Pregnancy with a single kidney: features, risks and recommendations

Pregnancy with a single kidney is a special clinical case in obstetrics and gynecology, characterized by the occurrence of gestation in a woman who has only one functional organ (due to a congenital anomaly or surgical removal). In situations where the remaining kidney fully performs its functions, pregnancy can proceed without specific symptoms. However, in cases of functional insufficiency, the patient's condition may be complicated by edema, changes in urine analyses, lumbar region pain, hypertension, and general malaise.

To ensure the safety of the mother and child, diagnosis includes regular ultrasounds, blood and urine tests in the laboratory, as well as functional evaluation methods such as thermography. The therapeutic approach in case of normal evolution is limited to preventive phytotherapy, while in case of complications, complex treatment with antibiotics, hormones, and spasmolytics is necessary.

General information and statistics

Patients with a single kidney are relatively rarely followed by obstetrician-gynecologists. Statistics show that the prevalence of this pathology varies between 4.4 and 9.0 cases per 1,000 births. This small percentage is explained by two factors:

1. The low frequency of congenital renal aplasia (from 0.067% to 0.11%), which affects men more often.
2. The significant advances of modern medicine in conservative treatment of urological diseases, which reduce the need for radical surgeries.

Nevertheless, nephrectomy (removal of the kidney) remains an unavoidable measure in case of discovery of malignant or benign tumors, complete destruction of the organ's parenchyma due to inflammatory processes or severe injuries.

Etiology: causes of the presence of a single kidney

Generally, the absence of the second organ is a factor that appeared long before pregnancy. Nonetheless, it is precisely the physiological changes during gestation that can worsen the woman's health. There are two main causes for this specificity:

1. Renal agenesis (aplasia)

This is a congenital malformation. Its frequency ranges from 1:1,000 to 1:4,000 cases among patients with renal pathologies. If the only organ handles the load, the woman may not suspect her condition until the first routine ultrasound during pregnancy. It is important to note that, due to the unity of embryonic development of the genitourinary system, the absence of a kidney is often accompanied by uterine anomalies (unicornuate uterus) or vaginal anomalies.

2. State after nephrectomy

In clinical practice, women who have undergone kidney removal are more commonly encountered. The reasons for such surgery can be various:

• Severe inflammations (pyonephrosis, tuberculosis);
• Tumor processes (in 10 to 12% of cases);
• Urinary stones or hydronephrosis;
• Traumatic injuries or donation to a relative.

Pathogenesis: how a single kidney functions during pregnancy

When a person has only one kidney, its structural units (nephrons) assume a double workload. Compensatory hypertrophy occurs: the organ increases in volume and the blood flow through it increases by 30 to 50%.

The adaptation process after surgery generally lasts between 1.5 and 2 years and occurs in two stages:

1. Resource mobilization: the kidney maximally activates all available nephrons to eliminate water and salts.
2. Functional hypertrophy: the organ's cells enlarge and its filtration capacity is restored to nearly 85 to 95% of the normal for two kidneys.

However, pregnancy imposes a significant additional load. The increase in circulating blood volume, uterine pressure on the ureters, and hormonal changes (which reduce the tone of the urinary pathways) can lead to functional exhaustion of the organ. This causes urine stagnation and facilitates the entry of infections.

Pregnancy with a single kidney in reproductive medicine (ART) protocols

The use of assisted reproductive technology (IVF, ICSI) in patients with a single kidney requires a particular multidisciplinary approach. The main difficulty is that ovarian stimulation protocols involve high doses of gonadotropins, which have systemic effects on hemodynamics and electrolyte balance.

Risks related to controlled ovarian stimulation

The main danger for women with a single kidney is ovarian hyperstimulation syndrome (OHSS). OHSS causes massive fluid leakage from the vascular system into the intercellular space (abdominal and pleural cavities). For a patient with a single kidney, this is critical for several reasons:

• Decreased perfusion: reduction in circulating blood volume leads to a sharp decrease in renal blood flow.
• Risk of acute renal failure (ARF): in the absence of a reserve organ, decompensation occurs much faster than in healthy women.
• Electrolyte disturbances: imbalance between sodium, potassium, and magnesium, which can lead to cardiac arrhythmias and severe edema.

Preparation specifics for the IVF protocol

Before starting the program, the gynecologist is obliged to refer the patient for thorough nephrological examination:

1. Determination of glomerular filtration rate (GFR): the "gold standard" for assessing renal function.
2. Reberg-Tareev test: to evaluate endogenous creatinine clearance.
3. Microalbuminuria: test for detecting minimal protein quantities in urine, an early marker of renal filter damage.
4. Ultrasound with Doppler imaging: evaluation of blood flow velocity parameters in the renal artery.

Risk mitigation strategies in reproductive medicine

To minimize load on the single organ, modern protocols include:

• "Gentle" stimulation: use of minimal doses of medications.
• Protocols with GnRH antagonists: they prevent prolonged desensitization and reduce the risk of OHSS.
• Cycle segmentation (Freeze-all): after oocyte retrieval and fertilization, embryos are cryopreserved and transfer occurs in a subsequent cycle without hormonal load. This allows the kidney to recover after stimulation.
• Use of donation programs: in cases where ovarian stimulation is absolutely contraindicated due to low renal reserve (e.g., chronic kidney disease beyond stage 2).

