A case control study is a type of observational study. In this study design, participants are selected to participate depending on their outcome status. Cases are participants with outcome of interest whereas controls are participants who do not have the outcome of interest. These studies estimate the odds ratio or the odds between the exposure and health outcome, however they cannot prove causality. Advantages of case control studies include the following: inexpensive, easy to design and implement, and are used to study rare outcomes. Case control studies are prone to certain research bias but can be addressed by the investigator through careful designing and planning. This paper describes the case control studies, their advantages, bias in case control studies and how to address them, and discuss the steps in how to conduct this type of study design.

Objective: To investigate the relationship between the levels of selenium, iron and copper in cord blood of neonates and the risk of congenital heart disease (CHD), and analyze their interaction effects. Methods: The subjects were obtained from the birth cohort in Lanzhou area established from 2010 to 2012. A baseline survey was conducted in the first trimester, and the follow-up was conducted in the second trimester, third trimester and 42 days after delivery. The umbilical vein blood was collected from newborns at delivery, and information on their birth outcomes was extracted from medical records. A nested case-control study was used to select 97 neonates with CHD newly diagnosed by echocardiography as the case group, and 194 neonates were selected as the control group by 1∶2 matching according to their mother's age, block and CHD onset time. Inductively coupled ion mass spectrometry was used to detect the concentrations of selenium, iron and copper in neonatal cord blood. The element exposure was categorized into three groups, the low, medium and high concentrations, according to the quartiles Q₁ and Q₃ of selenium, iron and copper concentrations in the control group. The association between cord blood selenium, iron and copper concentrations and CHD was analyzed by conditional logistic regression model using medium concentration as the reference standard. The association of their interactions with CHD was analyzed by a phase multiplication model. Results: The M (Q₁, Q₃) concentration of neonatal cord blood copper was 746.12 (467.48, 759.74) μg/L in the case group and 535.69 (425.21, 587.79) μg/L in the control group, with a statistically significant difference between the two groups (P<0.05). After adjustment for confounders, logistic regression models showed that the risk of CHD development was increased in neonates with either high copper in cord blood (OR=4.062, 95%CI: 2.013-8.199) or high copper combined with high iron (OR=3.226, 95%CI: 1.343-7.750). No correlation was observed between selenium and iron concentrations and the development of CHD in neonates. There was a multiplicative interaction between copper and iron in cord blood on the risk of developing CHD (OR=1.303, 95%CI: 1.056-1.608). Conclusion: There is a multiplicative interaction between iron and copper elements. The high copper and the high copper combined with high iron in umbilical cord blood are risk factors for neonatal CHD.
Humans ; Infant, Newborn ; Copper/analysis* ; Selenium ; Iron/analysis* ; Fetal Blood/chemistry* ; Case-Control Studies ; Heart Defects, Congenital

Objective: To analyze associated factors and adverse pregnancy outcomes of postpartum hemorrhage in the caesarean section of puerperae with different types of placenta previa. Methods: This retrospective research was a case-control study. Puerperae with cesarean section of placenta previa from January 2019 to December 2020 in Women's Hospital, School of Medicine, Zhejiang University were collected and divided into the<1 000 ml control group or ≥1 000 ml postpartum hemorrhage group according to the amount of blood loss during cesarean section. Differences in continuous variables were analyzed by t-test and categorical variables were analyzed by χ² test. The risk factors of postpartum hemorrhage were analyzed by logistic multivariate regression. Results: A total of 962 puerperae were enrolled with 773 cases in the control group and 189 cases in the postpartum hemorrhage group. The incidence of gestational weeks, gravidity, parity, induced abortion, placental accreta and preoperative hemoglobin<110 g/L was significantly different between two groups in different types of placenta previa (P<0.001). Logistic multivariate regression model analysis showed that the independent risk factors of postpartum hemorrhage in the caesarean section of low-lying placenta included placental accreta (OR=12.713, 95%CI: 4.296-37.625), preoperative hemoglobin<110 g/L (OR=2.377, 95%CI: 1.062-5.321), and prenatal vaginal bleeding (OR=4.244, 95%CI: 1.865-9.656). The independent risk factors of postpartum hemorrhage in the caesarean section of placenta previa included once induced abortion (OR=2.789, 95%CI:1.189-6.544), induced abortion≥2 (OR=2.843, 95%CI:1.101-7.339), placental accreta (OR=6.079, 95%CI:3.697-9.996), HBsAg positive (OR=3.891, 95%CI:1.385-10.929), and placental attachment to the anterior uterine wall (OR=2.307, 95%CI:1.285-4.142). The rate of postpartum hemorrhage and premature delivery in puerperae with placenta previa was higher than that in puerperae with low-lying placenta (P<0.001). Conclusions: The associated factors of postpartum hemorrhage in puerperae with different types of placenta previa are different. Placenta accreta is the common risk factor of postpartum hemorrhage in puerperae with low-lying placenta and placenta previa.
Female ; Pregnancy ; Humans ; Cesarean Section ; Postpartum Hemorrhage/surgery* ; Pregnancy Outcome ; Retrospective Studies ; Case-Control Studies ; Placenta Previa/surgery* ; Placenta ; Risk Factors

