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Smoking linked to endothelial dysfunction in pregnancy

Obstetrics and gynaecology

Obstetrics and gynaecology

A small study from Australia has demonstrated a dose-related link between smoking and vascular endothelial dysfunction in pregnancy. Four of out ten women who smoked had intrauterine growth retardation resulting in low birthweight babies.

Forty-one women between 28 and 32 weeks' gestation were recruited. Twenty were non-smokers, and 21 smoked at least ten cigarettes per day (mean 15.7 cigarettes per day). Ultrasonic measurement of the brachial artery diameter was performed before and after inducing reactive vasodilatation by keeping a blood pressure cuff at 200mmHg for five minutes. A blunted response strongly suggests endothelial dysfunction.

The two groups were broadly similar, although smokers were more likely to be parous. The test was done twice in both groups. Smokers were tested after a nine-hour period of abstinence, and ten minutes later after smoking one or two cigarettes.

Flow-mediated dilatation (FMD) scores were significantly lower in the smokers both following abstinence and after smoking than in the non-smokers (P=<0.001). No difference in FMD was seen within each group between the two tests, suggesting that the effect of smoking on endothelial function is persistent. Heart rate and diastolic blood pressure were raised in the smokers on retesting after smoking.

Pregnancy outcome was shown to be poorer in women who smoked. Pregnancy duration at delivery was similar in both groups but birthweight was significantly lower among smoking mothers compared with non-smokers (mean 3090g vs 3501g, P=0.014).

Thirty-eight per cent of smokers' babies weighed less than the 10th centile and 24% less than the 5th centile. Babies less than the 10th centile were more likely to be born to mothers with the lowest FMD scores. No small-for-dates babies were born to mothers from the non-smoking group.

The endothelium functions in regulating vascular tone and flow. When disordered, this results in reduced vasodilatatory effects and is associated with vessel wall inflammation, which predisposes the patient to thrombosis. Although, paradoxically, women who smoke are less likely to develop pre-eclampsia in pregnancy, they are far more likely to have babies with low birthweight.

Among these heavy smokers, nearly 40% had intrauterine growth retardation. Smoking cessation before pregnancy should be a priority.

Quinton AE, Cook C-M, Peek MJ. The relationship between cigarette smoking, endothelial function and intrauterine growth restriction in human pregnancy. BJOG 2008;115:780-4

Reviewer

Dr Chris Barclay
GP, Sheffield

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