Higher prevalence of hypertensive disorders of pregnancy in women who smoke: the Japan environment and children's study

Impact of maternal smoking and secondhand smoke exposure during singleton pregnancy on placental abruption: analysis of a prospective cohort study (the Japan Environment and Children's Study)

OBJECTIVES

This study aimed to investigate the association and population-attributable fraction (PAF) of maternal smoking and secondhand smoke (SHS) exposure during pregnancy with placental abruption.

DESIGN

Prospective cohort study.

SETTING

15 regional centres in Japan.

PARTICIPANTS

Pregnant women registered between January 2011 and March 2014 from the Japan Environment and Children's Study.

OUTCOME MEASURES

Data were transcribed from medical records and two self-administered questionnaires. The outcome measure was the incidence of placental abruption. Maternal smoking exposure during pregnancy was categorised based on the number of cigarettes smoked (≤10 or ≥11 cigarettes per day). SHS exposure during pregnancy was evaluated by frequency and duration (almost never or never, 1-3 days/week and/or <1 hour/day and 4-7 days/week and ≥1 hour/day). A modified Poisson regression model, adjusted for known placental abruption risk factors, calculated the risk ratio (RR) and PAF for placental abruption with a 95% Cl.

RESULTS

Of the 81 974 eligible pregnant women, pregnant women smoking ≥11 cigarettes/day during pregnancy had a significantly higher risk of placental abruption. The adjusted RR (aRR) was 2.21 (95% CI 1.21 to 4.06), and the adjusted PAF (aPAF) was 1.90% (95% CI 0.09 to 3.71%). Pregnant women among never-smokers with SHS exposure of 4-7 days/week and ≥1 hour/day had a significantly higher risk (aRR: 2.34, 95% CI 1.29 to 4.28), and the aPAF was 1.89% (95% CI -0.05 to 3.83). Additionally, pregnant women among those who smoked during pregnancy with similar SHS exposure had a significantly higher risk (aRR: 2.21, 95% CI 1.30 to 3.76), with the aPAF of 2.29% (95% CI 0.11 to 4.48).

CONCLUSIONS

Maternal smoking and SHS exposure during pregnancy significantly contribute to the risk of placental abruption in Japan. Therefore, preventive interventions and measures to reduce exposure are required to prevent placental abruption.

Maternal age and the rising incidence of hypertensive disorders of pregnancy: A comprehensive analysis of national claims data from Japan

BACKGROUND

Hypertensive disorders of pregnancy (HDP) significantly increase the risk of developing hypertension and cardiovascular disease (CVD) later in life and are a major cause of maternal mortality. However, little is known about the nationwide, long-term, all-inclusive status of HDP.

OBJECTIVE

To estimate the incidence of HDP from 2011 to 2019 in Hokkaido, Japan, with a focus on age groups.

METHODS

Using National Database (NDB) insurance medical data, a retrospective analysis was conducted. Due to the absence of direct pregnancy data, birth numbers were used as a surrogate for the number of pregnant women to calculate the incidence of HDP.

RESULTS

The average incidence rate of HDP over 9 years was 6.37%. The incidence rate was lowest among women aged 25-29 years, at 5.58% (95% confidence interval [CI]: 5.43-5.73), and increased with age, peaking at 10.58% (95% CI: 10.10-11.09) among women over 40 years. Notably, the incidence rate for women under 20 years of age was 6.70% (95% CI: 5.97-7.51), which was higher than that for women in their 20s. A mean annual increase of 0.25% in age-adjusted incidence was observed during this period, which was statistically significant (R² =  0.87, p <  0.01).

CONCLUSION

This study reveals that the risk of developing HDP is associated with both older childbearing and younger pregnancies and follows a J-curve, suggesting that factors other than maternal aging also contribute to the increased incidence of HDP and that further research on risk factors for HDP, which is on the rise worldwide, is urgently needed.

Adherence to Healthy Prepregnancy Lifestyle and Risk of Adverse Pregnancy Outcomes: A Prospective Cohort Study

OBJECTIVE

To quantify the association between a combination of modifiable prepregnancy lifestyle factors and the risk of adverse pregnancy outcomes (APOs).

DESIGN

Prospective cohort study.

SETTING

The Japan Environment and Children's Study.

