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Background/Aim: The median age at childbirth has risen over the past decades. Since the prevalence of chronic diseases also increases with age, drug exposure in women who have not yet completed family planning is an increasingly important topic. This includes potential exposure to anti-estrogenic drugs, which, among others, are used in breast cancer treatment and, in part, should not be taken in the nine months prior to pregnancy. Given the lack of drug utilization studies in this field, we aimed to systematically describe the prevalence of anti-estrogenic drug use in women of childbearing age and to characterize pregnancies occurring in women using these drugs.

Methods: We used German claims data covering ~20% of the German population and the years 2004–2023. For each year, we determined the age-specific and age-standardized prescription prevalence of anti-estrogenic drugs (tamoxifen, fulvestrant, letrozole, anastrozole, and exemestane) among females aged 13–49 years based on cross-sectional analyses. Further we identified all pregnancies occurring in women within one year after anti-estrogenic drug use and described the time between the last prescription and pregnancy onset.

Results: In age group 41–45 years, the prescription prevalences were 3 to 11 times higher compared to age group 31–35 years in 2023. For example, for tamoxifen, it was 3.67 per 1,000 in age group 41–45 vs. 0.55 per 1,000 in age group 31–35 years. The age-standardized prescription prevalence for any anti-estrogenic drug increased by 53% between 2004 (1.48 per 1,000) and 2023 (2.26 per 1,000). Overall, we identified 1,069 pregnancies occurring in women within one year after anti-estrogenic drug use. For tamoxifen (423 pregnancies), there was a prescription within nine months before pregnancy onset in 322 pregnancies (76.1%) and within three months in 116 pregnancies (27.4%).

Discussion/Conclusion: The age-standardized prescription prevalence of anti-estrogenic drug use has increased since 2004 in Germany. Given the parallel trend toward later motherhood, this means there will be an increasing number of pregnancies occurring in mothers after anti-estrogenic therapy. In view of the long half-life of these drugs due to their accumulation in adipose tissue, it will be important to monitor their use and the compliance with recommendations.