Interpretation
The results of this study are in line with most relevant scientific findings on this subject. We previously demonstrated a greater incidence of complications in women with values of SVR higher than 1069 d.s.cm-5 in the early stage of labor10. Kalafat e al. demonstrated that higher SVR correlates with an increased risk of operative delivery due to presumed fetal compromise in women undergoing induction of labor for several indications11Kalafat E, Barratt I, Nawaz A, Thilaganathan B, Khalil A. Maternal cardiovascular function and risk of intrapartum fetal compromise in women undergoing induction of labor: a pilot study. Ultrasound Obstet Gynecol. 2019 Nov 11.. Even in our study the SVR value is the best independent risk predictor for delivery complications and shows a strong association when is higher than 1135 d.s.cm-5 (OR = 9.01).
In our study, women who developed complications during the labor, showed increased SVR, reduced CO and higher PKR. The FTc, which represents the time of the left ventricular systole and is correlated to preload and cardiac performance, is apparently an independent predictor of complications on multivariate analysis when is higher than 365 ms. This hemodynamic pattern, characterized by a high resistance and hypodynamic circulation, is characteristic of a cardiovascular maladaptation and this condition is significantly correlated with the development of fetal sufferance during the labor.
We can only hypothesize which is the etiopathological mechanism that determines the development of complications during the labor in patients with suboptimal cardiovascular status even before labor starts. The cardiovascular adaptation to the pregnancy is fundamental for adequate perfusion of the uteroplacental unit during the pregnancy and prevent placental syndromes22Valensise H, Novelli GP, Farsetti D, Vasapollo B. Cardiac function. In: Lees C, Gyselaers W, editors. Maternal hemodynamics. Cambridge (UK): Cambridge University Press; 2018.
In normal pregnancies the vascular remodelling leads to a SVR reduction and a CO increment that are fundamental for a correct uterine perfusion and to prevent fetal hypoxia. During the labor there is an increase in demands on the cardiovascular system, in particular CO increases by 30% in the first stage of labor and by over 50% in the second stage21. Women with high SVR and poor cardiac performance at term have not fit properly to the pregnancy and have an increased risk to develop intrapartum complications. The poor cardiac performance could be the cause of a reduced uteroplacental perfusion and a consequence fetal sufferance. The subclinical alterations in cardiac function, in apparently healthy women, could compromise the delivery outcome.
Even in our results, the multiparity is a protective factor for the development of maternal and fetal adverse outcome. The OR value is superimposable to the OR calculated by Kalafat et al20. The maternal hemodynamic parameters, adjusted for multiparity and maternal height, showed to be independent risk factors for adverse outcome.
The CPR has been demonstrated to be able to identify fetal at risk for distress during labor, even in AGA fetuses3322DeVore GR. The importance of the cerebroplacental ratio in the evaluation of fetal well-being in SGA and AGA fetuses. Am J Obstet Gynecol 2015; 213: 5–15. Nevertheless, in our results the CPR value, adjusted for the gestational age, didn’t show significant difference in patients who will develop complications.