Linking birth records to hospital admission records enhances the identification of women who smoke during pregnancy

Smoking Cessation Pharmacotherapy Use in Pregnancy

Importance

Significant evidence gaps exist regarding the safety of smoking cessation pharmacotherapies during pregnancy, especially for the risk of congenital malformations. Consequently, professional bodies advise against the use of varenicline and bupropion and recommend caution with nicotine replacement therapy (NRT). Contemporary estimates of the use of smoking cessation pharmacotherapies during pregnancy are lacking.

Objective

To quantify the proportion of individuals using prescribed smoking cessation pharmacotherapies during pregnancy and during the first trimester specifically, in 4 countries.

Design, Setting, and Participants

This retrospective, population-based cohort study used linked birth records, hospital admission records, and dispensing records of prescribed medications from all pregnancies resulting in birth between 2015 and 2020 in New South Wales, Australia; New Zealand; Norway; and Sweden. Data analyses were conducted in October and November 2023.

Exposure

Prescribed smoking cessation pharmacotherapy use (varenicline, NRT, and bupropion) during pregnancy was defined as days' supply overlapping the period from date of conception to childbirth.

Main Outcomes and Measures

Prevalence of use among all pregnancies and pregnancies with maternal smoking were calculated. Among women who used a pharmacotherapy, the proportion of women with use during the first trimester of pregnancy was also calculated.

Results

Among 1 700 638 pregnancies in 4 countries, 138 033 (8.1%) had maternal smoking and 729 498 (42.9%) were younger than 30 years. The prevalences ranged from 0.02% to 0.14% for varenicline, less than 0.01% to 1.86% for prescribed NRT, and less than 0.01% to 0.07% for bupropion. Among pregnant individuals who smoked, use of pharmacotherapies was up to 10 times higher, with maximum prevalences of 1.25% for varenicline in New South Wales, 11.39% for NRT in New Zealand, and 0.39% for bupropion in New Zealand. Use in the first trimester occurred among more than 90% of individuals using varenicline, approximately 60% among those using NRT, and 80% to 90% among those using bupropion.

Conclusions and Relevance

In this cohort study of pregnant individuals in 4 high-income countries, the low prevalence of varenicline and bupropion use during pregnancy and higher prevalence of NRT use aligned with current clinical guidelines. As most use occurred in the first trimester, there is a need for evidence on the risk of congenital malformations for these medications.

Prevalence and Persistence of Prescription Opioid Use Following Hospital Discharge After Childbirth: An Australian Population-Based Cohort Study

BACKGROUND

Opioid analgesics are used for acute postpartum pain relief but carry risks, including persistent long-term opioid use. Our primary objective was to estimate the prevalence of persistent use following hospital discharge after childbirth.

METHODS

We conducted a population-based cohort study of women discharged from public or private hospitals in New South Wales, Australia, between 2012 and 2018 following vaginal birth (VB) or cesarean delivery (CD). We used linked hospitalization and medicine dispensing data to calculate the prevalence of opioid use within 14 days of hospital discharge for childbirth using an external estimate of the total number of hospital admissions for childbirth per year as the denominator. Among women dispensed an opioid postdischarge, we estimated the prevalence of persistent use defined as ≥3 dispensings between 30- and 365-days postdischarge. To calculate the odds of persistent opioid use, we performed a series of logistic regressions each including a single characteristic of interest. Included characteristics were maternal and birth characteristics, maternal medical conditions, prior use of certain medicines, and the initial opioid dispensed following discharge for childbirth.

