Scholarly article on topic 'Spontaneous preterm birth and small for gestational age infants in women who stop smoking early in pregnancy: prospective cohort study'

Spontaneous preterm birth and small for gestational age infants in women who stop smoking early in pregnancy: prospective cohort study Academic research paper on "Psychology"

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Academic research paper on topic "Spontaneous preterm birth and small for gestational age infants in women who stop smoking early in pregnancy: prospective cohort study"

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Spontaneous preterm birth and small for gestational age infants in women who stop smoking early in pregnancy: prospective cohort study

Lesley M E McCowan,1 Gustaaf A Dekker,6 Eliza Chan,1 Alistair Stewart,2 Lucy C Chappell,4 Misty Hunter,1 Rona Moss-Morris,5 Robyn A North,3 on behalf of the SCOPE consortium

EDITORIAL

by campbell and Murphy

'Department of Obstetrics and Gynaecology, Faculty of Medical and Health Sciences, School of Population Health, University of Auckland, Auckland, New Zealand department of Epidemiology and Biostatistics, Faculty of Medical and Health Sciences, University of Auckland

3Discipline of Obstetrics and Gynaecology, School of Paediatrics and Reproductive Health, University of Adelaide, Australia 4Division of Reproduction and Endocrinology, King's College London

5School of Psychology, University of Southampton 6Women and Children's Division, Lyell McEwin Hospital, University of Adelaide Correspondence to: L M E McCowan l.mccowan@auckland.ac.nz

Cite this as: BMJ 2009;338:bl081

doi: 10.1136/bmj.b1081

study questions What are the relative risks of spontaneous preterm birth and of having a small for gestational age baby among pregnant women who stop smoking by 15 weeks' gestation? SuMMARY answer There were no differences in these adverse pregnancy outcomes between women who stopped smoking by 15 weeks' gestation and non smokers, but women who continued to smoke had a 3.2fold increase in spontaneous preterm birth and a 1.8-fold increase in small for gestational age babies.

Participants and setting

Between November 2004 and July 2007, 2504 healthy nulliparous women were recruited to the Screening for Pregnancy Endpoints (SCOPE) study in Auckland, New Zealand, and Adelaide, Australia.

Design, size, and duration

After recruitment to this prospective multicentre cohort study at 15 weeks' gestation, participants were divided into three groups according to self reported smoking status—"non-smokers," who did not smoke at all during pregnancy; "stopped smokers," who had smoked at some time during pregnancy but who stopped before the 15 week interview; and "current smokers," who still smoked at the time of the interview. Small infant size for gestational age was defined as birth weight <10th customised centile, and spontaneous preterm birth was spontaneous labour or rupture of the membranes resulting in birth at <37 weeks' gestation. We compared the odds of these outcomes between stopped smokers and the other groups using logistic regression, adjusting for demographic and clinical risk factors

main results and the role of chance

Of the participants, 1992 (80%) were non-smokers, 261 (10%) were stopped smokers, and 251 (10%) were current smokers. We found no differences between non-smokers and stopped smokers in rates

of spontaneous preterm birth (4% v 4%, adjusted odds ratio 1.03 (95% CI 0.49 to 2.18), P=0.66) or small for gestational age infants (10% v 10%, 1.06 (0.67 to 1.68), P=0.8). Current smokers, however, had higher rates of spontaneous preterm birth than stopped smokers (10% v 4%, 3.21 (1.42 to 7.23), P=0.006) and higher rates of small for gestational age infants (17% v 10%, 1.76 (1.03 to 3.02), P=0.03).

Bias, confounding, and other reasons for caution

Participants' smoking status was not validated by biochemical measures, but, given the similarities in pregnancy outcomes between stopped smokers and non-smokers, it is unlikely that many women who continued to smoke falsely claimed to have stopped smoking. Of the women who had stopped smoking by the 15 week interview, 94% had already stopped by 12 weeks' gestation. It is therefore possible that the benefits we observed were due to stopping smoking in the first trimester.

Generalisability to other populations

As has been found in other studies, the women who continued to smoke were heavier smokers before pregnancy, younger, less well educated, less likely to be employed, and reported higher rates of alcohol use than the other participants. Those who stopped smoking by 15 weeks' gestation had intermediate values for these characteristics. Our results are therefore likely to be generalisable to other pregnant women.

study funding/potential competing interests

The New Zealand SCOPE study was supported by the Foundation for Research Science and Technology, Health Research Council, and Auckland District Health Board Charitable Trust. The Australian study was supported by the South Australian Government. The study sponsors had no role in study design, data analysis, or writing this report.

PREGNANCY OUTCOMES BY MATERNAL SMOKING STATUS

This is a summary of a paper that was published on bmj.com as BMJ 2009;338:b1081

Non-smokers Stopped Mean difference Current Mean difference

smokers (95% CI)* smokers (95% CI)t

Spontaneous preterm births 4% (88/1992) 4% (10/261) -0.6% (-2.6% to 2.6%) 10% (25/251) 6.1% (1.7% to 10.8%)

Small for gestational age 10% (195/1992) 10% (27/261) -0.5% (-5.0% to 2.9%) 17% (42/251) 6.4% (0.4% to 12.4%)

Mean (SD) birth weight (g) 3409 (592) 3479 (560) -70 (-146 to 6) 3139 (751) 270 (190 to 350)

Uncomplicated pregnancies 60% (1192/1992) 62% (162/261) -2.2% (-8.3% to 4.2%) 44% (111/251) -17.8% (-26.1% to -9.2%)

*Stopped smokers v non-smokers tStopped smokers v current smokers

BMJ | 27 JUNE 2009 | VOLUME 338

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