The difference in the heart rate from beat to beat is called variability. It is caused by the effect of teh sympathetic and the parasympathetic nervous system. The sympethetic nervous system acts to increase the heart rate while the parasympethetic acts to decrease it. Normal variability is between 6-25 beats per min). Severe oxygen deprivation always depresses our nervous system, resulting in very little or absent variability. Other things that may cause reduced variability include fetal sleep cycles, cns depression, fetal anomalies or previous damage to the fetal brain, as well as a lower gestational age. Also, if tachycardia(high heart rate) is present, variability is reduced. Normal variability indicates the absence of severe hypoxia, but should be evaluated in context.
Obstetrics: Normal and Problem Pregnancies, 5th ed. Gabbe et al.
Fanaroff and Martin's Neonatal-Perinatal Medicine, 8th ed. Martin et al.
Birth is a Journey: Does it have to be life changing?
One woman might have to climb on an overfilled boat, risking her life and nearly dying as she escapes over the ocean to come to this land. This experience could certainly be life altering. It may very well color the rest of her life, positively or negatively. (I overcame this amazing struggle and here I am triumphant! OR Holy crap, that was SO hard I don’t know if I can go on! By the way, neither response is “right”. No one would judge the woman with the 2nd response.)
One woman may buy an airplane ticket, sit on a comfortable 747 and fly to America with a nice smooth flight and landing. She is happy to be in America. Those welcoming her are glad she is here safe and sound. She may only travel by plane 2-4 times in her life, so it is pretty memorable. But the journey itself probably wouldn’t be life changing; it would simply be a journey.
One woman may learn to fly an ultra-light plane to lead a flock of geese into America teaching them to migrate. This experience could certainly be empowering and life altering.