RESULTS

The final cohort comprised of 38,832 women who were dispensed an opioid in the 14 days following discharge after childbirth. Between 2012 and 2018, the prevalence of opioid use was increased following CD (public hospital 16.6%-21.0%; private hospital 9.8%-19.5%) compared with VB (public hospital 1.5%-1.5%; private hospital 1.2%-1.4%) and was higher following discharge from public hospitals compared with private. The most commonly dispensed opioids following discharge for childbirth were oxycodone (44.8%; 95% confidence interval [CI], 44.3-45.3), codeine (42.1%; 95% CI, 41.6-42.6), and tramadol (12.9%; 95% CI, 12.6-13.2). Among women dispensed an opioid, the prevalence of persistent opioid use was 5.4% (95% CI, 5.1-5.6). This prevalence was 11.4% (95% CI, 10.5-12.3) following a VB as compared with 4.3% (95% CI, 4.1-4.6) among those who underwent a CD ( P < .001). Characteristics associated with persistent opioid use included smoking during pregnancy, age <25 years, living in remote areas, discharged from a public hospital, history of opioid use disorder, other substance use disorder, mental health diagnosis, or prior use of prescription opioids, nonopioid analgesics, or benzodiazepines.

CONCLUSIONS

The results of this cohort study indicate that Australian women have a higher prevalence of opioid use following CD compared to VB. One in 19 women dispensed an opioid postdischarge used opioids persistently. Careful monitoring of opioid therapy following childbirth is warranted, particularly among women with characteristics we identified as high risk for persistent opioid use.

Prevalence of smoking during pregnancy and associated social inequalities in developed countries over the 1995-2020 period: A systematic review

BACKGROUND

Smoking during pregnancy (SDP) is an important source of preventable morbidity and mortality for both mother and child.

OBJECTIVES

The aim of this study was to describe changes in the prevalence of SDP over the last 25 years in developed countries (Human Development Index >0.8 in 2020) and associated social inequalities.

DATA SOURCES

A systematic review was conducted based on a search in PubMed, Embase and PsycInfo databases and government sources.

STUDY SELECTION AND DATA EXTRACTION

Published studies between January 1995 and March 2020, for which the primary outcome was to assess the national prevalence of SDP and the secondary outcome was to describe related socio-economic data were included in the analysis. The selected articles had to be written in English, Spanish, French or Italian.

SYNTHESIS

The articles were selected after successive reading of the titles, abstracts and full-length text. An independent double reading with intervention of a third reader in case of disagreement allowed including 35 articles from 14 countries in the analysis.

RESULTS

The prevalence of SDP differed across the countries studied despite comparable levels of development. After 2015, the prevalence of SDP ranged between 4.2% in Sweden and 16.6% in France. It was associated with socio-economic factors. The prevalence of SDP slowly decreased over time, but this overall trend masked inequalities within populations. In Canada, France and the United States, the prevalence decreased more rapidly in women of higher socio-economic status, and inequalities in maternal smoking were more marked in these countries. In the other countries, inequalities tended to decrease but remained significant.

CONCLUSIONS

During pregnancy, that is a period described as a window of opportunity, smoking and social vulnerability factors need to be detected to implement targeted prevention strategies aiming at reducing related social inequalities.

Cigarette smoking during pregnancy and adverse perinatal outcomes: a cross-sectional study over 10 years

BACKGROUND

It has been shown that active exposure to tobacco is associated with adverse pregnancy outcomes including, but not limited to, intrauterine fetal death, reduced fetal weight, and higher risk of preterm birth. We want to investigate these effects in a high-income country.

METHODS

This cross-sectional study examined 20,843 pregnant women who delivered over 10 years at the Maternity Hospital of the Centre Hospitalier Universitaire Vaudois (CHUV) in Lausanne, Switzerland. The objective was to evaluate a dose-response relationship between daily cigarette use during pregnancy and possible adverse perinatal outcomes. The social and clinical characteristics as well as obstetric and neonatal outcomes were compared between the smoking and the non-smoking groups. Adjusted odds ratios (aOR) and trend analyses (p_trend) were calculated.

