Proposal for reference values for the developmental effects of valproate based on human data using a benchmark dose approach.

Following accidental release of valproate into ambient air during manufacture at a French production site in 2018, concerns were raised for inhabitants of the surrounding area. As no toxicological reference value (TRV) was available, the risks could not be properly assessed. The French Agency for Food, Environmental and Occupational Health and Safety (ANSES) was mandated to determine a TRV by inhalation to be used for risk assessment. Major congenital malformations (MCMs) in offsprings of mothers exposed to valproate during pregnancy have been reported in international scientific literature. As these adverse effects were the most sensitive effect identified, they were retained as the critical effect to be used for the TRV. The data from a robust registry on MCMs established by the International Registry of Antiepileptic Drugs and Pregnancy (EURAP) were modellized and support a strong DRR between the prevalence of MCMs in the fetus and in utero exposure. A benchmark dose (BMD) was then calculated as the dose that may trigger a 5% increase in this risk. A lower 95% confidence limit (BMD5%L95%) of 2.26 mg/kg/day, leading to an oral TRV of 0.08 mg/kg/day and a respiratory TRV of 0.26 mg.m-3 after applying an uncertainty factor of 30, was determined.

Antiepileptic Drug Teratogenicity and De Novo Genetic Variation Load.

OBJECTIVE: The mechanisms by which antiepileptic drugs (AEDs) cause birth defects (BDs) are unknown. Data suggest that AED-induced BDs may result from a genome-wide increase of de novo variants in the embryo, a mechanism that we investigated. METHODS: Whole exome sequencing data from child-parent trios were interrogated for de novo single-nucleotide variants/indels (dnSNVs/indels) and de novo copy number variants (dnCNVs). Generalized linear models were applied to assess de novo variant burdens in children exposed prenatally to AEDs (AED-exposed children) versus children without BDs not exposed prenatally to AEDs (AED-unexposed unaffected children), and AED-exposed children with BDs versus those without BDs, adjusting for confounders. Fisher exact test was used to compare categorical data. RESULTS: Sixty-seven child-parent trios were included: 10 with AED-exposed children with BDs, 46 with AED-exposed unaffected children, and 11 with AED-unexposed unaffected children. The dnSNV/indel burden did not differ between AED-exposed children and AED-unexposed unaffected children (median dnSNV/indel number/child [range] = 3 [0-7] vs 3 [1-5], p = 0.50). Among AED-exposed children, there were no significant differences between those with BDs and those unaffected. Likely deleterious dnSNVs/indels were detected in 9 of 67 (13%) children, none of whom had BDs. The proportion of cases harboring likely deleterious dnSNVs/indels did not differ significantly between AED-unexposed and AED-exposed children. The dnCNV burden was not associated with AED exposure or birth outcome. INTERPRETATION: Our study indicates that prenatal AED exposure does not increase the burden of de novo variants, and that this mechanism is not a major contributor to AED-induced BDs. These results can be incorporated in routine patient counseling. ANN NEUROL 2020;87:897-906.

Teratogenicity of antiepileptic drugs.

PURPOSE OF REVIEW: We review data on the comparative teratogenicity of antiepileptic drugs (AEDs), focusing on major congenital malformations (MCMs), intrauterine growth restriction, impaired cognitive development, and behavioral adverse effects following prenatal exposure. RECENT FINDINGS: Prospective registries and meta-analyses have better defined the risk of MCMs in offspring exposed to individual AEDs at different dose levels. Valproate is the drug with the highest risk, whereas prevalence of MCMs is lowest with lamotrigine, levetiracetam, and oxcarbazepine. For valproate, phenobarbital, phenytoin, carbamazepine, and lamotrigine, the risk of MCMs is dose-dependent. Prenatal exposure to valproate has also been confirmed to cause an increased risk of cognitive impairments and autistic traits. In a population-based study, the risk of AED-induced autistic traits was attenuated by periconceptional folate supplementation. SUMMARY: The risk of adverse fetal effects differs in relation to the type of AED and for some AEDs also the daily dose. Although for MCMs the risk is primarily associated with the first trimester of gestation, influences on cognitive and behavioral development could extend throughout pregnancy. Available information now permits a more rational AED selection in women of childbearing potential, and evidence-based counseling on optimization of AED treatment before conception.