POPULATION

A total of 79 703 pregnant Japanese women without chronic disease.

METHODS

Maternal lifestyle before pregnancy was assessed using a self-administered questionnaire. A healthy lifestyle score (HLS, 0-5 points) was calculated based on adherence to five prepregnancy healthy lifestyle factors: healthy weight, high-quality diet, regular physical activity, not smoking, and not drinking alcohol. Relative risks (RRs) and 95% credible intervals (CrIs) were estimated using a Bayesian log-binomial regression model.

MAIN OUTCOME MEASURES

Composite APOs, defined as the development of any APO, including gestational diabetes, hypertensive disorders of pregnancy, preterm birth, low birth weight, and small-for-gestational-age, transcribed from medical records.

RESULTS

A total of 13 894 women (17.4%) experienced one or more APOs. HLS was inversely associated with the risk of APOs in a dose-response manner. Women with an HLS of 5 points had a 33% (RR 0.67; 95% CrI, 0.61-0.74) lower risk of APOs than those with the lowest HLS (0-1 points). The population attributable fraction of five healthy lifestyle factors was 10.3%. A 1-point increase of HLS could have reduced APO cases by 6.6%.

CONCLUSIONS

A higher HLS was associated with a lower risk of APOs, suggesting that adopting a healthy lifestyle before pregnancy may reduce the risk of APOs, which can increase the risk of future chronic diseases in both mother and child.

Association between urinary cotinine level and hypertensive disorders of pregnancy in women with uterine myoma: findings from the Japan Environment and Children's Study

The effect of smoking on hypertensive disorders of pregnancy is a public concern. Recent evidence suggests that the risk of hypertensive disorders of pregnancy is influenced by the presence of uterine fibroids. We explored the association between maternal smoking exposure and the risk of hypertensive disorders of pregnancy in relation to the presence of uterine fibroids using data from Japan's largest birth cohort study. This study focused on first-time mothers, and the study population comprised 2752 and 35,294 first-time mothers with and without uterine fibroids, respectively. Hypertensive disorders of pregnancy was categorized as early-onset (before 34 weeks) and late-onset (after 34 weeks). Maternal smoking exposure was assessed by measuring the urinary cotinine concentration during the mid-trimester. Participants were classified into four quartiles based on their urinary cotinine levels as follows: Q1 (low concentration) to Q4 (high concentration). Multivariate analysis adjusted for potential confounders revealed that in women without uterine fibroids, the Q3 urinary cotinine level was associated with a modified risk of early-onset hypertensive disorders of pregnancy (adjusted odds ratio: 0.63, 95% confidence interval: 0.44-0.89). Conversely, for women with uterine fibroids, Q4 urinary cotinine level was associated with an increased risk of hypertensive disorders of pregnancy (adjusted odds ratio: 1.68, 95% confidence interval: 1.05-2.72). In conclusion, this study indicated that the impact of maternal smoking exposure varied based on the presence of uterine fibroids, underscoring the importance of personalized preconception care.

Early prediction of hypertensive disorders of pregnancy toward preventive early intervention

Background

Various disease prediction models have been developed, capitalizing on the wide use of electronic health records, but environmental factors that are important in the development of noncommunicable diseases are rarely included in the prediction models. Hypertensive disorders of pregnancy are leading causes of maternal morbidity and mortality and are known to cause several serious complications later in life.

Objective

This study aims to develop early hypertensive disorders of pregnancy prediction models using comprehensive environmental factors based on self-report questionnaires in early pregnancy.

Study Design

We developed machine learning and artificial intelligence models for the early prediction of hypertensive disorders of pregnancy using early pregnancy data from approximately 23,000 pregnancies in the Tohoku Medical Megabank Birth and Three Generation Cohort Study. We clarified the important features for prediction based on regression coefficients or Gini coefficients of the interpretable artificial intelligence models (i.e., logistic regression, random forest and XGBoost models) among our developed models.

Results

The performance of the early hypertensive disorders of pregnancy prediction models reached an area under the receiver operating characteristic curve of 0.93, demonstrating that the early hypertensive disorders of pregnancy prediction models developed in this study retain sufficient performance in hypertensive disorders of pregnancy prediction. Among the early prediction models, the best performing model was based on self-reported questionnaire data in early pregnancy (mean of 20.2 gestational weeks at filling) which consist of comprehensive lifestyles. The interpretation of the models reveals that both eating habits were dominantly important for prediction.

