Renal Function Tests useful in predicting the risk of preeclampsia.

Chronic hypertension affects 3-5% of all pregnancies and its prevalence is increasing recently because of rise in number of elderly and obese gravidas. The most prevalent complication in pregnant women with chronic hypertension is the development of preeclampsia.

According to a recent study it is estimated that 17% to 25% of women with chronic hypertension will develop superimposed preeclampsia and these women have worse birth outcomes than women with chronic hypertension without superimposed preeclampsia.

Diagnosing superimposed preeclampsia on chronic hypertension pose a significant challenge because blood pressures are already elevated and proteinuria may be present before pregnancy. There is a continuing search for improved tests to both predict and diagnose preeclampsia.

A recent paper published online June 6 in Obstetrics & Gynecology suggests that baseline renal parameters may be useful in predicting the risk for preeclampsia among pregnant women with chronic hypertension.

This is a retrospective cohort study of 755 women with singleton pregnancy with chronic hypertension. Renal function (urine protein-to-creatinine ratio and serum creatinine) assessment was done in all patients before 20 weeks.

The primary outcome was the development of early onset preeclampsia at less than 34 weeks' gestation; secondary outcomes evaluated were the development of severe preeclampsia at any gestational age, any preeclampsia, small for gestational age, preterm birth at less than 35 weeks' gestation, and composite adverse perinatal outcome including perinatal death, neonatal seizures, assisted ventilation, arterial cord pH lower than 7, and 5-minute Apgar score of 3 or lower.

A Receiver operating characteristic (ROC)curve was created to determine the cut-off for baseline serum creatinine in development of severe preeclampsia.  

It was seen that in these cohort of women, baseline serum creatinine and urine protein-to-creatinine ratio 0.75 mg/dL or greater and 0.12 or greater, respectively, are associated with increased risks of severe preeclampsia before 34 weeks of gestation, severe and mild preeclampsia at any gestational age and for urine protein-to-creatinine ratio, preterm birth at less than 35 weeks of gestation.

These levels are much below what is considered normal.

Further it was seen that 33.3% of women with levels above the arbitrary cut-off developed severe preeclampsia before 34 weeks and remaining 66.7% developed any kind of preeclampsia during pregnancy.

Conversely 97.4% of patients with urine protein-to-creatinine ratio less than 0.12 did not develop severe preeclampsia and 95.4% of patients with baseline serum creatinine less than 0.75 mg/dL did not develop severe preeclampsia.

Patients with UPCR above the cutoff had odds of preterm labor 2.4 times to those with normal levels.

The study results may not be generalized to other populations as it included mostly black women and the blood samples for baseline renal functions were not all collected at the same gestational age, although all were collected before 20 weeks.  The strength was a large study subjects, accurately recorded data and strict study criteria for development of preeclampsia.  

In summary, the study findings suggest that in women with chronic hypertension a creatinine 0.75 mg/dL or greater and a urine protein-to creatinine ratio 0.12 or greater is associated with adverse pregnancy outcomes. These values are much lower than what was previously thought to be normal.

"These findings should be validated in additional studies and, if validated, can be used to counsel women regarding their risk of adverse pregnancy outcomes and to alter surveillance for preeclampsia," the researchers concluded.

References:

http://journals.lww.com/greenjournal/Abstract/publishahead/Baseline_Renal_Function_Tests_and_Adverse_Outcomes.98712.aspx

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