Melatonin and Perinatal Outcomes in MVM-Related Fetal Growth Restriction (MIMVMFGR)

Inclusion Criteria: 1. Singleton pregnancy 2. intact membranes 3. detectable fetal cardiac activity, and normal fetal movements. 4. Diagnosis of isolated maternal vascular malperfusion-related fetal growth restriction (MVM-FGR) between 24+0 and 31+6 weeks of gestation, defined as: 1\) Estimated fetal weight (EFW) or abdominal circumference (AC) below the 10th percentile for gestational age, and uterine artery pulsatility index (UtA-PI) or umbilical artery pulsatility index (UA-PI) ≥95th percentile; or 2) Absent or reversed end-diastolic flow in the umbilical artery, regardless of estimated fetal weight. (5) Willingness to participate in the study, ability to comply with the observation and treatment protocol, and provision of written informed consent. Exclusion Criteria: 1. Presence of severe acute or chronic maternal diseases that make continuation of pregnancy unsafe. 2. Fetal structural anomalies, genetic abnormalities, or intrauterine infections. 3. Immediate need for pregnancy termination prior to enrollment, such as absent a-wave in the ductus venosus, preterminal cardiotocography (CTG), or a critically abnormal biophysical profile (BPP). 4. Treatment within 1 month prior to enrollment with medications such as low-molecular-weight heparin, aspirin, sildenafil, or traditional Chinese medicine aimed at preventing miscarriage or supporting pregnancy. 5. Individuals with legally defined disabilities (including visual impairment, hearing impairment, speech impairment, intellectual disability, mental disorders, or physical disability) and patients with psychiatric illness. 6. Participation in another clinical trial within the past 3 months. 7. A history of smoking more than 10 cigarettes per day within 3 months prior to screening. 8. Suspected or confirmed alcohol or substance abuse. 9. Known allergy to melatonin or any component of the investigational product. 10. Any other condition that, in the investigator's judgment, makes the participant unsuitable for this clinical trial.