Preeclampsia is a disorder of widespread vascular endothelial malfunction and vasospasm that occurs after 20 weeks gestation and can present as late as 4-6 weeks postpartum. It is clinically defined by hypertension and proteinuria, with or without pathologic edema [1]. The incidence of preeclampsia in the United States is estimated to range from 2% to 6% in nulliparous women, with a subset of those progressing into more severe forms of the disease, known as eclampsia [2,3]. It is a leading cause of maternal and prenatal morbidity and mortality, particularly when it occurs at a gestational age of less than 34 weeks [4,5]. Preeclampsia is associated with intrauterine growth restriction, chronic immune activation and multi-organ endothelial dysfunction thus contributing to the clinically visible elevation in maternal blood pressure. Early diagnosis and prompt to treat of disease can reduce its side effects on the mother [6-9]. Placental implantation with abnormal trophoblastic invasion of uterine vessels is a major cause of hypertension associated with preeclampsia syndrome [10,11]. The role of seasonal variation in its etiology is one of the factors being considered [12]. From the 19th century to now, Researchers began to notice increases in preeclampsia during cold seasons in non-tropical climates and rainy seasons in tropical climates [13,14,15]. Previous studies performed in the tropical climate of Mumbai, India, Subramanian and colleagues analyzed 29,562 deliveries during a 36-month period, showed that the incidence of eclampsia was significantly higher in the monsoon season when the weather is wet and colder [16]. Per Magnus and colleagues found preeclampsia in August is the lowest risk, and in the winter months is the highest risk [17]. Unlike, Tan et al. [18] have suggested that preeclampsia occurs in summer. In Texas, the prevalence of Preeclampsia was the highest in January (4.4%), and was the lowest in the fall (3.89%) [19].

Sis tan & Baluchistan province is located in southeastern Iran. Zahedan had a dry climate with dry dusty winds. This study was performed in order to survey the relationship of seasons and preeclampsia and to reduce its complications on the mother and fetus.

This case - control study was carried on using existing data in the files of Quads maternity care center of zahedan, from July 2004 to June 2007. 2488 pregnant women with diagnosis of Preeclampsia were selected for this study as the case group; with age 15-45 years and gravid 1-3, and 2488 pregnant women without preeclampsia were selected as the control group with the same situation. In Quads maternity care center, a patient with mild preeclampsia is characterized by the following: blood pressure equal or higher than 140/90 mm Hg after twenty weeks and protein urea more than 1+ on two consecutive urine specimens, but if the blood pressure was above 160/110 mmHg and proteinuria above 300mg/24 h (+++), and if patient has symptoms of headache, visual disorder, epigastria pain and decreased urine flow, was considered as severe preeclampsia. If patient don’t has none of the symptoms mentioned above, placed in the control group. Patients of the two groups were compared for the following factors: Previous pre eclamsia, Previous Diabetes, Previous Hypertension, without previous risk factors. Data were analyzed using statistical Chi score tests.

The description of results of the study on 2488 patients in two groups with and without preeclampsia: The case group (with preeclampsia ): 278 cases (11.2%), in spring, 570 cases (22.9%) in summer,1366 cases (54.9%) in autumn, and 274 cases (11%) in winter, visited and were admitted . In the control group (without preeclampsia): 441 cases (27.7%) in spring, 789 cases (31.7%) in summer, 966 cases (38.8%) in the autumn, and 292 cases (11.7%) in winter, were admitted. Figure 1 presents distribution of preeclampsia according to delivery in four seasons. This analysis demonstrates that there is an inverse correlation between preeclampsia and four seasons. At the start of spring it gradually begin to increase and reach to a sudden peak in autumn and then it suddenly decreased in the winter, but this correlation is not statistically significant (P = 0.327).Up to 65.2% of patients are in age group 15-25 years, 22.7% in age group 25-35 years and 12% 35-44 years in age group35-44 years ,in the control group: 64.2% of patients were in age group 15-25 years, 25.2% in age group 25-35 years and 10.6% in age group 35-44 years(P = 0.05). There was a significant difference in the preeclampsia incidence and diabetes, patients with history of hypertension and history of serious preeclampsia (p = 0.0001) Table 1. In patients with preeclampsia: 41.1% patients had low blood pressure 46.4% had average blood pressure and 12.5% had high blood pressure and there were proteins urea of +2 in 28.2% patients and proteins urea of +3 in 5.7% patients.