Conclusion

We have developed high-performance models for early hypertensive disorders of pregnancy prediction using large-scale cohort data from the Tohoku Medical Megabank project. Our study clearly revealed that the use of comprehensive lifestyles from self-report questionnaires led us to predict hypertensive disorders of pregnancy risk at the early stages of pregnancy, which will aid early intervention to reduce the risk of hypertensive disorders of pregnancy.

Hokkaido birth cohort study in Japan on the growth trajectory of children born with low birth weight until 7 years of age

BACKGROUND

Low birth weight (LBW) is a significant global health concern with potential health risks and developmental implications for infants. Catch-up growth, an accelerated growth following an inhibition period, may partially compensate for growth deficits in LBW children.

AIMS

This study investigated the prevalence of LBW and catch-up growth in height, weight, and body mass index (BMI) among LBW children in Japan, identified factors associated with LBW, and explored the potential for catch-up growth at different ages up to seven years.

STUDY DESIGN AND SUBJECTS

The Hokkaido birth cohort study included 20,926 pregnant Japanese women recruited during their first trimester from 37 hospitals and clinics. Follow-up assessments were conducted in children up to seven years of age, tracking LBW children's growth and development using the Maternal and Child Health Handbook, and providing valuable insights into catch-up growth patterns.

OUTCOME MEASURES

LBW was defined as a neonatal birth weight of <2500 g. The primary outcomes were catch-up growth in height, weight, and BMI at different ages. Z-scores were calculated to assess growth parameters with catch-up growth, defined as a change in z-score (> 0.67) between two time points.

RESULTS AND CONCLUSIONS

A LBW was prevalent in 7.6 % of the cohort, which was lower than that reported in other Japanese studies. Among LBW children, 19.3 % achieved catch-up growth in height by age seven, and 10.6 % in weight. Catch-up growth in LBW children could partially offset these deficits. Further research will help understand the long-term outcomes and inform interventions for healthy development.

Association of Gestational Hypertension with Sociodemographic and Anthropometric Factors, Perinatal Outcomes, Breastfeeding Practices, and Mediterranean Diet Adherence: A Cross-Sectional Study

Background and Objectives: Gestational hypertension has been associated with several pregnancy short-term and long-term complications, affecting both the mother and her infant's health. The present study aims to assess the potential association of gestational hypertension with sociodemographic and anthropometry factors, perinatal outcomes, breastfeeding habits, and Mediterranean diet (MD) compliance. Materials and Methods: This is a cross-sectional study conducted on 5271 mothers that was carried out after delivery. The anthropometry characteristics and perinatal outcomes were retrieved from the mothers' medical records. Sociodemographic characteristics, MD adherence, and breastfeeding habits were assessed via one-to-one interviews of the assigned women with qualified staff. Results: Maternal older age, being employed, family history of gestational hypertension, overweight/obesity before gestation, and abnormal gestational weight gain (GWG) independently increased the risk of developing gestational hypertension. Moreover, gestational hypertension was independently related with a greater incidence of abnormal childbirth body weight and preterm birth, not exclusively breastfeeding, and lower levels of MD adherence. Conclusions: This study highlights the importance of informing future mothers about the risk factors of gestational hypertension, underlining also that a healthy lifestyle, which simultaneously includes a healthy nutritional pattern such as MD, may decrease the risk of developing gestational hypertension and the subsequent pregnancy complications.

Association Between Smoking and Hypertension in Pregnancy Among Japanese Women: A Meta-analysis of Birth Cohort Studies in the Japan Birth Cohort Consortium (JBiCC) and JECS

BACKGROUND

Recent literature suggest the effect of maternal smoking on risk of hypertensive disorders in pregnancy (HDP) and preeclampsia may differ by ethnicity; however, studies on Asians are limited.

METHODS

We investigated the association of maternal smoking with HDP and preeclampsia using a common analysis protocol to analyze the association in six birth cohorts participating in a Japanese consortium of birth cohorts (JBiCC). Results were compared with-published results from cohorts not included in this consortium, and, where possible, we produced a meta-analysis including these studies.

