mild renal impairment (serum creatinine <1.4 mg/dL) generally have minimal effects on fetal survival 2
• Moderate to severe renal insufficiency may accelerate hypertension and worsen underlying kidney function 2

Fetal Risks

• Increased risk of:
  • Preterm delivery
  • Intrauterine growth restriction
  • Small for gestational age infants 3, 4
• The risk of adverse fetal outcomes is at least twice as high compared to women with normal kidney function 4
• Risk correlates with the degree of maternal renal insufficiency and presence of hypertension 4

Pre-conception Considerations

1. Baseline assessment:

   • Renal function (serum creatinine)
   • Protein excretion (urine albumin-to-creatinine ratio)
   • Blood pressure control 2

2. Medication review:

   • ACE inhibitors and ARBs must be discontinued prior to conception due to fetal toxicity 2
   • Switch to pregnancy-safe antihypertensives if needed (methyldopa, labetalol) 2

Management During Pregnancy

Blood Pressure Monitoring and Control

• Weekly home blood pressure monitoring is recommended 2
• Target blood pressure ≤130/85 mmHg 2
• Safe antihypertensive options include:
  • Labetalol
  • Nifedipine (long-release)
  • Methyldopa
  • Hydralazine
  • Clonidine 2

Infection Prevention and Management

• Monthly urinalysis
• Prompt treatment of bacteriuria, even if asymptomatic 2
• Lower threshold for antibiotic treatment

Preeclampsia Prevention

• Low-dose aspirin from week 12 to week 36 is recommended 2
• Regular monitoring for signs of preeclampsia
• Assessment of soluble fms-like tyrosine kinase 1-to-placental growth factor ratio from 24 weeks of gestation 2

Postpartum Care

• Early follow-up with a nephrologist (at 6 weeks) 2
• Additional follow-up within 6 months after delivery 2
• Monitoring for postpartum hypertension, which may peak after delivery 2
• Evaluation for long-term kidney function and cardiovascular risk

Important Caveats

• Most research on pregnancy with a single kidney is extrapolated from living kidney donors, who are typically carefully selected healthy individuals 1
• The study by 1 is particularly valuable as it includes women with both congenital and acquired single kidneys from various causes
• Women with a single kidney should be considered high-risk pregnancies and managed accordingly 3
• The outcomes are highly dependent on the availability and quality of renal and obstetric care 3

Women with a single kidney contemplating pregnancy should receive pre-conception counseling, education on kidney protection, preeclampsia prophylaxis with low-dose aspirin, and close monitoring during pregnancy for complications, particularly hypertension, proteinuria, and urinary tract infections.