document: anal incontinence is a bothersome ailment associated with many health complaints and discomfort in daily life : hygienic problems , limitations in occupational and social life , sexual dysfunction , reduced quality of life , and altered self - esteem . 
   prevalence and severity of anal incontinence are measured by patient self - reporting and no objective assessment methods exist . 
   obstetric anal sphincter injury ( oasis ) is one of the main causes for female ai reported in nonpregnant women . 
   additionally , multiple vaginal deliveries can increase the risk of ai regardless of anal sphincter injury [ 2 , 3 ] . 
   age , obesity and medical conditions such as diabetic neuropathy and gastrointestinal disorders also increase the risk of anal incontinence [ 2 , 4 , 5 ] . 
   prevalence of anal incontinence among women differs largely ( 228% ) in previous studies and differs between different study populations [ 46 ] . 
   postpartum studies show a high prevalence of ai in women having suffered from oasis , 3859% [ 68 ] . 
   women attending gynecological outpatient clinics have higher prevalence of ai ( 1628% ) compared with the general female population ( 4.4% ) [ 2 , 5 ] . 
   women with pelvic floor disorders have higher prevalence of ai than women without pelvic floor disorders . 
   community - based studies show differences in prevalence of ai between age groups , with increasing prevalence by increasing age [ 4 , 5 , 9 ] . 
   most frequent ai is found among nursing home residents ( 5060% ) , among the oldest women with frequent additional complaints and comorbidity . 
   few previous studies have assessed the prevalence of anal incontinence in a female population of fertile age , and few studies have included nulliparous women [ 1114 ] . 
   the aim of this study was therefore to assess the prevalence and risk factors for anal incontinence in an unselected female population across parity groups in second trimester of pregnancy . 
   this study is part of a comprehensive perineum research study , which was approved by the regional committee for medical research ethics in south - eastern norway ( ref . 
   this study was conducted as a survey of pregnant women attending free of charge routine ultrasound examination at second trimester , from september 2009 to august 2010 , in a large university hospital in oslo , norway . 
   the pregnant women attending the ultrasound screening in our hospital represent a nonselected population from the entire oslo area . all pregnant women in norway 
   are offered a free of charge second trimester routine ultrasound examination in gestational week 1820 , and 98% attend . in our hospital , this routine ultrasound is performed by specially educated midwives at the fetal medicine unit . 
   the hospital receives admission notes from the local general practitioners when the woman is pregnant in the first trimester . 
   the invitation to participate in our study , the questionnaire , and the informed consent were included as a part of the invitation to the routine ultrasound appointment . 
   midwives performing the routine ultrasound examination reminded the women of the study and collected the questionnaire and the signed informed consent . from the 7256 women who were posted a questionnaire , 
   973 women were not found in our postpartum labor ward database : they did not achieve 18 weeks pregnancy ( pregnancy loss ) , they did not deliver in our hospital , or they had moved out of oslo area or norway , resulting in 6283 women eligible for study participation . 
   four women returned two questionnaires ( twice during the same pregnancy ) , and one woman returned the questionnaire shortly after the index delivery . 
   thus , five filled - out forms were excluded from the analyses and the study group consisted of 2846 ( of 6283 invited ) women , resulting in a response rate of 45% . 
   the questionnaire consisted of 105 questions concerning anal and urinary incontinence , general health condition , drug use , and worries concerning pregnancy and delivery . 
   the major part of the questions was chosen from validated questionnaires such as due and ottesen , st . 
   mark 's , nugg , hunt , and cambridge worry scale ( cws ) [ 19 , 20 ] . 
   additionally , we collected demographic data , obstetrical history , educational level , household income , and country of origin of the participant . 
   anal incontinence was identified by self - reported leakage of gas , loose , or solid stools , lack of ability to defer defecation for 15 minutes ( fecal urgency ) , use of pads or plugs , and alteration of lifestyle described in st . 
   mark 's score from 0 to 2 were analyzed as a control group ( no or infrequent ai ) . 
   urinary incontinence was defined as self - reported symptoms of stress or urge urinary incontinence . 
   thus , women with cesarean delivery only ( never having delivered vaginally before ) were categorized as  vaginal primiparous . 
   continuous data were categorized and the independent variables are presented as frequencies . univariate analysis was performed to identify significant risk factors for anal incontinence . 
