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Little is known about the association between hypospadias and small fetuses, as well as the pathological implications of fetal growth restriction (FGR). Thus, we aimed to investigate the association between hypospadias and small fetuses using a database of fetal ultrasound and obstetric events.A cohort of male singleton infants delivered after 22 weeks of gestation at Keio University Hospital between 2013 and 2019 was retrospectively reviewed. FGR was defined according to the Delphi criteria. Logistic regression analysis was performed to identify the significant predictors of hypospadias. Placental pathology was reviewed in cases with hypospadias.Of the 2,040 male infants included in the present study, 23 had hypospadias. The prevalences of a single umbilical artery (SUA), small for gestational age, maternal hypertensive disorders of pregnancy, and a small placenta, were significantly higher in infants with hypospadias. Multiple logistic regression analysis revealed that FGR (odds ratio [OR] = 9.39; 95% confidence interval [CI], 2.50-35.3) and the presence of a SUA (OR = 33.4; 95% CI, 8.00-139.5) were independently and significantly associated with hypospadias. When FGR was stratified by the time of onset, its association with hypospadias was significant regardless of the time of onset. Moreover, placental histological findings suggested that fetal vascular malperfusion might play a role in hypospadias.FGR and SUAs are independent prenatal predictors of the development of hypospadias, and fetal vascular malperfusion of the placenta may be involved in the etiology of hypospadias.

Ascending inflammation from the vagina is a major cause of preterm birth. Currently, this condition-especially when uncontrolled-has no effective treatment. Human amniotic fluid stem cells (hAFSCs) are mesenchymal stem cells known to exert potent anti-inflammatory effects in animal models of perinatal diseases, such as periventricular leukomalacia, myelomeningocele, and neonatal sepsis. However, hAFSC therapy for inflammation-induced preterm birth has not been tested. In order to determine the therapeutic effect of hAFSC transplantation, we employed a preterm mouse model of ascending infection; this model was constructed by administering lipopolysaccharide to pregnant mice. We investigated the preterm birth rate and evaluated the inflammation of tissues, which is related to progressive infections, such as those involving the cervix, placenta, and lavage cells, using real-time qPCR. Further, we tracked the fluorescence of fluorescently labeled hAFSCs using an in vivo imaging system, and hAFSC aggregation was evaluated using immunohistochemistry analysis. We also investigated the presence of multiple types of peritoneal macrophages via flow cytometry analysis. Finally, we performed sphere culturing and co-culturing to determine the therapeutic effects of hAFSCs, such as their anti-inflammatory effects and their potential to alter macrophage polarization. We found that hAFSC administration to the peritoneal cavity significantly reduced inflammation-induced preterm birth in the mouse model. The treatment also significantly suppressed inflammation of the placenta and cervix. Transplanted hAFSCs may have aggregated with peritoneal macrophages, switching them from an inflammatory to an anti-inflammatory type. This property has been reported in vivo previously, but here, we examined the effect in vitro. Our findings support the hypothesis that hAFSCs suppress inflammation and reduce preterm birth by switching macrophage polarity. This study is the first to demonstrate that hAFSCs are effective in the treatment and prevention of inflammation-induced preterm birth.

Objective The opportunities for sequencing-based methylome analysis of clinical samples are increasing. To reduce its cost and the amount of genomic DNA required for library preparation, we aimed to establish a capture methyl-seq protocol, which adopts pre-pooling of multiple libraries before hybridization capture and TET2/APOBEC-mediated conversion of unmethylated cytosine to thymine. Results We compared a publicly available dataset generated by the standard protocol of SureSelect XT Human Methyl-Seq Kit and our dataset obtained by its modified protocol that adopted sample pre-pooling and enzymatic conversion. We confirmed that the quality of DNA methylation data was comparable between the two datasets. As our protocol, EMCap, is more cost-effective and reduces the amount of input genomic DNA, it would serve as a better choice for clinical methylome sequencing.

Radical trachelectomy (RT) is a surgery for early-stage cervical cancer treatment that preserves the childbearing ability, and its use has become increasingly common worldwide. Thus, the rate of conception in women who have undergone RT is increasing. However, pregnancy after RT is associated with a higher risk of several obstetric complications such as preterm delivery, preterm premature membrane rupture, and abnormal bleeding from varices at the site of uterovaginal anastomosis. Furthermore, since RT have a residual prophylactic cerclage, it is difficult to manage first- and second-trimester miscarriages. There is little previous data on the management of pregnancy after RT. In this review article, we summarize various management methods and experiences to provide a guide to clinicians for perinatal management after RT.

