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Obstetrics & Gynecology:
doi: 10.1097/AOG.0b013e3181a66f40
Original Research

Effect of Antenatal Pelvic Floor Muscle Training on Labor and Birth

Bø, Kari PhD, PT1; Fleten, Caroline MS2; Nystad, Wenche PhD2

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Author Information

From the 1Norwegian School of Sport Sciences, Department of Sports Medicine, Oslo, Norway; and the 2Norwegian Institute of Public Health, Division of Epidemiology, Oslo, Norway.

Supported by the Norwegian Ministry of Health, NIH/NIEHS (grant no. N01 -ES–85433), NIH/NINDS (grant no. 1 UO1 NS 047537-01), and Norwegian Research Council/FUGE (grant no. 151918/S10).

The authors thank the Norwegian Mother and Child Cohort Study participants for donating their questionnaire data and biologic material. The authors also thank Dr. Ingrid Nygaard, Consultant Urogynecologist, University of Utah, Department of Gynecology, for English revision of the manuscript.

Corresponding author: Kari Bø, Norwegian School of Sport Sciences, Department of Sports Medicine, PO Box 4014, Ullevól Stadion, 0806 Oslo, Norway; e-mail: kari.bo@nih.no.

Financial Disclosure The authors did not report any potential conflicts of interest.

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Abstract

OBJECTIVE: To estimate whether women doing pelvic floor muscle training before and during pregnancy have increased risk of perineal lacerations, episiotomy, vacuum/forceps delivery, or acute cesarean delivery.

METHODS: Participants were 18,865 primiparous women in the Norwegian Mother and Child Cohort Study, conducted by the Norwegian Institute of Public Health. Data were collected by self-completed questionnaires at gestational weeks 17 and 30 and analyzed by logistic regression analysis. Data about obstetric outcomes were obtained from the Medical Birth Registry of Norway. Pelvic floor muscle training was categorized as less than once per week, one to two times per week, and at least three times per week both before and during pregnancy. The results are presented as adjusted odds ratios (OR) with 95% confidence intervals (CIs).

RESULTS: Of women who performed pelvic floor muscle training less than once per week, 7.2% sustained a third-degree or fourth-degree laceration compared with 6.3% of women who performed pelvic floor muscle training at least three times per week. A similar pattern was present for rates of episiotomy (29.1% compared with 24.9%), vacuum/forceps delivery (15.9% compared with 15.0%), and acute cesarean delivery (9.5% compared with 7.5%). Adjusting for factors that might be associated with pelvic floor muscle training and the outcomes under study did not distort the effect of pelvic floor muscle training. Exercising at least three times per week was not associated with third-degree and fourth-degree perineal lacerations, episiotomy, vacuum/forceps delivery, or acute cesarean delivery (adjusted OR 0.86 [95% CI 0.60–1.24], 0.82 [0.67–1.01], 0.95 [0.74–1.22], and 0.75 [0.53–1.05], respectively).

CONCLUSION: Pelvic floor muscle training before and during pregnancy does not affect labor and birth outcomes or complication rates.

LEVEL OF EVIDENCE: II

A long time has elapsed since Kegel1 first recommended pelvic floor muscle training to prevent and treat pelvic floor dysfunctions such as urinary incontinence (UI) and pelvic organ prolapse in women after child birth. Since then, randomized controlled trials have shown that antenatal pelvic floor muscle training also can prevent and treat UI both during pregnancy and in the immediate postpartum period.2–4 However, only a small proportion of pregnant women actually exercise the pelvic floor muscle regularly.5 This may be because women lack knowledge and information about the possible positive effect of pelvic floor muscle training on UI.6 On the other hand, some health care providers claim that there is anecdotal evidence that elite athletes have rigid, inextensible pelvic floors that prolong the second stage of labor7 and that specific pelvic floor muscle training may make the pelvic floor muscle too strong and less elastic.8 Artal and Buckenmeyer9 concluded that the rationale of teaching pelvic floor exercises to avoid tears or episiotomies in labor never has been supported by scientific evidence.

Women participating in the Norwegian Mother and Child Birth Cohort Study10 respond to questions about antenatal pelvic floor muscle training and are linked to the Norwegian Birth Registry,11 thus providing a unique opportunity to assess a possible link between antenatal pelvic floor muscle training and birth complications in a large cohort. The aim of the present study was to estimate whether women doing pelvic floor muscle training before and during pregnancy have increased risk of first-degree and second-degree perineal lacerations, third-degree and fourth-degree perineal lacerations, episiotomy, vacuum and forceps delivery, and acute caesarean delivery.

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MATERIALS AND METHODS

This study is based on the Norwegian Mother and Child Cohort Study, conducted by the Norwegian Institute of Public Health.10 In brief, the Norwegian Mother and Child Cohort Study is a pregnancy cohort started in 1999 with the aim of including 100,000 pregnant women by 2008. The majority of all pregnant women in Norway are invited to participate, and the response rate is about 44%. However, the follow-up rate for questionnaire three is 92%. Pregnant women are recruited to the study through a mailed invitation in connection with a routine ultrasound examination offered to all pregnant women in Norway at 17–18 weeks of gestation (www.fhi.no/tema/morogbarn).