RESULTS

Meta-analysis of four cohort studies including 28,219 participants produced an odds ratio (OR) of 1.24 (95% confidence interval [CI], 0.88-1.87) for the effect of smoking beyond early pregnancy compared to women who did not smoke during pregnancy. These results combined with those from the Japan Environment and Children's Study (JECS) yielded an OR of 1.19 (95% CI, 1.00-1.43, P = 0.056). Meta-analysis results for categories of smoking volume were insignificant, but when combined with JECS yielded an OR of 0.86 (95% CI, 0.65-1.12) for smoking 1-4 cigarettes, 1.25 (95% CI, 0.98-1.60) for smoking 5-9 cigarettes, and 1.27 (95% CI, 1.04-1.54) for smoking 10 or more cigarettes per day. All effects were insignificant for preeclampsia.

CONCLUSION

Our results suggest that the protective effects of smoking longer and smoking more on HDP and preeclampsia repeatedly observed among Europeans and North Americans likely do not hold for the Japanese.

Hypertension and its correlates among pregnant women consuming tobacco in India: Findings from the National Family health Survey-4

Background

Hypertension (high blood pressure) during pregnancy has significant implications on maternal and perinatal morbidity and mortality. Tobacco use during pregnancy amplifies this burden and increases the risk of hypertensive disorders along with adverse birth outcomes. The current study aimed to evaluate the joint risk atpopulation-level of tobacco use and hypertension among pregnant women in India.

Methodology

Data of 32,428 "currently pregnant" women aged 15-49 years was obtained from the National Family Health Survey (NFHS-4) 2015-16to estimate bivariate (tobacco user vs. non-user) and binomial logistic regression analysis in order to get odds ratios of having hypertension. The analysis included socio-demographic variables such as the respondent's age, type of residence, wealth index, and education status.

Results

Prevalence of hypertension among pregnant tobacco users (7.5%) was significantly higher than that of non-users (6.1%). The unadjusted odds of having hypertension were 1.17 (95% CI: 1.02-1.35) times among tobacco users than non-users and increased with age (p < 0.001) and in rural areas (p = 0.02) after adjusting for other covariates. However, it varied inversely with education status (p > 0.05; NS) and wealth quintile (p = 0.01).

Conclusion

The present study identifies the higher co-existence of hypertension among tobacco-using pregnant women and highlights the need for tobacco control/cessation and hypertension prevention and management during pregnancy considering socio-demographic disparities.

Factors associated with postpartum smoking relapse at early postpartum period of Japanese women in the Japan Environmental and Children's Study

BACKGROUND

Postpartum smoking relapse is a serious public health concern. Previous studies have identified several risk factors for postpartum smoking relapse; however, very little is known about the predictors of early postpartum smoking relapse. This study aimed to determine postpartum smoking relapse status and its associated risk factors at 1 month postpartum among Japanese women.

METHODS

Data were obtained from 93,851 mothers with live births in an ongoing birth cohort study, the Japan Environment and Children's Study. Data on smoking status and confounding variables were collected using self-administered questionnaires and medical record transcripts. Self-administered questionnaires were administered during the first trimester, second/third trimester, and 1 month after delivery. A multiple logistic regression analysis was performed.

RESULTS

Among the 14,326 mothers who smoked during pregnancy, 10,917 (76.2%) quit smoking during pregnancy. Subsequently, 617 (5.7%) of the mothers who had quit relapsed smoking at 1 month postpartum. Maternal age (≤24, ≥35), maternal education (≤12 years), parity (≥Second), feeding method (Formula milk), partner smoking status during pregnancy (Smoker), number of cigarettes per day before the cessation of smoking (≥11), maternal alcohol consumption at 1-month postpartum (Drinker), postpartum depression (EPDS score ≥9), and spending time at the parents' home after delivery (≥14 days) were associated with smoking relapse.

CONCLUSIONS

A certain number of mothers relapsed even 1 month postpartum. Besides mother's alcohol and smoking habit before pregnancy, breastfeeding and partner smoking are important factors in early postpartum smoking relapse in Japan.