Objective: Exploring the neuropsychological developmental characteristics and influencing factors of children with speech disorder. Methods: A case-control study was conducted. A total of 395 children diagnosed with speech disorders were selected as speech sound disorder (SSD) group from January 2019 to September 2021 in the speech-speech outpatient department of the Children's Hospital Affiliated to Capital Institute of Pediatrics, and 1 179 healthy children who underwent physical examination in the health department during the same period were selected as the control group. All the children were examined by the "Children's Neuropsychological Behavior Scale 2016 Edition" (Children's Mind Scale 2016 edition). Independent sample t test was used to compare the developmental levels of the two groups of children, including total developmental quotient, gross motor, fine motor, adaptive ability, language and social behavior ability. The influential factors of children's speech disorders were analyzed by univariate Chi-square analysis and multivariate logistic regression. Results: There were 395 SSD children, including 296 males and 99 females, 4≤ age ≤6, (4.71±0.76) years. There were 1 179 children in the control group, including 864 males and 315 females, 4≤ age ≤6, (4.64±0.78) years. The mean value of total developmental factors in SSD group was lower than that in control group [(86.45±11.57)/(91.24±8.0), t=-7.78, P<0.01], and the mean values of total developmental markers in both boys and girls in SSD group were lower than those in control group [(86.00±11.40)/(90.78±7.86), t=-6.70, P<0.01; (87.82±12.03)/(92.87±8.49), t=-3.88, P<0.01]. The mean values of gross motor, fine motor, adaptive ability, language ability and social behavior in SSD group were lower than those in control group [(89.76±12.47)/(92.01±10.69), t=-3.21, P<0.01; (80.62±13.64)/(84.49±11.55), t=-5.06, P<0.01; (87.92±15.25)/(92.98±12.06), t=-6.00, P<0.01; (86.48±16.30)/(94.55±12.08), t=-9.04, P<0.01; (87.02±15.18)/(92.63±12.57), t=-6.62, P<0.01]; The mean value of fine motor in boys was lower than that in girls in SSD group [(79.80±13.42)/(83.08±14.05), t=-2.08, P<0.05]. Independent mealtimes. 2 years old (OR=1.527, 95%CI: 1.180-1.977, P=0.001), delay in adding supplemental food (OR=1.510, 95%CI: 1.123-2.029, P=0.006), dialect in the home language environment (OR=1.351, 95%CI: 1.060-1.723, P=0.015) were risk factors for children with speech disorders. Conclusion: Children with speech disorders are more common in boys. The overall development level of SSD children is lower than that of normal children, and the fine motor of SSD boys is lower than that of girls. The incidence of children's speech disorders is related to the addition time of supplementary food, independent meal time and family language environment.
Male ; Female ; Child ; Humans ; Child, Preschool ; Speech Sound Disorder/diagnosis* ; Case-Control Studies ; Speech Disorders ; Cognition

Objective: To analyze the clinical characteristics and risk factors of malignant vasovagal syncope (VVS) in children. Methods: This was a case-control study. The data of 368 VVS patients who were treated in the Department of Cardiology, Children's Hospital, Capital Institute of Pediatrics from June 2017 to December 2021 was collected and analyzed. They were divided into malignant VVS group and non-malignant VVS group according to the presence of sinus arrest, and then their demographic characteristics were compared. The children with malignant VVS and complete clinical information were recruited into the case group and were matched by age and sex (1∶4 ratio) with non-malignant VVS patients during the same period.Their clinical characteristics and lab tests were compared. Independent sample t test, Mann Whitney U or χ² test was used for comparison between groups.Logistic regression was used to analyze the risk factors for malignant VVS in children. Results: Eleven malignant VVS and 342 non-malignant VVS met the inclusion and exclusion critera. Eleven malignant VVS and 44 non-malignant children were recruited in the case-control study. Ten patients of the 11 malignant VVS had a cardiac arrest occurring at 35 (28, 35) minutes of the head-up tilt test, and the duration of sinus arrest was (9±5) s. One patient had syncope occurring while waiting for drawing blood, and the duration of sinus arrest was 3.4 s. The children with malignant vasovagal syncope were younger than non-malignant VVS patients (9 (7, 10) vs. 12 (10, 14) years old, P<0.05), and had higher mean corpuscular hemoglobin concentration (MCHC) and standard deviation of the mean cardiac cycle over 5-minute period within 24 hours ((347±9) vs. (340±8) g/L, (124±9) vs. (113±28) ms, both P<0.05). Logistic regression analysis showed that MCHC was an independent risk factor for malignant VVS in pediatric patients (OR=1.13, 95%CI 1.02-1.26, P=0.024). Conclusions: The onset age of malignant VVS was younger, with no other special clinical manifestations. MCHC was an independent risk factor for malignant VVS.
Humans ; Child ; Adolescent ; Syncope, Vasovagal/etiology* ; Case-Control Studies ; Syncope ; Risk Factors