Perinatal outcome and healthcare resource utilization in the first year of life after antiepileptic exposure during pregnancy.

Healthcare administrative databases of Italy's Lombardy Region were analyzed with the aim to assess perinatal outcomes and healthcare resource utilization during the first year of life in infants exposed to antiepileptic drugs (AEDs) during pregnancy. Drug prescriptions dispensed in the 12 months before delivery to women, who delivered between 2005 and 2011, were analyzed. Neonates were classified as cases if exposed to AEDs, and each case was randomly matched to seven controls. No significant differences were observed in the risk of congenital malformations between 526 cases and 3682 controls except for valproic acid (odds ratio (OR): 2.29; 95% confidence interval (CI): 1.24-4.22) where cases were more likely to be small for gestational age (χ2 = 7.66; p = 0.006). Cases also had a higher probability than controls of needing at least one specialist visit in a child neuropsychiatry outpatient service (OR: 1.74; 95% CI: 1.22-2.49).

Withdrawal of valproic acid treatment during pregnancy and seizure outcome: Observations from EURAP.

Based on data from the EURAP observational International registry of antiepileptic drugs (AEDs) and pregnancy, we assessed changes in seizure control and subsequent AED changes in women who underwent attempts to withdraw valproic acid (VPA) during the first trimester of pregnancy. Applying Bayesian statistics, we compared seizure control in pregnancies where VPA was withdrawn (withdrawal group, n = 93), switched to another AED (switch group, n = 38), or maintained (maintained-therapy group, n = 1,588) during the first trimester. The probability of primarily or secondarily generalized tonic-clonic seizures (GTCS) was lower in the maintained-therapy group compared with the other two groups, both in the first trimester and for the entire duration of pregnancy. GTCS were twice as common during pregnancy in the withdrawal (33%) and switch groups (29%) compared with the maintained-treatment group (16%). Limitations in the data and study design do not allow to establish a cause-effect relationship between treatment changes and seizure outcome, but these observations provide a signal that withdrawal of, or switch from, VPA during the first trimester could lead to loss of seizure control, and highlight the need for a specifically designed prospective observational study.

Gender issues in antiepileptic drug treatment.

The purpose of this review is to discuss gender-related aspects in the, pharmacokinetics, effects, selection and use of antiepileptic drugs (AED). In general, there are few known gender related differences in pharmacokinetics or efficacy of AEDs. Conversely, gender has a significant influence on the susceptibility to certain adverse effects, not the least those involving alterations in sex hormone metabolism. Particularly relevant are the teratogenic effects of AEDs, with important differences among AEDs in their potential to cause adverse effects on the fetus when used during pregnancy. Pregnancy can also markedly affect the pharmacokinetics of several AEDs, and dose adjustments are often needed during pregnancy to maintain seizure control. Some treatments that are used only by women, such as contraceptive steroids and hormone replacement therapy, can also interact with AEDs to an extent that may affect the utilization of both the AEDs and the other drug.

Risk of Major Congenital Malformations and Exposure to Antiseizure Medication Monotherapy.

