Constipation occurs in about 15% of North Americans,1 and people with constipation have lower quality of life when compared with healthy populations.2,3 Constipation during pregnancy, although described as frequent or even as “physiologic” in obstetric textbooks,4 has been poorly studied. Reported prevalence rates of constipation during pregnancy have ranged from 9% to 39%,5–9 but many of these studies were limited by retrospective study design and variable or poorly defined definitions for constipation.
In 1998, a consensus diagnosis for functional constipation was developed by a multi-national committee of experts.10 Their criteria for constipation, commonly called the Rome II criteria, include symptoms of difficulty with defecation as well as frequency of bowel movements. These criteria provide an explicitly stated definition of constipation and have become the research standard. The objectives of this study were to 1) estimate the prevalence of constipation during pregnancy, defined by the Rome II criteria, and 2) identify factors associated with constipation in pregnancy. In addition, we planned to estimate the prevalence of irritable bowel syndrome (IBS) during and after pregnancy using the Rome II criteria.
MATERIALS AND METHODS
This prospective, longitudinal study of constipation and bowel symptoms in pregnancy and the postpartum period was approved by the University of Iowa Institutional Review Board. Each subject signed an informed consent document before participation. Participants were recruited from the obstetrics clinics at the University of Iowa Hospitals and Clinics between November 2004 and March 2005. Most obstetric clinics were attended by a research nurse during this period. Consecutive prenatal patients who presented for new obstetric appointments during each attended clinic were screened for eligibility and invited to participate during the clinic visit if eligible. Inclusion criteria included first-trimester pregnancy (6 to 14 weeks of gestation), age at least 18 years, English speaking, and planning to continue prenatal care and delivery at the University of Iowa Hospitals and Clinics. Exclusion criteria included previous abdominal or pelvic radiation therapy, history of inflammatory bowel disease, history of bowel surgery (other than appendectomy), current treatment for thyroid disease, and regular narcotic use.
A self-administered questionnaire and a prospective 7-day stool diary were collected each trimester and at 3 months postpartum. The first-trimester questionnaires were completed immediately after enrollment, and the participants were given the first-trimester stool diary to complete at home and return by mail. Packets including questionnaires and a stool diary were then mailed to participants during their second trimester and third trimester and at 3 months after delivery. Participants completed the questionnaire and diary at home and returned them in a provided stamped return envelope. Reminder telephone calls were made to participants who did not respond at each data collection time point.
The study questionnaire included bowel symptom items from the Rome II Modular Questionnaire for Functional Gastrointestinal Disorders.11 Participants also responded to a nonvalidated question about difficult defecation: “In the last month, have you had difficulty having a bowel movement?” and if answered affirmatively were asked, “How much are you bothered by difficulty having a bowel movement?” with responses ranging from 0 (not at all bothered) to 10 (extremely bothered). Participants completed other validated measures including the Fecal Incontinence Symptom Index,12 the Bristol Stool Form Scale,13 the International Physical Activity Questionnaire,14 and the Block Dietary Fruit/Vegetable/Fiber Screener.15 Other data collected by questionnaire included demographics, medication use (including vitamins, supplements, stool softeners, and laxatives), obstetric and medical history, caffeine intake, and smoking habits.
The stool diary consisted of a 7-day written prospective record of stool frequency and form. Participants were asked to record when each bowel movement occurred and to mark the stool form type for each movement as described in words and pictures on the Bristol Stool Form Scale.13 The stool form types range from type 1, described as “separate hard lumps, like nuts (hard to pass)” to type 7 “watery, no solid pieces.” This validated stool form scale has been found to correlate strongly with whole gut transit times and to be acceptable to research subjects and patients.13,16
The primary outcome was constipation defined by the Rome II Criteria.11 These criteria define constipation by the presence of at least two of the following six symptoms: straining, lumpy or hard stools, sensation of incomplete evacuation, sensation of anorectal obstruction/blockade, manual maneuvers to facilitate defecation (eg, digital evacuation or support of the pelvic floor), and fewer than three defecations per week. Symptoms must be present in at least one quarter of defecations for at least 3 months of the preceding year. Also, loose stools cannot be present, and criteria for IBS must not be met. The Rome II criteria have not been validated for use in pregnant populations. As we aimed to identify constipation at different time points in pregnancy, we modified the duration criteria of the Rome II definition, so that symptoms had to be present in at least one quarter of defecations during the last 1 month (rather than 3 months).
