How should a pregnant woman (second pregnancy, ~30 weeks gestation) with 6‑7 years of type 2 diabetes mellitus controlled by insulin, a prior episode of possible renal colic, and a fetus with a suspected horseshoe kidney on routine ultrasound be managed?

Management of Pregnancy with Suspected Fetal Horseshoe Kidney and Maternal Diabetes

Immediate Fetal Assessment

Continue routine prenatal ultrasound surveillance with targeted third-trimester follow-up at ≥32 weeks to confirm the horseshoe kidney diagnosis and assess for associated anomalies, while maintaining standard aneuploidy screening protocols. 1, 2

Confirming the Horseshoe Kidney Diagnosis

• Measure the renal pelvic angle on axial ultrasound views—a pelvic angle <140° has 100% sensitivity and specificity for horseshoe kidney diagnosis, with normal fetuses showing angles of 161–172° in the third trimester. 3

• Perform a comprehensive fetal anatomic survey to exclude associated structural anomalies, as horseshoe kidney can occur in isolation (79% of cases) or with complex abnormalities including chromosomal anomalies like trisomy 18 (21% of cases). 3

• Evaluate for additional urinary tract abnormalities including urinary tract dilation (UTD), as horseshoe kidneys may have associated collecting system anomalies. 1, 4

Aneuploidy Risk Assessment

• If no previous aneuploidy screening has been performed, counsel regarding trisomy 21 risk and offer cell-free DNA testing or quad screen, as isolated renal anomalies carry minimal aneuploidy risk (positive likelihood ratio 1.5 for UTD). 1, 5

• Do not perform diagnostic testing (amniocentesis) solely for isolated horseshoe kidney if aneuploidy screening is negative. 1

• If other structural anomalies are present, consider diagnostic testing with chromosomal microarray analysis. 5

Maternal Diabetes Management During Pregnancy

Glycemic Control Optimization

• Continue insulin therapy throughout pregnancy as you are already doing—metformin should remain discontinued during pregnancy, and insulin is the preferred treatment for pre-existing diabetes in pregnancy. 1, 6

• Perform frequent patient-performed blood glucose measurements to achieve effective glycemic control and avoid both hyperglycemia and hypoglycemia, as this is essential for reducing fetal complications. 6

• Monitor HbA1c periodically to assess long-term glycemic control throughout pregnancy. 6

Fetal Surveillance for Diabetic Pregnancy

• Perform fetal ultrasound screening for congenital anomalies (which you have already done at 30 weeks)—this is recommended for women with diabetes presenting with HbA1c ≥7.0% or fasting plasma glucose ≥120 mg/dL due to increased risk of major congenital malformations. 1

• Schedule serial growth ultrasounds every 3–4 weeks starting from the anatomy scan to monitor for macrosomia or growth restriction, as maternal diabetes increases risk of abnormal fetal growth. 2

• Intensify fetal surveillance if pregnancy continues beyond 40 weeks, as data are limited regarding perinatal morbidity/mortality risk in well-controlled gestational diabetes beyond this point. 1

• Teach fetal movement monitoring during the last 8–10 weeks of pregnancy, with instructions to report immediately any reduction in perceived fetal movements. 1

Maternal Renal Assessment

Evaluation of Prior Renal Colic Episode

• Perform color Doppler ultrasound of maternal kidneys and bladder as the first-line study for diagnosis of maternal hydronephrosis or renal anatomic abnormalities in pregnancy. 1

• Measure renal resistive indices (RI) on ultrasound—RI elevations >0.70 suggest underlying kidney dysfunction, and an RI difference of 0.04 between kidneys indicates pathologic urinary tract obstruction. 1

• Evaluate ureteral jets in combination with RI measurement to distinguish between obstructive and nonobstructive hydronephrosis. 1

• Reserve MRI without IV contrast for situations where ultrasound findings are equivocal or nondiagnostic—MRI is preferred over CT in pregnancy, and gadolinium contrast should be avoided. 1

• Avoid CT imaging unless diagnosis cannot be made on ultrasound or MRI; if CT is absolutely required, use low-dose protocols. 1

Insulin Dose Adjustment Considerations

• Monitor for potential changes in insulin requirements related to renal impairment, as insulin dosage may need adjustment in patients with renal dysfunction. 6

• Be aware that intercurrent conditions (illness, stress, possible kidney stone) may alter insulin requirements and necessitate temporary dose increases. 6

Delivery Planning

Timing of Delivery

• Plan delivery at 38–40 weeks gestation in the absence of objective evidence of maternal or fetal compromise—there are no data supporting delivery before 38 weeks for isolated horseshoe kidney or well-controlled diabetes. 1

• Do not allow pregnancy to proceed beyond 40 weeks without intensified fetal surveillance, as delivery past 38 weeks can increase the rate of large-for-gestational-age infants. 1

Mode of Delivery

• The presence of fetal horseshoe kidney does not influence mode of delivery—vaginal delivery is appropriate unless obstetric indications for cesarean section exist. 1

Intrapartum Glucose Management

• Perform blood glucose monitoring during labor to guide correction of maternal hyperglycemia and prevent fetal hypoxia and neonatal hypoglycemia, though ideal target glucose concentrations during labor have not been established. 1

Postnatal Follow-Up

Neonatal Renal Assessment

• Inform pediatric providers of the antenatal horseshoe kidney finding at delivery for appropriate postnatal follow-up. 5

• Arrange postnatal ultrasound confirmation of the horseshoe kidney and comprehensive evaluation for associated urinary tract anomalies. 1, 4, 7

• Plan pediatric urology or nephrology consultation based on postnatal imaging findings. 1

Maternal Postpartum Care

• Screen for diabetes at 4–12 weeks postpartum using the 75-g oral glucose tolerance test with clinically appropriate non-pregnancy diagnostic criteria. 1

• Continue lifelong screening for diabetes or prediabetes every 1–3 years, as women with pre-existing diabetes require ongoing monitoring. 1

Critical Pitfalls to Avoid

• Do not assume isolated horseshoe kidney requires early delivery or cesarean section—these decisions should be based on standard obstetric indications, not the renal anomaly alone. 1

• Do not perform invasive diagnostic testing (amniocentesis) for isolated horseshoe kidney if aneuploidy screening is negative. 1

• Do not use CT imaging for maternal renal evaluation unless ultrasound and MRI are nondiagnostic—radiation exposure should be minimized in pregnancy. 1

• Do not discontinue insulin or switch to oral agents during pregnancy—insulin remains the standard of care for pre-existing diabetes in pregnancy. 1, 6

• Do not skip the third-trimester follow-up ultrasound—this is essential to reassess the horseshoe kidney, evaluate fetal growth, and guide postnatal management. 1, 2, 5