Risk Factors Of Hypertensive Disorders Complicating Pregnancy And Its Correlation To Placenta Previa

ObjectiveTo explore the risk factors and pregnancy outcome in patients with hypertensive disorders of pregnancy(HDP)and to compare the incidence between maternities with placenta previa and those without placenta previa,furthermore,the correlation between placenta previa and hypertensive disorders of pregnancy is to be evaluated.MethodsCase-control study,retrospective cohort study and a meta-analysis were conducted.(1)Case-control study.Those cases of patients diagnosed as hypertensive disorders of pregnancy were selected as the case group meantime the same number of normal pregnancies selected randomly as the control group from the Affiliated Chaohu Hospital of Anhui Medical during the period between May 31,2008 and July 31,2015.The data information included age,occupation,education,history of hypertensive disorders of pregnancy,history of diabetes and chronic nephritis,family history of hypertension,gravidity,parity,spontaneous or induce abortion,infitility,ectopic pregnancy,assisted reproduction,multiple pregnancy,ABO blood type,interpregnancy interval,deliveryweek,stillbirth,placenta abruption,postpartum hemorrhage,blood transfusion and hysterectomy,neonatal transfer or small for gestational age(SGA)and Apgar score.SPSS 21.0 was used for data entry and statistical analysis.Pearson or chi-square test or continuity correction was used to test independence between two dichotomous variables.Fisher'exact test was performed when a single cell in a 2×2 contingency table had an expected frequency less than 5.P-value of less than0.05 was considered significant.The odds ratio(OR)and 95% confidence interval(CI)was calculated to test a connection between an independent and factor variable.(2)Retrospective control study.To conducted a retrospective cohort study among all maternities in Affiliated Chaohu Hospital of Anhui Medical during the period between May 31,2008 and July 31,2015.Inclusion object: all singleton and multiple pregnancies after delivery or cesarean section at 28 weeks of gestation.Exclusion Criteria: those termination of pregnancy at less than 28 weeks of gestation,or termination due to family planning or fetal malformations and those missing data information for various reasons.Research content: the incidence of hypertensive disorders in pregnancy was compared between maternities with placenta previa and those without placenta previa.The rates of hypertensive disorders in different groups were compared using chi-square test.A multivariate logistic regression analysis was used to determine the association between hypertensive disorders and placenta previa,controlling for variables such as age,gravidity,parity and gestational week.OR with 95% CI,was calculated.P-value of less than 0.05 was considered significant.At the same time we took those without hypertensive disorders(NHDP)and without placenta pravia(NPP)as control group,and HDP and placenta pravia(PP)as case group respectively to compare the differences.We collected age,gravidity,parity and gestational age and compared them between 3 groups,which were HDP and NHDP group,PP and NPP group,HDP and PP group using chi-square test and logistic regression analysis.(3)Meta-analysis: A computerized literature search was carried out in PubMed to collect relevant articles on associations between placenta previa and hypertensive disorders of pregnancy before November 2013.Eligible studies had to meet all of the following criteria: first,cohort study or case-control study on the association between placenta previa and hypertensive disorder of pregnancy;second,with relative risk estimates and respective variance,or the relevant information needed to calculate them.Pooled RR and 95% CIs were used to assess the strength of the associations.All statistical analyses were conducted using Stata 12.0(Stata-Corp,College Station,TX,USA).Results(1)Risk factors and pregnancy outcome in patients with hypertensive disorders of pregnancy(Case-control study)There were 484 cases of hypertensive disorders of pregnancy diagnosed between May 31,2008 and July 31,2015.Four cases were excluded due to incomplete information.Of the 480 cases,145 were gestational hypertension,310 were preeclampsia,8 were eclampsia,9 were chronic hypertension with superimposed preeclampsia and 8 were chronic hypertension with pregnancy.Multivariate logistic regression analysis showed that the risk factors of hypertension disorders complicating pregnancy were the low level of education,maternal hypertension,twin pregnancy,and the interpregnancy interval compared with the control group.OR and 95% CI were1.867(1.278-2.729),3.77(1.652-8.600),8.665(3.328-22.561)and 7.205(3.567-14.553)respectively.While age,gravidity,parity,spontaneous abortion and infertility were showed significance in single logistic regression analysis,they were not in multivariate analysis.In addition,all of 5 cases of patients with a history of pregnancy induced hypertension