2025 年 13 巻 3 号 p. 85-86
Chronic abruption-oligohydramnios sequence (CAOS) is defined as a condition characterized by abnormal vaginal bleeding (AVB) without placenta previa, in which amniotic fluid volume is initially normal but later decreases, resulting in oligohydramnios without rupture of the membrane.1) CAOS is frequently associated with extremely preterm delivery (PD) and poor neonatal prognosis due to the high incidence of lung disease caused by the aspiration of bloody amniotic fluid.1,2) Chigusa et al. reported membrane rupture as the main cause of CAOS, with diffuse chronic hemosiderosis detected in all cases;3) however, the mechanism of CAOS remains unclear, and little is known about the disease. To the best of our knowledge, no further reports of CAOS since a report by Elliot et al. have been published in countries other than Japan. Why is CAOS more frequently reported in Japan? Are there more cases of CAOS among Japanese pregnant women?
In patients with CAOS, AVB is often detected from the first trimester. A previous report identified a duration of AVB over 11 weeks as an important risk factor for CAOS among patients with PD.2) Therefore, clinicians should carefully monitor pregnant women with AVB during early pregnancy, which may lead to the diagnosis of CAOS. One possible reason why CAOS is more frequently reported in Japan is that all pregnant women are entitled to receive prenatal checkups covered by government-funded programs. According to the Japanese Ministry of Health, Labour and Welfare, prenatal checkups are performed at medical institutions at least once a month (twice a month after the 24th gestational week and once a week after the 36th week) (https://www.mhlw.go.jp/bunya/kodomo/boshi-hoken10/dl/02.pdf, accessed on 1 February 2025). Thus, obstetricians conduct frequent prenatal checkups, which may improve the chances of diagnosing CAOS. Moreover, since Japan has a universal health insurance system which covers consultation fees for AVB, pregnant women can visit hospitals separately from their routine prenatal checkups for AVB. In contrast, in countries where prenatal checkups are less frequent or pregnant women with complications cannot easily access hospitals, CAOS may be classified as an unexplained pregnancy loss or PD. Although frequent therapeutic amnioinfusions have not been successful in preventing PD, they may help prevent lung injury.4) This suggests that the early diagnosis of CAOS could contribute to improved neonatal outcomes. Pregnancy loss and PD are global issues, and shared analyses of CAOS in Japan may help reduce unexplained pregnancy loss and PD.
None.
None declared.
We would like to thank Editage (www.editage.jp) for English language editing.
Y.K. wrote the manuscript and reviewed and edited the manuscript. Y.F. reviewed and edited the manuscript.
