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BackgroundPlacenta accreta spectrum (PAS) is a life-threating complication in the field of obstetrics. Sometimes we face with unexpected PAS cases which is potentially higher maternal mortality and morbidity compared with expected cases. The present study was conducted to examine the prevalence of PAS and to elucidate its risk factors using a large Japanese birth cohort study.MethodsWe reviewed the results of a nationwide prospective birth cohort study in Japan, and identified 90,554 participants treated from 2011 to 2014 in 15 regional centers. Multiple regression models were created to identify the risk factors for PAS. These data were obtained from self-reported questionnaires or patient medical records.ResultsThis analysis consisted of 202 cases of PAS (18 with placenta previa and 184 without placenta previa) and 90,352 cases without PAS. The multiple logistic regression analysis showed that placenta previa (adjusted odds ratio [aOR]: 12.86, 95% confidence interval [CI] 7.70–21.45, P < 0.001), assisted reproductive technology-related pregnancies (aOR: 6.78, 95% CI 4.54–10.14, P < 0.001), smoking during pregnancy (aOR: 1.95, 95% CI 1.15–3.31, P = 0.013), more than two previous cesarean sections (aOR: 2.51, 95% CI 1.35–4.67, P = 0.004), and uterine anomalies (aOR: 3.97, 95% CI 1.24–12.68, P = 0.020) increased the risk of PAS.ConclusionIn general population, placenta previa, assisted reproductive technology-related pregnancy, smoking during pregnancy, repeated cesarean sections, and uterine anomalies were risk factors for PAS in the Japanese population.

Introduction This study evaluated the risk of preterm birth, low birthweight and small‐for‐gestational‐age neonates born to mothers with adenomyosis during pregnancy. Material and methods We used the results of a Japanese nationwide prospective birth cohort study, identifying 93 668 singleton deliveries from 2011 to 2014. We identified 314 pregnancies with adenomyosis using self‐reported questionnaires. Multiple logistic regression analyses were conducted to examine whether adenomyosis was associated with adverse pregnancy outcome. Maternal age, smoking status, method of conception, history of parity, fibroids, endometriosis and body mass index before pregnancy were analyzed as confounding factors. Results Multiple logistic regression analysis showed that pregnancy with adenomyosis was a risk factor for preterm birth at less than 37 weeks (adjusted odds ratio [aOR: 2.49, 95% confidence interval [CI] 1.89‐3.41), preterm birth at less than 34 weeks (aOR 1.91, 95% CI 1.02‐3.55), low birthweight <2500 g (aOR 1.83, 95% CI 1.36‐2.45), low birthweight <1500 g (aOR 2.39, 95% CI 1.20‐4.77) and small‐for‐gestational‐age neonates (aOR 1.68, 95% CI 1.13‐2.51). Conclusions This study found that pregnancy with adenomyosis was associated with preterm birth, low birthweight and small‐for‐gestational‐age neonates.

Foetomaternal alloimmune thrombocytopenia (FMAIT) occurs when maternal antibodies of an antigen-negative mother cause destruction of sensitized foetal platelets. In Caucasian populations, 6-12% of human platelet antigen (HPA)-1a-negative women develop anti-HPA-1a, and the incidence of clinically affected cases is estimated to be 10-20% of immunized women. This study was performed in order to elucidate the rate of maternal immunization, incidence of FMAIT and the likely outcome of the condition in Asians. Excluding two or more pregnancies during the period, serum samples from 24 630 pregnant women, mainly Japanese, were screened for antibodies against platelet alloantigens by means of mixed passive haemagglutination (MPHA) (Anti-HPA-MPHA, Olympus, Tokyo). Antibodies were detected in 0.91% (223/24 630) of the women's samples and the immunization rate was correlated with the number of pregnancies. Antibody specificity included anti-HPA-4b (49), anti-HPA-5a (three), anti-HPA-5b (168), anti-HPA-4b + 5b (one) and anti-Nak(a) (CD36) (two). No alloimmunization was observed within the HPA-1, HPA-2, HPA-3 or HPA-6 systems. Among HPA-4b- or HPA-5b-negative women, 24% or 14% estimated, respectively, had antibodies and 26% (10/38) or 10% (12/125) of neonates, respectively, born to these mothers developed thrombocytopenia. Two neonates born to mothers having anti-HPA-4b developed generalized purpura. No cases of intracranial bleeding or death due to FMAIT were recorded. Generalized purpura due to FMAIT occurs in one in 9359 (95% CI: 1 in 77 519-1 in 2591) pregnancies solely because of HPA-4b incompatibility.