Trimethoprim use prior to pregnancy and the risk of congenital malformation: a register-based nationwide cohort study. (2024)

1. Introduction

The antibiotic trimethoprim is an inhibitor of dihydrofolatereductase (DHFR), which converts folate to more active components [1].This folate antagonism of trimethoprim has been associated with severaltypes of congenital malformations and miscarriage when given duringpregnancy [2, 3]. This effect is almost entirely abolished byconcomitant use of vitamin supplements containing folic acids [2]. Theuse of multivitamins including folic acid has been associated with areduced risk of having offspring with cardiovascular [46], urinary tract[5, 7], oral cleft [6, 7], limb [7, 8], and neural tube defects [6, 9,10]. This further strengthens the evidence of a direct associationbetween DHFR inhibition and malformation. Theoretically, DHFR inhibitorscan result in folate deficiency that lasts into the pregnancy period. Arisk of congenital malformations occasioned by DHFR inhibitor use priorto pregnancy could have serious consequences. Trimethoprim is widelyused throughout the world to treat urinary tract, respiratory tract, andgastrointestinal infections and is used as daily prophylaxis in HIVinfection and AIDS treatment in Africa [11]. Due to its common use,large numbers of fertile women are exposed to the drug before becomingpregnant.

We therefore tested the hypothesis that trimethoprim use during themonths prior to pregnancy increases the risk of congenitalmalformations. To this end, we performed a nationwide study in whichadministrative registers of trimethoprim use were coupled withregistrations of birth and congenital malformations.

2. Methods

2.1. Study Population. Using the Danish Fertility Database, [12] weidentified all conceptions in Denmark between January 1,1997, andDecember 31,2004, that resulted in live births (n = 521,611). Follow-updata was available to December 31 2005. From these, 344 were excludeddue to coding error. Information about maternal drug use before andduring pregnancy was obtained from the Register of Medicinal ProductStatistics (The National Prescription Register), and children withcongenital malformations were identified through the National HospitalRegister.

The Danish Fertility Database consists of individual-level dataabout the mother and the father, including a unique identificationnumber, age, previous births, and abortions, as well as birth weight andlength, death and cause of death, sex, and gestational age of thechildren [12]. The time of conception is based on ultrasound results orinformation about the date of the last menstruation. The Register ofMedicinal Product Statistics contains individual-level data about allprescribed drugs dispensed at a pharmacy in Denmark since 1995 [13]. Theregister has no information about over-the-counter drugs or theindication of treatment. The National Hospital Register containsinformation on all hospitalizations in the country, including admittancedata and discharge diagnosis [14].

Primary outcome was predefined as all congenital malformations(ICD-10 Q0.00-Q99.9). The secondary outcome was the subgroup ofmalformations. All major and minor malformations and malformationgroupings are those of the European Surveillance of Congenital Anomalies(EUROCAT) classification system guide 1.3 [15]. Exposure was defined asat least one dispensed prescription of a systemic drug containingtrimethoprim (Anatomical Therapeutic Chemical Classification System(ATC) J01EA01 and J01EE01). The exposure period was predefined as the 12weeks prior to conception since this is the previously estimated riskperiod of methotrexate [16].

Several different analyses were done. Offspring of mothers with nodispensed trimethoprim prescriptions in the 12 weeks before conceptionwere used as the primary reference group as well as off spring ofmothers with no dispensed prescriptions in the 12 weeks before pregnancyand during pregnancy. To avoid confounding by indication, we used theoffspring of mothers with one or more dispensed prescriptions of themecillinam, a penicillin used to treat urinary tract infections, duringthe 12 weeks before pregnancy as a reference group. Furthermore, wecompared the results with the number of children diagnosed with acongenital malformation in women exposed to trimethoprim solely in weeks13-24 and in weeks 25-36 before conception.

