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.