reoccurred again while such history couldn't be found in any of the control group.In subgroup,spontaneous abortion,maternal hypertension,long interpregnancy interval were the risk factors for gestation hypertension group,and low level ofeducation,maternal hypertension,long interpregnancy interval and twins for preeclampsia group.Compared with control group,the termination of gestational week were earlier in hypertension disorders of pregnancy and the incidence of placenta abruption,postpartum hemorrhage,blood transfusion and Apgar score <7 and neonatal transfer were increased.There were 11 cases of blood transfusion and 7 stillbirth in case group while none in control group.Preeclampsia group had more cases of placenta abruption,postpartum hemorrhage,Apgar score <7 and neonatal transfer than gestational group.When compared with gestational hypertension group,the termination of gestational week were earlier in preeclampsia group and the incidence of placenta abruption,neonatal transfer,SGA and stillbirth were significantly higher,while there were no significant difference in postpartum hemorrhage,blood transfusion and Apgar score.(2)Association between placenta previa and risk of hypertensive disorders of pregnancy(Retrospective control study)There were 12285 deliveries during 5 years period from May 31,2008 to July 31,2015(those termination of pregnancy at less than 28 weeks of gestation,or termination of pregnancy due to family planning or other reasons were not included).There were 29 deliveries excluded due to loss of some information,and then a total of 12256 were selcted.Of the 12256 deliveries,there were 484 cases of hypertensive disorders of pregnancy and 155 cases of placenta previa,which account a percentage of 3.85,1.26 respectively.There were statistically significance between the two groups(HDP and NHDP,PP and NPP)in age,gravidity,parity and gestational age using chi-square test or single logistic regression analysis,while using multivariate analysis,there were no differences in gravidity and parity between HDP and NHDP group,and no difference in parity between PP and NPP group.When comparing the HDP group and PP group,the constituent ratio of ages in30-34 and ?35 were significantly lower in the former group,showing patients with placenta previa were more likely to be older.The gravidity of more than or 2 times and multipara compostion were significantly higher and the termination of gestational age was significantly earlier in PP group than in HDP group.The incidence of hypertension disorders in pregnancy was 3.98% in normal position of the placenta,and 1.29% in placenta previa,showed that the incidence of former was 1/3 of the latter,when compared with each other,there was statistically significance(P value is 0.048).Multivariate logistic regression analysis was used to adjust the incidence of hypertensive disorders complicating pregnancy in placenta previa.Result showed that OR and 95% CI were 0.238(0.059-0.967)after adjusting for age,showing that placent previa had an effect of protection for hypertensive disorders of pregnancy,however,this protective effect weakened and even disappeared when adjusted for gravidity,parity and gestational age,its corresponding OR value and 95% CI were 0.289(0.071-1.171),0.271(0.067-1.100),0.249(0.061-1.012).When adjusted all the factors(age,gravidity,parity and gestational age,the OR and 95% CI were 0.193(0.047-0.787),which showed a negative relationship between hypertensive disorders of pregnancy and placenta previa.(3)Association between placenta previa and risk of hypertensive disorders of pregnancy(meta-analysis)A total of 7 cohort studies and 2 case control studies were identified according to the inclusion criteria.Overall,a significantly inverse correlation between placenta previa and HDP was found when all study results were pooled into the meta-analysis(RR=0.45,95%CI: 0.24-0.82),and the RR and 95% CI in cohort study and in case-control study were 0.94(95% CI: 0.44-2.00),0.27(95% CI: 0.14-0.54)respectively.For subgroup analyses,the same results were found in pregnancy-induced hypertension(PIH)group(RR=0.27,95%CI: 0.14–0.54)but not in other HDPs group(RR=0.94,95%CI:0.44-2.00).ConclusionHypertensive disorders of pregnancy is closely associated with adverse pregnancy outcomes such as placenta abruption,postpartum hemorrhage,blood transfusion and Apgar score <7 and neonatal transfer,SGA and stillbirth,the risk factors are low level of education,maternal hypertension,twins and long interpregnancy interval.Advanced age is a common risk factor for both hypertensive disorder of pregnancy and placenta previa,but the patients with placenta previa tend to be older than the patients with hypertensive disorder of pregnancy,and premature delivery is more likely to occur in patients with placenta previa than in hypersive disorder of pregnancy.Moreover,placenta previa decreases the risk especially PIH.There is a negative correlation between placenta previa and hypertensive disorders,and may play a protective role.