Comorbidity of mothers was assessed through the National HospitalRegister on the basis of diagnoses made between 1995 and 2005.This wasdone to assess whether women treated with trimethoprim were more likelyto be diagnosed with a teratogenic infection or conditions potentiallyharmful to the fetus. Diagnoses of infection, alcoholism, amniocentesis,and folate deficiency were included if they were given during pregnancy,whereas chronic conditions were included if the diagnoses were givenbefore or during pregnancy. All prescribed drugs dispensed before andduring pregnancy were classified according to the US Food and DrugAdministration's Pregnancy Risk Factor Category X [17] (drugs withevidence of human foetal risk) in order to identify the usage of thesedrugs in the cohort. The use of folic acid was defined as redemption ofa prescription of folic acid in the period from 84 days beforeconception to the end of the first trimester.

2.2. Statistical Analysis. All data management and analyses wereperformed using SAS software, version 9.1 (SAS Institute Inc., Cary, NC,USA). Three logistic regression models were used on dichotomous outcomesto estimate the odds ratios of congenital malformation. Model one wasunadjusted; model two was adjusted for maternal age (as a continuousvariable) and parity (as a continuous variable). We adjusted model threefor maternal age (as a continuous variable), parity (as a continuousvariable), income (four categories), education (four categories), usageof X-classified drugs (dichotomous variable), calendar time (1997-1998,1999-2000, 2001-2002, 2003-2004), teratogenic infections (dichotomousvariable, if the mother had at least one diagnosis of either syphilis,toxoplasmosis, rubella viruses, varicella virus, parvovirus B-19,cytomegalovirus, herpes simplex virus 1 and 2, or Venezuelan equineencephalitis virus during pregnancy), and folate deficiency, myastheniagravis, virilizing tumors, diabetes mellitus, alcoholism, amniocentesis,and Sjogren's syndrome (all as dichotomous variables). Thesevariables had less than 0.5% missing values except for education (2.5%in the trimethoprim exposed group and 2.6% in the unexposed group (P =0.93)).

For all analyses, a two-sided value of P < 0.05 was consideredstatistically significant and odds ratios are presented with 95%confidence intervals.

2.3. Ethics. All data were linked in computers held by StatisticsDenmark and were made available with encrypted personal information[18]. This ensured that no individuals could be identified. Ethicalpermission is not required in Denmark for retrospective registerstudies. The Danish Data Protection Agency approved the study (no.2008-41-2517). We report our findings according to strengthening thereporting of observational studies in epidemiology (STROBE) [19].

3. Results

We identified 521,267 births during the study period. A total of402 children were born to 395 women exposed to a drug containingtrimethoprim (trimethoprim or sulfamethoxazole plus trimethoprim) duringthe 12 weeks before conception (Table 1). Women exposed to trimethoprimwere more likely to be younger (P < 0.001)and have lower education (P= 0.02) and lower household income (P = 0.02) in comparison tononexposed women (Table 1).

Of the children born to an exposed mother,25(6.2%) were diagnosedwith a major congenital malformation compared with 17,465 (3.4%) amongthose born to unexposed mothers. Among the exposed women, 40 (10.0%)children were born with a diagnosed congenital malformation (includingminor malformations) compared with 27,173 (5.2%) born to unexposedmothers.

The odds ratio (OR) for the occurrence of a major congenitalmalformation after exposure to trimethoprim during the 12 weeks beforepregnancy (model 1) was 1.91 (95% confidence interval 1.28-2.87)compared to unexposed women. Adjusting for age and parity (model 2), theOR was 1.91 (1.27-2.86). Furthermore, we included usage of X-classifieddrugs, teratogenic infections, folate deficiency, myasthenia gravis,virilizing tumors, diabetes mellitus, alcoholism, amniocentesis,Sjogren's syndrome, education, calendar time, income, and use offolic acid in addition to age and parity(model3) in the regression modelwithout any influence on the result (OR = 1.87;1.24-2.80) (Table 2).