The decision to pursue IVF is only made after consultation with a reproductive medicine specialist gynecologist, a nephrologist, and a therapist. If the single kidney shows signs of sclerosis or unstable filtration indicators, the ART program may be rejected in favor of surrogate motherhood.

Specifics of pregnancy course

Under favorable conditions, gestation proceeds similarly to a standard pregnancy. Pathological changes in kidney function may be indicated by:

• Changes in diuresis (excessive or insufficient urination);
• Urine opacity or presence of blood;
• Twinge pain in the lower back radiating to the groin or thigh;
• Facial swelling (especially in the morning);
• Headaches, ringing in the ears, and blood pressure variations.

Possible complications

The most common problem is pyelonephritis (inflammation), diagnosed in 78% of pregnant women with a single kidney. This rate is significantly higher than in women with both organs (2 to 20%).

Other serious risks include:

• Anuria: cessation of urine production due to ureter blockage by a stone.
• Obstetric risks: risk of miscarriage in the first trimester, increased risk of preeclampsia (1.87 times higher), preterm birth (2.46 times more frequent), and intrauterine growth retardation (2.92 times more frequent).
• Perinatal mortality: can reach 6.1%.
• Cesarean section: performed in 39.4% of cases for various indications.

Diagnostic measures

The primary goal of diagnostics is to assess how well the kidney performs its function. Main methods:

1. Ultrasound and Doppler ultrasound of renal vessels: allows to evaluate organ structure and blood circulation status.
2. Thermography (thermal imaging): helps detect hidden inflammatory processes via infrared radiation.
3. Urine analysis: general analysis, microbial culture, Zimnisky and Reberg tests (assessment of filtration).
4. Blood biochemistry: monitoring of creatinine, urea, and electrolytes levels.

Important: radiological methods (scintigraphy, angiography) are contraindicated during pregnancy due to fetal risk.

Management and treatment

Doctors (gynecologist-obstetrician and urologist) must decide on the feasibility of continuing pregnancy. Absolute contraindications: presence of active tuberculosis, hydronephrosis, stones in the only kidney, as well as persistent hypertension and azotemia.

If there are no contraindications, the following measures are applied:

• Prevention: urinary antiseptic plants (heather, bearberry, oxeye daisy, epilobium) throughout pregnancy.
• Antibiotics: in cases of infections (penicillins in the first trimester, cephalosporins in the 2nd and 3rd trimesters).
• Support: progestogens and spasmolytics to reduce uterine tone.
• Delivery: natural childbirth is preferred. Cesarean only in cases of urgent obstetric indication.

Prognosis and prevention

In 95% of cases, with proper medical follow-up, pregnancy outcome is favorable. It is believed that women with a left single kidney tolerate effort better.

Preventive measures

• Early planning of pregnancy at least 2 years after nephrectomy.
• Early registration.
• Strict diet: limiting salt, proteins, and excess liquids.
• Exclusion of coffee, intense physical efforts, and hypothermia.

Bibliography

1. UK Kidney Association (UKKA). Clinical Practice Guideline: Pregnancy and Renal Disease. 2019. (Guideline of the UK Kidney Association on pregnancy management in renal disease).
2. European Association of Urology (EAU). Guidelines on Urolithiasis. 2024. (European recommendations on urinary stone management, including aspects related to a single kidney and pregnancy).
3. Piccoli G.B., et al. Pregnancy, CKD and solitary kidney: kidney donation between clinical logic and taboos. Italian Journal of Nephrology, 2015. (Italian study on risks related to CKD and solitary kidney in obstetrics).
4. European Journal of Obstetrics & Gynecology and Reproductive Biology. Any reduction in maternal kidney mass makes a difference during pregnancy in gestational and fetal outcome. 2024. (Article on the impact of renal mass reduction on pregnancy outcome).
5. KDIGO. Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease. (International recommendations widely used in European practice for risk stratification in case of reduced renal function).

FAQ: Frequently Asked Questions

1. Can I carry a pregnancy to term with a single kidney? Yes, in 95% of cases, in the absence of concomitant renal diseases and with quality medical supervision, pregnancy ends successfully.

2. Is having a single kidney a sufficient reason for cesarean? No, having a single kidney is not itself an indication for surgery. If there are no obstetric complications, doctors recommend natural delivery.

3. How long after nephrectomy can pregnancy be considered? The recommended duration is at least 1.5 to 2 years. This period is necessary for the remaining kidney to undergo hypertrophy and fully adapt to the increased workload.

4. Which foods should be excluded from the diet? It is recommended to minimize table salt intake, limit meat proteins, and avoid coffee, spicy, smoked foods, and alcohol to reduce the load on the renal filtration system.

5. Is it dangerous for the fetus? The main risk for the fetus is developmental delay or premature birth due to disturbed blood circulation or maternal gestosis. Therefore, more frequent monitoring of the baby's condition using ultrasounds and dopplerometry is necessary.