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Objectives: To evaluate fetal heart rate (FHR) patterns during sleep in pregnancies complicated by preterm fetal growth restriction (FGR). To determine whether co-existing sleep-disordered breathing (SDB) impacts on acute FHR events or perinatal outcome., Design: Observational case control study., Setting and Population: Women with preterm FGR and gestation-matched well grown controls (estimated fetal weight above the 10th percentile with normal Doppler studies); tertiary maternity hospital, Australia., Methods: A polysomnogram, a test used to measure sleep patterns and diagnose sleep disorders, and concurrent cardiotocography (CTG), were analysed for respiratory events and FHR changes., Main Outcome Measures: Frequency of FHR events overnight in FGR cases versus controls and in those with or without SDB., Results: Twenty-nine patients with preterm FGR and 29 controls (median estimated fetal weight 1st versus 60th percentile, P < 0.001) underwent polysomnography with concurrent CTG at a mean gestation of 30.2 weeks. The median number of FHR events per night was higher among FGR cases than among controls (3.0 events, interquartile range [IQR] 1.0-4.0, versus 1.0 [IQR 0-1.0]; P < 0.001). Women with pregnancies complicated by preterm FGR were more likely than controls to be nulliparous, receive antihypertensive medications, be supine at sleep onset, and to sleep supine (32.9% of total sleep time versus 18.3%, P = 0.03). SDB was common in both FGR and control pregnancies (48% versus 38%, respectively, P = 0.55) but was generally mild and not associated with an increase in overnight FHR events or adverse perinatal outcome., Conclusions: Acute FHR events overnight are more common in pregnancies complicated by preterm FGR than in pregnancies with normal fetal growth. Mild SDB was common in late pregnancy and well tolerated, even by fetuses with preterm FGR., Tweetable Abstract: Mild sleep-disordered breathing seems well tolerated even by highly vulnerable fetuses., (© 2022 John Wiley & Sons Ltd.)