Importance: Women with epilepsy (WWE) require treatment with antiseizure medications (ASMs) during pregnancy, which may be associated with an increased risk of major congenital malformations (MCMs) in their offspring. Objective: To investigate the prevalence of MCMs after prenatal exposure to 8 commonly used ASM monotherapies and changes in MCM prevalence over time. Design, Setting, and Participants: This was a prospective, observational, longitudinal cohort study conducted from June 1999 to October 2022. Since 1999, physicians from more than 40 countries enrolled ASM-treated WWE before pregnancy outcome was known and followed up their offspring until 1 year after birth. Participants aged 14 to 55 years who were exposed to 8 of the most frequently used ASMs during pregnancy were included in this study. Data were analyzed from April to September 2023. Exposure: Maternal use of ASMs at conception. Main Outcomes and Measures: MCMs were assessed 1 year after birth by a committee blinded to type of exposure. Teratogenic outcomes across exposures were compared by random-effects logistic regression adjusting for potential confounders and prognostic factors. Results: A total of 10 121 prospective pregnancies exposed to ASM monotherapy met eligibility criteria. Of those, 9840 were exposed to the 8 most frequently used ASMs. The 9840 pregnancies occurred in 8483 women (mean [range] age, 30.1 [14.1-55.2] years). MCMs occurred in 153 of 1549 pregnancies for valproate (9.9%; 95% CI, 8.5%-11.5%), 9 of 142 for phenytoin (6.3%; 95% CI, 3.4%-11.6%), 21 of 338 for phenobarbital (6.2%; 95% CI, 4.1%-9.3%), 121 of 2255 for carbamazepine (5.4%; 95% CI, 4.5%-6.4%), 10 of 204 for topiramate (4.9%; 95% CI, 2.7%-8.8%), 110 of 3584 for lamotrigine (3.1%; 95% CI, 2.5%-3.7%), 13 of 443 for oxcarbazepine (2.9%; 95% CI, 1.7%-5.0%), and 33 of 1325 for levetiracetam (2.5%; 95% CI, 1.8%-3.5%). For valproate, phenobarbital, and carbamazepine, there was a significant increase in the prevalence of MCMs associated with increasing dose of the ASM. Overall prevalence of MCMs decreased from 6.1% (153 of 2505) during the period 1998 to 2004 to 3.7% (76 of 2054) during the period 2015 to 2022. This decrease over time was significant in univariable logistic analysis but not after adjustment for changes in ASM exposure pattern. Conclusions and Relevance: Of all ASMs with meaningful data, the lowest prevalence of MCMs was observed in offspring exposed to levetiracetam, oxcarbazepine, and lamotrigine. Prevalence of MCMs was higher with phenytoin, valproate, carbamazepine, and phenobarbital, and dose dependent for the latter 3 ASMs. The shift in exposure pattern over time with a declining exposure to valproate and carbamazepine and greater use of lamotrigine and levetiracetam was associated with a 39% decline in prevalence of MCMs, a finding that has major public health implications.

Antiepileptic drug treatment in pregnancy: changes in drug disposition and their clinical implications.

Pregnancy is a state where pharmacokinetic changes are more pronounced and more rapid than during any other period of life. The consequences of such changes can be far reaching, not least in the management of epilepsy where the risks with uncontrolled seizures during pregnancy need to be balanced against potential teratogenic effects of antiepileptic drugs (AEDs). This article aims to review the literature on gestational effects on the pharmacokinetics of older and newer generation AEDs and discuss the implications for the treatment of epilepsy in women during pregnancy. Pregnancy can affect the pharmacokinetics of AEDs at any level from absorption, distribution, metabolism, to elimination. The effect varies depending on the type of AED. The most pronounced decline in serum concentrations is seen for AEDs that are eliminated by glucuronidation (UGT), in particular lamotrigine where the effect may be profound. Serum concentrations of AEDs that are cleared mainly through the kidneys, for example, levetiracetam, can also decline significantly. Some AEDs, such as carbamazepine seem to be affected only marginally by pregnancy. Data on pharmacokinetics during pregnancy are lacking completely for some of the newer generation AEDs: pregabalin, lacosamide, retigabine, and eslicarbazepine acetate. Where data are available, the effects of pregnancy on serum concentrations seem to vary considerably individually and are thus difficult to predict. Although large-scale systematic studies of the clinical relevance of the pharmacokinetic alterations are lacking, prospective and retrospective case series have reported an association between declining serum concentrations and deterioration in seizures control. The usefulness of routine monitoring of AED serum concentrations in pregnancy and of dose adjustments based on falling levels, are discussed in this review. We suggest that monitoring could be important, in particular when women have been titrated to the lowest effective AED dose and serum concentration before pregnancy, and when that individual optimal concentration can be used as reference.

Seizure control and treatment changes in pregnancy: observations from the EURAP epilepsy pregnancy registry.