RESULTS

Nineteen thousand five hundred fifty-four pregnant women met the inclusion criteria and 2,714 (13.9%) of them were smokers. Even after adjusting for confounding factors, smoking during pregnancy was associated with preterm birth, birthweight < 2500 g, intrauterine growth restriction, neonatal respiratory and gastrointestinal diseases, transfer to the neonatal intensive care unit, and neonatal intensive care unit admissions > 7 days. Intrauterine death and neonatal infection were associated with heavy smoking (≥ 20 cigarettes/day). Smoking appeared to be a protective factor for pre-eclampsia and umbilical cord arterial pH below 7.1. A significant trend (p_trend < 0.05) was identified for preterm birth, intrauterine growth restriction, birthweight < 2500 g, umbilical cord arterial pH below 7.1, transfers to our neonatal intensive care unit, and neonatal intensive care unit admissions more than 7 days.

CONCLUSION

Cigarette smoking is associated with several adverse perinatal outcomes of pregnancy with a dose-dependent effect.

Use of smoking cessation pharmacotherapies during pregnancy is not associated with increased risk of adverse pregnancy outcomes: a population-based cohort study

BACKGROUND

Varenicline, bupropion and nicotine replacement therapy (NRT) are three effective pharmacotherapies for smoking cessation, but data about their safety in pregnancy are limited. We assessed the risk of adverse perinatal outcomes and major congenital anomalies associated with the use of these therapies in pregnancy in Australia.

METHODS

Perinatal data for 1,017,731 deliveries (2004 to 2012) in New South Wales and Western Australia were linked to pharmaceutical dispensing, hospital admission and death records. We identified 97,875 women who smoked during pregnancy; of those, 233, 330 and 1057 were exposed to bupropion, NRT and varenicline in pregnancy, respectively. Propensity scores were used to match exposed women to those who were unexposed to any smoking therapy (1:10 ratio). Propensity scores and gestational age at exposure were used to match varenicline-exposed to NRT-exposed women (1:1 ratio). Time-dependent Cox proportional hazards models estimated hazard ratios (HR) with 95% confidence intervals (95% CI) for any adverse perinatal event (a composite of 10 unfavourable maternal and neonatal outcomes) and any major congenital anomaly.

RESULTS

The risk of any adverse perinatal event was not significantly different between bupropion-exposed and unexposed women (39.2% versus 39.3%, HR 0.93, 95% CI 0.73-1.19) and between NRT-exposed and unexposed women (44.8% vs 46.3%, HR 1.02, 95% CI 0.84-1.23), but it was significantly lower in women exposed to varenicline (36.9% vs 40.1%, HR 0.86, 95% CI 0.77-0.97). Varenicline-exposed infants were less likely than unexposed infants to be born premature (6.5% vs 8.9%, HR 0.72, 95% CI 0.56-0.92), be small for gestational age (11.4% vs 15.4%, HR 0.68, 95% CI 0.56-0.83) and have severe neonatal complications (6.6% vs 8.2%, HR 0.74, 95% CI 0.57-0.96). Among infants exposed to varenicline in the first trimester, 2.9% had a major congenital anomaly (3.5% in unexposed infants, HR 0.91, 95% CI 0.72-1.15). Varenicline-exposed women were less likely than NRT-exposed women to have an adverse perinatal event (38.7% vs 51.4%, HR 0.58, 95% CI 0.33-1.05).

CONCLUSIONS

Pregnancy exposure to smoking cessation pharmacotherapies does not appear to be associated with an increased risk of adverse birth outcomes. Lower risk of adverse birth outcomes in varenicline-exposed pregnancies is inconsistent with recommendations that NRT be used in preference to varenicline.

Trajectories of antipsychotic use before and during pregnancy and associated maternal and birth characteristics

OBJECTIVE

To identify distinct trajectories of antipsychotic use prior to and during pregnancy and describe the associated maternal and birth characteristics.

METHODS

We conducted a population-based cohort study of births (2005-2012) using linked administrative data in New South Wales, Australia. We used group-based trajectory modelling to classify trajectories of antipsychotic use in the 450 days prior to pregnancy and during pregnancy. We characterised women with different trajectories according to maternal sociodemographic characteristics, mental health diagnoses and hospitalisations, use of psychotropic medicines and birth outcomes.

