Preliminary results on pregnancy outcomes in women using lamotrigine

In 1992, the International Lamotrigine Pregnancy Registry was initiated to enroll prospectively and to monitor pregnancies exposed to lamotrigine (LTG) for the occurrence of major birth defects. This study presents results as of September 2001 on 168 outcomes exposed to LTG monotherapy and 166 outcomes after pregnancies exposed to LTG polytherapy during the first trimester.

LTG pregnancy exposures are voluntarily reported to the registry by health care providers before they are aware of each pregnancy outcome. Pregnancy-outcome ascertainment is obtained through subsequent follow-up with the reporting health care provider, and each reported birth defect is reviewed by an expert pediatrician. The percentage with major birth defects in pregnancies with known birth defect status was calculated for LTG monotherapy and for polytherapy stratified by trimester of exposure.

The registry identified 334 first-trimester LTG pregnancy outcomes exposed to LTG monotherapy or polytherapy during the first trimester and involving either a live birth with or without a major birth defect or an abortion with a major birth defect. After exposure to LTG monotherapy, the percentage with major birth defects exposed to LTG monotherapy was three (1.8%) of 168 [95% confidence interval (CI), 0.5-5.5%]. There were five (10%) major birth defects observed in 50 outcomes after LTG polytherapy involving valproic acid (VPA; 95% CI, 3.7-22.6%) during the first trimester. The observed proportion of major defects after LTG polytherapy without VPA during the first trimester was five (4.3%) of 116 (95% CI, 1.6-10.3%). No specific patterns of major birth defects in any subgroup or within the registry as a whole were observed.

The sample sizes for individual regimens are too small to rule out small increases in frequency of all major birth defects or even large increases in frequency of rare major birth defects. However, the percentage of outcomes with major birth defects after LTG monotherapy in this study and in another similar pregnancy registry in the United Kingdom did not differ from that reported in the recent literature for women with epilepsy receiving antiepileptic drug monotherapy (4%). The frequency of major malformations after exposures of LTG-VPA is higher than that after the LTG monotherapy or LTG polytherapy regimens without VPA. Although there are published data on frequency of major malformations after VPA exposures in pregnancy, between-study differences in methods and source populations and the wide confidence intervals around the estimate for LTG and VPA limit the utility of comparison with such data, and no conclusions are made at this time about this combination. The continued registration of exposed pregnancies to an exposure registry as early as possible in the pregnancy before any knowledge of the outcome, and before any prenatal testing, will enhance the power of such data.