Influence of maternal characteristics and gestational age on hemodynamic indices: NICOM device-specific reference ranges.

OBJECTIVES: To construct reference ranges for stroke volume, cardiac output and systemic vascular resistance (SVR) in normal pregnancy for the NICOM® device, and to explore associations between maternal characteristics and these hemodynamic variables. METHODS: This was a prospective cohort study of healthy singleton pregnancies between 10 and 40 weeks' gestation attending a tertiary referral hospital between September 2012 and May 2018. Measurements of stroke volume, cardiac output and SVR were obtained throughout pregnancy using NICOM, a non-invasive device based on bioreactance technology. NICOM device-specific reference ranges were created with respect to gestational age and maternal characteristics. Once the distribution of the data had been determined with respect to the gestational age, patient characteristics were added to the model to test whether they provided a significant improvement in prediction of the median value. The effect was assessed of maternal weight, height, smoking status, conception using assisted reproductive technology, nulliparity and ethnicity. RESULTS: We included 411 women in this study. The relationships between cardiac variables and gestational age observed in the NICOM-specific reference ranges are consistent with previous findings, with increasing cardiac output values until around 35 weeks and a decrease thereafter until term, and decreasing SVR until around 36 weeks, followed by an increase towards 40 weeks. Stroke volume showed a small linear increase across gestation with lower variability in observations close to term. Maternal weight, height and age were associated with cardiac output (all P < 0.05) and SVR (all P < 0.01), whilst maternal weight and height were associated with stroke volume (both P < 0.001). Ethnicity was significantly associated with stroke volume (P = 0.001) but not with cardiac output or SVR. CONCLUSIONS: This study presents device-specific reference ranges for stroke volume, cardiac output and SVR for the NICOM device in healthy pregnancy and describes the maternal characteristics that are associated with the values of these hemodynamic measurements. Studies using NICOM in pregnancy can use these ranges in order to evaluate observations relative to those expected in uncomplicated pregnancy conditional on maternal characteristics. Copyright © 2018 ISUOG. Published by John Wiley & Sons Ltd.

Maternal hemodynamics in normal pregnancy: reference ranges and role of maternal characteristics.

OBJECTIVES: The main aim of this study was to construct reference ranges of maternal central hemodynamic parameters during pregnancy. The second aim was to determine the maternal and pregnancy characteristics that influence these hemodynamic parameters. METHODS: This was a prospective cohort study of low-risk pregnant women attending for routine antenatal care at St George's Hospital, London, UK. Exclusion criteria included any medical disorder present at the time of study recruitment, or development of hypertension or intrauterine fetal growth restriction following study recruitment. Stroke volume (SV), cardiac output (CO) and systemic vascular resistance (SVR) were obtained using non-invasive cardiac output monitoring (USCOM-1A®). USCOM-1A utilizes a non-imaging probe in the suprasternal notch to obtain velocity-time integrals of transaortic blood flow at the left ventricular outflow tract. Once the distribution of the data with respect to gestational age had been determined, maternal characteristics were added to the model to test whether they provided a significant improvement in the prediction of the median value. RESULTS: The study included 627 women with a singleton pregnancy. The estimated median CO was constant for a maternal age above 32 years, but was around 0.5 L/min higher for women aged ≤ 25 years (P < 0.001). Maternal weight (P < 0.001) and height (P < 0.001) significantly affected CO values and there was a significant interaction (P = 0.002) between them. In women with a height of less than 1.60 m, there was no association between median CO and weight; however, in those with a height exceeding 1.60 m, an increase in weight was associated with an increase in CO. SV was primarily associated with height (P < 0.001), although some positive association with weight (P < 0.001) could also be observed within the normal body-mass-index range. Greater height (P < 0.001) was associated with lower median values of SVR, with an estimated difference of around 120 dynes × s/cm5 between 1.60 m and 1.80 m. Advancing maternal age was associated with higher median SVR, with an estimated difference of around 50 dynes × s/cm5 between 25 and 35 years. Smokers had a lower SVR by 73.5 (95% CI, 8.6-138.4) dynes × s/cm5 . CONCLUSION: Maternal hemodynamics are influenced significantly by maternal age, height and weight. We provide USCOM-1A-specific reference ranges and a calculator for SV, CO and SVR in uncomplicated pregnancies that correct for maternal age, height and weight. This should enable clinical application and comparison in both uncomplicated and pathological pregnancies. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.

Impaired maternal hemodynamics in morbidly obese women: a case-control study.

