Ultrasonography is widely used for fetal monitoring but it requires sonographers and is limited to snapshot evaluations at discrete intervals. Here we report a wearable ultrasound patch (UPatch) for continuous and autonomous fetal monitoring. The UPatch can acquire anatomical structures and blood flow velocities, demonstrating good agreement with a handheld clinical ultrasound device on 62 pregnancies. Real-time image segmentation allows autonomous tracking of target vessels to acquire continuous blood flow spectra during fetal and maternal movements without a sonographer. Continuous monitoring data from 52 pregnant women aligned with stratified perinatal conditions, including healthy, small for gestational age, large for gestational age, gestational diabetes, preeclampsia and gestational hypertension. With further technology development, integration with a miniaturized circuit could enable fully wireless operation and greater user mobility. The UPatch could provide continuous assessment of fetal compromise in high-risk pregnancies, expanding prenatal-care capabilities.