RESULTS

Of 137,993 women who gave birth, 2741 (2.0%) were exposed to antipsychotics prior to or during pregnancy. We identified six trajectories of antipsychotic use: two involved short-term use of low daily doses prior to pregnancy (51.1%), while three involved long-term use of low (20.9%), moderate (11.0%) and high (2.0%) daily doses throughout pregnancy. One trajectory (15.0%) involved increasing use during pregnancy. Women with long-term use were more likely to have a schizophrenia or bipolar disorder diagnosis, to have used multiple psychotropics and to have a mental health hospitalisation during pregnancy. Overall, women using antipsychotics had elevated rates of adverse birth outcomes compared to unexposed women. Women with the greatest antipsychotic exposure had the highest rates of gestational diabetes and gestational hypertension.

CONCLUSION

Women using antipsychotics around pregnancy are heterogeneous, with varying patterns of use and associated birth outcomes, reflecting underlying differences in the indications for treatment and/or severity of illness. This diversity should be considered when developing clinical guidelines and designing safety studies.

Utilisation of teratogenic medicines before and during pregnancy in Australian women

BACKGROUND

Given the potential hazards of teratogenic medicines, to a fetus exposed in utero, monitoring their use around pregnancy is imperative.

AIM

To measure utilisation of teratogenic medicines (Therapeutic Goods Administration's category D or X) in women who gave birth in New South Wales, Australia, during pregnancy and the 24 months prior.

MATERIALS AND METHODS

We used linked population-based datasets including dispensing and perinatal data for all deliveries in NSW between 2005 and 2012. We included pregnancies among concessional beneficiaries only, with complete ascertainment of dispensing claims. Pre-pregnancy and during-pregnancy periods were based on birth dates and gestational age. We determined prevalence of exposure using percent of pregnancies in which women had at least one dispensed teratogenic medicine in three-month time periods.

RESULTS

The study included 191 588 pregnancies (145 419 women). Prevalence of exposure to D/X medicines anytime during pregnancy was 2.0% (<20 pregnancies category X), decreasing from pre-pregnancy (3.8-6.0%) to first trimester (1.5%), further decreasing in second and third trimesters (0.8% and 0.6% respectively). We observed large reductions in antibiotic prevalence but only modest reductions for psychotropics and antilipidemic agents (all category D). Our results suggest higher use of potentially teratogenic medicines (category D) than those strictly contraindicated for use (category X), during pregnancy. Overall, use was higher in the first trimester than the rest of pregnancy. The high prevalence of potentially contraindicated psychotropics in all three trimesters may suggest a higher benefit-to-risk ratio and warrants future research focusing on the reasons for their prescribing to pregnant women.

Prevalence and safety of acamprosate use in pregnant alcohol-dependent women in New South Wales, Australia

AIMS

To estimate the prevalence of exposure to acamprosate in pregnancy in New South Wales (NSW), Australia, to compare the maternal health of women exposed to acamprosate during pregnancy with non-exposed women, and to compare neonatal outcomes in neonates exposed to acamprosate in utero with non-exposed neonates.

DESIGN

A population-based retrospective cohort study, comparing maternal and neonatal health outcomes in women exposed to acamprosate during pregnancy with women with a recent history of problematic alcohol use (alcohol comparison group), and women from the general community (community comparison group) using state-wide linked health data.

SETTING

New South Wales, Australia.

PARTICIPANTS

The study included women treated with acamprosate for more than 30 days during pregnancy between 2003 and 2012 (n = 54) and two matched comparison groups (1 : 3); an alcohol comparison group (n = 162) and a community comparison group (n = 162).

MEASUREMENTS

The prevalence of acamprosate exposure was calculated per 100 000 pregnancies. Three primary measures of maternal and neonatal health were used: maternal hospital admissions, birth weight and fetal alcohol syndrome (FAS).