PURPOSE: To analyze seizure control, dose adjustments, and other changes of antiepileptic drug (AED) treatment during pregnancy in a large cohort of women with epilepsy entering pregnancy on monotherapy with carbamazepine, lamotrigine, phenobarbital, or valproate. METHODS: Seizure control and AED treatment were recorded prospectively in 3,806 pregnancies of 3,451 women with epilepsy taking part in European and International Registry of Antiepileptic Drugs and Pregnancy (EURAP), an international AED and pregnancy registry. KEY FINDINGS: Of all cases, 66.6% remained seizure-free throughout pregnancy. Generalized tonic-clonic seizures (GTCS) occurred in 15.2% of the pregnancies. Women with idiopathic generalized epilepsies were more likely to remain seizure-free (73.6%) than women with localization-related epilepsy (59.5%; p < 0.0001). Worsening in seizure control from the first to second or third trimesters occurred in 15.8% of pregnancies. The AED dose was increased during pregnancy in 26.0% and a second AED added to the initial monotherapy in 2.6% of all pregnancies. Seizures were more likely to occur in the first trimester in pregnancies with an increased drug load (35%; increased dose and/or addition of another AED) than in pregnancies without an increased drug load (15.3%) (p < 0.0001). Compared with other monotherapies, pregnancies exposed to lamotrigine were less likely to be seizure-free, 58.2% (p < 0.0001); had more GTCS, 21.1% (p < 0.0001); had a greater likelihood of deterioration in seizure control from first to second or third trimesters, 19.9% (p < 0.01), and were more likely to require an increase in drug load, 47.7% (p < 0.0001). The mean dose increases from the first to third trimesters were 26% for lamotrigine, 5% for carbamazepine, 11% for phenobarbital, and 6% for valproate. There were 21 cases of status epilepticus (10 convulsive): none with maternal mortality and only one with a subsequent stillbirth. SIGNIFICANCE: Although the majority of women remain seizure-free throughout pregnancy, our data suggest that a more proactive approach to adjusting the dose of all AEDs in pregnancy should be considered, in particular for those pregnancies with seizures occurring in the first trimester and those exposed to lamotrigine, to reduce the risk of deterioration in seizure control.

Breastfeeding while on treatment with antiseizure medications: a systematic review from the ILAE Women Task Force

We carried out a systematic review of published information on transfer of antiseizure medications (ASMs) into breastmilk, ASM serum concentrations in breastfed infants, and the wellbeing of infants breastfed by mothers on ASM treatment. Information was extracted from 85 relevant articles. No data on ASM levels in breastmilk or in breastfed infants was identified for cannabidiol, cenobamate, clobazam, eslicarbazepine-acetate, everolimus, felbamate, fenfluramine, retigabine, rufinamide, stiripentol, tiagabine, and vigabatrin. For ASMs, with available information on levels in breastfed infants, very low concentrations (in the order of 10% or less of maternal serum concentrations) were reported for carbamazepine, gabapentin, levetiracetam, oxcarbazepine, phenytoin, valproate, and clonazepam. Slightly higher levels (up to approximately 30% of maternal serum concentrations) have been observed with lamotrigine and topiramate, and in single case reports for brivaracetam, lacosamide, and perampanel. High infant levels (30% up to 100% of maternal serum concentrations) have been reported with ethosuximide, phenobarbital and zonisamide. Adverse infant effects during breastfeeding by mothers on ASMs appear to be rare regardless of the type of ASM, but systematic study is limited. Prospective long-term follow-up studies of developmental outcomes among children who have been breastfed by mothers taking ASMs are sparse and have mainly involved children whose mothers were taking carbamazepine, lamotrigine, levetiracetam, phenytoin or valproate as monotherapy while breastfeeding. Although these studies have not indicated poorer outcome among breastfed children compared with those who were not breastfed, further data on long-term outcomes are needed to draw firm conclusions. It is concluded that breastfeeding should in general be encouraged in women taking ASMs, given the well-established benefits of breastfeeding with regard to both short- and long-term infant health in the general population. Counselling needs to be individualized including information on the current knowledge regarding the woman's specific ASM treatment.

Antiepileptic treatment in pregnant women: morphological and behavioural effects.