BackgroundProgress in reducing the global low birthweight (LBW) has been insufficient. Although the focus has been on preventing preterm birth, evidence regarding LBW in term births is limited. Despite its low preterm birth prevalence, Japan has a higher LBW proportion than other developed countries. This study aimed to examine the prevalence of LBW in term singleton births and its associated factors using a national database.MethodsWe retrospectively analyzed the data of neonates registered in the Japan Society of Obstetrics and Gynecology Successive Pregnancy Birth Registry System who were born 2013-2017. Exclusion criteria included stillbirths, delivery after 42 gestational weeks, and missing data. Logistic regression analyses were performed to investigate the maternal and perinatal factors associated with LBW in term singletons using the data of 715 414 singleton neonates.ResultsThe overall prevalence of LBW was 18.3%, and 35.7% of LBWs originated from singleton term pregnancies. Multiple logistic regression analyses indicated that both modifiable and non-modifiable factors were independently associated with LBW in term neonates. The modifiable maternal factors included pre-pregnancy underweight, inadequate gestational weight gain, and smoking during pregnancy, while the non-modifiable factors included younger maternal age, nulliparity, hypertensive disorders of pregnancy, cesarean section delivery, female offspring, and congenital anomalies.ConclusionsUsing the Japanese pregnancy birth registry data, more than one-third of LBWs were found to originate from singleton term pregnancies. Both modifiable and non-modifiable factors were independently associated with LBW in term neonates. Prevention strategies on modifiable risk factor control will be effective in reducing LBW worldwide.

Even in the context of modern medicine, infants with fetal and neonatal neurological diseases such as cerebral palsy and myelomeningocele suffer serious long-lasting impairment due to the irreversible neuronal damage. The promotion of neurologically intact survival in patients with perinatal intractable neurological diseases requires the development of novel strategies. One promising strategy involves the use of human amniotic fluid stem cells (hAFSCs), which have attracted much attention in recent years and are known to exert anti-inflammatory and neuroprotective effects. In recent years, the therapeutic effects of hAFSCs on fetal-neonatal neurological diseases have become evident as per intense research efforts by our group and others. Specifically, hAFSCs administered into the nasal cavity migrated to the brain and controlled local inflammation in a rodent model of neonatal hypoxic-ischemic encephalopathy. In contrast, hAFSCs administered intraperitoneally did not migrate to the brain; they rather formed spheroids in the abdominal cavity, resulting in the suppression of systemic inflammation (including in the brain) via the secretion of anti-inflammatory cytokines in concert with peritoneal macrophages in a rodent model of periventricular leukomalacia. Moreover, studies in a rat model of myelomeningocele suggested that hAFSCs administered in utero secreted hepatocyte growth factor and protected the exposed spinal cord during pregnancy. Importantly, autologous hAFSCs, whose use for fetal-neonatal treatment does not raise ethical issues, can be collected during pregnancy and prepared in sufficient numbers for therapeutic use. This article outlines the results of preclinical research on fetal stem cell therapy, mainly involving hAFSCs, in the context of perinatal neurological diseases.

Pregnancy after conization is associated with a high risk of preterm delivery. However, because risk factors for preterm delivery after conization remain unknown, we conducted a multicenter observational study to investigate risk factors associated with preterm delivery.We selected patients who had previously undergone conization and reviewed medical records from 18 hospitals in cooperation with Keio University School of Medicine between January 2013 and December 2019. Women were classified as nulliparous and primiparous, and a multiple logistic regression analysis was performed to evaluate the relative contributions of the various maternal risk factors for preterm delivery (i.e. delivery before 37 gestational weeks).Among 409 pregnant women after conization, 68 women delivered preterm (17%). The incidence of nulliparity (Pregnant women who previously underwent conization are at risk for preterm delivery. The histological type of AIS and cervical cancer was evaluated as a risk factor for preterm delivery. KEY MESSAGESPrior preterm delivery, presence of a short cervix, and cervical cancer or AIS were predictors of preterm delivery after conization.The depth of conization in cervical cancer or AIS group was significantly larger than that in the CIN group.

