Prediction and sequelae of smoking in pregnancy

Thesis

Introduction: Maternal smoking during pregnancy remains a leading modifiable risk factor for adverse fetal outcomes such as low birthweight, preterm birth, and stillbirth. The aim of this thesis was to inform the appropriate method and timing for surveillance in pregnancies of smokers, by assessing how smoking exposure affects pregnancy outcomes and how it can be most accurately identified and managed.

Methods: Three complementary studies were conducted. First, a systematic review and meta-analysis (registered with PROSPERO: CRD42024592194) synthesised evidence from 145 studies on maternal smoking and fetal outcomes. Second and third, retrospective observational studies using data from the Oxford Growth Restriction Identification Programme (OxGRIP) examined how smoking exposure measured by exhaled carbon monoxide (CO) and self- report relates to pregnancy outcomes, and how fetal growth and Doppler findings differ between smokers and non-smokers across gestation.

Results: The meta-analysis showed that smoking during pregnancy significantly increased the risks of small-for-gestational-age birth, preterm delivery, and stillbirth, with risk magnitude rising with higher cigarette consumption and later cessation. Breath carbon monoxide was associated with low birthweight and adverse neonatal outcomes, with a clear dose–response above a threshold of >2 ppm. In the ultrasound analysis, fetal growth and Doppler findings were largely similar between smokers and non-smokers at 20 weeks but showed clear divergence by 36 weeks.

Conclusions: In conclusion, this thesis demonstrates that smoking in pregnancy is an independent risk factor for adverse outcomes, with effects that become more pronounced as pregnancy progresses. Early identification, reliable exposure testing, and cessation support remain central to mitigating these risks. Incorporating smoking status and measured CO levels into antenatal risk prediction models could help guide the need for enhanced fetal surveillance and targeted interventions, particularly in the third trimester when Doppler and growth changes are most evident.

Authors: Galka, K

• DOI: 10.5287/ora-erbeaddbk
• Type of award: MSc by Research
• Level of award: Masters
• Awarding institution: University of Oxford
• Language: English
• Keywords: low birth weight; pregnancy outcomes; maternal smoking; antenatal surveillance; small for gestational age; preterm birth; fetal growth restriction
• Subjects: Fetal monitoring; Medicine; Obstetrics; Women's health services