It is well established that children exposed to antiepileptic drugs (AEDs) in utero have an increased risk of adverse pregnancy outcomes including foetal growth retardation, major congenital malformations and impaired postnatal cognitive development. However, due to the significant maternal and foetal risks associated with uncontrolled epileptic seizures, AED treatment is generally maintained during pregnancy in the majority of women with active epilepsy. The prevalence of major malformations in children exposed to AEDs has ranged from 4 to 10%, 2-4 times higher than in the general population. More recent studies suggest a smaller increase in malformation rates. Malformation rates have consistently been higher in association with exposure to valproate than with carbamazepine and lamotrigine. Some prospective cohort studies also indicate reduced cognitive outcome in children exposed to valproate compared to carbamazepine and possibly lamotrigine. Information on pregnancy outcomes with newer generation AEDs other than lamotrigine are still insufficient.

Pregnancy registries: differences, similarities, and possible harmonization.

Epilepsy and pregnancy registries have been operational for more than 10 years, have accrued considerable experience, and collected an impressive amount of data. As findings have been published, it has become important to understand how observations from the different registries are comparable, especially since their methodologies differ somewhat. In September 2008, representatives of the UK Epilepsy and Pregnancy Register, the North American AED Pregnancy Registry (NAAPR), and the European and International Registry of Antiepileptic Drugs in Pregnancy (EURAP) met for a workshop. Their objectives were to exchange information on their methodologies and to discuss areas where harmonization might be possible. This report summarizes these discussions.

Global Survey of Guidelines for the Management of Epilepsy in Pregnancy: A report from the International League Against Epilepsy Task Force on Women and Pregnancy.

The ILAE Task Force on Women and Pregnancy conducted a survey among ILAE Chapters of their use of guidelines or recommendations for the management of women with epilepsy during pregnancy. A web-based questionnaire including 10 questions was sent to the 118 ILAE Chapters in December 2017 with repeated reminders until the end of February 2018. In total, 77 chapters (65%) responded, although not to all questions. Out of those responding, 68% reported having guidelines or recommendations, 34% of which were from 2014 or earlier. At least 20% of the guidelines did not include information on possible risk to cognitive development, information regarding specific risks with specific antiepileptic drugs, nor recommendations regarding selection of antiepileptic drugs. Among those responding to the question, 91% reported that recommendations were made regarding folate supplementation, but the recommended dose ranged from 0.4 mg/d to 4 mg/d or more; 34% did not include recommendations regarding drug level monitoring during pregnancy, and 19% did not include guidelines on breastfeeding. Our survey demonstrates that there is a need for the development of up-to-date, globally applicable recommendations for the management of epilepsy during pregnancy.

Italian consensus conference on epilepsy and pregnancy, labor and puerperium.

To facilitate an integrated and rational approach to the care of women with epilepsy of childbearing potential, a group of experts appointed by Italian scientific societies in the fields of epileptology, neonatology, pediatrics, neuropediatrics, child neuropsychiatry, obstetrics, and gynecology held a joint meeting in Santa Trada di Cannitello, Reggio Calabria, Italy, on October 15-16, 2004, with the aim of reaching consensus on the optimal management of these women. An ad hoc system for the classification of available published evidence and the opinions of experts was developed and used to grade recommendations on different aspects related to counseling, diagnostic, and treatment issues. The present document summarizes available evidence on the reciprocal interactions between epilepsy, antiepileptic drugs, fertility, contraception, pregnancy, delivery, breastfeeding, and the offspring. Recommendations are made concerning the information and counseling that should be provided to women with epilepsy with respect to issues related to contraception, conception, pregnancy, labour, and puerperium. More detailed recommendations on the same issues are provided to physicians and other healthcare professionals involved in the care of these women, with special reference to choice of effective contraception, optimization of antiepileptic drug therapy, use of prenatal diagnostic tests and other monitoring procedures, and appropriate management practices in relation to childbirth, puerperium, and the care of the child.

Management of epilepsy in pregnancy: a report from the International League Against Epilepsy Task Force on Women and Pregnancy.

