Strengths and limitations
A major strength of the present study is use of a large sample of a
nationwide cohort study that yields robust findings regarding the impact
of uterine myomas on APOs. The presented aORs provide estimates of risk
of APOs associated with uterine myomas in pregnancy. Specifically, the
aOR of PTB before 34 weeks in women with uterine myomas was nearly twice
that of the control group, suggesting that uterine myomas during
pregnancy might be directly linked to neonatal outcomes. The present
findings suggest the need to appropriately evaluate the PTB risk and
manage pregnancies in women with uterine myomas for suitable PTB
prevention, and improve neonatal outcomes, including administration of
vaginal progesterone, antenatal corticosteroids, antibiotics, and
magnesium sulfate.31–33
The present findings suggest a characteristic etiology of PTB, and pPROM
in women with uterine myomas. Although the biological mechanism of PTB
induced by uterine myomas remains unclear,1,8 studies
have shown that spontaneous PTB including pPROM in cases with uterine
myomas was associated with distortion of the uterine cavity and loss of
uterine distensibility.34,35 In addition, hormonal
changes have been implicated in spontaneous PTB.2Uterine myomas may compromise the myometrium and cause decidualization
of endometrial stromal fibroblasts, inducing spontaneous PTB, as is the
case in endometriosis.2,36,37 Therefore, the present
findings support the notion of a mechanical mechanism of uterine myomas
rather than one depending on inflammatory factors in PTB and pPROM.
Clinically, PTB, and pPROM without II may lack clinical features and may
lead to occult incidence of PTB, and pPROM.
The present study has several limitations. First, the protocol for
diagnosing uterine myomas in early stage of pregnancy was not unified,
and variations in their number, size, and site, as well as history of
myomectomy were not considered. As these factors may affect obstetric
outcomes,2,38 future studies should include
evaluations of these factors. Nevertheless, this may support the notion
that uterine myomas by itself increase APOs regardless of number, size,
and location. Second, several maternal characteristics previously
associated with PTB were not considered, i.e. certain demographic and
psychological characteristics, history of PTB in detail, adverse
behaviors, uterine contractions, cervical length, and biological and
genetic markers. These implicated factors of PTB39should be evaluated in future studies. Nevertheless, we included a large
sample and accounted for factors such as smoking status, maternal
educational status, and annual household income, all of which contribute
to the robustness of the present findings.