Sarah Lee Research Midwife

Central Manchester University Hospitals NHS Foundation Trust

Master of Clinical Research

School of Nursing, Midwifery and Social Work

The University of Manchester

A PROSPECTIVE COHORT STUDY OF THE ASSOCIATION

BETWEEN VIGOROUS EXERCISE DURING PREGNANCY

AND PREGNANCY OUTCOME

NHS guidelines recommend that adults should undertake 150 minutes of moderate intensity aerobic activity every week (NHS, 2013)

The Royal College of Obstetricians and Gynaecologists recommend that pregnant women should participate in four aerobic exercise sessions per week lasting at least 30 minutes each (RCOG, 2006)

A Cochrane review from 2010 reported the impact of prolonged and repeated aerobic exercise on clinical outcomes for mother and infant are still unknown (Kramer and McDonald, 2010)

Introduction

The broad aim of the literature search was to examine the evidence for undertaking recreational exercise whilst pregnant

The PICO framework was used to frame and answer the clinical question (Schardt et al., 2007)

Patient = pregnant women

Intervention = recreational exercise in pregnancy

Comparison = no exercise in pregnancy

Outcome = all relevant clinical outcomes of pregnancy

“Do pregnant women who carry out recreational exercise in pregnancy have different clinical outcomes than those who

do not carry out recreational exercise?”

Literature Review

An online search was undertaken in September 2011 and repeated in September 2013

Seventeen papers reporting primary research studies and two systematic reviews formed the basis of the literature review

Four themes emerged concerning exercise in pregnancy and pregnancy outcome

1. Effect of exercise on mode of birth

2. Effect of exercise on birth weight

3. Effect of exercise on gestation at birth

4. Effect of exercise on length of labour

Literature Review

Findings were mixed with all studies having faults in their design

One small study showed that exercise increases the chance of a spontaneous vaginal birth when compared with instrumental birth

One study found women who exercise have a non-significant increased chance of a vaginal birth (unassisted or assisted)

Two studies established that exercise does not affect mode of birth

Exercise and mode of birth

There is conflicting evidence regarding exercise in pregnancy and birth weight

The latest Cochrane review (Kramer and McDonald, 2010) shows that exercise has no impact on birth weight

Other studies demonstrate that women who exercise:

– are less likely to have an LGA infant

– are protected against LBW infants

Exercise and birth weight

Exercise may influence all of these outcomes

Data are inconsistent and conflicting

The main gaps in current knowledge are how exercise in pregnancy affects

– mode of birth

– birth weight.

Summary of findings

The study aimed to investigate the relationship between vigorous exercise during the first 21 weeks of pregnancy and its effect on

– mode of birth

– birth weight

– onset of labour

– length of labour

The hypothesis was that women undertaking vigorous exercise in the first 21 weeks of pregnancy had an increased chance of a spontaneous vaginal birth at term

Research Question

Data for this study were collected as part of the SCOPE study from 2004 to 2012

– A prospective, international multicentre cohort study of healthy nulliparous women with a singleton pregnancy

– Participants completed a lifestyle questionnaire at two time points in their pregnancy to provide data on vigorous exercise

Secondary analysis of data from SCOPE to examine the influence of exercise on pregnancy outcome

3376 women with uncomplicated pregnancies were extracted from the SCOPE dataset for this study

A quantitative approach to analysis was used

Methods

Vigorous exercise question in the SCOPE lifestyle questionnaire

How often have you engaged in vigorous exercise in the last month? (exercise which made you breathe harder or puff or pant such as tennis, jogging, aerobics, heavy gardening, rollerblading, skiing, rowing, rowing/cycling machine)

1 - Never 2 - Once a week 3 - 2-3 time each week

4 - 4-6 times per week 5 - Daily 6 - More than once a day

The Lifestyle Questionnaire

Closed questions answered by participants in the lifestyle questionnaires were converted into numerical answers for statistical analysis using IBM SPSS 20

Main analysis involved the estimation of associations between vigorous exercise and clinical outcomes of pregnancy, adjusted for the presence of other potentially confounding factors

A statistical significance level of p ≤ 0.05 was used for all tests performed

Analysis

• Pregnancy weeks 11-15

– 2175 (64.4%) never exercised

– 1105 (32.7%) exercised 1-3 times per week

– 96 (2.8%) exercised 4+ times per week

• Pregnancy weeks 16-20

– 2012 (61.9%) never exercised

– 812 (25.0%) exercised 1-3 times per week

– 426 (13.1%) exercised 4+ times per week

Prevalence of Exercise in Pregnancy

Engaged in vigorous

exercise between 11-15

weeks

Whole

cohort

Statistical

Analysis

Never 1-3 times

per week

≥ 4 times

per week

Sample size (N) 2175

(64.4%)

1105

(32.7%)

96 (2.8%) 3376

Mode of

birth Spontaneous

vaginal birth

973

(44.8%)

543

(49.1%)

51

(53.1%)

1567

(46.4%)

X2 = 11.67

df = 6

p=0.070

Operative

vaginal

Birth

641

(29.5%)

275

(24.9%)

27

(28.1%)

943

(27.9%)

Pre-labour

Caesarean

152

(7.0%)

83

(7.5%)

5

(5.2%)

240

(7.1%)

