Date Published: February 23, 2017
Publisher: Public Library of Science
Author(s): Miriam Abraham, Salem Alramadhan, Carmen Iniguez, Liesbeth Duijts, Vincent W. V. Jaddoe, Herman T. Den Dekker, Sarah Crozier, Keith M. Godfrey, Peter Hindmarsh, Torstein Vik, Geir W. Jacobsen, Wojciech Hanke, Wojciech Sobala, Graham Devereux, Steve Turner, Raymond Niaura.
Maternal smoking during pregnancy is linked to reduced birth weight but the gestation at onset of this relationship is not certain. We present a systematic review of the literature describing associations between maternal smoking during pregnancy and ultrasound measurements of fetal size, together with an accompanying meta-analysis.
Studies were selected from electronic databases (OVID, EMBASE and Google Scholar) that examined associations between maternal smoking or smoke exposure and antenatal fetal ultrasound measurements. Outcome measures were first, second or third trimester fetal measurements.
There were 284 abstracts identified, 16 papers were included in the review and the meta-analysis included data from eight populations. Maternal smoking was associated with reduced second trimester head size (mean reduction 0.09 standard deviation (SD) [95% CI 0.01, 0.16]) and femur length (0.06 [0.01, 0.10]) and reduced third trimester head size (0.18 SD [0.13, 0.23]), femur length (0.27 SD [0.21, 0.32]) and estimated fetal weight (0.18 SD [0.11, 0.24]). Higher maternal cigarette consumption was associated with a lower z score for head size in the second (mean difference 0.09 SD [0, 0.19]) and third (0.15 SD [0.03, 0.26]) trimesters compared to lower consumption. Fetal measurements were not reduced for those whose mothers quit before or after becoming pregnant compared to mothers who had never smoked.
Maternal smoking during pregnancy is associated with reduced fetal measurements after the first trimester, particularly reduced head size and femur length. These effects may be attenuated if mothers quit or reduce cigarette consumption during pregnancy.
Maternal smoking during pregnancy is associated with a reduction in birth weight of approximately 250g and is known to adversely affect the health of both fetus and mother. Knowledge of the age at onset of faltering fetal growth in association with maternal smoking would be useful evidence to underpin public health advice for mothers not to smoke during pregnancy. The advent of ultrasound in the mid-1980s provided an opportunity to study antenatal fetal size and growth as indices of fetal wellbeing, and there is now a rapidly expanding literature of “fetal epidemiology”.
This systematic review of the literature and meta-analysis were designed to describe the gestation at which exposure to maternal smoking became associated with reduced antenatal fetal size and growth. Biparietal diameter and femur length were reduced by at least 0.06 standard deviations (SD) by the second trimester, and all fetal measurements were reduced in the third trimester, typically by 0.2 SD. The reductions in fetal size associated with maternal smoking are statistically significant but small. In the studies where data were available, we also observed an exposure-response relationship for maternal cigarette consumption and reduced second and third trimester fetal head size, and we saw no evidence of reduced measurements among fetuses whose mothers quit before or after becoming pregnant compared to non-smokers. Collectively our findings support current public health advice that mothers should quit whilst pregnant and also suggest that harm reduction might be achieved by reduced cigarette consumption and this now needs exploring in longitudinal studies.