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Increased aminoterminal C-type natriuretic peptide may predict adverse events in pregnancy
In pregnant women, significant increases in aminoterminal C-type natriuretic peptide may be predictive of various obstetric adverse events, according to a recent study.
The prospective, observational study recruited 51 pregnant women under two circumstances: routine checkups for apparently healthy pregnancies, and high-risk referrals to Christchurch Women’s Hospital Antenatal Outpatients Clinic. The researchers also evaluated data from 25 healthy, nonpregnant volunteer women (mean age, 31 years) who were participants in another study. These women served as an age-matched reference range for plasma C-type natriuretic peptide (CNP) measurements.
The study participants underwent ultrasound scans at 4-week intervals, as well as uterine artery Doppler scanning at 24 weeks, umbilical artery Doppler scanning each month and monthly blood samplings for aminoterminal proCNP (NTproCNP). A final blood draw was taken immediately post-partum.
Of the 51 pregnancies, 28 involved an adverse event while 23 were uneventful. The researchers found that in comparison to the nonpregnant reference group women, the women with uneventful pregnancies experienced significant decreases in plasma NTproCNP until 36 weeks gestation. Conversely, women whose pregnancies had complications did not experience a decrease in NTproCNP, but instead showed significant higher levels (P<.001) than in a normal pregnancy from 20 weeks gestation.
Women who would later develop hypertension and disorders of fetal growth had the highest NTproCNP levels. The concentration of NTproCNP in the placenta did not correspond with the changes in maternal NTproCNP. Rather, there was a strong association between placental NTproCNP concentrations and umbilical arterial plasma NTproCNP.
“Our findings raise the prospect that NTproCNP could be used in the prediction of adverse events,” the researchers wrote. “Further, high values might prove helpful in selecting cases for treatment aimed to improve blood flow to a growth-restricted fetus.”
Disclosure: The researchers report no relevant financial disclosures.
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Reid and colleagues demonstrated that levels of a biologically inactive component of C-type naturiuretic peptide (NTproCNP) are lower in pregnant than non-pregnant women and that in normal pregnancy levels fall from early to late gestation. In contrast, in women with complicated pregnancies, levels of NTproCNP increase from early to late gestation. This finding is of interest as CNP is a vasoactive peptide that may play a role in placentation and placental function during pregnancy. However, the investigators did not find an association between maternal NTproCNP levels and concentrations of CNP peptides in placental tissue and surmise that increased levels in maternal circulation result as a compensatory response to threatened nutrient supply to the fetus.
It is also possible that the stimulus to maternal NTproCNP is being mediated by factors other than the placenta. In this study, women with complicated pregnancies had a wide range of complications; from eight with small for gestational age infants to a single case of preeclampsia. It is possible that only some categories of pregnancy complications drive the changes in NTproCNP.
Further studies with larger numbers in different categories will help elucidate this question. Although there was no significant difference in BMI between groups, the means did differ (normal 23.9 vs. complicated 26.3); it would be of interest to determine whether BMI has any impact on NTproCNP levels. Larger studies will be needed to determine whether levels of NTproCNP can be used clinically to predict which pregnancies are at increased risk for growth restriction.