A growing body of research confirms that adverse environmental exposures during pregnancy can disrupt normal fetal development and pose long-term risks to offspring [1,2]. Among these, maternal drug exposure is one of the most common types of adverse prenatal environments [3,4]. It is reported that 90 % of pregnant women take at least one drug during pregnancy, and 50 % take four or more drugs [5,6]. While many drugs are known to cause severe birth defects when used during pregnancy, the safety and potential risk assessment of most commonly used clinical drugs remain inadequate. Moreover, environmental pollutants complicate the issue, as they can lead to unintended maternal ingestion of or exposure to substances that are harmful to fetal development [[7], [8], [9]]. Notably, the irrational use of drugs during the COVID-19 pandemic in recent years has significantly increased the risk of fetal exposure to potentially hazardous drugs [[10], [11], [12]]. Therefore, it is critical to determine whether prenatal drug exposure affects fetal development and long-term health.

Hydroxychloroquine is a synthetic 4-aminoquinoline antimalarial drug. In addition to its traditional antimalarial effect, it has multiple functions such as immune regulation, immunosuppression, anti-inflammation, protection of vascular endothelium, prevention of thrombosis, blood glucose and lipid regulation, and anti-infection [13]. Currently, hydroxychloroquine is widely used, either alone or in combination with other agents, in the treatment of systemic lupus erythematosus, rheumatoid arthritis and various other autoimmune diseases [[14], [15], [16]]. Due to the relatively high incidence of these diseases in women of childbearing age, hydroxychloroquine is often used to treat maternal autoimmune diseases during pregnancy. It suppresses disease activity in pregnant patients with rheumatic diseases through its anti-inflammatory and immunomodulatory properties, thereby lowering the risk of adverse maternal and fetal outcomes [17]. It is generally considered safe for the treatment of autoimmune diseases during pregnancy, and authoritative guidelines recommend that women with such diseases continue using hydroxychloroquine throughout pregnancy to improve disease and pregnancy outcomes [18]. Recent studies have also shown that hydroxychloroquine is beneficial for the treatment of antiphospholipid syndrome, pregnancy with Sjögren's syndrome, and recurrent miscarriage [[19], [20], [21]]. Furthermore, during the COVID-19 pandemic, hydroxychloroquine was considered a potential first-line drug for treating COVID-19 [22,23], leading to a significant increase in its use among women of childbearing age and pregnant women. Of particular concern is that hydroxychloroquine's slow environmental degradation, persistent residues, and potential for bioaccumulation can collectively lead to increased indirect exposure levels in pregnant women [[21], [22], [23]]. In summary, pregnant women are at high risk of hydroxychloroquine exposure, whether through intentional clinical prescription or inadvertent environmental and dietary sources.

The elimination half-life of hydroxychloroquine during pregnancy is 11 days, and it can still be detected in plasma 42 days after administration [24,25]. Meanwhile, hydroxychloroquine has been proven to cross the placental barrier, thus potentially directly affecting fetal development. It is worth noting that hydroxychloroquine has a slow degradation rate in the environment, with persistent residues and bioaccumulation effects [[26], [27], [28]], which may indirectly affect exposure levels in pregnant women. However, relevant research on developmental toxicity of hydroxychloroquine remains relatively scarce. Studies on the safety of hydroxychloroquine in pregnant women with rheumatic diseases (such as systemic lupus erythematosus) suggest that hydroxychloroquine does not increase the risk of common adverse pregnancy outcomes such as spontaneous abortion, preterm birth, and intrauterine growth restriction [[29], [30], [31], [32]]. However, large-scale population studies on hydroxychloroquine use during pregnancy indicate that in utero exposure to hydroxychloroquine may increase the risk of offspring malformations [33,34]. Moreover, studies have reported ototoxicity and retinotoxicity in infants exposed to chloroquine in utero [[35], [36], [37], [38]], which has raised concerns about the potential fetal toxicity of hydroxychloroquine. Consequently, a comprehensive and systematic evaluation of its impact on pregnancy outcomes, fetal development, and multi-organ function is urgently needed.

In this study, based on the conventional dosage regimen of hydroxychloroquine in pregnant women (https://www.drugs.com/dosage/hydroxychloroquine.html), we administered different doses of hydroxychloroquine to pregnant mice. By observing changes in pregnancy outcomes, maternal/fetal blood metabolic phenotype, fetal physical development, morphological and functional indicators of multi-organ development, we systematically evaluated the impact on fetal development and explored the potential mechanisms. This study will contribute to a more comprehensive understanding of the developmental toxicity of hydroxychloroquine, and provide experimental evidence for further exploration of its long-term hazards.