FINDINGS

Exposure to acamprosate occurred in 7.7 [95% confidence interval (CI) = 6.0-9.7] in every 100 000 pregnancies. Rates of hospital admissions during pregnancy and 42 days post-partum in acamprosate-treated women were not significantly different from women in the community comparison group [adjusted rate ratio (RR) = 0.85, 95% CI = 0.65-1.11], but were significantly lower compared with the alcohol comparison group (adjusted RR = 1.26, 95% CI = 1.00-1.60). Acamprosate-exposed neonates were not significantly different from the alcohol comparison group or the community comparison group in terms of birth weight or proportion of small-for-gestational-age neonates or incidence of congenital abnormalities (including FAS).

CONCLUSIONS

The prevalence of acamprosate use in pregnancy in New South Wales, Australia is low. Acamprosate exposure in utero is not clearly associated with poor maternal or neonatal health outcomes.

Maternal and perinatal outcomes associated with the use of renin-angiotensin system (RAS) blockers for chronic hypertension in early pregnancy

OBJECTIVE

Previous research reported greater risk of adverse perinatal outcomes associated with first trimester exposure to angiotensin converting enzyme inhibitors (ACEIs) in comparison to unexposed pregnancies among non-hypertensive women. We examined the relationship between first trimester exposure to ACEIs and angiotensin receptor blockers (ARBs), and maternal and perinatal outcomes, whilst controlling for the underlying hypertension.

STUDY DESIGN

We performed a population-based cohort study among 130,061 pregnancies resulting in birth in NSW, Australia between 2005 and 2012. Birth data were linked to hospital discharge and pharmaceutical dispensing records. After restricting to women with chronic hypertension, 67 and 73 pregnancies exposed to ACEIs and ARBs respectively during the first trimester were compared with 316 pregnancies exposed to methyldopa.

STUDY OUTCOMES

Preterm delivery, caesarean section, low birth weight, small for gestational age and Apgar score <7.

RESULTS

Compared to pregnancies exposed to methyldopa, the adjusted odds ratio (aOR) for ACEI exposure was 0.5 (95% CI: 0.2-1.1) for preterm delivery, 1.6 (0.8-3.1) for caesarean section, 0.6 (0.2-1.3) for LBW and 0.8 (0.4-1.9) for SGA. The corresponding aORs and confidence intervals for ARB exposure were 0.7 (0.3-1.5), 1.2 (0.6-2.6), 1.3 (0.7-2.6), and 1.2 (0.6-2.4).

CONCLUSION

No association between early pregnancy exposure to ACEIs and ARBs and perinatal outcomes was observed, however, the possibility of an association cannot be ruled out due to limited power. Nonetheless, this study suggests that the magnitude of risk is smaller than that reported previously.

Algorithm for resolving discrepancies between claims for smoking cessation pharmacotherapies during pregnancy and smoking status in delivery records: The impact on estimates of utilisation

BACKGROUND

The linkage of routine data collections are valuable for population-based evaluation of smoking cessation pharmacotherapy in pregnancy where little is known about the utilisation or safety of these pharmacotherapies antenatally. The use of routine data collections to study smoking cessation pharmacotherapy is limited by disparities among data sources. This study developed an algorithm to resolve disparity between the evidence of pharmacotherapy utilisation for smoking cessation and the recording of smoking in pregnancy, examined its face validity and assessed the implications on estimates of smoking cessation pharmacotherapy utilisation.

METHODS

Perinatal records (n = 1,098,203) of women who gave birth in the Australian States of Western Australia and New South Wales (2004-2012) were linked to hospital admissions and pharmaceutical dispensing data. An algorithm, based on dispensing information about the type of smoking therapy, timing and quantity of supply reclassified certain groups of women as smoking during pregnancy. Face validity of the algorithm was tested by examining the distribution of factors associated with inaccurate recording of smoking status among women that the algorithm classified as misreporting smoking in pregnancy. Rate of utilisation among smokers, according to original and reclassified smoking status, was measured, to demonstrate the utility of the algorithm.

