Elevated amniotic fluid C-reactive protein at the time of genetic amniocentesis is a marker for preterm delivery

A pre-existing intrauterine inflammation in the first half of gestation has been proposed as a possible condition that leads to preterm delivery. Indeed, elevated levels of inflammatory mediators (eg, interleukin-6, tumor necrosis factor) in midtrimester amniotic fluid have been found in cases of preterm delivery and/or spontaneous abortion. The objective of this study was to investigate whether the amniotic fluid C-reactive protein level at the time of genetic amniocentesis is a marker for spontaneous preterm delivery before 34 and 37 weeks of gestation.

Women who underwent genetic amniocentesis between 15 and 18 weeks of gestation with (1) singleton gestation, (2) uneventful pregnancy course before the amniocentesis, and (3) absence of fetal abnormalities were included in the study. Patients with abnormal karyotype were excluded. C-reactive protein concentration was measured in amniotic fluid and in maternal blood immediately after genetic amniocentesis. All patients were followed until delivery for the occurrence of pregnancy complications. Nonparametric tests and receiver-operating characteristic curve analysis were used for statistical purposes.

The prevalence of spontaneous preterm delivery before 34 and 37 weeks was 3.3% (10 of 306 pregnancies) and 8.5% (26 of 306 pregnancies), respectively. Women with preterm delivery at <37 weeks had a higher median (range) of amniotic fluid C-reactive protein concentration than those women who delivered at term (median, 113.3 ng/mL [range, 16-623 ng/mL] vs median, 57.8 ng/mL [range, 0-808.9 ng/mL]; P <.005). Women with preterm delivery at <34 weeks had a higher median (range) amniotic fluid C-reactive protein concentration than those women who delivered at term (median, 183.8 ng/mL [range, 46.5-447 ng/mL] vs median, 57.8 ng/mL [range, 0-808.9 ng/mL]; P <.005]. No correlation was found between amniotic fluid C-reactive protein and maternal blood C-reactive protein concentrations. No relationship was found between maternal blood C-reactive protein concentration and preterm delivery before either 34 or 37 weeks. Amniotic fluid C-reactive protein concentration of >110 ng/mL had a sensitivity of 80.8% and a specificity of 69.5% in the prediction of spontaneous preterm delivery at <34 weeks.

This study supports the theory that a subclinical intrauterine/fetal inflammatory process early in gestation may be important for the occurrence of preterm delivery in the second half of gestation.