Association between first trimester platelet to lymphocyte ratio and stillbirth

Neutrophil to lymphocyte ratio (NLR) and platelet to lymphocyte ratio (PLR) have been investigated as inflammatory markers of malignancies, cardiovascular and autoimmune diseases. We explored the association between NLR, PRL, measured during pregnancy, and stillbirth (SB).

We conducted a retrospective case control study at a tertiary hospital center in New York City from May 2015 to July 2018. Cases were defined as SB pregnancies and controls as uncomplicated pregnancies. We calculated NLR and PLR using the complete blood count components routinely collected during prenatal care in the first trimester. The groups were matched by age, parity, body mass index (BMI) and race. We used receiver operating characteristic (ROC) curve analysis to evaluate the association of NLR and PLR to SB.

We identified 28 patients with SB pregnancies and matched them with 28 controls. Age, parity, BMI, and race were equally distributed between the groups. The median gestational age of SB was 30 weeks (22-34). In the first trimester PLR was significantly lower in SB cases compared to controls (124.8 vs. 153.4, P=0.044) with an area under the curve (AUC) of 0.65. A PLR value higher than 156.4 accurately excluded SB with a sensitivity of 0.50, specificity of 0.89, positive predictive value of 0.013 and a negative predictive value of 0.998. NLR did not show a significant difference in the first trimester.

A PLR higher than 156.4 in the first trimester appears to reliably exclude the occurrence of SB later during pregnancy. Lower platelet and higher lymphocyte levels may be related to an early inflammatory process. We speculate that pregnancies in which the initial myometrial invasion by the placental cells is dysfunctional and reflected by a high level of inflammation in the peripheral maternal blood, may contribute to fetal demise. Larger studies are needed to confirm our results.