RESULTS

Smoking cessation pharmacotherapy were dispensed to 2184 women during pregnancy, of those 1013 women were originally recorded as non-smoking as per perinatal and hospital data. Application of the algorithm reclassified 730 women as smoking during pregnancy. The algorithm satisfied the test of face validity-the expected demographic factors of marriage, private hospital delivery and higher socioeconomic status, were more common in women whom the algorithm identified as misreporting their smoking status. Application of the algorithm resulted in smoking cessation pharmacotherapy utilisation estimates ranging from 2.3-3.6% of all pregnancies.

CONCLUSION

Researchers can use the algorithm presented herein to improve the identification of smoking among women who use cessation pharmacotherapies during pregnancy. Improved identification can improve the validity of safety analyses of smoking cessation pharmacotherapy-providing clinicians with valuable evidence to use when counselling women on the role of pharmacotherapy for smoking cessation during pregnancy.

Neonatal Morbidity at Term, Early Child Development, and School Performance: A Population Study

OBJECTIVES

Investigate the association between severe neonatal morbidity (SNM) and child development and school performance among term infants.

METHODS

The study population included term infants without major congenital conditions born between 2000 and 2007 in New South Wales, Australia, with a linked record of developmental assessment at ages 4 to 6 years in 2009 or 2012 (n = 144 535) or school performance at ages 7 to 9 years from 2009 to 2014 (n = 253 447). Developmental outcomes included special needs or being vulnerable and/or at risk in 1 of 5 developmental domains. School performance outcomes were test exemption, or performing <-1 SD on reading or numeracy tests. Binary generalized estimating equations were used to estimate associations between SNM and outcomes, adjusting for sociodemographic, perinatal, and assessment and/or test characteristics.

RESULTS

Overall, 2.1% of infants experienced SNM. The adjusted odds ratio (95% confidence interval) for SNM and physical health was 1.18 (1.08-1.29), 1.14 (1.02-1.26) for language and cognitive skills, and 1.14 (1.06-1.24) and 1.13 (1.05-1.21) for scoring <-1 SD in reading and numeracy, respectively. SNM was most strongly associated with special needs 1.34 (1.15-1.55) and test exemption 1.50 (1.25-1.81). SNM infants born at 37 to 38 weeks' gestation and who were small for gestational age had the greatest likelihood of poorer outcomes.

CONCLUSIONS

Term infants with SNM have greater odds of poor neurodevelopment in childhood. These findings provide population-based information for families and can inform clinical counseling and guidelines for follow-up and early intervention.

Tobacco policy reform and population-wide antismoking activities in Australia: the impact on smoking during pregnancy

Introduction

This study examined the impact of antismoking activities targeting the general population and an advertising campaign targeting smoking during pregnancy on the prevalence of smoking during pregnancy in New South Wales (NSW), Australia.

Methods

Monthly prevalence of smoking during pregnancy was calculated using linked health records for all pregnancies resulting in a birth (800 619) in NSW from 2003 to 2011. Segmented regression of interrupted time series data assessed the effects of the extension of the ban on smoking in enclosed public places to include licensed premises (evaluated in combination with the mandating of graphic warnings on cigarette packs), television advertisements targeting smoking in the general population, print and online magazine advertisements targeting smoking during pregnancy and increased tobacco tax. Analyses were conducted for all pregnancies, and for the population stratified by maternal age, parity and socioeconomic status. Further analyses adjusted for the effect of the Baby Bonus maternity payment.

Results

Prevalence of smoking during pregnancy decreased from 2003 to 2011 overall (0.39% per month), and for all strata examined. For pregnancies overall, none of the evaluated initiatives was associated with a change in the trend of smoking during pregnancy. Significant changes associated with increased tobacco tax and the extension of the smoking ban (in combination with graphic warnings) were found in some strata.

Conclusions

The declining prevalence of smoking during pregnancy between 2003 and 2011, while encouraging, does not appear to be directly related to general population antismoking activities or a pregnancy-specific campaign undertaken in this period.

