Table 2.
Fetal growth and heart rate variability (HRV; n=5988).
| Author, year, country | Case | Control | Study design | Measures | Findings |
| Odendaal et al [29], 2019, South Africa | 5655 pregnant in the first trimester (GAa: ≥6 weeks) between 16 years and 45 years old, singleton; prior history of heart disease, hyperthyroidism, diabetes, and placental abruption was found in <1%; hypertension was found in 12.1%; preeclampsia was found in 3.9%; mean age 24.5 (SD 6.0) years; mean BMI 25.5 (SD 5.7) kg/m2; exclusion criteria: N/Ab | N/A | Retrospective study using data from 2007-2015; exposure of HRV (SDNN, RMSSD) was assessed for 36-55 minutes at 3 times, at 20-24, 28-32, and ≥34 weeks; outcome of birth weight was assessed on a case report form. | HRV: ECGc with 5 electrodes was used and imported into MATLAB. Dawes-Redman guidelines were used to quantify IBId features. Artifact management and sparsity-based epoch rejection were used for data preprocessing. Fetal growth: birth weight and z score | At both 20-24 weeks and ≥34 weeks, birth weight correlated positively with maternal heart rate but negatively with SDNNe (Spearman correlation=−0.0437; P<.02) and RMSSDf (Spearman correlation=−0.0627; P<.01). |
| Christian et al [27], 2021, United States | 39 pregnant (19 African American; 20 White), at GA of 21-24 weeks; exclusion criteria: tobacco/drug use; chronic diseases such as endocrine, cardiovascular, cancer, diabetes, hypertensive disorder, anemia, medication use (psychotic, antibiotic), and excessive caffeine use; BMI ≥30 kg/m2 | N/A | Retrospective study; secondary data analysis between 2009 and 2011; exposure of HRV (HFg) was assessed for 10 min in the afternoon once in the second trimester; outcome of birth weight was assessed once right after childbirth using the medical record. | HRV: ECG (Task Force of the European Society of Cardiology) was used for signal capturing and artifact management; offline signal inspection with Mindware Technology’s HRV 2.51 software; fetal growth: birth weight (grams) collected postdelivery and from the medical chart | White group had a negative relationship between HF and birth weight (correlation coefficient=–0.757, P=.002); no relationship was found in the African American group. |
| Ecklund-Flores et al [30], 2016, United States | 227 pregnant; GA: 36 weeks; 50% obese or overweight; 54% primigravidae, singleton; 68% Latino; mean age 26.45 (SD 6.02) years; mean BMI 25.32 (SD 4.99) kg/m2; exclusion criteria: no GDM, hypertension, or other related medical conditions, and no cigarette, alcohol, or drug use during pregnancy | N/A | Longitudinal observational study: outcome of birth weight adjusted for GA at birth and sex; exposure of adjusted HRV (RMSSD) was assessed for 5 min at baseline (GA: 36 weeks) | HRV: ECG digitized at 500 Hz (National Instruments 16XE50); fetal growth: birth weight was assessed after birth, and the data collection method was not reported. | RMSSD and birth weight had significant negative associations (Pearson correlation: –0.13; P<.001). |
| Voss et al [28], 2006, Germany | 16 pregnant with abnormal uterine perfusion and normal outcome (AP-NO), age: 29 (range 28 to 33) years; 19 women with abnormal uterine perfusion and pathologic outcome (AP-PO; small for GA, gestational hypertension, preeclampsia), singleton, age: 26 (range 25 to 30) years | 32 healthy pregnant with normal uterine perfusion (CON), age: 28 (24 to 31) years; analogous to the case group in maternal age, gravidity, and parity | Longitudinal observational study: exposure of HRV (normalized LFh, VLFi, mean NNj, SDNN, RMSSD) for 30 min between 8 AM and 12 PM, 5 times during pregnancy (GA: 18-22, 23-26, 27-30, 31-34, 35-37weeks); outcome of small for GA was assessed (birth weight <10th percentile of an own-reference group). | Fetal growth: data collection record was not reported; HRV: ECG (1600 Hz) based on task force standards | RMSSD decreased (P=.009), and VLF (P<.001) and LF (n; P=.003) increased in CON during pregnancy. No HRV parameter changed significantly in the course of gestation in AP-NO and AP-PO. No intergroup differences in HRV were found between CON and AP-NO. The comparison of AP-PO with CON and AP-NO, however, revealed a significant increase in mean NN (P=.03) as well as RMSSD (CON vs AP-PO: P=.008; AP-NO vs AP-PO: P=.01). AP-PO group had a significantly increased SDNN compared with AP-NO (P=.03). Effect measure amount was not clear. |
aGA: gestational age.
bN/A: not applicable.
cECG: electrocardiogram.
dIBI: interbeat interval.
eSDNN: standard deviation of the normal-to-normal R-R intervals.
fRMSSD: root mean square of successive differences between normal heartbeats.
gHF: high frequency.
hLF: low frequency.
iVLF: very low frequency.
jNN: N-N interval.