Prenatal Tobacco Exposure and Newborn Outcomes: A Maternal Urinary Cotinine 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-u