Pregnancy after conization is associated with a high risk of preterm delivery. However, because risk factors for preterm delivery after conization remain unknown, we conducted a multicenter observational study to investigate risk factors associated with preterm delivery. We selected patients who had previously undergone conization and reviewed medical records from 18 hospitals in cooperation with Keio University School of Medicine between January 2013 and December 2019. Women were classified as nulliparous and primiparous, and a multiple logistic regression analysis was performed to evaluate the relative contributions of the various maternal risk factors for preterm delivery (i.e. delivery before 37 gestational weeks). Among 409 pregnant women after conization, 68 women delivered preterm (17%). The incidence of nulliparity (p = .014) was higher and a history of preterm delivery (p = .0010) was more common in the preterm delivery group than in the term delivery group. Furthermore, the proportion of women diagnosed with adenocarcinoma in situ (AIS) and cervical cancer in the preterm delivery group was higher than that in the term delivery group (p = .0099 and .0004, respectively). In multiple regression models in nulliparous women, cervical cancer or AIS (Odds ratio [OR]: 4.16, 95% CI: 1.26–13.68, p = .019) and a short cervix in the second trimester (OR: 13.41, 95% CI: 3.88–46.42, p < .0001) increased the risk of preterm delivery. Furthermore, a history of preterm delivery (OR: 7.35, 95% CI: 1.55–34.86, p = .012), cervical cancer or AIS (OR: 5.07, 95% CI: 1.24–20.73, p = .024), and a short cervix in the second trimester (OR: 4.29, 95% CI: 1.11–16.62, p = .035) increased the risk of preterm delivery in the multiple regression models in primiparous women. Pregnant women who previously underwent conization are at risk for preterm delivery. The histological type of AIS and cervical cancer was evaluated as a risk factor for preterm delivery. KEY MESSAGESPrior preterm delivery, presence of a short cervix, and cervical cancer or AIS were predictors of preterm delivery after conization.The depth of conization in cervical cancer or AIS group was significantly larger than that in the CIN group. Prior preterm delivery, presence of a short cervix, and cervical cancer or AIS were predictors of preterm delivery after conization. The depth of conization in cervical cancer or AIS group was significantly larger than that in the CIN group.

IntroductionGenome-wide methylation analyses of gestational diabetes mellitus (GDM) diagnosed after 24 gestational weeks (late GDM (L-GDM)) using cord blood have been reported. However, epigenetic changes in neonates born to mothers with GDM diagnosed before 24 gestational weeks (early GDM (E-GDM)) have not been reported. We investigated DNA methylation in neonates born to mothers with E-GDM using cord blood samples.Research design and methodsGenome-wide DNA methylation analysis was performed using an Illumina EPIC array to compare methylation rates of 754 255 autosomal sites in cord blood samples from term neonates born to 162 mothers with GDM (E-GDM: n=84, L-GDM: n=78) and 60 normal glucose tolerance (normal OGTT) pregnancies. GDM was diagnosed based on Japan Society of Obstetrics and Gynecology criteria modified with International Association of Diabetes in Pregnancy Study Group criteria. In this study, all GDM mothers underwent dietary management, while self-monitoring of blood glucose and insulin administration was initiated when dietary modification did not achieve glycemic control.ResultsThere were no significant differences in genome-wide DNA methylation of cord blood samples between the GDM (E-GDM and L-GDM) groups and normal OGTT group or between the E-GDM and normal OGTT groups, L-GDM and normal OGTT groups, and E-GDM and L-GDM groups.ConclusionsThis is the first report to determine the DNA methylation patterns in neonates born to mothers with E-GDM. Neonates born to mothers with GDM, who were diagnosed based on Japan Society of Obstetrics and Gynecology criteria, may not differ in DNA methylation compared with those born to normal OGTT mothers.

Based on epidemiological and experimental evidence, the origins of childhood obesity and early onset metabolic syndrome can be extended back to developmental processes during intrauterine life. It is necessary to actively investigate antecedent conditions that affect fetal growth by developing reliable measures to identify variations in fetal fat deposition and body composition. Recently, the resolution of ultrasonography has remarkably improved, which enables better tissue characterization and quantification of fetal fat accumulation. In addition, fetal fractional limb volume has been introduced as a novel measure to quantify fetal soft tissue volume, including fat mass and lean mass. Detecting extreme variations in fetal fat deposition may provide further insights into the origins of altered fetal body composition in pathophysiological conditions (i.e., fetal growth restriction or fetal macrosomia), which are predisposed to the metabolic syndrome in later life. Further studies are warranted to determine the maternal or placental factors that affect fetal fat deposition and body composition. Elucidating these factors may help develop clinical interventions for altered fetal growth and body composition, which could potentially lead to primary prevention of the future risk of metabolic dysfunction.

