Strengths and limitations
The strength of the present study is that the aORs of LBW and SGA provide clear information for perinatal counseling. Owing to the large study population, including >80,000 participants, our results must be reliable. Since pregnant women have more sleep problems, affected by gestational age and hormonal changes,24than their non-pregnant counterparts, the effect of MSD on fetal and neonatal health may be a great concern for pregnant women. There is no consensus on appropriate MSD required to prevent adverse obstetric outcomes. Therefore, the present study may help to suggest adequate MSD required to prevent LBW and SGA.
The present study has several limitations. First, MSD in the present study is based on self-reported questionnaire data, which might have resulted in an inaccurate calculation of actual MSD. In addition, MSD is a volatile index because it varies daily in the individuals and may vary with gestational age.24 Careful interpretation is needed regarding these instabilities of MSD. Further study with polysomnography and unified gestational age may preclude this limitation. Second, we did not account for the quality of sleep by evaluating factors such as time zone, division, where to sleep, and with whom to sleep. We evaluated MSD as a simple quantitative measurement of maternal sleep. Careful interpretation of the results is needed because the quality of maternal sleep, in addition to MSD, may also affect obstetric outcomes.