Of the children with major malformations in the trimethoprim group,seven had a malformation of the heart (OR = 2.49; 1.18-5.26) and ninehad a congenital malformation of the limbs (OR = 2.18;1.13-4.23)(Table3, Figure 1). No other subgroupings of malformations were significantlyincreased (Table 3).

3.1. Other Analyses. In Denmark, trimethoprim exists in packagesfor 7.5 defined daily doses (DDD), 25 DDD, and in combination withsulfamethoxazole as 7.5 DDD. The 7.5 DDD trimethoprim package is themost common, accounting for 77% of exposures. To confirm that thefindings relate to preconception exposure, we performed a logisticregression analysis that only included women redeeming prescriptions of7.5 DDD trimethoprim and only 14-84 days before conception; this ensureda minimum of one-week washout period before conception. In thisanalysis, the odds ratio was 1.81 (1.11-2.96) compared to unexposedwomen in the same period.

Despite the very low statistical power, we analysed the effect ofthe three treatment regimes. Women with a prescription of 7.5 DDDtrimethoprim (n = 285) were more likely to give birth to children withmajor congenital malformations (OR = 2.06; 1.29-3.28). Women redeemingprescriptions for 25 DDD trimethoprim (n = 45) or trimethoprim andsulfamethoxazole in combination (n = 75) had a higher risk of having achild with a major congenital malformation (OR = 2.06;0.64-6.64 and OR =1.62;0.59-4.44, resp.).

There was no difference in the risk estimate when adjusting for ageof offspring at the time of diagnosis and no association between theyear of conception and the number of children born with a majormalformation (P = 0.15).

A secondary reference group of women exposed to mecillinam in the12 weeks before conception was used in a direct comparison with thewomen exposed to trimethoprim in the same period. For this calculation,there was still an increased risk of having a child with a congenitalmalformation when exposed to trimethoprim compared to being exposed tomecillinam in the 12 weeks before conception (OR =1.78; 1.15-2.77). Ofthe children with major malformations, seven (28.0%) had multiplemalformations in the exposed group compared with 4799 (27.5%) in theunexposed group (OR = 1.03; 0.43-2.46).

There was no difference in the incidence of major congenitalmalformations in children born to women dispensing trimethoprim solelyin weeks 13-24 (OR = 1.20; 0.73-1.98) or weeks 25-36 (OR = 1.13;0.68-1.90) before conception.

A post hoc analysis regarding the women exposed to trimethoprimwithin the 50 days before conception was made and the odds ratio wasonly minimally different compared to the 12-week period prior toconception (OR = 2.06; 1.26-3.37). Two women in the trimethoprim groupwere exposed to a drug classified X during their pregnancy, but neitherof them had offspring with congenital malformations.

4. Discussion

In the present study, we found a doubling in the prevalence ofmajor congenital malformations in offspring of women exposed totrimethoprim during the 12 weeks before conception. According to theEUROCAT subgrouping, there was an increased prevalence of heart and limbdefects.

We considered several sources of possible bias. Infections may beteratogenic, and in Denmark, for younger women, trimethoprim is almostexclusively used to treat urinary tract infections. To rule out thepossibility that these infections are the cause of malformations, wecompared our results with those from women receiving mecillinam, inDenmark, a widely used penicillin primarily to treat urinary tractinfections.

The result of this analysis (Table 2) shows that the use during thesame preconceptional period of mecillinam is not associated with asimilarly increased risk of congenital malformations. This indicatesthat confounding due to urinary tract infections is unlikely. Thetrimethoprim-exposed and -unexposed groups are not comparable withrespect to age, education, and income. On average, the women exposed totrimethoprim were 1.2 years younger and had a lower income andeducational status. Nevertheless, additional logistic regressionanalyses taking these differences into account did not change theresults substantively. To exclude the importance of othercharacteristics of women using trimethoprim, we compared the result withdispensing of trimethoprim much earlier than the pregnancy period butfound no increased risk with dispensing 13-24 weeks and 25-36 weeksbefore pregnancy.

