Oral Presentation 46th Annual Meeting of the Fetal and Neonatal Physiological Society 2019

Fetal Behavioural state and heart rate variation of small for gestational age compared to normal infants (#24)

John M D Thompson 1 , Edwin A Mitchell 2 , Jordan McIntyre 2 , Jaijus Johny 1 , Victoria King 3 , Peter R Stone 1
  1. Obstetrics & Gynaecology, University of Auckland, Auckland, New Zealand
  2. Paediatrics: Child and Youth Health, University of Auckland, Auckland, New Zealand
  3. Physiology, University of Auckland, Auckland, New Zealand

Background:

Small for gestational age infants are known to have an increased risk of stillbirth but little is known about their behavioural state in comparison to normal pregnancies. We have previously reported differences in fetal behavioural state (FBS) in healthy late gestation pregnancies in relation to maternal position during overnight studies at home.

Method:

We assessed the FBS and heart rate variation (HRV) in two groups of pregnancies; 36 SGA infants (defined as ≤10th percentile on customized growth charts) and 33 appropriately grown infants in otherwise normal pregnancies. Fetal ECG recordings were made using a Monica AN24 device overnight from which CTGs were derived and FBS scored independently by two obstetricians. Fetal heart rate and HRV were also determined from these recordings.

Results:

Over the period of maternal sleep, SGA infants spent a greater proportion of time in 1F (16.4% vs 14.0%, p<0.0001) and less time in 4F (3.0% vs 5.3%, p<0.0001) than appropriately grown infants. SGA infants particularly were at increased risk of been in 1F in the few hours prior to waking. Fetal heart rate showed a diurnal pattern in both groups.

After controlling for FBS and time of night, there was no clinically significant difference in fetal heart rate between the two groups (1.2 beats). Fetal SDNN (-8.6ms, p<0.0001) and RMSSD (-1.7ms, p<0.0001) were significantly lower in 1F compared to 2F, but did not differ between groups.

Conclusion:

In late gestation pregnancy, SGA infants are more likely to spend time in 1F which may be a mildly hypoxic state. This study adds further to the potential mechanisms associated with the increased risk of stillbirth for SGA fetuses.