Population attributable fraction of risk factors for low birth weight in the Japan Environment and Children's Study

BACKGROUND

Low birth weight (LBW), which is considered a birth weight of <2500  g, poses significant health problems for children. However, population attributable fraction (PAF) of risk factors for LBW have not been well studied.

OBJECTIVE

We aimed to re-evaluate associations between risk factors for LBW reported in previous studies that used the Japan Environment and Children's Study (JECS) data, and to estimate the magnitude of risk using PAF.

METHODS

Data including 91,559 mother-child dyads were obtained from JECS. Risk factors identified by previous studies that used JECS data were used to calculate odds ratios for LBW using a Bayesian logistic regression model. Based on calculated odds ratios, the PAF was calculated.

RESULTS

Parity, history of adenomyosis, hypertension disorder of pregnancy, maternal age at birth, prepregnancy body mass index, gestational weight gain (GWG), maternal smoking and lead (Pb) exposure were all significantly associated with LBW. The sum of the PAF of all factors was 79.4 %, with the largest PAF among single risk factors being GWG (16.5 %); the environmental portion of the PAF (Pb exposure, 14.6 % + maternal smoking, 12.1 %) surpassed the PAF of GWG.

CONCLUSION

Our findings suggest that the number of births classified as LBW can be reduced by approximately 27% if Pb exposure is reduced to the lowest quartile and maternal smoking is eliminated. Further investigations are needed to identify unknown risk factors for LBW.

Hypertensive disorders of pregnancy: definition, management, and out-of-office blood pressure measurement

Hypertensive disorders of pregnancy increase the risk of adverse maternal and fetal outcomes. In 2018, the Japanese classification of hypertensive disorders of pregnancy was standardized with those of other countries, and a hypertensive disorder of pregnancy was considered to be present if hypertension existed during pregnancy and up to 12 weeks after delivery. Strategies for the prevention of hypertensive disorders of pregnancy have become much clearer, but further research is needed on appropriate subjects and methods of administration, and these have not been clarified in Japan. Although guidelines for the use of antihypertensive drugs are also being studied and standardized with those of other countries, the use of calcium antagonists before 20 weeks of gestation is still contraindicated in Japan because of the safety concerns that were raised regarding possible fetal anomalies associated with their use at the time of their market launch. Chronic hypertension is now included in the definition of hypertensive disorders of pregnancy, and blood pressure measurement is a fundamental component of the diagnosis of hypertensive disorders of pregnancy. Out-of-office blood pressure measurements, including ambulatory and home blood pressure measurements, are important for pregnant and nonpregnant women. Although conditions such as white-coat hypertension and masked hypertension have been reported, determining their occurrence in pregnancy is complicated by the gestational week. This narrative review focused on recent reports on hypertensive disorders of pregnancy, including those related to blood pressure measurement and classification.

Genetic Variations in Metallothionein Genes and Susceptibility to Hypertensive Disorders of Pregnancy: A Case-Control Study

Background: The involvement of oxidative stress in the pathological process of hypertensive disorders of pregnancy (HDP) gives rise to the interest in exploring the association of genetic variations in antioxidant metallothionein (MT) genes with HDP susceptibility.

Methods: Seventeen single-nucleotide polymorphisms(SNPs) in MT genes were selected to conduct genotyping based on a case-control study consisting of 371 HDP cases (pregnancy with chronic hypertension (66), gestational hypertension (172), and preeclampsia or preeclampsia superimposed on chronic hypertension (133)) and 479 controls. The association between SNPs in MTs and the risk of HDP was estimated with unconditional logistic regression analysis and further tested with the false-positive report probability (FPRP) procedure. The joint effects of SNPs on the HDP risk were assessed by haplotype analysis.