   the results from this regression analysis are presented as adjusted odds ratios ( aors ) for ai with 95% ci . for each model 
   the assumptions underlying a valid logistic regression analysis were checked and found to be adequately met . 
   mark 's score 3 or more ) in the entire study group was 8.4% ( 238/2846 ) . 
   most of the women ( 80.3% ) reported complete anal continence ( 2268/2846 ) with st . 
   mark 's score 0 , and 11.3% ( 322/2846 ) women reported infrequent ai with st . 
   mark 's score 1 or 2 . inability to control flatus was the most frequent complaint , reported by 18.0% ( 513/2846 ) . of these , 
   fecal incontinence was reported by 6.0% ( 171/2846 ) and fecal urgency by 3.2% ( 90/2846 ) of the women . 
   urinary incontinence ( ui ) was significantly associated with reported anal incontinence among all parity groups and 32.4% of the women with ai also reported ui ( p < 0.001 ) . 
   prevalence of ui was threefold among parous women compared to nulliparous women and increased slightly with increasing vaginal parity ( p < 0.001 ) ( data not shown ) . 
   the majority of the 2846 women had answered the questionnaire when they were in the second trimester ( 84% ) , 12.2% in the first trimester , and 1.2% in the third trimester . 
   mean height was 168  cm and mean weight was 66.7  kg . mean bmi was 23.6 , range 16.042.4 . 
   smoking was infrequent ; only 2% ( 57/2851 ) women reported that they smoked during this pregnancy ( table 1 ) . 
   there was a significant difference in prevalence of ai among women with different obstetric histories . 
   mark 's score of 3 or above ) increased with increasing vaginal parity ( data not shown ) . of the nulliparous women , 7.8% ( 139/1792 ) reported anal incontinence . in the univariate analysis , non - western background , low household income , 
   being unmarried or single , low educational level , age 35 or more , answering the questionnaire in the first trimester ( as opposed to second trimester ) , dermatological disease , ulcerative stomach disease , hypertension , rheumatoid arthritis , and muscle - skeletal complaints were significantly associated with anal incontinence among the nulliparous women ( tables 1 and 2 ) . in the multivariate analysis , low educational level , dermatological disease , and rheumatoid arthritis remained as significant factors for ai ( table 2 ) . after excluding the 140 women with previous cesarean delivery only , the subgroup of vaginal parous women consisted of 914 women . 
   overall anal incontinence among parous women was 9.8% ( 90/914 ) . in the group of women with one previous vaginal delivery , 8.5% ( 61/714 ) reported ai , whereas the group of women with more than one previous vaginal delivery , as many as 14.5% ( 29/200 ) , reported ai ( p = 0.004 ) . 
   of the parous women , 15.9% had previously delivered at least one macrosomic ( > 4000  g ) infant ( 145/914 ) , 156 reported previous delivery with vacuum extraction , and 24 women reported a previous forceps delivery . an obstetric history with instrumental delivery or a macrosomic infant 
   previous delivery with oasis was reported by 41 women ( 4.5% ) and was strongly associated with ai .   in the univariate analysis , 
   previous delivery with oasis , non - western background , low household income , being unmarried or single , low educational level , age 35 or more , bmi 25 or more , dermatological disease , and use of pain killers were significantly associated with anal incontinence among the parous women ( tables 1 and 2 ) . in the multivariate analysis , 
   previous delivery complicated with oasis and dermatological disease remained as significant risk factors for ai ( table 2 ) . 
   the risk of ai was threefold among women with previous oasis compared to women without ( 24.4% and 8.1% , resp . ) . 
   the higher risk of ai associated with previous oasis remained threefold in the more severe forms of ai , if defining ai as self - reported st . 
   mark 's score of 5 or above ( 12.2% and 3.8% ) or if 7 or above ( 7.3% and 2.3% ) instead of 3 or above ( table 3 ) . 
   the subgroup of parous women with previous cesarean only ( n = 140 ) and no vaginal deliveries was also analyzed separately . in this subgroup 
   the prevalence of ai was the lowest ( 6.4% , 9/140 ) compared with all other parity groups but was too small to further analysis of risk factors . when the analyses were repeated with this subgroup of women added to the subgroup of nulliparous women , the conclusions remained unaltered ( data not shown ) . 
   women who reported having a dermatological disease reported also more anal incontinence than women without this disease ( table 2 ) . there was a significant association between dermatological disease and several other complaints : allergy , migraine and headache , constipation , and psychological problems . 
