The effect of cigarette smoking on first‐trimester crown–rump length

Objectives: Does cigarette smoking impact the embryonic growth rate in the first trimester? Methods: This is a retrospective multicentre observational study of 2912 pregnancies. Women who presented to the early pregnancy and perinatal ultrasound units between 2010 and 2019 were included in the study. The data collected included the following: smoking status, the crown-rump length (CRL) of the pregnancy at the first ultrasound that showed an embryonic heart rate, the gestation in days and the CRL at another ultrasound up to the nuchal translucency scan and the gestation in days. Additional demographic data included the following: age, weight, height, parity and mode of delivery.Of the 2912, complete smoking and demographic data were available for 657 pregnancies. One hundred and thirty-seven (26.3%) were smokers, and 520 (73.7%) were not. The rate of change of smokers vs non-smokers between two CRLs and two different days of gestation was calculated. The Wilcoxon rank sum test with continuity correction was used for statistical analysis. Results: This gives a value of W = 31,940 and a P-value = 0.06. There is a slight shift in location for the smokers; however, it is not statistically significant. The insignificance may be due to the general large variance in growth rate. Conclusion: The impact of cigarette smoking on embryonic growth rate detected by CRL in the first trimester is statistically insignificant.