As a common clinical reproductive health problem, recurrent miscarriage is defined as 2 or more consecutive spontaneous miscarriages before 20 weeks of pregnancy, affecting 1%-2% of people who are trying to conceive. At present, the etiology of most cases is complex, and some of them are still unclear, resulting in a lack of accurate early risk assessment methods in clinical practice.
As a key coenzyme for maintaining cellular energy metabolism, redox balance and DNA repair, nicotinamide adenine dinucleotide (NAD) metabolic abnormalities are closely related to congenital NAD deficiency (CNDD), and CNDD patients are often accompanied by recurrent miscarriage and fetal malformations.
An Australian prospective study published in Human Reproduction in 2025 focused on the association between NAD-related metabolites and recurrent miscarriage, providing a new basis for clinical risk assessment and intervention.
NAD plays a central role in the gestation process, and its synthesis relies on three major pathways: the de novo synthesis pathway starting from tryptophan, the Preiss-Handler pathway with niacin as the precursor, and the remedial pathway with nicotinamide (NAM) as the core. Previous studies have confirmed that NAD synthesis disorders caused by genetic or environmental factors can cause CNDD and be accompanied by embryo loss. In the mouse CNDD model, dietary supplementation with vitamin B3 (NAD precursor) significantly reduced the rate of embryo loss. In clinical practice, traditional risk factors for recurrent miscarriage (such as advanced age, abnormal BMI, inflammation, environmental exposure, etc.) may indirectly affect NAD metabolism: for example, chronic inflammation activates NAD-depleting enzymes, leading to NAD depletion; With age, NAD levels naturally decrease, affecting oocyte quality and endometrial receptivity. However, the direct association between human NAD-related metabolites and recurrent miscarriage has not been clarified, and this study fills this gap. The study included 88 non-pregnant women aged 20-40 years at the Royal Women's Hospital in Sydney, Australia, of which 37 had a history of recurrent miscarriage (6 weeks to 2 years after the last miscarriage), and 51 had no history of miscarriage as a control, and the levels of 26 NAD-related metabolites in whole blood, plasma and urine were detected by ultra-performance liquid chromatography-tandem mass spectrometry, and the following key conclusions were drawn: The levels of 1-methylnicotinamide (1MNA), 2-pyridine formamide (2PY), and 4-pyridine formamide (4PY) in the whole blood, plasma, and urine of women with a history of recurrent miscarriage were significantly higher than those in the control group. These three metabolites are the terminal excretion products of the NAD salvage pathway, and their elevation indicates that NAM metabolism is active in the body, and NAM, as a decomposition product of NAD, needs to be converted into the above substances by methylation and excreted from the body, which indirectly reflects the abnormal NAD metabolic cycle. More importantly, these three metabolites show a strong positive correlation in whole blood, plasma, and urine, indicating that all three detection matrices can be used for clinical testing without relying on a single specimen, which improves the flexibility of clinical application. Univariate analysis showed that plasma 1MNA levels were directly associated with the risk of recurrent miscarriage: for every unit increase in 1 unit of 1 MNA, the risk of miscarriage increased by 2%, and this association remained significant after age adjustment. Furthermore, through the verification of machine learning models such as logistic regression and random forest, it was found that when the prediction model was constructed with three metabolites, 1MNA, 2PY, and 4PY, the area under the receiver operating characteristic curve (AUROC) reached 0.89, indicating that the combination has good risk differentiation ability and can be used as an important reference for clinical risk stratification. The study also focused on the effect of vitamin B3 supplementation on metabolite levels, and found that even if patients taking vitamin B3 supplements were excluded, the levels of 1MNA, 2PY, and 4PY in the recurrent miscarriage group were still significantly increased, and the NAD levels in whole blood were also higher than those in the control group. This suggests that such metabolic abnormalities are not caused by insufficient vitamin B3 intake, but are more likely to reflect the inherent abnormalities of the NAD metabolic pathway in the body, providing important hints for subsequent mechanism research and intervention directions. The three NAD-related metabolites found in this study can be included in the risk assessment system as supplementary indicators, especially for patients with unknown etiology, detecting the levels of 1MNA, 2PY, and 4PY in whole blood or urine, which will help further clarify risk stratification and avoid missing potential metabolic-related risks. Although studies have not directly confirmed that NAD precursor supplementation can improve the outcome of recurrent miscarriage, combined with the protective effect of vitamin B3 in previous mouse models, patients at high risk of abnormal NAD metabolism can consider optimizing their diet (increasing the intake of foods rich in vitamin B3 such as lean meats, nuts, and whole grains) or targeted supplementation under the guidance of doctors after full evaluation, and more clinical studies are needed to verify the effect of intervention in the future. The study also found that 28.6% of patients with recurrent miscarriage had been initially misdiagnosed as "incomplete miscarriage" or "low pregnancy", and the complication rate of such misdiagnosed patients (50.0%) was significantly higher than that of the correctly diagnosed group (20.0%). This suggests that it is necessary to strengthen the ability to accurately diagnose recurrent miscarriage, combine ultrasound and other imaging methods and metabolite detection, and clarify the cause and risk factors as soon as possible to buy time for follow-up treatment. The study was a single-center cohort study with a relatively limited sample size and a short follow-up time, and the impact of long-term metabolic changes on subsequent pregnancy outcomes still needs to be further observed. In addition, the study did not include people of different ethnicities and socioeconomic backgrounds, and the extrapolation of results requires caution. Future clinical research can focus on three aspects: The first is to expand the multicenter sample to verify the universality of metabolite markers; second, to carry out interventional research to clarify the effect of NAD precursor supplementation on the improvement of pregnancy outcomes in high-risk patients; The third is to deeply explore the specific mechanisms of metabolic abnormalities, such as the interaction between NAD metabolism and inflammation and oxidative stress, to provide targets for precision treatment. This study clarified for the first time the association between 1MNA, 2PY, and 4PY NAD-related metabolites and the risk of recurrent miscarriage, providing new risk assessment indicators for clinical practice and enriching the etiological understanding of recurrent miscarriage. For clinicians, NAD-related metabolite testing can be included in the comprehensive evaluation system of patients with recurrent miscarriage, especially for those with unknown causes, and the accuracy of risk stratification can be improved through multi-dimensional assessment. At the same time, combined with the metabolic mechanism of NAD, it provides more targeted health guidance for patients and promotes the transformation of recurrent miscarriage diagnosis and treatment from "empirical" to "precise". [References] 1 Alijotas-Reig J, Garrido-Gimenez C. Current concepts and new trends in the diagnosis and management of recurrent miscarriage. Obstet Gynecol Surv 2013; 68:445–466. 2 Broekhuizen M, Danser AHJ, Reiss IKM, Merkus D. The function of the kynurenine pathway in the placenta: a novel pharmacother apeutic target? Int J Environ Res Public Health 2021; 18:11545. 3 Canto C, Menzies KJ, Auwerx J. 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