Results: After the adjustment for age and pre-pregnancy body mass index (pre-BMI) in the logistic regress analysis and followed by the FPRP test, the genetic variation rs10636 (OR = 0.46, 95% CI: 0.30–0.71 for GG vs. CC, p = 0.000 and OR = 0.48, 95% CI: 0.32–0.73 for GG vs. CG/CC, p = 0.001) in MT2A was associated with gestational hypertension. Other four SNPs, that is, rs11076161 (OR = 1.89, 95% CI: 1.35–2.63 for GG vs. GA/AA, p = 0.000) in MT1A; rs7191779 (OR = 1.54, 95% CI: 1.11–2.13 for CC vs. CG/GG, p = 0.010) in MT1B; rs8044719 (OR = 0.57, 95% CI: 0.40–0.80 for GT vs. GG, p = 0.001) in MT1DP; and rs8052334 (OR = 1.52, 95% CI: 1.10–2.11 for TT vs. TC/CC, p = 0.012) in MT1B were significantly associated with the susceptibility of HDP. The haplotype analysis among 11, 10, 10, and seven SNPs in MT (MT1A, MT2A, MT1M, MT1B, and MT1DP) genes showed that eight (A-C-G-T-C-G-A-G-C-G-C, OR = 4.559; A-C-T-C-C-C-A-G-C-G-C, OR = 5.777; A-C-T-T-C-G-A-G-C-G-C, OR = 4.590; G-A-T-C-C-G-C-G-G-C-C, OR = 4.065; G-A-T-C-G-C-C-G-G-C-C, OR = 4.652; G-A-T-T-C-C-C-G-G-C-C, OR = 0.404; G-C-T-C-C-C-A-G-G-C-C, OR = 1.901; G-C-T-T-C-C-A-G-G-C-C, and OR = 3.810), five (C-G-A-T-C-A-C-C-G-G, OR = 2.032; C-G-A-T-C-G-C-C-G-G, OR = 2.077; G-A-C-T-C-A-C-C-T-G, OR = 0.564; G-G-A-G-C-A-C-C-G-G, OR = 5.466; G-G-A-T-T-A-G-C-G-G, and OR = 0.284), five (A-C-G-T-C-G-A-G-C-C, OR = 2.399; A-C-T-C-C-C-C-T-G-G, OR = 0.259; G-A-T-C-C-C-C-G-G-C, OR = 1.572; G-A-T-C-G-C-C-G-G-C, OR = 0.001; G-C-T-C-G-C-A-G-G-C, and OR = 2.512), and five (A-C-T-C-C-C-G, OR = 0.634; G-A-G-C-C-C-G, OR = 4.047; G-A-T-T-G-C-G, OR = 0.499; G-C-G-T-C-A-G, and OR = 7.299; G-C-T-C-C-A-G, OR = 1.434) haplotypes were significantly associated with pregnancy with chronic hypertension, gestational hypertension, preeclampsia, or preeclampsia superimposed on chronic hypertension and HDP.

Conclusion: These variant MT alleles and their combination patterns may be used as genetic markers for predicting HDP susceptibility.

Heated tobacco product use and hypertensive disorders of pregnancy and low birth weight: analysis of a cross-sectional, web-based survey in Japan

OBJECTIVES

Knowledge on the impact of heated tobacco product (HTP) use in pregnant women with associated maternal and neonatal risks for hypertensive disorders of pregnancy (HDP) and low birth weight (LBW) is limited. We aimed to assess the status of HTP use among pregnant women in Japan and explore the association of HTP use with HDP and LBW.

DESIGN

Cross-sectional study.

SETTING

Data from the Japan 'COVID-19 and Society' Internet Survey study, a web-based nationwide survey.

PARTICIPANTS

We investigated 558 postdelivery and 365 currently pregnant women in October 2020.

PRIMARY AND SECONDARY OUTCOME MEASURES

Information on HDP and LBW was collected from the postdelivery women's Maternal and Child Health Handbooks (maternal and newborn records). We estimated the age-adjusted ORs and 95% CIs of ever HTP smokers for HDP and LBW and compared them with those of never HTP smokers in a logistic regression analysis.

RESULTS

The prevalence of ever and current HTP use were 11.7% and 2.7% in postdelivery women and 12.6% and 1.1% in currently pregnant women, respectively. Among currently pregnant women who were former combustible cigarette smokers, 4.4% (4/91) were current HTP smokers. Among postdelivery women, ever HTP smokers had a higher HDP incidence (13.8% vs 6.5%, p=0.03; age-adjusted OR=2.48, 95% CI 1.11 to 5.53) and higher LBW incidence (18.5% vs 8.9%, p=0.02; age-adjusted OR=2.36, 95% CI 1.16 to 4.87).

CONCLUSIONS

In Japan, the incidence of ever HTP use exceeded 10% among pregnant women, and HTP smoking may be associated with maternal and neonatal risks.