Multivitamin supplementation containing folic acid used prior toand during early pregnancy has been associated with a reduced risk ofhaving offspring with malformations, amongst others, of the limbs andheart [4-8]. Furthermore, heart and limb defects are typicallyassociated with genetic factors and exposure to thalidomide, rubellavirus, and alcohol during pregnancy. Since we found an increase in thesemalformations only, this could indicate that folate deficiency couldexplain the observed association between malformations andpreconceptional dispensing of trimethoprim. We also found a higher oddsratio of neural tube defects and orofacial clefts, which aremalformations that are also reduced by the use of folic acid (Figure 1).However, this was statistically insignificant and it was based on a verysmall number of cases in our study. Overall, we do not have sufficientexposed cases to conduct valid analyses for all EUROCAT subgroups.

The mechanism of trimethoprim as a folic acid antagonist couldexplain the association found, and the previous studies have shown thattrimethoprim can reduce serum folate levels [20, 26-28]. We find itpossible that women with a low folate level before commencing treatmentcould be especially vulnerable to trimethoprim and thereby be exposed tofolate deficiency that affects the foetus during the first trimester.Trimethoprim works by inhibiting dihydrofolate reductase, with a similarmode of action to that of the recognized teratogenic drug methotrexate,which, like other cytotoxic agents, is suspected of inducingmalformations when given during the months leading up to pregnancy. Eventhough no studies have been able to show an association betweenpreconceptional methotrexate and congenital malformations [29, 30], itis recommended that safe contraception be used during and for at least3-6 months after treatment with methotrexate [16, 31, 32]. Methotrexateis thought to be retained for several weeks in the kidneys and formonths in the liver, thereby affecting the fertilized ova [16], but weare unaware of any equivalent reports of the retention of trimethoprim.

In the present study, the period of interest was predefined asbeing 12 weeks but, in truth, we do not know how long the vulnerableperiod prior to pregnancy is. One previously published study hasindicated that treatment with trimethoprim may lower plasma folate forup to 50 days [20]. We therefore made a post hoc analysis of the 50 daysperiod before pregnancy and found an increased risk of having a childwith a malformation (OR = 2.06; 1.26-3.37) compared to trimethoprim usein the 84 days period prior to pregnancy (Figure 2). However, we foundno increase in the number of malformations when using trimethoprim 13-24and 25-36 weeks prior to conception.

If the association between trimethoprim and malformations was dueto induced folate deficiency, we would expect to find fewer childrenborn with malformations in the study population in the years afterintroduction of an official folic acid supplementation policy. Officialrecommendations regarding folic acid supplementations were introduced inDenmark in 1997. At that time, it was estimated that only 5% of theDanish women received the recommended daily dosage of folate [21]. In2004, at the end of our study period, compliance was very low, such thatonly 22% of women with a planned pregnancy followed the officialrecommendations [22]. In the present study, we did not find anyassociation between the numbers of malformations and the year ofconception. This could very well be because of the poor compliance inDanish women during the study period.

Prescription data and malformation data have been studied beforeand found to be accurately recorded [13, 23, 24]. Pharmacies arerequired to register prescriptions and this activity is coupled with thereimbursem*nt of expenses from the state, which ensures highly accurateprescription data [13]. Completeness has previously been estimated to be97.5% [23]. The quality of the diagnoses of congenital malformations hasbeen validated and found to have a predictive value of 88.2% for havinga congenital malformation, with a completeness of 89.9% [24]. More than99.5% of the births in Denmark since 1978 are registered in the DanishFertility Database [12].

The strengths of this study are the large number of cases and itsnationwide coverage, including all women giving birth in Denmark duringthe study period. This ensures very high completeness of the dataindependent of age, race, and social, educational, and economicstatuses, which thereby minimizes the selection bias. Furthermore, thestudy only includes women who obtained and paid for the medication atthe pharmacy.