OBJECTIVE: The aim of this case-control study was to explore the association between serum uric acid to high density lipoprotein cholesterol ratio (UHR) and the risk of nonalcoholic fatty liver disease (NAFLD) in Chinese adults. METHODS: A total of 636 patients with NAFLD and 754 controls were enrolled from the Affiliated Hospital of Qingdao University, China, between January and December 2016. All patients completed a comprehensive questionnaire survey and underwent abdominal ultrasound examination and a blood test. NAFLD was diagnosed using ultrasonography after other etiologies were excluded. Logistic regression and restricted cubic spline model were conducted to evaluate the relationship of UHR with NAFLD risk. RESULTS: The multivariable adjusted odds ratio (95% confidence interval, CI) for NAFLD in the highest versus lowest quartile of UHR was 3.888 (2.324-6.504). In analyses stratified by sex and age, we observed significant and positive associations between UHR and the risk of NAFLD in each subgroup. In analyses stratified by body mass index (BMI), a significant and positive association was found only in individuals with a BMI of ≥ 24 kg/m². Our dose-response analysis indicated a linear positive correlation between UHR and the risk of NAFLD. CONCLUSION UHR is positively associated with the risk of NAFLD and may serve as an innovative and noninvasive marker for identifying individuals at risk of NAFLD.
Adult ; Humans ; Case-Control Studies ; Cholesterol, HDL ; East Asian People ; Non-alcoholic Fatty Liver Disease ; Risk Factors ; Uric Acid ; China

Objective: To analyze the safety, effectiveness, economics, innovation, suitability and accessibility of tetrandrine in the treatment of pneumoconiosis, and provide evidence-based basis for health policy decision-making and clinical practice. Methods: In July 2022, the system searched PubMed, Embase, the Cochrane Library, CNKI, Wanfang, SinoMed databases (the retrieval time was from the establishment of the database to June 30, 2022), screened the documents that meet the standards, extracted and evaluated the data, and used the "HTA checklist" developed by the International Network of Agencies for Health Technology Assessment (INAHTA) to evaluate the HTA report. AMSTAR-2 Scale was used to evaluate the quality of systematic evaluation/Meta analysis. CHEERS Scale was used to evaluate the quality of pharmacoeconomics research. The included cohort study or case-control study was evaluated with the Newcastle-Ottawa Scale. The included randomized controlled trial (RCT) studies were evaluated using the Cochrane Risk Bias Assessment Tool (Cochrane RCT) quality evaluation criteria. Comprehensive comparison and analysis based on the characteristics of the data included in the study. Results: A total of 882 related literatures were detected from the initial screening. According to relevant standards, 8 RCT studies were finally selected for analysis. Statistical results showed that basic treatment with tetrandrine could better improve FEV(1) (MD=0.13, 95%CI: 0.06-0.20, P<0.001), FEV(1)/FVC (MD=4.48, 95%CI: 0.61-8.35, P=0.02) and clinical treatment efficiency. Tetrandrine had a low incidence of adverse reactions. The affordability coefficient of tetrandrine tablets was 0.295-0.492. Conclusion: Tetrandrine can improve the clinical symptoms and pulmonary ventilation function of pneumoconiosis patients, most of the adverse reactions are mild, and the clinical application is safe.
Humans ; Pneumoconiosis/drug therapy* ; Benzylisoquinolines/therapeutic use* ; Drugs, Chinese Herbal ; Case-Control Studies

OBJECTIVE: To assess the association of rs55829688 and rs75315904 polymorphisms of the lncRNA-GAS5 gene with susceptibility to systemic lupus erythematosus (SLE) in Guangxi population. METHODS: Peripheral venous blood samples were collected from the SLE group and control group. Following extraction of genomic DNA, SNPscan and Sanger sequencing were carried out to determine the genotypes for the rs55829688 and rs75315904 loci of the lncRNA-GAS5 gene. RESULTS: No difference was found between the two groups with regard to the genotypic frequencies for rs55829688 and rs75315904 (P > 0.05). However, the frequencies of C allele of rs55829688 between the two groups was significantly different (P < 0.05). In the SLE group, the frequencies of C allele and CT+CC genotype for rs55829688 among SLE patients with nephritis were significantly lower than those of SLE patients without nephritis (P < 0.05). In addition, haplotype analysis showed that the frequency of rs55829688 C/rs75315904 A allele in the SLE group was lower than that of the control group (P < 0.05). CONCLUSION In Guangxi population, the carrier status of rs55829688 C allele of the lncRNA-GAS5 gene may reduce the risk of SLE and its complicated nephritis, and the rs55829688 C/rs75315904 A haplotype may reduce the risk for SLE.
Humans ; Case-Control Studies ; China/epidemiology* ; Gene Frequency ; Genetic Predisposition to Disease ; Genotype ; Lupus Erythematosus, Systemic/genetics* ; Nephritis ; Polymorphism, Single Nucleotide ; RNA, Long Noncoding/genetics*