OBJECTIVE: Maternal obesity is associated with significant pregnancy complications and is a risk factor for the development of hypertensive disorders of pregnancy as well as other adverse outcomes. There are few data regarding the hemodynamic aberrations observed in maternal obesity. The aim of this study was to investigate maternal hemodynamics in morbidly obese women. METHODS: This was a prospective, case-control study of morbidly obese women (body mass index (BMI) ≥ 40 kg/m2 ) and controls (BMI 20-29.9 kg/m2 ). The control population was matched for maternal age and gestational age. BMI was calculated based on maternal height and weight at the time of recruitment to the study, which occurred on the same day as the hemodynamic assessment. Pregnant women in the second or third trimester of pregnancy were included. Women who were found to be hypertensive at any time were excluded from the study. A USCOM-1A® device was used to assess hemodynamic parameters (heart rate, stroke volume (SV), cardiac output and systemic vascular resistance (SVR)). The parameters were corrected for body surface area (BSA) to provide the SV index (SVI), cardiac index (CI) and SVR index (SVRI). Mann-Whitney U-test was used to compare the medians of the hemodynamic variables between the two groups. RESULTS: In total, 23 morbidly obese women and 327 controls were included in the analysis. There was no difference in maternal (P = 0.506) or gestational (P = 0.693) age at recruitment between the groups. Mean arterial pressure was higher both at pregnancy booking (90 vs 80 mmHg, P < 0.001) and study recruitment (91 vs 85 mmHg, P < 0.001) in the obese group compared with the controls. Heart rate was higher in the obese group (P = 0.003), but there was no difference in SV (P = 0.271), cardiac output (P = 0.238) or SVR (P = 0.635). Following correction of these parameters for BSA, compared with the control group, SVI (34 vs 45 mL/m2 , P < 0.001) and CI (2.96 vs 3.64 L/min/m2 , P < 0.001) were significantly reduced in the obese group, whereas SVRI was significantly higher (2354 vs 1840 dynes × s/cm5 , P < 0.001). CONCLUSIONS: The findings of our study suggest that cardiac function is significantly altered in morbidly obese pregnant women. In order to make appropriate comparisons between individuals, it is imperative that hemodynamic parameters are indexed for BSA, as is standard practice in pediatric cardiology. The novel finding of reduced CI in morbidly obese pregnant women may explain the predisposition to pre-eclampsia and other adverse outcomes in this population and warrants further investigation. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.

Cardiac output assessment in pregnancy: comparison of two automated monitors with echocardiography.

OBJECTIVE: To compare non-invasive hemodynamic measurements obtained in pregnant and postpartum women using two automated cardiac output monitors against those obtained by two-dimensional (2D) transthoracic echocardiography (TTE). METHODS: This was a cross-comparison study into which we recruited 114 healthy women, either with normal singleton pregnancy (across all three trimesters) or within 72 hours following delivery. Cardiac output estimations were obtained non-invasively using two different monitors, Ultrasound Cardiac Output Monitor (USCOM®, which uses continuous-wave Doppler analysis of transaortic blood flow) and Non-Invasive Cardiac Output Monitor (NICOM®, which uses thoracic bioreactance), and 2D-TTE. The performance of each monitor was assessed relative to that of TTE by calculating bias, precision, 95% limits of agreement and mean percentage difference (MPD). Intraobserver repeatability was assessed for both monitors and interobserver reproducibility was assessed for USCOM, NICOM being operator-independent. RESULTS: Following exclusions due to poor-quality results of a monitor or TTE, or for medical reasons, our analysis included 98 women (29 in the first trimester, 25 in the second and 21 in the third, and 23 postpartum). For cardiac output estimation, when compared with TTE, USCOM had a bias ranging from 0.4 to 0.9 L/min. The MPD of USCOM was 29% in the third-trimester cohort. NICOM had a bias ranging from -1.0 to 0.6 L/min, with a MPD of 32% in the third-trimester group. There was limited agreement between the cardiac output monitors and TTE in the first and second trimesters, with a MPD of 38% for USCOM in both first and second trimesters, and 71% and 61% for NICOM in first and second trimesters, respectively. For cardiac output estimation using USCOM, we found excellent intraobserver repeatability (intraclass correlation coefficient (ICC), 0.97; 95% CI, 0.95-0.98) and interobserver reproducibility (ICC, 0.90; 95% CI, 0.81-0.94), and the repeatability for NICOM was comparable (ICC, 0.95; 95% CI, 0.93-0.97). CONCLUSIONS: We found good agreement of both USCOM and NICOM when compared with 2D-TTE, specifically in the third trimester of pregnancy. Both devices had good intraobserver repeatability and either had good interobserver reproducibility or were operator-independent. Future studies should take into account the significant differences in the precise maternal hemodynamic values obtained by these devices, and consider developing device-specific reference ranges in pregnancy and the postpartum period. Copyright © 2016 ISUOG. Published by John Wiley & Sons Ltd.