The main limitation of the study is a potential existence ofunaccounted confounding. Women using trimethoprim preconceptionally maydiffer in important characteristics from women who do not receive thetreatment. Such characteristic could be causally related to thepregnancy outcome and confound partially or entirely the observedassociation. Another limitation is the lack of information concerningdosage and compliance. Even though we know about package and tabletsize, we have no precise information about the dose prescribed. For thisreasons we have restricted the analysis to treatment or no treatment.Furthermore, we do not know about the indication for treatment, forwhich reason we cannot completely rule out the possibility that theresults are confounded by indication. To meet and thereby minimize theselimitations, we have adjusted the analyses for teratogenic conditions,age, parity, and so forth and used an alternative reference group ofmecillinam users. Low compliance would bias the study towards a lack ofeffect and the estimated risk may therefore be underestimated. If thetreatment was taken later, then the effect might be overestimatedbecause of possible postconception administration. This would have onlya minor effect since trimethoprim is mainly used for acute infections inDenmark. Furthermore, it has previously been estimated that the majorityof prescription drugs redeemed are taken [25].

In model 3 we tried to adjust the analyses for conditionspotentially harmful to the fetus. These conditions include medicalconditions such as some autoimmune diseases and diabetes mellitus,infections during pregnancy potential harmful to the fetus, anddiagnoses of folate deficiency This information was taken from theNational Hospital Register and only included women actually diagnosedwith the conditions. If women had any of the conditions but were notdiagnosed at a hospital, the information was not available to us. Thisis a limitation and could potentially confound our adjusted result.Furthermore, we adjusted for use of folic acid. This information isbased on redeemed prescriptions on folic acid and is very deficientsince the majority of folic acid and multivitamin containing folic acidused in Denmark are sold over the counter.

Trimethoprim is used by millions of fertile women worldwide. TheWorld Health Organization (WHO) recommends that adults with symptomaticHIV or AIDS should use lifelong daily prophylaxis with co-trimoxazole(trimethoprim and sulfamethoxazole) [11]. This recommendation affectsmore than 12 million fertile women in sub-Saharan Africa who areestimated to live with HIV infection or AIDS [33, 34]. Furthermore,worldwide, huge numbers of women use shorter courses of trimethoprim totreat urinary infections.

The scale of the problem could be even larger in some countries. Inthe United Kingdom, the Medicines and Healthcare Products RegulatoryAgency has been discussing whether trimethoprim should be reclassifiedfor over-the-counter availability [35]. This could make trimethoprim theprimary medication for urinary tract infections and thereby increase itsuse and the exposure of fertile women. A very large number of pregnantwomen could be exposed prior to pregnancy as a result of such areclassification, especially as only 50% of fertile women are estimatedto plan their pregnancy [36].

Viewed together, although we find the results of the present studybiologically plausible, it is the first time this hypothesis has beentested. It is important to test the hypothesis in other studies.Furthermore, it is important to keep in mind that prophylaxis withtrimethoprim-sulfamethoxazole in people living with HIV or AIDS insub-Saharan Africa has been shown to reduce morbidity and mortality[37-39]. A more general implication of our study concerns pharmaceuticaltreatment prior to pregnancy. If trimethoprim can be retained or is ableto induce lasting folate deficiency, then the use of other drugs mayalso bear a risk. Our study identifies the need for further researchinto the risk of teratogenicity in the months leading up to pregnancy.

In conclusion, we have found an association of maternal exposure totrimethoprim during the 12 weeks before conception and a doubling of therate of congenital malformations in the subsequent offspring. This callsfor further investigation, both epidemiological and in vivo animalstudies.

http://dx.doi.org/10.1155/2013/364526

Conflict of Interests

All authors declare that they have no conflict interests todeclare.

