Strengths and limitations
The strength of the present study is that it is the first large-scale,
nationwide, birth cohort study in Japan that investigated various
factors contributing to placental abruption in pregnant women.
Therefore, the findings of this study can be considered to be
representative of the general pregnant population in
Japan.24 The prospective data were collected by the
physicians, midwives, nurses, and trained research coordinators, and
therefore, are more likely to be accurate.
This study also has a few limitations. First, this study lacked the
definition of placental abruption along with the data for type (occurred
during antepartum or intrapartum) and severity. The severity of
placental abruption could have been graded based on the maternal (DIC,
hypovolemic shock, renal failure), fetal (non-reassuring fetal status,
intrauterine fetal growth restriction, intrauterine fetal death), or
neonatal (preterm delivery, small for gestational age, or neonatal
death) complications.25 The severity usually causes
the premature placental separation. Second, regarding the maternal
background data, we relied on a self-reported questionnaire instead of
objective measurements of uterine myoma before pregnancy. As such, we
were not aware of the size and location of uterine myoma. Third, the
specific ART methods (IVF and/or ICSI; cryopreserved, frozen, or
blastocyst embryo transfer) were not classified in this study. Finally,
although we accounted for several confounding factors based on the
questionnaire, unknown risk factors for placental abruption might have
existed. Further studies are warranted to elucidate the potential impact
of these confounding factors on placental abruption and how these
factors can impact the clinical practice of all obstetric care
providers.