Interventions for gestational diabetes mellitus (GDM), diagnosed in early pregnancy, have been a topic of controversy. This study aimed to elucidate factors that predict patients with GDM diagnosed before 24 gestational weeks (early GDM: E-GDM) who require insulin therapy later during pregnancy. Furthermore, we identified patients whose impaired glucose tolerance should be strictly controlled from early gestation onward. Women diagnosed with GDM were categorized based on the gestational age at diagnosis into E-GDM (n = 388) or late GDM (L-GDM, diagnosed after 24 weeks, n = 340) groups. Clinical features were compared between the groups, and the predictors for insulin therapy was evaluated in the E-GDM group. There were no significant between-group differences in terms of perinatal outcomes (e.g., gestational weeks at delivery, fetal growth, hypertensive disorder of pregnancy), with the exception of the Apgar score at 5 min. Moreover, there was no significant difference in the frequency of insulin therapy during pregnancy between the two groups. Using multiple logistic regression analysis, pre-pregnancy body mass index (BMI) ≥25 kg/m2, a family history of diabetes, and higher fasting plasma glucose (FPG), 1 h-plasma glucose (PG), and 2 h-PG values increased insulin therapy risk during pregnancy in the E-GDM group. Furthermore, since E-GDM patients with abnormal levels of FPG, as well as 1 h-PG or 2 h-PG, and those with pre-pregnancy BMI ≥25 kg/m2 and a family history of diabetes had a higher risk of later insulin therapy during pregnancy, they may require more careful follow-up in the perinatal period.

During the coronavirus disease 2019 pandemic, the Japanese Society of Diabetes and Pregnancy proposed the use of random plasma glucose and glycated hemoglobin measured 1 month after delivery combined with pre‐pregnancy body mass index to detect postpartum glucose intolerance instead of carrying out the oral glucose tolerance test in women with gestational diabetes. We retrospectively evaluated the clinical utility of this strategy to detect postpartum glucose intolerance evaluated by the oral glucose tolerance test after delivery. A total of 275 Japanese women with gestational diabetes were included in the present study. The specificity of 1‐month postpartum random plasma glucose and glycated hemoglobin combined with pre‐pregnancy body mass index to predict postpartum glucose intolerance was 98.0%, with a negative predictive value of 72.6%. However, sensitivity was 6.4%, with a positive predictive value of 55.6%. In conclusion, this Japanese Society of Diabetes and Pregnancy strategy showed high specificity, but low sensitivity, for detecting glucose intolerance postpartum., During the coronavirus disease 2019 pandemic, the Japanese Society of Diabetes and Pregnancy (JSDP) proposed the use of random plasma glucose and HbA1c measured 1 month after delivery combined with pre‐pregnancy body mass index to detect postpartum glucose intolerance instead of performing oral glucose tolerance test in women with gestational diabetes. This JSDP strategy showed high specificity of 98.0% but low sensitivity of 6.4% for detecting glucose intolerance postpartum.

Cardiotocography records fetal heart rates and their temporal relationship to uterine contractions. To identify high risk fetuses, obstetricians inspect cardiotocograms (CTGs) by eye. Therefore, CTG traces are often interpreted differently among obstetricians, resulting in inappropriate interventions. However, few studies have focused on quantitative and nonbiased algorithms for CTG evaluation. In this study, we propose a newly constructed deep neural network model (CTG-net) to detect compromised fetal status. CTG-net consists of three convolutional layers that extract temporal patterns and interrelationships between fetal heart rate and uterine contraction signals. We aimed to classify the abnormal group (umbilical artery pH

The Japanese abnormal glucose tolerance before 24 gestational weeks diagnostic strategy in the evolving coronavirus disease 2019 pandemic published by the Japanese Society of Diabetes and Pregnancy.

No reports have focused on the clinical and metabolic characteristics of gestational diabetes (GDM) in underweight women. The aim of this study is to investigate the clinical and metabolic features of underweight GDM (pregravid BMI,18.5 kg/mWomen diagnosed with GDM were categorized based on their pre-pregnancy BMI as either underweight (There were no notable differences in maternal age at delivery and the rate of nulliparous between the U-GDM and N-GDM groups. Regarding antepartum oral glucose tolerance test profiles, women with U-GDM exhibited significantly lower fasting plasma glucose (FPG) levels than those with N-GDM (Impaired early phase insulin secretion was associated with GDM onset in underweight women.

