Maternal erythrocyte indices in late pregnancy and neonatal 17-hydroxyprogesterone levels: a retrospective cohort study

Maternal erythrocyte indices, including the mean corpuscular hemoglobin concentration (MCHC) and red blood cell distribution width (RDW), are potential indicators of adverse birth outcomes. However, their association with neonatal 17-hydroxyprogesterone (17OHP) levels remains unexplored. This study investigated the relationship between maternal erythrocyte indices in late pregnancy and neonatal 17OHP levels, and secondarily with fetal growth outcomes. This retrospective cohort study included 10,141 mother–neonate pairs. Maternal MCHC and RDW were categorized into low, normal, and high groups based on the clinical reference ranges. Linear regression was used for neonatal 17OHP levels and birth weight, and logistic regression was used for small-for-gestational age (SGA) and large-for-gestational age (LGA). Generalized additive models and two-piecewise linear regression were used to explore the nonlinear relationships and threshold effects. The models were adjusted for maternal age, pre-delivery body mass index, parity, gestational age, blood pressure, pregnancy complications, assisted reproductive technology, delivery mode, and neonatal sex. 17OHP models were additionally adjusted for Apgar score and postnatal age at sampling. Elevated maternal MCHC (> 348 g/L) was independently associated with higher neonatal 17OHP levels (adjusted β = 2.30 nmol/L; P < 0.001). Compared with the low RDW (< 12.3%), both normal RDW (12.3–19.8%) and high RDW (> 19.8%) were associated with lower 17OHP levels, with similar effect estimates (adjusted β =− 1.68 nmol/L and β =− 1.78 nmol/L, respectively; both P < 0.001), suggesting that the association was primarily driven by the low-RDW category. Nonlinear modeling revealed threshold effects: a positive association with 17OHP was observed above an MCHC of 326 g/L, whereas RDW showed an inverse association below 13.9%. Higher MCHC was associated with lower birth weight and higher SGA odds, whereas higher RDW was associated with higher birth weight and higher LGA odds (all P < 0.05). All 17OHP values remained within the laboratory reference range (0–30 nmol/L), with only six infants exceeding this cutoff. Sensitivity analyses excluding these infants and using log-transformed 17OHP yielded consistent results. This study reports significant associations between maternal erythrocyte indices, neonatal 17OHP levels, and fetal growth outcomes. However, the clinical significance remains uncertain, and the findings are hypothesis-generating, given the observational design. Future research integrating longitudinal hormonal profiling and mechanistic studies is required to validate these associations.