The risks associated with use of antiepileptic drugs during pregnancy are a major concern for all women with epilepsy with childbearing potential. These risks have to be balanced against foetal and maternal risks associated with uncontrolled seizures. This report from the International League Against Epilepsy Task Force on Women and Pregnancy aims to provide a summary of relevant data on these risks as a basis for expert opinion recommendations for the management of epilepsy in pregnancy. The report reviews data on maternal and foetal risks associated with seizures as well as teratogenic risks associated with antiepileptic drug exposure, including effects on intrauterine growth, major congenital malformations, and developmental and behavioural outcomes. The impact of pregnancy on seizure control and on the pharmacokinetics of antiepileptic drugs are also discussed. This information is used to discuss how treatment may be optimized before conception and further managed during pregnancy.

Declining malformation rates with changed antiepileptic drug prescribing: An observational study.

OBJECTIVE: Changes in prescribing patterns of antiepileptic drugs (AEDs) in pregnant women with epilepsy would be expected to affect the risk of major congenital malformations (MCMs). To test this hypothesis, we analyzed data from an international pregnancy registry (EURAP). METHODS: EURAP is an observational prospective cohort study designed to determine the risk of MCMs after prenatal exposure to AEDs. The Cochrane-Armitage linear trend analysis was used to assess changes in AED treatment, prevalence of MCMs, and occurrence of generalized tonic-clonic seizures (GTCs) over 3 time periods: 2000-2005 (n = 4,760), 2006-2009 (n = 3,599), and 2010-2013 (n = 2,949). RESULTS: There were pronounced changes in the use of specific AEDs over time, with a decrease in the use of valproic acid and carbamazepine and an increase in the use of lamotrigine and levetiracetam. The prevalence of MCMs with monotherapy exposure decreased from 6.0% in 2000-2005 to 4.4% in 2010-2013. The change over time in MCM frequency after monotherapy exposure showed a significant linear trend in the crude analysis (p = 0.0087), which was no longer present after adjustment for changes in AED treatment (p = 0.9923). There was no indication of an increase over time in occurrence of GTCs during pregnancy. CONCLUSIONS: There have been major changes in AED prescription patterns over the years covered by the study. In parallel, we observed a significant 27% decrease in the prevalence of MCMs. The results of adjusting the trend analysis for MCMs for changes in AED treatment suggest that changes in prescription patterns played a major role in the reduction of teratogenic events.

Levetiracetam Pregnancy Registry: Final results and a review of the impact of registry methodology and definitions on the prevalence of major congenital malformations.

BACKGROUND: To evaluate pregnancy outcomes among women participating in the antiepileptic drug (AED) Levetiracetam Registry (LEV-Registry), and to review the impact of using two other registries' outcome definitions on the number of major congenital malformations (MCMs). METHODS: This US-based prospective study (ClinicalTrials.gov NCT00345475) was overseen by an independent Expert Panel. Women exposed to levetiracetam at any time during pregnancy enrolled, directly, or via their healthcare provider. The primary outcome was prevalence of MCMs, defined according to a modified version of the Metropolitan Atlanta Congenital Defects Program criteria. RESULTS: Of 491 women enrolled, 465 (94.7%) had a documented outcome. Most (92.3%) received levetiracetam for epilepsy; 323 (69.4%) as monotherapy and 142 (30.5%) as polytherapy. With three twin pregnancies, there were 468 outcomes-444 livebirths, 3 stillbirths, 19 miscarriages, and 2 terminations. Based on the MCM definition used by LEV-Registry, 46 infants among 444 livebirths had MCMs resulting in 10.4% (95% CI 7.7, 13.6) for overall prevalence, 9.4% (95% CI 6.4, 13.2) with monotherapy, and 12.6% (95% CI 7.5, 19.4) with polytherapy. When MCM reports were reviewed independently by staff at EURAP (International Registry of AEDs) and North American AED Pregnancy Registry according to their respective criteria, only 22 and 7 infants of the 46, respectively, were classified as having MCMs. CONCLUSION: The LEV-Registry Expert Panel did not find evidence suggestive of teratogenic association with prenatal exposure to levetiracetam. The substantial differences in which physical findings were considered MCMs highlight the major impact of pregnancy registry methodology on MCM prevalence estimates.

Teratogenic effects of antiepileptic drugs.