Calcium and nutrients are transferred from mothers to fetuses or infants during pregnancy or lactation, respectively, promoting metabolic changes in the mother, many uncharacterized. To evaluate these changes, we undertook two parallel studies. In one we analyzed fourteen clinical cases of vertebral fragility fractures, at or before three months after partum, in mothers who breastfed their infants. In the other, we enrolled 79 additional pregnant subjects, some who chose to breastfeed and others who did not, and analyzed changes in bone metabolic status starting between 34 and 36 weeks of gestation and ending one month after partum. In the larger group, bone-resorbing and bone-forming parameters such as serum TRACP5b and osteocalcin, respectively, significantly increased after partum. Among parameters that changed after partum, serum PTH and the bone-resorbing markers serum TRACP5b and urine NTX were significantly higher in mothers who only breastfed infants compared to mothers who fed infants formula or a mix of both. However, bone-forming parameters were comparable between breastfeeding and non-breast-feeding groups after partum, suggesting that elevated bone-resorption occurs only in the breastfeeding group. Radiographic analysis after partum demonstrated that no subject among the 79 analyzed showed vertebral fractures, even those who breastfed exclusively. Among fracture cases analyzed, subjects exhibited significantly lower bone mineral density than did non-fracture cases in breastfeeding-only subjects. We conclude that bone metabolic status significantly changes over the period between pregnancy and post-partum lactation, and that low bone mineral density seen in a small subset of breastfeeding-only cases likely causes post-partum vertebral fragility fractures.

Although maternal pre-pregnancy body mass index (BMI) and gestational weight gain (GWG) are related to fetal growth, there is a paucity of data regarding how offspring sex affects the relationship between maternal BMI in underweight mothers (pre-pregnancy BMI 2) and size for gestational age at birth. The aim of this study was to investigate the effect of offspring sex on the relationships among maternal pre-pregnancy BMI, GWG and size for gestational age at birth in Japanese underweight mothers. Records of women with full-term pregnancies who underwent perinatal care at Kawasaki Municipal Hospital (Kawasaki, Japan) between January 2013 and December 2017 were retrospectively reviewed. The study cohort included underweight (n=566) and normal-weight women (18.5 kg/m2⩽pre-pregnancy BMI2; n=2671). The incidence of small for gestational age (SGA) births in the underweight group was significantly higher than that in the normal-weight group (PPP=0.30) neonates. In the women with female neonates, pre-pregnancy underweight was associated with a significantly increased probability of SGA (odds ratio [OR]: 1.80; PP=0.11). In contrast, in women with male neonates, inadequate GWG was associated with a significantly increased probability of SGA (OR: 1.53; P=0.03), but not with pre-pregnancy underweight (OR: 1.30; P=0.10). In conclusion, the present results suggest that pre-pregnancy underweight is associated with SGA in female offspring but not in male offspring.

A number of data on gestational diabetes mellitus (GDM) in singleton pregnancy is available, however, little is known about the glycemic characteristics of twin pregnancy with GDM. The aim of this study was to compare the severity of dysglycemia between twin and singleton pregnancies with GDM (T-GDM and S-GDM). We retrospectively analyzed pregnancies with GDM defined by the Japan Diabetes Society criteria (T-GDM, n = 20; S-GDM, n = 451) in our hospital. During the study period, women with GDM underwent self-monitoring of blood glucose measurements as well as dietary management. Insulin treatment was initiated when dietary treatment did not achieve the glycemic goal. The glycemic and metabolic characteristics were compared between T-GDM and S-GDM, as follows: gestational week at the diagnosis of GDM, 75 g oral glucose tolerance test (OGTT) results, HbA1c, insulin secretion (i.e. insulinogenic index [IGI] and Insulin Secretion-Sensitivity Index-2 [ISSI-2]), and insulin requirement before delivery. The rate of one abnormal OGTT value in T-GDM was similar to that in S-GDM (60% vs. 71%). There were no significant differences in gestational week and levels of HbA1c at diagnosis, levels of IGI and ISSI-2 between T-GDM and S-GDM (median, 20 weeks vs. 17 weeks, 5.0% vs. 5.2%, 0.58 vs. 0.71, 1.7 vs. 1.8, respectively). The rate of insulin treatment and a median dosage of insulin needed before delivery was comparable between the two groups (T-GDM vs. S-GDM: 45% vs. 32% and 14 vs. 13 unit/day). Our data suggested that the severity of dysglycemia in T-GDM was similar to that in S-GDM during pregnancy.

