Prenatal exposure to tobacco smoke, whether from active maternal smoking or secondhand exposure, has been associated with adverse neonatal adaptation, metabolic stress, and impaired fetal oxygenation. This single-center prospective observational cohort study will quantify prenatal tobacco exposure using cord blood cotinine measured at delivery and examine its association with early neonatal biochemical, metabolic, and physiologic outcomes.

Participants will consist of mother-newborn dyads recruited consecutively at a tertiary academic hospital. After informed consent, cord blood obtained at delivery will be used for cotinine measurement. Based on pre-specified cotinine thresholds and maternal smoking history, newborns will be classified into three exposure groups: active exposure, passive exposure, or no exposure. No experimental intervention will be administered, and neonatal assessments will be based on routine perinatal and postnatal care.

Neonatal data collected will include umbilical cord blood gas parameters (pH, pCO2, pO2, base excess, bicarbonate, and lactate), fetal carboxyhemoglobin (FCOHb), birthweight and anthropometric measurements, Apgar scores, oxygen saturation, heart rate, blood pressure, and routine laboratory indices obtained during the first postnatal day. These laboratory measures may include complete blood count parameters, inflammatory and hematologic ratios such as NLR and PLR, metabolic markers including albumin and lactate-to-albumin ratio, lipid parameters such as HDL and LDL, thyroid-stimulating hormone from the standard newborn screening program, and hearing screening results. Early follow-up data, including postnatal weight loss and bilirubin measurements at routine visits, will also be recorded where available. Maternal and perinatal covariates, including maternal age, parity, gestational age, delivery mode, intrapartum factors, smoking history, and relevant maternal comorbidities, will be collected to support adjusted analyses.

The primary objective is to determine whether higher cord blood cotinine-defined exposure is associated with greater metabolic stress and impaired fetal oxygenation at birth, particularly as reflected by cord lactate, related blood gas parameters, and FCOHb. Secondary objectives include evaluating associations with early neonatal hematologic, metabolic, endocrine, and clinical indices, including birthweight, blood pressure, bilirubin levels, thyroid screening results, and hearing screening outcomes.

The study will recruit consecutive eligible dyads in a prospective manner. Statistical analyses will follow a pre-specified plan and will include multivariable regression models to adjust for potential confounding factors. Sensitivity and subgroup analyses, including analyses by delivery mode and other clinically relevant strata, will be performed when feasible.

This study is designed to provide prospectively collected, biochemically verified evidence on how prenatal tobacco exposure, classified by cord blood cotinine, relates to immediate neonatal metabolic, hematologic, and physiologic outcomes using measurements that are feasible within routine clinical care.

Inclusion Criteria:

• Liveborn neonate delivered at the study hospital, aged 0-72 hours at assessment.
• Routine umbilical cord blood gas available at birth (pH, base excess, lactate).
• Cord blood cotinine available or obtainable at delivery for exposure classification.
• Singleton live birth at ≥35 weeks of gestation.
• Availability of routine umbilical cord blood gas parameters at birth, including at minimum pH, base excess, and lactate, with FCOHb recorded where available.
• Availability of routine first postnatal day clinical and laboratory data according to unit practice.
• Parent/guardian provides informed consent for use of neonatal data obtained from routine care.
• Standard newborn assessments obtainable within 72 hours (e.g., birthweight, ~6-hour vitals/BP, TSH at 24-48 h, hearing screen ≤72 h per unit practice).

Exclusion Criteria:

• Emergent clinical scenarios where any research step could delay urgent care.
• Major congenital anomaly, known chromosomal/genetic disorder, or major metabolic disease likely to affect neonatal adaptation or study outcomes.
• Severe perinatal condition preventing acquisition of core study data or making outcome interpretation unreliable, including major birth trauma or prolonged intensive care requirement.
• Missing cord blood cotinine measurement or missing core primary outcome data.
• Multiple gestation.
• Prior enrollment of the same neonate (no re-enrollment).

This is a single-center prospective cohort study conducted at a tertiary hospital. Eligible participants are consecutively recruited mother-newborn dyads during birth hospitalization. Newborns are stratified into three prenatal tobacco exposure groups according to cord blood cotinine levels and maternal exposure history: active exposure, passive exposure, and no exposure.

Study outcomes are derived from routine clinical care and early scheduled follow-up. Collected data include umbilical cord blood gas parameters (including pH, base excess, lactate, and FCOHb where available), birthweight and anthropometric measurements, Apgar scores, oxygen saturation, heart rate, blood pressure, first postnatal day laboratory parameters, newborn screening TSH, hearing screening results, and follow-up weight loss and bilirubin measurements where available. No experimental intervention is administered, and no extra phlebotomy beyond routine care is planned.