Association of Prenatal Tobacco Exposure Verified by Maternal Urinary Cotinine With Umbilical Cord Blood Lactate, Fetal Carboxyhemoglobin, and Early Neonatal Outcomes: A Prospective Single-Center Observational Study

Prenatal exposure to tobacco smoke, through either active maternal smoking or secondhand exposure, has been associated with impaired fetal oxygenation, metabolic stress, and adverse early neonatal outcomes. This prospective, single-center observational cohort study will objectively assess maternal tobacco exposure using cotinine measured in maternal urine and examine its association with early neonatal biochemical, metabolic, and clinical outcomes.

Consecutive eligible mother-newborn dyads will be recruited at a tertiary academic hospital after written informed consent is obtained. A clean-catch midstream maternal urine sample will be collected within 24 hours before delivery, preferably at admission to the delivery unit and before intravenous fluid administration, for quantitative cotinine and creatinine measurement. Maternal tobacco exposure will be assessed using the urinary cotinine concentration, the cotinine-to-creatinine ratio, and maternal self-reported smoking and secondhand smoke exposure. Based on prespecified biomarker thresholds and exposure history, participants will be classified as having active exposure, passive exposure, or no exposure. No experimental intervention will be administered.

Neonatal data will include umbilical cord blood gas parameters, including pH, pCO2, pO2, base excess, bicarbonate, lactate, and fetal carboxyhemoglobin (FCOHb). Birthweight, length, head circumference, Apgar scores, oxygen saturation, heart rate, and blood pressure will also be recorded. Routine laboratory measurements obtained during the early postnatal period will include complete blood count parameters, hematologic and inflammatory indices such as NLR and PLR, albumin, the albumin-to-lactate ratio, HDL, LDL, and other routinely available biochemical markers. Thyroid-stimulating hormone results from the national newborn screening program and newborn hearing screening results will be recorded. Postnatal weight loss and bilirubin measurements from routine follow-up visits will also be collected when available.

The primary objective is to determine whether increasing maternal urinary cotinine exposure is associated with higher umbilical cord blood lactate and FCOHb levels, indicating greater metabolic stress and impaired fetal oxygenation. Secondary objectives include evaluating associations with cord blood gas parameters, birthweight, early hematologic and biochemical indices, albumin and the albumin-to-lactate ratio, blood pressure, bilirubin levels, thyroid screening results, and hearing screening outcomes.

Maternal, obstetric, and perinatal variables, including maternal age, parity, gestational age, mode of delivery, smoking history, intrapartum factors, and relevant maternal comorbidities, will be recorded for adjusted analyses. Statistical analyses will include comparisons among the three exposure groups and multivariable regression models evaluating urinary cotinine both as a continuous measure and as a categorical exposure variable.

This study is designed to provide prospectively collected, biomarker-verified evidence regarding the relationship between maternal tobacco exposure and immediate neonatal metabolic, hematologic, and physiologic outcomes using measurements that are feasible within routine clinical care.