Why do babies hiccough in utero?

I am looking for a good resource for use with childbirth education clients, on why babies hiccough in utero.

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Peg Plumbo CNM

Peg Plumbo has been a certified nurse-midwife (CNM) since 1976. She has assisted at over 1,000 births and currently teaches in the... Read more

Dear Barbara,

There is not a great deal written in the medical resources about fetal hiccoughing beyond that it is fetal reflex similar to our own. Only the more mature fetuses do this because of the development of the central nervous system. Some think that it is a response to fetal drinking or fetal breathing which causes the flow of amniotic fluid in and out of the lungs, stimulating the diaphragm to contract.

Here is what I found in Medline.

Fetal hiccups in the baboon.
American Journal of Physiology.
267(6 Pt 2):R1479-87, 1994 Dec.

Bouts of hiccuping are recognized by pregnant women as distinct episodic movements of their fetuses. Ultrasound imaging of these fetuses has documented the occurrence of hiccups from early gestation through parturition. This study provides a systematic characterization of prenatal hiccuping in the fetal baboon (Papio species). Tracheal fluid pressure was recorded from 11 chronically instrumented fetal baboons for 21.5 +/- 7.3 consecutive days (mean +/- SD) over a range in gestation from 124 to 164 days (term 175 days). In an initial review of pressure recordings by visual inspection, hiccups were recognized as distinctive high-amplitude fluctuations in tracheal pressure that were readily discriminated from fetal breaths. Automated techniques were then developed and validated to detect hiccups and summarize their features. The mean hiccup amplitude was w 23.0 +/- 3.1 mmHg, inspiratory time was 0.26 +/- 0.03 s, and expiratory time was 0.27 +/- 0.02 s. Each of these features discriminated hiccups from breaths (P < 0.001). Hiccuping incidence (1.8 +/- 0.4% of time), rate (26.2 +/- 6.2 min-1), bout duration (4.3 +/- 0.8 min), and the interval between bouts (3.35 +/- 0.60 h) were also different (P < 0.01) from breathing. These features of hiccups remained relatively constant over the latter third of gestation with the exception of an increase in duration of the expiratory time interval (r = 0.54, P < 0.01). Despite their vigorous nature, bouts of hiccuping were not associated with transitions in behavioral state. Moreover, the features of hiccups were not differentiated by state. Bouts of hiccuping recurred in a cyclic fashion, on average every 3-4 h.

Journal of Ultrasound in Medicine. 12(11):641-3, 1993 Nov

Absent and reversed UA end-diastolic blood flow is usually a poor prognostic sign. However, in 19 fetuses evaluated in the Fetal Diagnosis and Treatment Unit, we observed an unusual pattern of intermittent, significantly decreased, or reversed UA blood flow that coincided with a demonstration of fetal hiccuping. No evidence of cardiac arrhythmia, heart failure, or uteroplacental dysfunction was found in these fetuses. With one exception, all Doppler evaluations were otherwise normal. A potential mechanism of intermittent fetal UA blood flow reversal is discussed.

Thanks for asking.
Peg

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