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Saturday, June 30, 2012

Accelerations

An acceleration is a visually abrupt increase in the fetal heart rate (FHR) above the baseline with onset to peak of the acceleration less than 30 seconds .


For fetuses > 32 weeks gestational age the peak heart rate must be > 15 beats per minute (BPM) above the baseline and must last for > 15 seconds but less than 2 minutes from the initial change in heart rate to the time of return of the fetal heart rate to the baseline. For fetuses < 32 weeks of gestation the accelerations must have a peak heart rate > 10 beat and a duration of > 10 seconds but less than 2 minutes .

An acceleration >  2 minutes but less than 10 minutes in duration is called a prolonged acceleration.   An acceleration lasting > 10 minutes is a baseline change. Accelerations may be further categorized as episodic or periodic. Episodic accelerations occur independent of uterine contractions.  Periodic accelerations are associated with uterine contractions.  Accelerations may be present or absent in an otherwise normal category I fetal heart rate tracing.[1].

Accelerations are usually, but not always, associated with either spontaneous fetal activity, stimulation, or uterine activity [2-4]. Accelerations have also been attributed to partial umbilical cord occlusion caused by a baroreceptor-mediated response to decreased venous return [5].

The presence of either spontaneous or stimulated FHR accelerations reliably predicts the absence of fetal metabolic acidemia at the time they are observed provided the heart rate being recorded is truly the fetus and not the mother [1,6].  Periodic accelerations caused by partial umbilical cord compression are not as reassuring as episodic accelerations since continued cord compression may cause progression to a category II or category III tracing [10]. A rise in the fetal heart rate provoked by fetal scalp stimulation during a prolonged deceleration is of uncertain significance since the rise in heart rate is not by definition an acceleration.
The tracing below shows accelerations assocated with maternal pushing.



Although the accelerations in Figure 1  might be attributed to partial umbilical cord occlusion, fetuses typically show decelerations with pushing while mothers show accelerations in their heart rate when pushing. The heart rate could, therefore, be either fetal or maternal. In this situation (as well as in other situations where signal ambiguity might occur such as with a low baseline FHR or maternal tachycardia) placing a pulse oximeter on the mother,  and comparing the maternal heart rate (MHR) with FHR (Figure 2)  may help to clarify the source of the heart rate pattern being traced [7-9].



REFERENCES
1. Macones GA, et al.  The 2008 National Institute of Child Health and Human Development workshop report on electronic fetal monitoring: update on definitions, interpretation, and research guidelines. Obstet Gynecol. 2008 Sep;112(3):661-6.PMID: 18757666
2. Rabinowitz R, The relation between fetal heart rate accelerations and fetal movements.
Obstet Gynecol. 1983 Jan;61(1):16-8.PMID: 6823344
3. Vintzileos AM, et al., Relation between fetal heart rate accelerations, fetal movements, and fetal breathing movements.
Am J Perinatol. 1986 Jan;3(1):38-40.PMID: 3510628
4. Sadovsky E, et al. ,The relationship between fetal heart rate accelerations, fetal movements, and uterine contractions.Am J Obstet Gynecol. 1984 May 15;149(2):187-9.PMID: 6720797
5. Lee CY, Di Loreto PC, O'Lane JM.A study of fetal heart rate acceleration patterns.
Obstet Gynecol. 1975 Feb;45(2):142-6.PMID: 1118084
6. Skupski DW, et al. Intrapartum fetal stimulation tests: a meta-analysis.Obstet Gynecol. 2002 Jan;99(1):129-34. PMID: 11777523
7. Sherman DJ, Characteristics of maternal heart rate patterns during labor and delivery.
Obstet Gynecol. 2002 Apr;99(4):542-7.PMID: 12039107
8. VAN Veen TR, et al,. Maternal heart rate patterns in the first and second stages of labor.
Acta Obstet Gynecol Scand. 2012 May;91(5):598-604.PMID: 22313165
9. Neilson DR Jr, et al., Signal ambiguity resulting in unexpected outcome with external fetal heart rate monitoring.Am J Obstet Gynecol. 2008 Jun;198(6):717-24. .PMID:
18377859
10. Gaziano EP, et al. FHR variability and other heart rate observations during second stage labor.
Obstet Gynecol. 1980 Jul;56(1):42-7.PMID:
7383486

1 Comments:

Anonymous Ida said...

This is cool!

September 22, 2013 at 8:03 PM  

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