Authors' Contributions

J. T. Andersen, M. Petersen, C. T. Pedersen, and H. E. Poulsenconceived and planned the work that led to the paper. J. T. Andersen andH. E. Poulsen obtained funding and J. T. Andersen wrote the paper. Allauthors played an important role in data analyses and interpretation ofthe results and made substantive suggestions for critically revision forimportant intellectual content and approved the final version of thepaper.

Disclaimer

The funders had no role in study design, data collection andanalysis, decision to publish, or preparation of the paper.

Acknowledgments

The study is supported by grants from the Danish Agency forScience, Technology and Innovation (http://en.fi.dk/)and the P. CarlPetersen Foundation (http://www.pcarlp-fond.dk/).

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Jon Traerup Andersen, (1,2) Morten Petersen, (1,2) EspenJimenez-Solem, (1,2) Jeppe Nergaard Rasmussen, (3) Nadia Lyhne Andersen,(4) Shoaib Afzal, (1,2) Kasper Broedbaek, (1,2) Brian Rafn Hjelvang,(1,2) Lars Keber, (5,6) Christian Torp-Pedersen, (6,7) and HenrikEnghusen Poulsen (1,2,6)

(1) Laboratory of Clinical Pharmacology, Copenhagen UniversityHospital Rigshospitalet, Blegdamsvej 9, 2100 Copenhagen, Denmark

(2) Department of Clinical Pharmacology, Bispebjerg Hospital,Bispebjerg Bakke 23, 2400 Copenhagen, Denmark

(3) Center for Healthy Ageing, Faculty of Health Sciences,University of Copenhagen, Blegdamsvej 3, 2200 Copenhagen, Denmark

(4) Mental Health Centre Copenhagen, Bispebjerg Bakke 23, 2400Copenhagen, Denmark

(5) The Heart Centre, Copenhagen University HospitalRigshospitalet, Blegdamsvej 9, 2100 Copenhagen, Denmark

(6) Department of Cardiology, Gentofte University Hospital, NielsAndersens Vej 65, 2900 Hellerup, Denmark

(7) Faculty of Health Sciences, University of Copenhagen,Blegdamsvej 3, 2200 Copenhagen, Denmark

Correspondence should be addressed to Jon Traerup Andersen;[emailprotected]

Received 26 November 2012; Accepted 11 January 2013

Academic Editor: J. C. Morrison

Copyright [C] 2013 Jon Traerup Andersen et al. This is an openaccess article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproductionin any medium, provided the original work is properly cited.