OBJECTIVES: To identify the perinatal risk factors for the occurrence of singleton apparently stillborn infants. METHODS: This was a case-control study. A total of 154 singleton neonates with gestational age ≥28 weeks and Apgar score of 0-1 who were subsequently successfully resuscitated in the Obstetrics and Gynecology Hospital of Fudan University from January 2006 to December 2015 were enrolled as the case group (apparently stillborn group). A total of 616 singleton infants born from January 2006 to December 2015 (1-minute Apgar score >1) were randomly selected in a 1:4 ratio as the control group. Univariate analysis and multivariate logistic regression were used to analyze the perinatal risk factors for the occurrence of apparently stillborn infants. RESULTS: The gestational age and birth weight in the apparently stillborn group were significantly lower than those in the control group (P<0.05). The incidences of fetal hydrops, cord prolapse, grade III meconium-stained amniotic fluid, placental abruption, breech presentation, severe pre-eclampsia, maternal general anesthesia at delivery, abnormal antenatal fetal heart monitoring and decreased fetal movement were significantly higher in the apparently stillborn group than those in the control group (P<0.05). The multivariate logistic analysis showed that the mother had general anesthesia at delivery (OR=34.520), decreased antenatal fetal movement (OR=28.168),placental abruption (OR=15.641), grade III meconium-stained amniotic fluid (OR=6.365), abnormal antenatal fetal heart monitoring (OR=5.739), and breech presentation (OR=2.614) were risk factors for the occurrence of apparently stillborn infants (P<0.05), while higher gestational age was a protective factor (OR=0.686, P<0.05). CONCLUSIONS Attention needs to be paid to mothers with abnormal prenatal fetal heart monitoring, decreased fetal movement, preterm labor, placental abruption, breech presentation, grade III meconium-stained amniotic fluid, and general anesthesia. Preparations for resuscitation should be done to rescue apparently stillborn infants.
Female ; Humans ; Infant ; Infant, Newborn ; Pregnancy ; Abruptio Placentae/epidemiology* ; Apgar Score ; Breech Presentation ; Case-Control Studies ; Placenta ; Pregnancy Complications/epidemiology* ; Risk Factors ; Stillbirth

BACKGROUND: Congenital heart disease (CHD) is one of the most common congenital malformations in humans. Inconsistent results emerged in the existed studies on associations between air pollution and congenital heart disease. The purpose of this study was to evaluate the association of gestational exposure to air pollutants with congenital heart disease, and to explore the critical exposure windows for congenital heart disease. METHODS: The nested case-control study collected birth records and the following health data in Tianjin Women and Children's Health Center, China. All of the cases of congenital heart disease from 2013 to 2015 were selected matching five healthy controls for each case. Inverse distance weighting was used to estimate individual exposure based on daily air pollution data. Furthermore, the conditional logistic regression with distributed lag non-linear model was performed to identify the association between gestational exposure to air pollution and congenital heart disease. RESULTS: A total of 8,748 mother-infant pairs were entered into the analysis, of which 1,458 infants suffered from congenital heart disease. For each 10 µg/m³ increase of gestational exposure to PM_2.5, the ORs (95% confidence interval, 95%CI) ranged from 1.008 (1.001-1.016) to 1.013 (1.001-1.024) during the 1^st-2^nd gestation weeks. Similar weak but increased risks of congenital heart disease were associated with O₃ exposure during the 1^st week and SO₂ exposure during 6^th-7^th weeks in the first trimester, while no significant findings for other air pollutants. CONCLUSIONS This study highlighted that gestational exposure to PM_2.5, O₃, and SO₂ had lag effects on congenital heart disease. Our results support potential benefits for pregnancy women to the mitigation of air pollution exposure in the early stage, especially when a critical exposure time window of air pollutants may precede heart development.
Infant ; Pregnancy ; Child ; Humans ; Female ; Air Pollutants/analysis* ; Case-Control Studies ; Prenatal Exposure Delayed Effects/epidemiology* ; Heart Defects, Congenital/etiology* ; China/epidemiology* ; Particulate Matter/adverse effects* ; Maternal Exposure/adverse effects*