The association between smoking during pregnancy and hypertensive disorders of pregnancy: A systematic review and meta-analysis

BACKGROUND

Smoking is a major public health problem. However, its association with hypertensive disorders of pregnancy (HDP) is inconclusive.

OBJECTIVE

To find the association between smoking during pregnancy and HDP.

SEARCH STRATEGY

We searched PubMed, Ovid and Cochrane Library up to March, 2021, using terms including "smoking" and "HDP".

SELECTION CRITERIA

Observational studies that assessed the relationship between smoking during pregnancy and HDP were included.

DATA COLLECTION AND ANALYSIS

Odds ratios (OR) and 95% confidence intervals (CI), and other necessary data were extracted. Stata16.0 MP was used to analyze statistics.

MAIN RESULTS

A total of 13 studies were included. Meta-analysis revealed that smoking during pregnancy was a protective factor for HDP (OR 0.78, 95% CI 0.67-0.92), gestational hypertension (OR 0.74, 95% CI 0.69-0.79), and pre-eclampsia (OR 0.65, 95% CI 0.58-0.73). Subgroup analysis showed that smoking during pregnancy was a risk factor for HDP in Asia but a protective factor in Europe and North America. Neither quitting smoking before pregnancy nor during pregnancy had a statistically significant association with HDP.

CONCLUSION

This meta-analysis revealed that smoking during pregnancy might prevent HDP, gestational hypertension, and pre-eclampsia. Smoking during pregnancy was a risk factor for HDP in Asia but a protective factor in Europe and North America.

Hypertensive Disorders during Pregnancy (HDP), Maternal Characteristics, and Birth Outcomes among Japanese Women: A Hokkaido Study

Hypertension during pregnancy causes a greater risk of adverse birth outcomes worldwide; however, formal evidence of hypertensive disorders during pregnancy (HDP) in Japan is limited. We aimed to understand the association between maternal characteristics, HDP, and birth outcomes. In total, 18,833 mother-infant pairs were enrolled in the Hokkaido study on environment and children’s health, Japan, from 2002 to 2013. Medical records were used to identify hypertensive disorders and birth outcomes, namely, small for gestational age (SGA), SGA at full term (term-SGA), preterm birth (PTB), and low birth weight (LBW). The prevalence of HDP was 1.9%. Similarly, the prevalence of SGA, term-SGA, PTB, and LBW were 7.1%, 6.3%, 7.4%, and 10.3%, respectively. The mothers with HDP had increased odds of giving birth to babies with SGA (2.13; 95% Confidence Interval (CI): 1.57, 2.88), PTB (3.48; 95%CI: 2.68, 4.50), LBW (3.57; 95%CI: 2.83, 4.51) than normotensive pregnancy. Elderly pregnancy, low and high body mass index, active and passive smoking exposure, and alcohol consumption were risk factors for different birth outcomes. Therefore, it is crucial for women of reproductive age and their families to be made aware of these risk factors through physician visits, health education, and various community-based health interventions.

Epidemiological studies regarding hypertensive disorders of pregnancy: A review

A hypertensive disorder of pregnancy (HDP) is defined as hypertension emerging after 20 weeks of gestation and resolving up to 12 weeks post-partum, and occurs in about 5% of all pregnancies. Complications associated with HDP have poor prognoses, and maternal deaths attributable to HDP are predicted to exceed 70 000 per year worldwide. Understanding the pathogenesis and risk factors of hypertensive disorders of pregnancy is important, and they are often investigated in observational studies. Given that therapeutic interventions cannot be controlled in observed studies, it is necessary to interpret which factors correspond to exposure and which factors correspond to confounding and intermediate factors in each study. From the Babies and their parents' longitudinal observation in the Suzuki Memorial Hospital on Intrauterine period study, blood pressure in early pregnancy was not only predictive of a child's birthweight, but the trajectory was also associated with the birthweight. From the larger-scale birth cohort studies currently conducted in Japan will provide the novel potential risk factors of hypertensive disorders of pregnancy and preventive strategies of them. In Japan, observational or intervention studies are just beginning to emerge. The continuation of both a distinctive cohort and a large cohort is needed, and the development of good quality intervention trials based on the results of observational studies is important.