Aims/Introduction Risk factors of type 2 diabetes mellitus in Japanese women with recent gestational diabetes mellitus are unknown. The objective of the present study was to investigate the clinical and genetic characteristics associated with postpartum abnormal glucose tolerance in Japanese women with gestational diabetes mellitus. Materials and Methods A total of 213 Japanese women with recent gestational diabetes mellitus who underwent a postpartum 2‐h oral glucose tolerance test were investigated. The association between antepartum clinical characteristics and postpartum abnormal glucose tolerance (diabetes or prediabetes based on the Japan Diabetes Society criteria) was examined. Frequencies of 45 known type 2 diabetes mellitus‐associated genetic variants were also compared between women with and without postpartum abnormal glucose tolerance. Results A total of 59 women showed postpartum abnormal glucose tolerance (prediabetes, n = 51; diabetes, n = 8). Plasma glucose levels at 1 or 2 h, the insulinogenic index and the insulin secretion‐sensitivity index‐2 of the antepartum oral glucose tolerance test were independent of postpartum abnormal glucose tolerance risk factors (P = 0.006, P = 0.00002, P = 0.01 and P = 0.006, respectively). Four genetic variants (rs266729 [ADIPOQ], rs6017317 [HNF 4A], rs5215 [KCNJ 11] and rs7177055 [HMG 20A]) showed a nominally significant association with postpartum abnormal glucose tolerance (P

Introduction Women who have undergone radical trachelectomy as a fertility-sparing treatment for early-stage cervical cancer may be at higher risk for retained tissues after early-term miscarriage due to cervical cerclage or cervical necrosis. Dilatation and curettage or aspiration may present additional risks in these women. The aim of this study was to assess the efficacy of expectant management for early pregnancy miscarriage after radical trachelectomy. Material and methods Keio University Hospital records were reviewed for women who conceived after abdominal radical trachelectomy and received perinatal care between 1 April 2012 and 31 March 2020. A total of 62 women (76 pregnancies) were identified, and 13 of these women experienced miscarriage before 12 gestational weeks. The management and outcome of these cases were reviewed in detail. Results The median maternal age at miscarriage was 39 years (range 31-42 years) and the median duration from abdominal radical trachelectomy to conception was 2.60 years (range 0.49-7.30 years). Cervical necrosis before conception occurred in one case (8%). One patient requested treatment with aspiration and the remaining 12 cases were managed with observation for a median of 23 days (range 7-50 days). There were no cases of endometritis or cases requiring dilatation and curettage for residue tissue. Further, no cases developed laceration of the residual cervix and no loss of cerclage sutures after discharge was noted. Conclusions Expectant management seems to be safe and appropriate for first trimester miscarriage after abdominal radical trachelectomy.

Background: Progress on reducing global low birthweight (LBW) prevalence has been insufficient. Although focus has been on preventing preterm birth, evidence surrounding LBW in term birth is limited. Japan has a higher LBW proportion despite a low preterm birth prevalence than other developed countries. The study aim is to examine LBW prevalence in term singleton birth and investigate their causes using a national database. Methods: Retrospective analysis was conducted on 852,351 babies born between 2013 and 2017 registered in the Japan Society of Obstetrics and Gynecology Successive Pregnancy Birth Registry System. Findings: Prevalence of LBW was 18·3%, and a third (35·7%) of LBW derived from singleton term pregnancy. Multiple logistic regression analysis indicated various factors to be independently associated with LBW in term babies. Modifiable maternal factors included pre-pregnancy underweight (adjusted odds ratios [aOR] 1·65, 95% confidence intervals [CI] 1·62-1·69), inadequate gestational weight gain (aOR 1·90, 1·86-1·94), and smoking during pregnancy (aOR 1·78, 1·71-1·85). Non-modifiable factors included younger maternal age, nulliparity, hypertensive disorder of pregnancy, pre-eclampsia, delivery at 37 gestational weeks, cesarean section, female offspring, and congenital anomaly. Interpretation: LBW in term singleton birth was as common as in multiple and preterm births in Japan. Factors causing LBW in term singletons were similar to those in preterm birth, including maternal malnutrition, suggesting that strategies to reduce preterm birth could be equally effective in preventing LBW in term pregnancy. Evaluating the status and monitoring progress within countries on this issue may contribute to the overall reduction of LBW worldwide. Funding: None to declare. Declaration of Interest: None to declare. Ethical Approval: This study was approved by the Ethics committee of the Keio University School of Medicine, Tokyo, Japan (No. 20190220, approved November 25, 2019) and the Clinical Research Review Board, Japan Society of Obstetrics and Gynecology, Tokyo, Japan, (No. 2019-15, approved September 14, 2020).