Background: Cardiovascular adaptations to pregnancy involve complex physiological mechanisms that increase cardiac output, decrease total vascular resistance, and decreases both systolic and diastolic blood pressure (BP). These changes start early in the first trimester and continue through gestation. More so, these changes affect the fetus. The gold standard to assess hemodynamic status has been the Swan–Ganz pulmonary artery catheter (PAC) to assess central BP. Compared to peripheral BP, central BP more accurately represents the BP that affects the internal organs, namely the uterus and vis-à-vis, the feto-placental unit. The PAC requires central venous access and is associated with a range of complications, making it impractical in large scale studies. Central BP can also be measured non-invasively using the Uscom BP+ device, a supra-systolic oscillometric central BP (cBP) monitoring device, which measures BP and BP waveforms at the heart, as well as peripherally in the arm. The BP+ device also measures arterial stiffness, augmentation index, pulse rate variability and performs central and peripheral Pulse Waveform Analysis. From this information, the BP+ device calculates central BP and pulse pressure waves using a physics-based model of the arteries between the aorta and the cuff.
Objective: Our objective was to create maternal cardiac profiles of women throughout pregnancy using non-invasive measurements of central BP in order to further understand changes in maternal hemodynamics during pregnancy and how these changes affect the fetus.
Study Design: This was a prospective cohort study of all pregnancies followed in a single perinatal referral center between January 2018 and April 2018. All pregnant women were eligible for the study. Antenatal visit summaries were collected with information from the ultrasound performed at the visit and data from the Uscom BP+ device was noted. The Student’s t-test was used to compare categorical variables and means. Spearman rank correlation was used to evaluate the relationships between central BP and peripheral BP, gestational age (GA), estimated fetal weight (EFW), and the pulsatility index (PI) of both the umbilical artery (UA) and middle cerebral artery (MCA).
Results: 299 patient visits were included, of which 279 distinct women were recruited in the study cohort with the demographics found in Table 1. The Uscom BP+ device information was categorized by patient and GA based on the ultrasound at the visit. For first trimester (n=131), the mean central systolic BP was 103.11mmHg (standard deviation (SD) 12.46), the mean central diastolic BP was 67.31 mmHg (SD 10.09), and the mean pulse was 81.13 bpm (SD 11.92). For second trimester (n=132), the mean central systolic BP was 100.51mmHg (SD 11.96), the mean central diastolic BP was 66.69 mmHg (SD 10.81), and the mean pulse was 83.90 bpm (SD 13.20). For third trimester (n=36), the mean central systolic BP was 105.78mmHg (SD 13.10), the mean central diastolic BP was 72.81 mmHg (SD 11.70), and the mean pulse was 91.81 bpm (SD 9.74). Both central systolic BP and central diastolic BP were correlated to peripheral systolic (p<0.01) and diastolic BP (p<0.01). Neither central systolic BP, nor central diastolic BP was correlated to gestational age (p>0.26). The EFW percentiles, (n=167) were not correlated to either central systolic BP (p=0.23), or central diastolic BP (p=0.42). The PI for the MCA (n=19) was correlated to both the central systolic BP (p<0.01) and to the central diastolic BP (p<0.05). However, the UA PI (n=33) was not correlated to the central systolic BP (p =0.06), or to the central diastolic BP (p=0.14). Further, the cerebroplacental ratio (CPR), defined as (MCA PI)/(UA PI), was not correlated to the cBP (p>0.40). We demonstrated that the estimated fetal weight was significantly correlated to the PI of the MCA (p<0.05), but not to the PI of the UA (p=0.52).
Conclusion: Non-invasive maternal hemodynamic measurements are surrogates of the fetal-placental unit. The maternal central BP correlates to the fetal MCA pulsatility index and, more specifically, to the estimated fetal weight.