Table 1: Study population characteristics. Use of trimethoprim No use of in the trimethoprim 12-week period in the 12-week prior to period prior pregnancy to pregnancy n = 402 n = 520,865Age (year) 28.5 29.7Parity (mean) 1.80 1.85Household income--number (%) <$50,000 76 (19) 80,899 (16) $50,000-$100,000 194 (48) 241,907 (46) $100,000-$150,000 110 (27) 150,163 (29) >$150,000 22 (5) 48,240 (9)Education--number (%) Low 168 (42) 182,072 (35) Medium 123 (31) 165,132 (32) Long 98 (24) 149,324 (29) No information available 10 (2) 13,333 (3)Comorbidity (b)--number (%) Teratogenic infectious diseases (c) 1 (a) (0.3) 133 (0.0) Folate deficiency 0 (0) 39 (0.0) Myasthenia gravis 0 (0) 38 (0.0) Virilizing tumors 0 (0) 84 (0.0) Diabetes Mellitus 4 (1) 6258 (1) Alcoholism 0 (0) 111 (0.0) Amniocentesis 1 (a) (0.3) 5381 (1.0) Sjogren's syndrome 0 (0) 38 (0.0) HIV/AIDS 0 (0) 60 (0.0) Pneumocystis carinii pneumonia 0 (0) 2 (0.0) Previous organ transplantation 1 (a) (0.0) 49 (0.0) Use offolic acid--number (%) 9 (2) 4296 (1)(a) None had offspring with a congenital malformation.(b) All information on comorbidity were based on diagnoses fromthe National Hospital Register.(c) Syphilis, toxoplasmosis, rubella virus, varicella virus,parvovirus B-19, cytomegalovirus, herpes simplex viruses 1 and 2,and Venezuelan equine encephalitis virus.Table 2: Risk of congenital malformations associated with trimethoprimuse during the 12-week period prior to conception. All unexposed All unexposed children born 1997- children born 1997-Reference group 2004 2004 adjusted (a) n = 520,865 n = 520,865Major congenital 1.91 (1.28-2.87) 1.87 (1.25-2.80)malformations or(CI 95%)All congenital 2.01 (1.45-2.78) 1.96 (1.41-2.72)malformations or(CI 95%) Children born 1997- Children born 1997- 2004 by mothers with 2004 by mothers with one or more no usage prescription of prescription drugs of mecillinam prior prior to and duringReference group to pregnancy pregnancy n = 3510 n = 91,332Major congenital 1.78 (1.15-2.77) 2.05 (1.37-3.08)malformations or(CI 95%)All congenital 1.90 (1.33-2.72) 2.18 (1.57-3.03)malformations or(CI 95%)(a) Adjusted for age, parity, usage of X-classified drugs,teratogenic infections, folate deficiency, myasthenia gravis,diabetes mellitus, alcoholism, amniocentesis, Sjogren's syndrome,virilizing tumors, education, and income.Table 3: Types of major congenital malformations observed. Number of malformat Odds ratioType of majormalformation Exposed Unexposed (95% CI)Congenital 2 (0.5%) 686 (0.1%) 3.79 (0.94-15.25)malformations of thenervous systemNeural tube defects 1 (0.3%) 234 (0.0%) 5.55 (0.78-39.68)Congenital 0 (0%) 586 (0.1%)malformations of theeyeCongenital 0 (0%) 274 (0.1%)malformations of theear, face, and neckCongenital 7 (1.7%) 3682 (0.7%) 2.49 (1.18-5.26)malformations of theheartCongenital 0 (0%) 469 (0.1%)malformations of therespiratory systemOrofacial clefts 2 (0.5%) 1036 (0.2%) 2.51 (0.62-10.09)Congenital 2 (0.5%) 993 (0.2%) 2.62 (0.65-10.52)malformations of thedigestive systemAbdominal wall 0 (0%) 145 (0.0%)defectsCongenital 1 (0.3%) 1442 (0.3%) 0.82 (0.13-6.40)malformations of theexternal genitalorgansCongenital 1 (0.3%) 1273 (0.2%) 1.02 (0.14-7.25)malformations of theinternal urinarysystemCongenital 9 (2.2%) 5416 (1.0%) 2.18 (1.13-4.23)malformations of thelimbsCongenital 1 (0.3%) 798 (0.2%) 1.62 (0.22-11.60)malformations of themusculoskeletalsystemOther malformations 1 (0.3%) 662 (0.1%) 1.96 (0.28-13.98)Teratogenic 0 (0%) 38 (0.0%)syndromes withmalformationsGenetic syndromes 1 (0.3%) 315 (0.1%) 4.62 (0.58-29.44)and microdeletionsChromosomal 1 (0.3%) 653 (0.1%) 1.99 (0.28-14.17)abnormalitiesAll major congenital 25 (6.2%) 17,465 (3.4%) 1.91 (1.28-2.87)malformationsAll minor congenital 18 (4.5%) 11,600 (2.2%) 2.06 (1.28-3.31)malformationsAll congenital 40 (10.0%) 27,173 (5.2%) 2.01 (1.45-2.78)malformationsMajor congenital malformations among children of mothers exposedto trimethoprim in the 12-week period prior to conception andamong unexposed according to the EUROCAT classification system.