Medical Professionals Online

Study Shows Perils Of Smoking And Pregnancy

September 25, 2017

New research to be published in BJOG: An International Journal of Obstetrics and Gynaecology has found significant association between smoking during pregnancy, endothelial dysfunction and growth restriction in the unborn baby. Endothelial dysfunction can lead to reduced dilation of blood vessels, inflammation of the vascular wall and an increase in the incidence of blood clots.

The University of Sydney study included 41 pregnant women, 21 of whom smoked ten or more cigarettes a day and 20 who were non-smokers. The women were studied between week 28 and week 32 of their pregnancy and for those who smoked, the average number of cigarettes per day was 15.7 +/- 4.9.

Endothelial function is responsible for modulating vascular tone, vessel size and regulation of blood flow and in this study it was assessed by the ultrasound technique flow-mediated dilatation (FMD). This tests the main blood vessel of the upper arm, the brachial artery, by measuring its diameter following induced reactive hyperemia - when blood collects in an organ of the body because of a blockage in the veins that move the blood out.

The smokers in the group were asked to refrain from cigarettes from midnight before the test commenced at nine am. After 10 minutes of rest, a blood pressure cuff was placed on the lower arm and inflated for five minutes to cause reactive hyperemia. At the completion of the test the women had a 10 to 15 minute break during which time the smokers could choose to have none, one or two cigarettes. The test was then repeated on all the women.

Results showed that the women who smoked during pregnancy had persistent endothelial dysfunction which remained at a constant level whether one or two cigarettes had just been smoked or following a nine-hour break from smoking. The study also found strong links between endothelial dysfunction and intrauterine growth restriction, which carries an increased risk of perinatal mortality and morbidity.

Although gestational age was similar in both groups, birth weight was significantly reduced in the smokers with 38% (8/21) of babies at less than the 10th percentile and 24% (5/21) less than the 5th percentile. Those babies whose birth weight was less than the 10th percentile were born to mothers with a significantly lower endothelial function (4.7 +/- 2.2 compared to 7.3 +/- 4.6). There were no small-for-gestational age babies in the non-smoking group.

Ann Quinton, senior research sonographer, said "Our work provides evidence that smoking has a direct and long term deleterious effect on vascular function in pregnancy and thus provides evidence to why babies of smokers are growth restricted."

Professor Philip Steer, BJOG editor-in-chief said, "There is extensive evidence that women who smoke during pregnancy do so at great risk to themselves and to their baby. Smoking is linked to miscarriage, premature birth, placental abruption and placenta praevia - all very serious conditions indeed.

"This research is further proof that pregnant women must stop smoking to ensure that their babies have the healthiest start. Women should speak with their midwife, GP or local PCT who will be able to provide important information and support while they break the habit".

Notes

BJOG: An International Journal of Obstetrics and Gynaecology is owned by the Royal College of Obstetricians and Gynaecologists (RCOG) but is editorially independent and published monthly by Wiley-Blackwell. The journal features original, peer-reviewed, high-quality medical research in all areas of obstetrics and gynaecology worldwide. Please quote 'BJOG' or 'BJOG: An International Journal of Obstetrics and Gynaecology' when referring to the journal.

Reference

The relationship between cigarette smoking, endothelial function and intrauterine growth restriction in human pregnancy.
Quinton A, Cook C, Peek M.
BJOG 2008;115:780-84 DOI: 10.1111/j.1471-0528.2008.01691.x.

Royal College of Obstetricians and Gynaecologists