   women who reported dermatological problems also more frequently reported use of vitamins , allergy medication , and stomach and bowel regulators . 
   these women also reported more worries about the cambridge worry scale than the women without dermatological problems . 
   this population - based study showed that previous obstetric anal sphincter injury was the strongest risk factor for self - reported ai among pregnant parous women . among the nulliparous women , a low educational level and comorbidity 
   the group of women with previous deliveries with cesarean section only had the lowest prevalence of ai , indicating that pregnancy per se may not represent a major risk factor for ai . 
   these findings support the notion that the process of vaginal delivery may be more damaging to the anal continence mechanisms than pregnancy per se . 
   we found a surprisingly high frequency of self - reported ai among nulliparous women ( 7.8% ) . 
   low socioeconomic status ( low income , low education ) is a well - known reason for lower health status and increased morbidity , and previous studies show that self - rated health predicts morbidity well [ 2123 ] ; therefore , there is now a reason to doubt the correctness of the self - reported ai . 
   socioeconomic differences have been found in occurrence of almost all conditions and illnesses [ 22 , 23 ] . 
   this might explain part of the results for the group of nulliparous pregnant women in our study , where low educational level remained as significant risk factor for ai in the multivariate analysis . 
   a previous oasis was the strongest risk factor for self - reported anal incontinence in all analyses in parous women , with and without adjusting for other factors , and in all categories of severity of anal incontinence . in our study , women with previous oasis reported a lower prevalence of ai than women in previous studies on nonpregnant women [ 68 , 24 ] . 
   all the participants in our study were pregnant , and the low prevalence of ai among women with previous oasis might indicate that fewer women with severe complaints of ai embark on a new pregnancy . the risk of ai increased with increasing number of vaginal deliveries , a result similar to previous studies . 
   interestingly , previous delivery with a macrosomic infant ( > 4000  g ) was not associated with self - reported ai during pregnancy in our study , and was not a previous delivery with vacuum extraction or forceps . 
   this is in contrast to some previous studies , where previous forceps delivery and macrosomy are reported as risk factors for ai [ 8 , 26 , 27 ] . in our study of pregnant women , 
   maternal age was not a significant risk factor for ai in the subgroup of parous women , probably because our study group was young , the oldest participant was 45 years old , and age related increased risk of anal incontinence is probably more important in older age groups [ 2 , 5 , 27 ] . 
   women with overweight ( bmi 2529.9 ) and obesity ( bmi > 30 ) were more likely to suffer from anal incontinence than women with normal bmi ( < 25 ) in our study , but in the multivariate analysis this effect disappeared , due to the strong effect of previous oasis . 
   the large effect of oasis exceeded all other factors ( except dermatological illness ) . 
   many previous studies of ai describe only the frequency of the different components of ai . 
   we chose to describe the prevalence of ai as a score , to be able to perform multivariable analyses of the assessed variables in our study . 
   mark 's score 3 as cutoff for ai was to be able to compare the results from this study to our previous study   and also to our future study , a followup of the participating women after delivery . as a limit of 3 for defining ai 
   may be questioned for clinical relevance , we repeated all statistical analyses with different cutoffs ( 4 , 5 , and 7 ) for st . 
   the main conclusions remained unaltered , oasis was the most important predictor for ai ( for all these cutoffs for st . 
   mark 's score ) among parous women , and low socioeconomic status and comorbidity were the most important indicators for ai among nulliparous women . 
   variables with a p value over 0.05 were also included in the primary analyses to ensure that no risk factors were missed among our registered variables , but no such factors were revealed . similarly to our previous study of nonpregnant women , urinary incontinence was reported by 19.2% of the participants . 
   prevalence of urinary incontinence was threefold among women who reported ai compared to women without ai , in both nulliparous and parous subgroups of women ( p < 0.001 ) . 
   this might indicate that some women are in higher overall risk for incontinence , possibly associated with tissue type , or the pathophysiological mechanism may be the same for both diseases . 
   strength of this study is that the pregnant population was unselected and consisted of all parity groups , including nulliparous women . 
   the majority of studies on female anal incontinence have assessed nonpregnant women 624 months after delivery . 
   another strength of this study is that we also assessed comorbidity and medication use in addition to obstetrical history . to our knowledge , 
   no previous studies have assessed anal incontinence and comorbidity among pregnant women . among nulliparous women 
   further research is needed to explore whether this is a consistent finding across population groups and to explore which mechanisms could underlie such an association . 
