In the literature, the relationships between ZO and various inflammatory and chronic diseases[5] have been evaluated, but our study is the first to focus on PPROM patients. ZO levels did not significantly differ between the PPROM and control groups. However, in the PPROM group, a strong relationship was observed between newborn birthweight and both maternal serum ZO levels and fetal cord blood ZO levels. Additionally, a significant correlation was found between maternal serum ZO levels and fetal cord blood ZO levels in all patients.
ZO has been tested as a new diagnostic marker for intestinal permeability in newborns showing signs of infection and/or inflammation in the gut or at risk of intestinal pathology. Tarko et al.[12] evaluated 81 newborns who were diagnosed with sepsis, necrotizing enterocolitis (NEC), rotavirus infection, or gastroschisis. ZO levels did not correlate with CRP or procalcitonin (PCT) levels in their study. Therefore, the authors suggested that an increase in ZO might not match the release of inflammatory markers, and low CRP should not rule out intestinal injury in newborns [12]. In our study, despite the expected development of infection secondary to PPROM, no correlation was found between maternal serum and umbilical cord serum zonulin levels and CRP levels in the PPROM patients. In another study conducted in patients with preterm rupture of membranes (PROM), zonulin levels were compared between groups with and without PROM. The mean zonulin concentration was greater in the PROM group (155.3 ± 50.2 ng/ml) than in the non-PROM group (128.8 ± 59 ng/ml). However, no statistically significant difference was found between them. Among the inflammatory markers, only C-reactive protein levels were significantly increased in the PROM group [13]. Similarly, in our study, there was no significant difference in zonulin levels between the PPROM group and term pregnant women. However, the level of zonulin, which is high in maternal blood, was also found to be high in cord blood. This finding was significant in terms of intestinal permeability. However, since our study did not routinely measure CRP in term pregnant women, it could not be compared with the PPROM group.
In another study involving 100 healthy newborns and their mothers, ZO levels in blood samples and calprotectin levels in stool samples were assessed. This study demonstrated that cesarean section delivery and antibiotic use led to an increase in ZO levels [14]. Another study showed that long-term cesarean section delivery or antibiotic use did not influence ZO or other intestinal permeability-related factors [15]. In our study, neither of these two factors resulted in a change in ZO levels. Patients who used antibiotics had p values of 0.235 for maternal blood and 0.681 for fetal cord blood, while patients who underwent cesarean section had p values of 0.438 for maternal blood and 0.334 for fetal cord blood.
For pregnant patients, a weight gain during pregnancy greater than 18 kg or a body mass index increase (BMI) > 5.7 during pregnancy is associated with a decrease in zonulin concentrations in the mother's stool and an increase in calprotectin concentrations in the newborn's stool on the seventh day [14]. Changes in maternal body mass index during pregnancy can affect intestinal permeability in both the newborn and the mother. The health consequences of increased intestinal permeability in the first days of life are not yet known. Before zonulin and calprotectin tests can be widely used to diagnose increased intestinal permeability, we need to validate these tests [14, 16]. In our study, when BMI values were divided into two groups above and below 30, no significant difference was found when comparing maternal serum and fetal cord blood zonulin levels. This result was attributed to the lack of a significant difference in BMI values between both the study and control groups (28.8 ± 4.2 kg/m2 vs. 30.4 ± 7.3 kg/m2, p = 0.366) and the presence of only two patients with morbid obesity (BMI 42 kg/m2 and 55 kg/m2).
Regardless of disease, there are numerous studies on the relationship between newborn birthweight and intestinal permeability. For instance, in a case‒control study involving 368 infants categorized as born below 2500 grams and above 2500 grams, a notable link was discovered between intestinal permeability and newborn birthweight based on maternal serum ZO levels [11]. The serum levels of ZO and zinc in mothers of infants weighing more than 2500 grams were found to be significantly greater than those in mothers of low-birth-weight infants [11]. In our study, a positive correlation was found between newborn birthweight and maternal serum ZO levels and fetal cord blood levels in the PPROM group (p = 0.003 and p = 0.002, respectively).
In our study, a positive correlation was found between maternal serum zonulin levels and fetal cord zonulin levels (r = 0.837 and r = 0.944, respectively). This correlation suggests that changes in zonulin levels may lead to complicated pregnancies with impaired glucose tolerance, insulin resistance, gestational diabetes mellitus and intrahepatic cholestasis, as indicated in the literature [17, 18].
In complex diseases such as PCOS and PROM, which can present with metabolic disorders or chronic inflammatory bowel diseases, the expected increase in zonulin levels could not be observed in the literature. This is attributed to the unclear relationship between the mechanism of action of zonulin and these diseases [13, 19, 20].
The major strength of the present study was that it was the first, to our knowledge, to investigate the association between PPROM and zonulin levels. The prospective design was the other strength of the study. Conversely, the small sample size was a significant limitation. Due to the sample size of obese women, a significant association could not be demonstrated between BMI and zonulin levels.
In conclusion, no significant association was found between PPROM and maternal serum/umbilical cord blood zonulin levels in this study. This outcome was attributed to the clinical presentation of PPROM characterized by a localized inflammatory process rather than a systemic process. A positive correlation was found between newborn birthweight and maternal serum zonulin levels, as well as fetal umbilical cord levels, in the PPROM group. Additionally, there was a positive correlation between maternal serum and fetal umbilical cord zonulin levels in all patients.