Participating women receive three questionnaires during pregnancy. In week 17, a questionnaire regarding general health issues covering the period before conception and the time up to week 17 (questionnaire 1) is filled out by the mother. In week 20, a food frequency questionnaire is received (questionnaire 2), and in week 30, another questionnaire (questionnaire 3) on general health is sent out. Additional questionnaires are administered when the child is 6 months (questionnaire 4), 18 months (questionnaire 5), and 3 years old (questionnaire 6).

Informed consent was obtained from each participant before the study, and the Regional Committee for Medical Research (S-95113) and the Norwegian Social Science Data Service (01/4325-69) approved the study.

The current study is based on version three of the quality-assured data files of the Norwegian Mother and Child Cohort Study, which includes 52,547 pregnancies in which the women have responded to the 17-week and 30-week questionnaires. Women were excluded (n=2,426 [4.6%]) because of missing information on the variables included in the regression analyses. Among these, 55 women had missing information on pelvic floor muscle training on all three exercise items. Furthermore, we excluded 327 pregnancies with unrealistic values for the central variables, 1,856 pregnancies with more than one fetus, 4,434 pregnancies with abnormal presentation at labor, 1,413 pregnancies in which elective caesarean delivery was performed, and 265 pregnancies in which the type of caesarean delivery performed was not stated. Only nulliparous women were included in the analyses, and thus, an additional 22,961 pregnancies were excluded. Consequently, the present analyses include 18,865 primiparous women who gave birth to singleton fetuses, enrolled between 2000 and 2005, answered questionnaires one and three, and who were registered both in the Norwegian Mother and Child Cohort Study and the Medical Birth Registry.

The questionnaires cover a variety of issues, with detailed questions on nutrition, health, pregnancy-related topics, socioeconomic status, and environmental, familial, and psychological factors before, during, and after pregnancy (www.fhi.no/morogbarn). In addition, women are asked how often they are exercising the pelvic floor muscles, which is the main exposure factor in the present study.

Pelvic floor muscle training was explained explicitly in the questionnaires as “training of the muscles surrounding the urethra, vagina, and rectum.” The question was identical in all questionnaires, and answering alternatives were never, less than once a week, one time per week, two times per week, and at least three times a week at both week 17 and 30 (the questionnaire at week 17 [questionnaire 1] also covered the 3 months before conception). Pelvic floor muscle exercise level was categorized as less than once a week, one to two times a week, and at least three times per week. In the statistical analyses, women were classified as exercising less than once a week (never), one to two times a week, and more than three times a week only if they had exercised with this frequency both before pregnancy and at weeks 17 and 30. Women were classified as “varied exercisers” if they had changed training frequency among the three response points.

The main outcomes (from the Norwegian Medical Birth Registry) were occurrence of first-degree and second-degree perineal laceration, third-degree and fourth-degree perineal laceration, episiotomy, use of instrumental delivery (forceps and vacuum combined), and acute cesarean delivery.11

The analyses were conducted in SPSS 14.0 (SPSS, Inc., Chicago, IL). We investigated the effect of pelvic floor muscle training on the different complications during labor by using logistic regression analyses. In the multiple regression analyses, we adjusted for potential confounders believed to be associated with the complications and with pelvic floor muscle training, namely maternal age, maternal prepregnancy body mass index (BMI), cohabitant status (defined as married/cohabitant or not), education (defined as years of education), smoking (smoker or nonsmoker), and abdominal muscle training. In addition, the analyses were rerun including birth weight as a confounder, defined as birth weight less than or more than 4,000 g, and with general physical activity before pregnancy, defined as the frequency of participation in the combination of any recreational activity. The results are presented in crude and adjusted odds ratios with 95% confidence intervals.

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RESULTS

Mean age of the study group was 27.7 years (range 14–45), and mean prepregnancy BMI was 23.8 (standard deviation ±4.2).

Table 1 shows the number of women who reported doing pelvic floor muscle training 3 months before conception, in the period before week 17, and in the period before week 30. Few women did pelvic floor muscle training before pregnancy, but this increased during pregnancy, with 36.4% reporting pelvic floor muscle training at least once a week before week 17 and 57.4% at least once a week before week 30.

Table 1
Table 1
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The number of women reporting exercise less than once per week, one to two times per week, and at least three times per week at all three response points combined and the number of participants who changed training frequency between the three response points (varied exercisers) are shown in Tables 2 and 3. The proportion of women in each subgroup of the maternal characteristics age, prepregnancy BMI, education, cohabitant status, and smoking status in week 17 was distributed equally according to the frequency of pelvic floor muscle training (data not shown). Most women in each subgroup performed a varied frequency of pelvic floor muscle training (ranging from 55–78%) followed by large proportions performing pelvic floor muscle training less than once per week (ranging from 18–40%) and small proportions performing pelvic floor muscle training once per week or more (ranging from 1 to 4.3%).

