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research letter

Indian Pediatr 2013;50: 705-706

Latency Intervals of Moro Response: A Valuable Neuro-screening Tool

Bijesh S, Jyoti Singh and H P Singh

Department of Pediatrics, Gandhi Memorial Hospital, and Shyam Shah Medical College, Rewa, MP. India.
Email: [email protected]


Moro response in healthy term newborns were studied to determine latency interval, time taken for optimal response (embracing movement of arms), and total duration of reflex response. Latency interval for onset of response was 0.41-0.49. Time taken for optimal response was 0.910-1.041s. Total duration of Moro response was 2.34 -2.59 s. Values were similar for males and females. Optimal response in babies born by cesarean section were significantly delayed than vaginal babies.

Key words: Latency, Moro response, Newborn, Screening.


Moro response is usually described as normal/abnormal or present/absent. However, deviant responses like, vigorous, weak and asymmetric responses have been shown to be closely linked with developmental outcome [1] and neurological impairment in newborns [2]. Studies on duration and quality of different events in normal response like the latency interval, optimal response and total duration of reflex response are few, and standard values for these durations are not available. The present study was undertaken to evaluate Moro response qualitatively, and determine normative values for latency interval and other components of a normal response

Latency interval of Moro reflex was defined as the time taken for onset of first sign of reflex response. Arc like embracing movement of arms following initial abduction was considered as Optimal response. The total time taken for a complete response was labeled as Completion. 91 healthy full term newborns, who remained asymptomatic for the first 48 hours after birth, were included in this prospective observational study. The study was carried on newborns after 48 hours (time for physiological stabilization) of birth. Head drop method was used to elicit Moro response [3] while the baby was alert, active and moving the limbs but not crying. Video recording was done simultaneously, and the investigator analyzed the video-clippings and calculated the various parameters with the help of a stop watch. Mean values were calculated for latency interval, optimization and total duration of response. Upper and lower limit was obtained by calculating the 95 % confidence interval for the means.

TABLE I	Values of Various Parameters of moro Reflex  in Healthy  term  Newborns  (n=91)
Parameter Values (s), mean (SD)
Male Female Overall
(n=48)    (n=43)       
Latency interval 0.42 (0.172) 0.48 (0.197) 0.45 (0.186)
Time taken for optimal response 0.97 (0.226) 1.02 (0.292) 0.998(0.259)
Duration of complete response 2.55 (0.59) 2.38 (0.625) 2.47 (0.61)

The range for latency interval of Moro response was found to be 0.41-0.49 seconds. The time taken for optimal Moro response was 0.91-1.04 seconds and the total duration for Moro response was 2.34-2.59 s. The values were similar for males and females. The mean values of newborn delivered through cesarean section were longer than babies delivered vaginally but was found to be statistically significant only for time taken for optimal response.

In view of these findings, a better assessment is possible by a standardized grading of Moro reflex in the form of an ordinal scale, as follows: 0 - Absent reflex; 1 - Long latency (>0.49 s); 2 - Normal range (0.41 -0.49s); and 3 - Short latency (< 0.41s).

For day-to-day use, the time taken to pronounce the word "thousand and one" is approximately 0.4-0.5 sec and will be a fair estimate of latency interval. Say "thousand and one" with the head drop. Onset of response both before and after the completion of the word "thousand and one" shall be considered as abnormal.

Hyperexcitability (short latency) may indicate behavior problems in later life like short concentration span, mood instability and learning difficulty while delayed excitability (long latency) may indicate severe nervous system pathology[4]. Results of our study are comparable with other studies [5,6], taking in to consideration the difference in methods and analysis.

Contributors: BS : conducted the study under the supervision of HPS & JS and wrote the first draft of the manuscript. HPS and JS: conceived and designed the study and revised the manuscript for important intellectual content. They will act as guarantors of the study. The final manuscript was approved by all the authors.

Funding: None; Competing interests: None stated.

References

1. Sohn M, Ahn Y, Lee S. Assessment of primitive reflexes in high-risk newborns. J Clin Med Res. 2011;3:285-90.

2. Zafeiriou DI. Primitive reflexes and postural reactions in the neurodevelopmental examination. Pediatr Neurol.  2004; 31:1-8.

3. Nair MKC, Russell P. Illingworth’s The development of the infant and young child: Normal and abnormal, Tenth edition. New Delhi: Elsevier; 2012.

4. Prechtl H. The neurological examination of the full-term newborn infant. In: Clinics In Developmental Medicine, Vol. 63, 2nd ed. Spastics International Medical Publications;1977.

5. Ronnqvist L, Hopkins B, Van Emmerik R, De Groot L. Lateral biases in head turning and the Moro response in the human newborn: are they both vestibular in origin? Dev Psychobiol.1998;33:339-49.

6. Ronnqvist L. A critical examination of the Moro response in newborn infants—symmetry, state relation, underlying mechanisms. Neuropsychologia. 1995;33:713-26.

 

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