Study Explores Factors Linked to Uncomplicated Pregnancy

Steven Fox

November 27, 2013

Individually targeted lifestyle changes may increase the likelihood nulliparous women will have normal pregnancies, according to results from a large, newly published cohort study. The changes identified include normalizing maternal weight, increasing consumption of fruits before pregnancy, reducing blood pressure, and avoiding use of drugs.

Lucy C. Chappell, PhD, clinical senior lecturer in maternal and fetal medicine, Division of Women's Health, Women's Health Academic Centre, King's College London and King's Health Partners, United Kingdom, and colleagues, published their study in November current issue of BMJ.

"Previous literature has focused on the association between risk factors and subsequent adverse pregnancy outcomes," Dr. Chappell and colleagues write. "Little is known of factors associated with subsequent healthy pregnancies."

Therefore, the researchers designed a prospective international multicentre observational cohort study called Screening for Pregnancy Endpoints (SCOPE). They enrolled 5628 healthy nulliparous women with singleton pregnancies who lived in New Zealand, Australia, the United Kingdom, and Ireland. All pregnancies took place between 2004 and 2008.

"We aimed to identify, replicate, and confirm variables at 15 and 20 weeks' gestation associated with a subsequent uncomplicated pregnancy, and to highlight those factors amenable to modification before pregnancy, to inform interventions that could increase the likelihood of a normal outcome," the authors write.

They collected comprehensive data from each patient, including socioeconomic status; obstetric, gynecological, and medical history; family history of obstetric complications and medical conditions; early pregnancy complications; dietary information, both before conception and during pregnancy; information on use of therapeutic and recreational drugs, including cigarettes and alcohol; and details of birth.

In addition, the women underwent comprehensive physical exams and completed a lifestyle questionnaire that asked about work, exercise, domestic violence, social support, and psychological issues.

The researchers' primary outcome measure was uncomplicated pregnancy, defined as a normotensive pregnancy, with a normal-weight fetus delivered without complications at more than 37 weeks' gestation.

The researchers used a stepwise logistic regression analysis to compare women with normal pregnancies with women who experienced complications during pregnancy.

Overall, 3452 women (61.3%) had an uncomplicated pregnancy. Factors associated with reduced likelihood for uncomplicated pregnancies were:

  • increased body mass index (relative risk [RR], 0.74; 95% confidence interval [CI], 0.65 - 0.84),

  • misuse of drugs during the first trimester (RR, 0.90; 95% CI, 0.84 - 0.97),

  • mean diastolic blood pressure (for each 5 mm Hg increase: RR, 0.92; 95% CI, 0.91 - 0.94), and

  • mean systolic blood pressure (for each 5 mm Hg increase: RR, 0.95; 95% CI, 0.94 - 0.96).

In contrast, the researchers found that women who consumed fruit at least 3 times daily before their pregnancies were more likely to have an uncomplicated pregnancy than those who consumed less fruit (RR, 1.09; 95% CI, 1.01 - 1.18). Another beneficial factor was being employed (per 8 hours' increase: RR, 1.02; 95% CI, 1.01 - 1.04).

The investigators also identified detrimental factors that were not amenable to change. Those included a history of hypertension while using oral contraceptives, low socioeconomic status, a family history of hypertensive complications or vaginal bleeding during pregnancy, and an increase in uterine artery resistance index.

Part of the data indicated that smoking might be a detrimental factor, but that association was not borne out in the final analysis.

"To our knowledge this is the first study to comprehensively investigate and identify factors present early in pregnancy that are associated with an uncomplicated outcome," the authors write.

"Identification of these factors could inform development of interventions to increase normal pregnancy outcomes," they conclude.

In an accompanying editorial, Marian Knight, MBChB, MPH, Dphil, FFPH, National Institute for Health Research professor in public health, National Perinatal Epidemiology Unit, Nuffield Department of Public Health, University of Oxford, United Kingdom, praises the study. "This robust approach is welcome in the context of initiatives to step back from the medicalisation of pregnancy and provides useful information for women, clinicians, and policy makers."

She adds, "As Chappell and colleagues note, the most important next step is to replicate their approach, shift the focus of research from abnormality to normality, obtain clear evidence of causality, and start to build a robust evidence base to guide population interventions."

This study was funded by New Enterprise Research Fund, Foundation for Research Science and Technology; Health Research Council; Evelyn Bond Fund, Auckland District Health Board Charitable Trust; Premier's Science and Research Fund, South Australian Government; Guy's and St Thomas' Charity, Tommy's Charity; UK National Health Services, University of Manchester Proof of Concept Funding, National Institute for Health Research; Health Research Board, Ireland. One of the coauthors is supported by an Action Medical research endowment fund and Manchester Biomedical Research Centre. Full conflict-of-interest information is available from the corresponding author. Dr. Knight declares that her institution has received money to fund studies on pregnancy complications from various noncommercial grant-giving bodies and that some of this funding has formed part of her salary.

BMJ. 2013;347:f16398, f16470. Article full text, Editorial full text

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