Irritable bowel syndrome, also defined using the Rome II criteria, was considered present if the subject reported abdominal discomfort or pain occurring often during the last month that had two of the following three features: relieved with defecation, onset associated with a change in frequency of stool, and onset associated with a change in stool form.11 Similar to constipation, we modified the criteria to be more sensitive to changes during pregnancy by identifying IBS if the discomfort or pain was present over the past 1 month, rather than 3 months.
Continuous variables were summarized by mean and standard deviation (SD). Variables with non-normal distributions (determined by the Shapiro-Wilk test) were summarized by median with interquartile range. Prevalence estimates with exact 95% confidence intervals (CIs) were calculated. Univariable associations were studied using the Student t or Wilcoxon rank-sum test for continuous data and the χ2 or Fisher exact test for categorical data. A multivariable, longitudinal analysis based on generalized linear (logistic) models was used to explore the effects of time and other potential risk factors on constipation during pregnancy. Parameters in the model were estimated via the generalized estimation equation method.17 Constipation, defined by the Rome II criteria, was the dependent variable in the model. Risk factors associated with the dependent variable (P<.2) were included in the multivariable model along with time (first, second, or third trimester). A backward model selection process was performed. Odds ratios (ORs) with 95% CI for significant risk factors were computed from the fitted model. Statistical analyses were performed using SAS 9.1 (SAS Institute, Inc., Cary, NC). P values were considered significant if <.05.
For the risk factor analysis, with 103 subjects and a constipation rate of 24%, there is 80% power to identify a change of 0.7 SD between means or approximately 30% between proportions using a two-tailed 5% level of significance.
Of 142 women who were found eligible, 114 (80.3%) agreed to participate in the study. Women who agreed to participate were similar in age and race to those who refused participation (data not shown), but were more often nulliparous (53% compared with 23% of those who did not participate, P=.01).
Ten (8.8%) of the participants had a spontaneous or missed abortion and 1 (0.9%) was diagnosed with a molar pregnancy soon after enrollment. Of the 103 remaining participants, the mean (±SD) age was 28.4±5.0 years and body mass index 26.2±6.7 kg/m.2 Ninety five women (92.2%) were white, 2 (1.9%) black, 2 (1.9%) Hispanic, and 4 (3.8%) of “other” or unknown race. Fifty-six (54.4%) were nulliparous, 34 (33.0%) had one prior delivery, and 13 (12.6%) had two or more prior deliveries. Eighty-three (80.6%) were married or living as married. Most (59.2%) had completed a college degree. Twenty-six (25.2%) reported a history of constipation, and 18 (17.5%) reported past treatment for constipation. Health, diet, and lifestyle characteristics measured at baseline and throughout the study are presented in Table 1.
Follow-up data were returned by 77 (74.8%) women in the second trimester, 70 (68.0%) in the third trimester, and 63 (61.2%) at 3 months postpartum. Women who failed to return the follow-up questionnaires were more likely to be nonwhite, less educated, single, and of higher parity than women who returned all or most of the questionnaires (P<.05 for all). General health status, history of constipation or constipation treatment, and first-trimester constipation (diagnosed by the Rome II criteria) did not differ in those who did and did not return the follow-up questionnaires.