Table 2
Table 2
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Table 3
Table 3
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The percentage of women and crude and adjusted odds ratios, by level of pelvic floor muscle training, for the obstetric outcomes of interest are reported in Tables 2 and 3. Women doing pelvic floor muscle training weekly or three or more times per week were not more likely to have third-degree and fourth-degree perineal laceration, episiotomy, vacuum/forceps extraction, or acute cesarean delivery than were women who did not exercise these muscles.

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DISCUSSION

This cohort study on primiparous women showed that there was no association between regular pelvic floor muscle training before and during pregnancy and third-degree and fourth-degree perineal laceration, episiotomy, vacuum or forceps delivery, and acute caesarean delivery.

Strengths of the present study are the large, population-based cohort of pregnant women, which improves the ability to generalize the results to a larger group of women; we also have clinical information on different pregnancy and labor outcomes from the Medical Birth Registry of Norway. Limiting factors are a nonrandomized design and the lack of clinical data on participants’ abilities to perform a correct pelvic floor muscle contraction in addition to a lack of data on pelvic floor muscle strength. Several studies from different countries have shown that more than 30% of women initially may not be able to contract the pelvic floor muscle correctly12–15 because some confuse pelvic floor muscle training with exercises for outer pelvic muscles such as the gluteals, hip adductors, and abdominal muscles.12 Hence, to mitigate possible misinterpretations, we explicitly explained the location of the pelvic floor muscle in the questionnaire. However, we still cannot ascertain whether all the women contracted the muscles correctly.

Another potential limitation of our study is that responders to questionnaires about physical activity and exercise level generally tend to overestimate the frequency of training.16,17 Hence, results from self-administered questionnaires about exercise level should be interpreted with caution. In addition, another bias that may have been introduced by this study design is that we cannot rule out the possibility that those exercising the pelvic floor muscles may be those who experience symptoms of pelvic floor dysfunction during pregnancy due to weak connective tissue and increased joint laxity. These women also may have easier vaginal births.

Only 6.5%, 13.6%, and 28.1% of this cohort of primiparous women reported training the pelvic floor muscles at least three times a week before pregnancy and at gestational weeks 17 and 30, respectively. Studies from the United Kingdom and Australia found that 69% and 54% of pregnant women, respectively, reported doing regular pelvic floor muscle training during pregnancy.18,19 In a smaller cohort study from Norway,5 the number of women who reported doing pelvic floor muscle training at least weekly was 12.9% in the first trimester and 17.4% in the third trimester. These studies used different definitions of regular exercise, and some also included multiparous women. Hence, a direct comparison between results of different studies is impossible. The present study showed that most women varied their frequency of training at the three evaluation points (before pregnancy, before week 17, and before week 30). Some also started and some stopped exercising at the different evaluation points. To strengthen our data on true regular pelvic floor muscle exercisers, those who reported varied training frequency were classified and analyzed as a separate group.

Although the response rate of the present study is somewhat low, we do not expect differential bias related to nonparticipation. The primary aims of the Norwegian Mother and Child Cohort Study are to estimate maternal and pediatric outcomes and not specifically to address pelvic floor muscle training. Participants would not have been aware of any hypotheses related to pelvic floor muscle training before they completed the questionnaires. The follow-up rate for questionnaire three was more than 90%.

Our results support the results of two small, randomized controlled trials showing that antenatal pelvic floor muscle training did not negatively affect birth in primiparous women.20,21 In both studies, the ability to perform correct contractions was assessed by vaginal palpation. One study assessed pelvic floor muscle strength and found that it increased significantly after the 8-week training period.2 Somewhat contradictory to the above-cited studies, Lanzarone and Dietz22 found no consistent correlation between levator dimensions and delivery mode, but a significant inverse correlation was observed between the area of the levator hiatus, particularly on pelvic floor contraction, and length of total stage of labor. Unfortunately, information on stage of labor is not available in the Norwegian Birth Registry.

Magnetic resonance imaging and ultrasound studies have shown that, during a voluntary pelvic floor muscle contraction, there is closing of the levator hiatus,23,24 lifting of the levator plate into a higher pelvic position,25,26 squeezing around the pelvic openings, and increasing urethral, vaginal, and rectal pressures.27 Possible permanent morphologic changes after regular training are not well known.28 However, regular pelvic floor muscle training has been shown to increase pelvic floor muscle strength2,29–32 and muscle volume (Bernstein I. The pelvic floor muscles. PhD thesis. University of Copenhagen, Hvidovre Hospital Department of Urology, Denmark, 1997), to lift the levator plate into a higher pelvic position,33 and to narrow the hiatus.34 All these factors potentially may prolong the total length of labor. On the other hand, recent studies using magnetic resonance imaging and ultrasonography have found that 20–36% of women delivering vaginally were diagnosed with levator avulsion,35–37 and women with this injury were more likely to report symptoms of pelvic floor dysfunction. It can be hypothesized that well-trained muscles may contribute to a reduced risk of injury during labor and may heal faster than untrained muscles.38 These many and diverging hypotheses underscore the need for further investigation of pelvic floor muscle training and labor and birth performance. Our data suggest that regular pelvic floor muscle training before and during pregnancy does not seem to affect labor and birth negatively.

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© 2009 by The American College of Obstetricians and Gynecologists.

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