   a weakness in our study is that the response rate among the invited women was less than 50% , and this can cause self - selection bias among the study participants . 
   similar selection bias was observed in the norwegian moba study , where higher educated women more likely agreed to participate . 
   however , the effect of such selection bias was found low in the moba study , and we have no reason to believe that our response rate of 45% negatively affected our study either . 
   low prevalence of comorbidity and medication use may indicate that the participants did not have lower health status than nonparticipants or the general population in oslo . 
   bias of women with a previous oasis and complaints of ai having been more eager to participate in the study is unlikely , since the prevalence of ai in the subgroup of women with previous oasis was lower ( 24.4% ) than that in the previously reported studies ( from norway ) [ 6 , 7 ] . 
   we compared the study population 's basic clinical data with an anonymous electronic database covering all patients delivering at the same time period as the participants in this study . 
   the distribution of nulliparous women in our study population was higher than in the overall delivery population in our hospital ( 63% and 52% , resp . ) . 
   we did not find any differences in mean age between responders and nonresponders , but the distribution of women with non - western background was higher among the nonresponders ( data not shown ) , as expected , as the questionnaire and patient information were in norwegian . 
   all data in this study was based on self - reporting from the participants , and thus information of their obstetric history can include errors . 
   it is likely that women remember correctly the number of previous deliveries , delivery mode , and infant birth weight , but not all women are aware of having suffered from oasis   when they leave the hospital after delivery . lacking information of oasis 
   might strengthen our conclusions of oasis being a strong risk factor for ai : if women unaware of previous oasis reported ai and were analyzed as having no previous oasis , the risk of ai after oasis is even higher than calculated in this study . 
   on the other hand , if more women who were unaware of having oasis reported no ai , our results would show too strong effect of oasis as a risk factor to ai . 
   we found an association between self - reported dermatological disease and self - reported ai for all parity groups , which has not been reported before . 
   we can only speculate reasons for this association ; women that have ai may also be more sensitive to dermatological bother than others , perhaps associated with the fecal incontinence with affection of perianal skin . possibly , there could be a common tissue specific risk for both ai and dermatological conditions . 
   women who reported dermatological problems also reported more worries ; another explanation could be that these women were in general more sensitive to different symptoms and signs . in a further study 
   more detailed questions about the type of dermatological disease would be of interest when assessing comorbidity in relation to symptoms of ai . 
   we have performed a large number of analyses due to a large number of detailed information about obstetric history and maternal characteristics . 
   the study population is relatively young , and thus , frequency of comorbidity and medication use was very low among the participants , which can give results by chance . 
   this did not alter the conclusions ; low educational level among nulliparous and oasis among parous women were the most important factors associated to ai . 
   we conclude that among parous women , previous oasis is the most important risk factor for anal incontinence and other obstetrical events only had a minor effect on development of ai . as oasis is a modifiable risk factor , and frequency 
   may rapidly be altered after introduction of obstetrical perineal support programs [ 3033 ] , prevention of obstetrical sphincter injury is likely the most important factor for reducing bothersome anal incontinence in fertile women .
summary: the aim of this study was to assess the prevalence and risk factors of anal incontinence in an unselected pregnant population at second trimester . 
   a survey of pregnant women attending a routine ultrasound examination was conducted in a university hospital in oslo , norway . a questionnaire consisting of 105 items concerning anal incontinence ( including st . 
   mark 's score ) , urinary incontinence , medication use , and comorbidity was posted to women when invited to the ultrasound examination . 
   results . 
   prevalence of self - reported anal incontinence ( st . mark 's score  3 ) was the lowest in the group of women with a previous cesarean section only ( 6.4% ) and the highest among women with a previous delivery complicated by obstetric anal sphincter injury ( 24.4% ) . among nulliparous women the prevalence of anal incontinence was 7.7% and was associated to low educational level and comorbidity . 
   prevalence of anal incontinence increased with increasing parity . 
   urinary incontinence was associated with anal incontinence in all parity groups . 
   conclusions . 
   anal incontinence was most frequent among women with a history of obstetric anal sphincter injury . 
   other obstetrical events had a minor effect on prevalence of anal incontinence among parous women . 
   prevention of obstetrical sphincter injury is likely the most important factor for reducing bothersome anal incontinence among fertile women .