Interpretation
The present study, using a large prospective cohort, showed that both MSD and gestational BWG affected neonatal birth weight. Previous studies with relatively small sample sizes have shown a conflicting relationship between MSD and neonatal birth weight.15,19–21 On the basis of the findings of the present study, we speculate that long MSD, along with gestational BWG, decreases the incidence of LBW and SGA.14 Although the effect of MSD on gestational BWG is not clearly defined,30,31 recent studies have reported that excessive sleep duration increased obesity in non-pregnant adults.32,33 The fetuses in mothers with excessive gestational BWG may receive more nutrients and fetal growth through increased plasma volume, which may increase cardiac output and utero-placental blood flow compared to those in mothers with insufficient gestational BWG.34,35 Therefore, sufficient BWG by proper diet and sufficient MSD is required to prevent LBW and SGA; however, the concerns about disadvantages of maternal obesity prevail.36,37
Conversely, the direct effect of MSD on obstetric outcomes in the appropriate gestational BWG group has not been yet reported. As well as maternal inflammatory stress has been reported to be related to several obstetric outcomes such as PTB, FGR, and preeclampsia,38–40 previous studies have also reported that disturbed maternal sleep may cause adverse obstetric outcomes, with augmentation of maternal inflammatory response.15,41 Increased inflammation may interfere with the remodeling of spiral arteries in the placenta, thereby leading to PTB, FGR, and preeclampsia.42–44 Thus, preventing reduced MSD may reduce maternal inflammation and prevent these adverse obstetric outcomes. Further, maternal inflammatory stress is also affected by lifestyle, including dietary habits and exercises45,46; and comprehensive modification of these lifestyles may help in reducing inflammatory stress.
However, >10 h of MSD did not decrease the incidence of LBW and SGA in women with appropriate gestational BWG, which implies that >10 h of MSD did not affect neonatal birth weight. This may be because >10 h of MSD might be affected by maternal diseases, conditions, and behaviors, such as depression, excessive mental stress, and use of sleeping pills,24,47,48which may potentially decrease the neonatal birth weight.49–51 Moreover, because too long MSD may have other unfavorable effects including excessive BWG,32,33 we do not suggest that pregnant women should have >10 h of sleep.