Individual constipation symptoms were common at all time points in pregnancy and postpartum. (Table 2.) In each trimester and postpartum, straining and lumpy or hard stools were the most common symptoms and requiring manual maneuvers to aid in defecation was the least common symptom reported. By the Rome II criteria, prevalence rates of constipation in those who returned questionnaires at each study time point were 24% (95% CI 16–33%), 26% (95% CI 17–38%), 16% (95% CI 8–26%), and 24% (95% CI 13–36%) in the first, second, and third trimesters and at 3 months postpartum, respectively. Overall, 51% (95% CI 39–62%) of women in the study reported constipation at some point during pregnancy. The median (interquartile range) degree of bother in those who had difficulty having a bowel movement was 4.0 (3.0, 6.0) in the first trimester, 3.0 (3.0, 5.0) in the second trimester, 4.0 (3.0, 6.0) in the third trimester, and 4.0 (3.0, 6.5) at 3 months postpartum.
Of individual bowel symptoms, women identified with constipation in the first trimester were more likely to report straining, lumpy or hard stools, sensation of incomplete evacuation, and fewer than 3 defecations per week but not sensation of anorectal obstruction/blockade and manual maneuvers to facilitate defecation (Table 3). Fecal incontinence symptoms were also more commonly reported by those with constipation as reflected in a higher Fecal Incontinence Symptom Index score. Bowel movement frequency and median stool form (reported by diary) were not significantly different in those with and without constipation in the first trimester.
Irritable bowel syndrome (by Rome II criteria) was identified in 20, 10, 9, and 3 women corresponding with prevalence rates (95% CI) of 19% (12–28%), 13% (6–23%), 13% (6–23%) and 5% (1–13%) in the first, second, and third trimesters and at 3 months postpartum, respectively.
Most demographic and other characteristics of women with constipation compared with those without constipation in the first trimester did not differ, including daily fiber intake (mean [SD]17.2 [5.6] compared with 17.5 [5.2], P=.81), physical activity level (12 [50.0%] compared with 43 [55.1%] sufficiently or highly active, P=.83), fiber supplementation (3 [12.5%] compared with 3 [4.0%], P=.15), and use of stool softeners (1 [4.2%] compared with 2 [2.6%], P=.57). However, those who reported a history of or past treatment for constipation were more likely to have constipation. Ten (41.7%) women with constipation and 16 (20.5%) without constipation reported a history of constipation (P=.04), and 9 (37.5%) women with constipation compared with 9 (11.5%) without constipation reported past treatment for constipation (P<.01).
In the final longitudinal multivariable model, only iron supplements (OR 3.5 [95% CI 1.04–12.10]) and history of constipation treatment (OR 3.58 [95% CI 1.50–8.57]) were associated with constipation during pregnancy. Time (first, second, and third trimesters) was also significant in the model (P=.045). Specifically, women were less likely to have constipation in the third trimester compared with the first (OR 0.50 [95% CI 0.23–1.08) or second (OR 0.42 [95% CI 0.21–0.85]) trimesters.
This longitudinal study of pregnant women supports the commonly held belief that many pregnant women experience constipation. We found that functional constipation, defined using the Rome II criteria, occurred in 16–26% of women studied in each pregnancy trimester. Overall, 1 in 2 women in the study had constipation at some point during their pregnancy. A nonpregnant control group was not included in this study, but we previously found that constipation (using the same criteria) was less common (7%) in 122 nonpregnant women of similar ages (18–41 years) recruited for a different study at the general gynecologic clinic at the same institution.18
The prevalence rates of constipation during pregnancy in a recent prospective study of 98 pregnant women had results similar to ours.9 Also based on a modified Rome II criteria (measuring symptoms using a diary over a 7-day period), they found 35%, 39%, 21%, and 17% of women had constipation during the first, second, and third trimesters and at 6 weeks postpartum, respectively. A prospective cohort study of 487 nulliparous pregnant Dutch women defined constipation as fewer than three bowel movements per week and straining in more than 25% of defecations.8 Using this narrower definition of constipation, they found only 9% of women were constipated in the first trimester, 5% in the third trimester, and 5% at 3 months postpartum. In both studies, rates of constipation were lower in the third trimester, also consistent with our findings.8,9 Other studies have reported variable rates of constipation during pregnancy (11–38%), but these are limited by retrospective study design and the use of nonvalidated and nonstandardized definitions for constipation.5–7