Gestational age, mode of birth and breastmilk feeding all influence acute early childhood gastroenteritis: a record-linkage cohort study

Background

Acute gastroenteritis (AGE) is a leading cause of infectious morbidity in childhood. Clinical studies have implicated caesarean section, early birth and formula feeding in modifying normal gut microbiota development and immune system homeostasis in early life. Rates of early birth and cesarean delivery are also increasing worldwide. This study aimed to investigate the independent and combined associations of the mode and timing of birth and breastmilk feeding with AGE hospitalisations in early childhood.

Methods

Population-based record-linkage study of 893,360 singleton livebirths of at least 33 weeks gestation without major congenital conditions born in hospital, New South Wales, Australia, 2001–2011. Using age at first AGE hospital admission, Cox-regression was used to estimate the associations for gestational age, vaginal birth or caesarean delivery by labour onset and formula-only feeding while adjusting for confounders.

Results

There were 41,274 (4.6 %) children admitted to hospital at least once for AGE and the median age at first admission was 1.4 years. Risk of AGE admission increased with decreasing gestational age (37–38 weeks: 15 % increased risk, 33–36 weeks: 25 %), caesarean section (20 %), planned birth (17 %) and formula-only feeding (18 %). The rate of AGE admission was highest for children who were born preterm by modes of birth other than vaginal birth following the spontaneous onset of labour and who received formula-only at discharge from birth care (62–78 %).

Conclusions

Vaginal birth following spontaneous onset of labour at 39+ weeks gestation with any breastfeeding minimised the risk of gastroenteritis hospitalisation in early childhood. Given increasing trends in early planned birth and caesarean section worldwide, these results provide important information about the impact obstetric interventions may have on the development of the infant gut microbiota and immunity.

Electronic supplementary material

The online version of this article (doi:10.1186/s12887-016-0591-0) contains supplementary material, which is available to authorized users.

Preterm birth and future risk of maternal cardiovascular disease - is the association independent of smoking during pregnancy?

BACKGROUND

While the association of preterm birth and the risk of maternal cardiovascular disease (CVD) has been well-documented, most studies were limited by the inability to account for smoking during pregnancy - an important risk factor for both preterm birth and CVD. This study aimed to determine whether the increased future risk of maternal cardiovascular disease (CVD) associated with preterm birth is independent of maternal smoking during pregnancy.

METHODS

A population-based record linkage study of 797,056 women who delivered a singleton infant between 1994 and 2011 in New South Wales, Australia was conducted. Birth records were linked to the mothers' subsequent hospitaliation or death from CVD. Preterm births were categorised as late (35-36 weeks), moderate (33-34 weeks), or extreme (≤32 weeks); and as spontaneous or indicated. Cox proportional hazard regression was used to estimate adjusted hazard ratios (AHR) [95 % CI].

RESULTS

During the study period, 59,563 women (7.5 %) had at least one preterm birth. After adjustment for CVD risk factors other than smoking, AHR [95 % CI] of CVD among women who ever had a preterm birth was 1.78 [1.61-1.96]. Associations were greater for extreme (AHR = 1.98 [1.63-2.42]) and moderate (AHR = 2.06 [1.69-2.51]) than late preterm birth (AHR = 1.63 [1.44-1.85]), for indicated (AHR = 2.04 [1.75-2.38]) than spontaneous preterm birth (AHR = 1.65 [1.47-1.86]), and for having ≥ two (AHR = 2.29[1.75-2.99]) than having one preterm birth (AHR = 1.73[1.57-1.92]). A further adjustment for maternal smoking attenuated, but did not eliminate, the associations. Smoking during pregnancy was also independently associated with maternal CVD risks, with associations being stronger for mothers who smoked during last pregnancy (AHR = 2.07 [1.93-2.23]) than mothers who smoked during a prior pregnancy (AHR = 1.64 [1.41-1.90]).

CONCLUSIONS

Associations of preterm birth and maternal CVD risk are independent of maternal smoking during pregnancy. This underscores the importance of smoking cessation in reducing CVD and suggests that a history of preterm delivery (especially if severe, indicated or recurrent) identifies women who could be targeted for CVD screening and preventative therapies.