Caesarean in

Labour

408

(18.8%)

204

(18.5%)

13

(13.5%)

625

(18.5%)

Mode of Birth

Engaged in vigorous

exercise between 16-20

weeks

Whole

Cohort

Statistical

Analysis

Never 1-3 times

per week

≥ 4 times

per week

Sample Size (N) 2012

(61.9%)

812

(25.0%)

426

(13.1%)

3250

Mode of

birth

Spontaneous

vaginal birth

891

(44.3%)

418

(51.5%)

201

(47.2%)

1510

(46.5%)

X2 = 14.64

df=6

p=0.023 Operative

Vaginal

594

(29.5%)

202

(24.9%)

112

(26.3%)

908

(27.9%)

Pre-labour

Caesarean

137

(6.8%)

59

(7.3%)

29

(6.8%)

225

(6.9%)

Caesarean in

labour

389

(19.3%)

133

(16.4%)

84

(19.7%)

606

(18.7%)

Mode of Birth

A Significant Result!

Mode of Birth Statistical

Analysis

SVD Operative

vaginal

birth

Prelabour

LSCS

LSCS in

labour

Whole

Cohort

Sample size (N) 1567 943 240 625 3375

Engaged in

vigorous

exercise at

15 weeks

Never 973

(44.8%)

641

(29.5%)

152

(7.0%)

408

(18.8%)

2174

(100%)

Pearson X2=9.22

df = 3

p=0.026 ≥ 1 per

week

594

(49.5%)

302

(25.1%)

88

(7.3%)

217

(18.1%)

1201

(100%)

Engaged in

vigorous

exercise at

20 weeks

Never 891

(44.3%)

594

(29.5%)

137

(6.8%)

389

(19.3%)

2011

(100%)

Pearson X2=11.57

df = 3

p=0.009 ≥ 1 per

week

619

(50.0%)

314

(25.4%)

88

(7.1%)

217

(17.5%)

1238

(100%)

very similar results and both statistically significant

Mode of Birth

Bivariable analyses demonstrated that women who performed vigorous exercise in weeks 11-15 or 16-20 of pregnancy were more likely to have a spontaneous vaginal birth compared with an operative vaginal birth or caesarean section in labour

Multivariable analyses confirmed that any vigorous exercise in weeks 11-20 was associated with spontaneous vaginal birth

Study findings: Mode of Birth

Engaged in vigorous exercise

between 11-15 weeks

Whole

cohort

Statistical

Analysis

Never 1-3 times

per week

≥ 4 times

per week

Sample Size (N) 2175

(64.4%)

1105

(32.7%)

96

(2.8%)

3376

Birth weight

(grams)

Mean birth

weight

(SD)

3581g

(400.19)

3624g

(392.75)

3524g

(409.98)

3593.46

(398.60)

F = 5.670

df = 2 and 3373

p=0.003 95%

confidence

Interval

3564.35

to

3598.01

3600.48 to

3646.84

3441.01

to

3607.24

3580.01

to

3606.91

Range 2546 to

5110

2600 to

4940

2645 to

4990

2646 to

5110

Birth weight

A Significant Result!

Engaged in vigorous exercise

between 16-20 weeks

Whole

Cohort

Statistical

Analysis

Never 1-3 times

per week

≥ 4 times

per week

Sample Size (N) 2012

(61.9%)

812

(25.0%)

426

(13.1%)

3250

Birth weight

(grams)

Mean birth

weight

(SD)

3586g

(401.39)

3607g

(405.02)

3580g

(361.26)

3590.56

(397.29)

F = 0.985,

df = 2 and

1083.302

p=0.374 95%

confidence

interval

3568.46

to

3603.56

3579.31 to

3635.11

3545.90 to

3614.70

3576.89

to

3601.22

Range 2546 to

5060

2600 to

5110

2605 to

4635

2546 to

5110

Birth weight

Difference in

birth weight

p-value 95% confidence interval for

birth weight

Lower bound Upper bound

Vigorous

exercise at 15

weeks

33g p=0.021 5.036 60.852

Vigorous

exercise at 20

weeks

13g p=0.352 -14.639 41.108

BMI at 15 weeks 17g <0.001 13.72 19.906

Age of participant -1.7g 0.252 -4.783 1.253

Smoking status at

15 weeks

-118g <0.001 -165.649 -69.589

Birth weight

Bivariable analyses demonstrated that in pregnancy weeks 11-15 exercise was associated with a slight increase in birth weight

– Women who vigorously exercised 1-3 times per week during weeks 11-15 were more likely to give birth to heavier infants than those who did not exercise at all

– Women who vigorously exercised four or more times per week had the lightest infants

– Difference in mean birth weight was only 100g

Multivariable analyses confirmed any vigorous exercise in weeks 11-15 was associated with an increase in birth weight

Study findings: Birth weight

The results of this study suggest that vigorous exercise in low risk nulliparous women

– slightly, but significantly, increases the chance of a normal vaginal birth

– slightly, but significantly, increases birth weight

The result of this study supports the current guidance advocating that women continue to exercise in pregnancy

Conclusion

Supervisors

Dr Tracey Mills and Dr Malcolm Campbell

The women who participated in the SCOPE study, the research midwives and the SCOPE consortium for allowing me access to this data

Any Questions?

Acknowledgements