The use of older generation antiepileptic drugs (AEDs) during pregnancy is known to be associated with a two- to threefold increased risk of birth defects in the offspring and possible also other adverse outcomes in the exposed infant. Much less has been known about newer generation AEDs in this respect. Recent studies based on national registries as well as specific epilepsy and pregnancy registries are beginning to provide information on comparative teratogenic effects of different AEDs. Hence, the prevalence of birth defects appears to be higher with exposure to valproate compared with carbamazepine and possibly also in comparison with lamotrigine. Further studies based on larger cohorts are needed to compare AEDs at different dosages and to analyse the possible impact of confounding factors. Furthermore, data is insufficient to assess the human teratogenic potential of other newer generation AEDs than lamotrigine. Retrospective and a few small prospective studies suggest that exposure to valproate also might be associated with a lower verbal IQ at school age, but further prospective studies are needed to draw firm conclusions.

Comparative risk of major congenital malformations with eight different antiepileptic drugs: a prospective cohort study of the EURAP registry.

BACKGROUND: Evidence for the comparative teratogenic risk of antiepileptic drugs is insufficient, particularly in relation to the dosage used. Therefore, we aimed to compare the occurrence of major congenital malformations following prenatal exposure to the eight most commonly used antiepileptic drugs in monotherapy. METHODS: We did a longitudinal, prospective cohort study based on the EURAP international registry. We included data from pregnancies in women who were exposed to antiepileptic drug monotherapy at conception, prospectively identified from 42 countries contributing to EURAP. Follow-up data were obtained after each trimester, at birth, and 1 year after birth. The primary objective was to compare the risk of major congenital malformations assessed at 1 year after birth in offspring exposed prenatally to one of eight commonly used antiepileptic drugs (carbamazepine, lamotrigine, levetiracetam, oxcarbazepine, phenobarbital, phenytoin, topiramate, and valproate) and, whenever a dose dependency was identified, to compare the risks at different dose ranges. Logistic regression was used to make direct comparisons between treatments after adjustment for potential confounders and prognostic factors. FINDINGS: Between June 20, 1999, and May 20, 2016, 7555 prospective pregnancies met the eligibility criteria. Of those eligible, 7355 pregnancies were exposed to one of the eight antiepileptic drugs for which the prevalence of major congenital malformations was 142 (10·3%) of 1381 pregnancies for valproate, 19 (6·5%) of 294 for phenobarbital, eight (6·4%) of 125 for phenytoin, 107 (5·5%) of 1957 for carbamazepine, six (3·9%) of 152 for topiramate, ten (3·0%) of 333 for oxcarbazepine, 74 (2·9%) of 2514 for lamotrigine, and 17 (2·8%) of 599 for levetiracetam. The prevalence of major congenital malformations increased with the dose at time of conception for carbamazepine (p=0·0140), lamotrigine (p=0·0145), phenobarbital (p=0·0390), and valproate (p<0·0001). After adjustment, multivariable analysis showed that the prevalence of major congenital malformations was significantly higher for all doses of carbamazepine and valproate as well as for phenobarbital at doses of more than 80 mg/day than for lamotrigine at doses of 325 mg/day or less. Valproate at doses of 650 mg/day or less was also associated with increased risk of major congenital malformations compared with levetiracetam at doses of 250-4000 mg/day (odds ratio [OR] 2·43, 95% CI 1·30-4·55; p=0·0069). Carbamazepine at doses of more than 700 mg/day was associated with increased risk of major congenital malformations compared with levetiracetam at doses of 250-4000 mg/day (OR 2·41, 95% CI 1·33-4·38; p=0·0055) and oxcarbazepine at doses of 75-4500 mg/day (2·37, 1·17-4·80; p=0·0169). INTERPRETATION: Different antiepileptic drugs and dosages have different teratogenic risks. Risks of major congenital malformation associated with lamotrigine, levetiracetam, and oxcarbazepine were within the range reported in the literature for offspring unexposed to antiepileptic drugs. These findings facilitate rational selection of these drugs, taking into account comparative risks associated with treatment alternatives. Data for topiramate and phenytoin should be interpreted cautiously because of the small number of exposures in this study. FUNDING: Bial, Eisai, GlaxoSmithKline, Janssen-Cilag, Novartis, Pfizer, Sanofi-Aventis, UCB, the Netherlands Epilepsy Foundation, and Stockholm County Council.