During pregnancy several hemodynamic, biochemical and hematological modifications occur as part of the physiological adaptation of the body to this condition. For instance, maternal blood pressure (BP) initially decreases at 8 weeks of gestation or earlier, the decrease in diastolic BP is higher than that in systolic BP . The diastolic BP has the lowest value at midpregnancy and returns to prepregnancy levels by term; in most studies it rarely exceeds prepregnancy or postpartum values. However, some investigators have reported that at term and in the third trimester, BP is higher than in matched nonpregnant controls [2, 3]. In contrast, several respiratory parameters do remain essentially unchanged during pregnancy, such as total lung capacity, vital capacity, lung compliance and diffusion capacity. Respiratory rate (RR) does not change also during pregnancy and tachypnea with greater than 20 breaths per minute should be considered abnormal in the pregnant woman [4, 5]. Nonetheless, minute ventilation, tidal volume and oxygen consumption increase 20% to 50%, whereas functional residual capacity raise only 20%, total lung capacity decreases by about 4% to 5%, mostly caused by the upward displacement of the diaphragm, increased metabolic rate, changes in the mechanics of breathing, and increases in progesterone level [5, 6]. Additionally, oxygen consumption increases by 30% to 60% during the course of pregnancy and maternal arterial partial pressure of CO2 decreases to a level of 26 to 32 mm Hg as a result of increased minute ventilation [4–7]. With respect to blood analysis, only slight changes in the amount of different white cells, platelets, hemoglobin and creatinine have been described [8, 9]. The mean of hemodynamic, such as BP, heart rate (HR), respiratory rate (RR); biochemical, as blood urea nitrogen (BUN), creatinine, hemoglobin, hematocrite, and glucose; and cellular reference values have been adopted from textbooks that mainly refer to Caucasian subjects [10, 11]; few studies report hemodynamic [12, 13], biochemical [9, 14], and hematological [15, 16] values for female living in developing countries, being scantly or absent for Mexican women.
In addition, since labor constitutes a stress situation, therefore, heat shock proteins (Hsps), particularly Hsp70, could be increased in serum in the active labor phase (ActLP). Hsps represent 2-15% of total cell proteins, being their main function preventing inadequate activity inside the cell (apoptosis, non regulated inflammation, abnormal protein degradation, abnormal metabolite production, etc,) . As part of their homeostatic response, stress proteins are fundamental in the adaptive responses of unicellular and multicellular organisms. They are implicated in a great variety of phenomena, including immune response modulation, hyperthermia, hyperoxia, ischemia and other alterations [17, 18]. Elevated serum Hsps levels are associated with various physiopathological situations during pregnancy and Hsp70 is consistently expressed in normal female reproductive tissues during pregnancy [19–21]. Women with preterm delivery and preeclampsia have higher Hsp70 concentrations (mean ± Standard error of the mean) (35.3 ± 9.6 and 24.4 ± 3.6 ng/mL, respectively), as compared to normal pregnant (6.1 ± 0.6 ng/mL) and non pregnant (2.4 ± 0.6 ng/mL) women [22–24]. It has been also found elevated Hsp70 levels in transient hypertension of pregnancy, preeclampsia and superimposed preeclampsia (median (25-75 percentile) 0.66 (0.52-0.84), 0.55 (0.42-0.80) and 0.61 (0.42-0.91) ng/mL respectively) [25, 26] as well as in pregnant asthmatics (0.44 (0.36-0.53) ng/mL), compared to healthy pregnant women (0.21 (0-0.27) ng/mL). Fetal birth weight of asthmatic mothers was significantly smaller than of healthy controls, but in the normal range (3,230 g (2,690-3,550) versus 3,550 g (3,450-3,775) . In preeclampsia, increased serum Hsp70 levels reflect systemic inflammation, oxidative stress and hepatocellular injury . Moreover, serum Hsp70 levels are significantly higher in patients with the syndrome of hemolysis, elevated liver enzymes, and low platelet count (HELLP syndrome, 2.02 (0.76-2.23) ng/mL) than in severely preeclamptic patients without it (0.54 (0.47-0.79) ng/mL). In HELLP syndrome, elevated serum Hsp70 level indicates tissue damage (hemolysis and hepatocellular injury) and disease severity [29, 30]. However, circulating levels of anti-Hsp antibodies are not altered in preeclampsia . Recently, significantly lower serum Hsp70 levels in healthy pregnant women than in healthy non-pregnant women were described; also a statistically significant negative correlation between maternal age and serum Hsp70 concentration and a significant positive correlation between gestational age and serum Hsp70 level in healthy pregnant women were found .