Although definitions of constipation in the past have often focused solely on bowel movement frequency, more recent studies suggest that other symptoms are equally important in defining this disorder.19 Our results in pregnant women demonstrate that symptoms of straining, lumpy or hard stools, and sensation of incomplete evacuation were more commonly reported than infrequent defecation at all time points. Furthermore, although more women with constipation reported infrequent defecation by questionnaire compared with nonconstipated women, defecation frequency documented in the stool diary did not differ between those with and without constipation. This difference may result from the different time periods assessed (the questionnaire referred to symptoms occurring more than 25% of the time in the last month, and the diary recorded a single 7-day period) or because of the different methods of data collection. Investigators studying bladder diaries have also reported that patients may overestimate voiding frequency when compared with diary reports.20 Regardless, other studies of constipation during pregnancy have not provided frequencies of individual symptoms, so we are unable to compare our results to past findings to confirm that this pattern of symptoms is specific to pregnancy.8,9
In our multivariable, longitudinal analysis, a history of treatment for constipation and current iron supplementation were associated with constipation during pregnancy, but level of physical activity and dietary fiber intake were not. Other investigators have also found a lack of association between dietary fiber intake and constipation during pregnancy.9,21 Derbyshire et al9 found that dietary iron intake was lower in late pregnancy in constipated women, but they did not study the use of iron supplements. Iron supplementation is commonly thought to result in gastrointestinal side effects including constipation, but clinical trials studying iron supplementation during pregnancy have had differing conclusions as to whether this is true. In a randomized clinical trial of four different doses of ferrous fumarate in 404 healthy pregnant women, rates of constipation was not associated with treatment and did not differ between the dose groups during treatment.22 On the other hand, a randomized crossover open-label trial of 135 pregnant women found that constipation was associated with intake of a prenatal vitamin with a higher dose of elemental iron compared with one with a lower dose.23 These results might differ because of different iron formulations used. We did not collect information on dietary iron intake or specific types or doses of iron supplementation used.
Interestingly, we found that constipation was still quite common (24%) at 3 months after delivery, but we were unable to study risk factors specifically for postpartum constipation because of the smaller number of women with data at this time point. It seems likely that specific postpartum factors (obstetric events, breastfeeding, etc) may affect bowel function during this period.
In this study, IBS was identified in 5% to 19% of women at time points during and after pregnancy. Irritable bowel syndrome appeared to occur less frequently than constipation, especially in the postpartum period. Epidemiologic studies suggest that IBS affects 5–20% of varying populations and is more common in women than men.24,25 However, the effect of pregnancy on IBS remains unclear and poorly studied.26 Given the relatively small numbers of women with IBS in this study, future studies including larger numbers of women will be needed to better understand these relationships.
Strengths of this study include the prospective design, use of a stool diary to more accurately and objectively document stool consistency and frequency, and most importantly, the use of a validated standardized definition for constipation. We also included validated measures of physical activity and dietary fiber intake, allowing us to study these as potential risk factors for constipation. We acknowledge limitations to our results as well. This is a single center study with a homogenous study population, and our results may not be generalizable to other groups of women. Additionally, women with constipation or other colorectal symptoms might be more likely to enroll in the study, potentially biasing our results. This study also lacked a nonpregnant control group, which would strengthen our ability to make conclusions about the direct effects of pregnancy on constipation. Lastly, our sample size might not provide the power necessary to detect smaller differences between women with and without constipation, and the loss to follow-up (especially for the later study time points) may have affected our results.
In conclusion, we found that constipation was common, affecting about half of women at some point during pregnancy, and more often associated with symptoms of straining, hard stools, and incomplete evacuation, rather than infrequent defecation. Given our findings, we suggest that pregnant women who report a history of constipation at their initial obstetric visit or those who require iron supplementation be screened and counseled about constipation treatment options during pregnancy.
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