Figure 1: Abundance distribution of preeclampsia according to delivery in 4 seasons.

Table 1: Correlation of preeclampsia with previous history of risk factors.

The purpose of this investigation is to study the relationship between factors such as season, blood pressure and diabetes with preeclampsia incidence in pregnancy. The results of the study showed negatively relationship between the incidence of preeclampsia and season. Preeclampsia incidence gradually increased with the onset of spring, and reached to its maximum in autumn, and had a sudden decrease in winter. The highest amount of incidence were in autumn and after that in summer and the lowest was in winter .Considering the pathophysiology of preeclampsia based on vascular contraction the increased preeclampsia incidence in cold and humid seasons of year can be result of temperature and humidity effect on the vasoconstriction. A study that conducted in Zimbabwe as “the effect of seasons change associated with blood pressure attacks” has good correlation with the results of our study [20].

In our study at start of rain and cold seasons (autumn) preeclampsia reaches to the highest frequency .While in the most studies of preeclampsia, in the peak of cold and rainy seasons (winter) is at highest frequency, Such as study from South Africa reveal that preeclampsia happen more in winter frequently [21]. Another study from Sweden shows that the incidence of eclampsia was nearly doubled during winter season as compared to other seasons [22]. The result of studies from the United States of America exhibits that the incidence of preeclampsia/ eclampsia is not influenced by climatic factors even in periods of high humidity [12].

Of course some of these inconsistencies may be due to sample selection and criteria of our study. In this study, stated that the humidity and temperature may be effective on blood vessels and Vasospasm cases, and the dry and rainy seasons can affect the status of agriculture and nutrition consequently and thus may play a role in the preeclampsia pathophysiology [20,23].

Vidya has studied changes of season in prevalence of hypertension disorders ,and clients were divided to three groups of healthy women, with Eclampsia and Preeclampsia groups and the results showed that the prevalence of preeclampsia has no relation with rainy season but the incidence of Eclampsia in the rainy season and colder temperature is higher than the warm and dry seasons [24]. The Results of this study has some agreement with our study but in our study Preeclampsia and eclampsia were put in a same group are not separated.

A survey of Canadian hospitals in 2000 showed early pregnancy age, rainy seasons, first pregnancy, multiple pregnancies or prolonged pregnancy and lack of prenatal care are among the risk factors for preeclampsia [25]. In current study the age and the number of pregnancies of the study group or control group became identical and also other factors were not evaluated due to incomplete records. In Japan a study carried out in 2008 on blood pressure changes in relation to season. By repeated measurement of blood pressure in pregnant women at home in various months of pregnancy these results came out. There has been the lowest blood pressure by 20 week and the highest blood pressure by week 26. By 10°C increase in temperature has been meaningful reduce in systolic pressure after 2.5 mmHg. That of course is associated with pregnancy age [26]. According to a study in the United States in 2004, unlike the present study there was no association with pregnancy age and preeclampsia incidence. However, a strong significant relation between the month (season) of pregnancy and preeclampsia was observed. So that pregnancy in summer is associated with highest preeclampsia risk whereas a moderate relationship between spring , autumn and winter was observed, and there was no relationship between race (black and white) and infant gender (being female) with preeclampsia [27]. Therefore, further research need to survey of etiology of preeclampsia and eclampsia

Our results showed that there is an inverse correlation between preeclampsia and seasons.In the Sis tan & Baluchistan Province as the second cause of maternal mortality and since preeclampsia prevalence increase and season are associated in this study, the results of this research can initiate studies such as survey of effect of maternal nutritional conditions and other factors associated with various seasons on preeclampsia occurrence. Also learning the preventive factors of preeclampsia such as role of nutrition of pregnant women in prenatal care can reduce the risk of serious complications that endangers mother and fetus. Preeclampsia prevalence increase is associated with the season so in the seasons of the year that preeclampsia incidence is higher with Preventive measures and timely medical care and public education of pregnant women in prenatal care reduce the risk of serious complications that endangers mother and fetus.

We thank the Quads maternity center staff for their help in our research and Dr. Yasseri and Dr. Shahrakipoor for data analysis.