Effect of maternal carbon dioxide inhalation on human fetal breathing movements in term and preterm labor

Induced maternal hypercapnia is a potent stimulus to fetal breathing movements in nonlaboring pregnant women. To determine the effect of maternal CO2 administration on fetal breathing movements during spontaneous labor, 14 healthy pregnant volunteers at term and 34 in preterm labor were recruited. If fetal breathing movements were markedly decreased or absent, the subjects were administered a prepared gas mixture of 3% CO2 in air. In term labor and in true preterm labor, fetal breathing movements were markedly decreased and could not be induced by maternal hypercapnia. Among women with suspected preterm labor, initial absence of fetal breathing movements and failure to evoke this response by maternal hypercapnia predicted delivery within 48 hours with a sensitivity of 80% and specificity of 95.5%. Induced maternal hypercapnia fails to stimulate fetal breathing movements in true term and preterm labor and may assist in distinguishing between true and false preterm labor.     

The variability of fetal breathing movements in normal human fetuses at term

With the use of a B-scan phase-locked tracking system, 108 observations of fetal breathing were performed on 97 normal antenatal patients at term. One hundred thirty-three recorded segments of fetal breathing movements were obtained. Breath-to-breath variability was analyzed in 79 segments and expressed as a coefficient of variability. The mean coefficient of variability was 28.6% ± 13.2%, and a histogram plot revealed a normal distribution. All fetuses had normal antepartum testing and all Apgar scores and neonatal courses were normal. The potential application of human fetal breathing variability as a test for fetal health is discussed.     

The effect of intermittent maternal fasting on human fetal breathing movements.

In order to determine the effect of maternal fasting on human fetal breathing movements (FBM), 63 healthy pregnant women with singleton uncomplicated pregnancies of 30 weeks' gestation or more, and who were fasting during Ramadan, were recruited. Maternal blood glucose level and fetal movements were recorded during and after fasting. Statistical comparison of samples before and after a meal was made using Wilcoxon's signed-ranks test. Maternal glucose level during fasting (5.1 +/- 0.5 mmol/l) was significantly (P = 0.01) lower than after breakfast (5.3 +/- 1.0 mmol/l). There was a significant association between maternal glucose levels and numbers of days faster (P = 0.01). The time needed to detect breathing movements was significantly longer (P = 0.005) during fasting than postprandial. The continuous variety of fetal breathing movement was significantly (P = 0.02) less during fasting compared to postprandial. It is concluded that intermittent maternal fasting is associated with a significant alteration in the frequency and pattern of human FBM.     

The dynamics of human fetal breathing movements; a multiscan echofetographic approach

Fetal breathing movements are characterized by retractions of the thoracic cage, an increase in the thoracic kyphosis and an expansion of the abdominal wall during each such thoracic movement. These findings can be explained by assuming that the movements of the thoracic cage and abdominal wall are initiated by contractions of the diaphragm itself, as well as the intrathoracic and intraabdominal pressure changes belonging to them. When an echographic technique is used, a positive identification of the start of each inspiratory phase will only be possible if these breathing movements can be clearly differentiated.     

Fetal breathing movements and the response to carbon dioxide in patients on methadone maintenance

Fetal breathing movements were monitored on six methadone maintenance patients and ten healthy control patients, studied while breathing room air and while breathing a prepared gas mixture with 5% carbon dioxide, both before and 2 hours after either the usual daily dose of methadone or a diet drink. There was no difference before and after the diet drink in control patients, who showed a significant increase in the incidence of fetal breathing movements from 37.1% +/- 5.9% (SEM) on room air to 69.4% +/- 2.8% while breathing 5% carbon dioxide (p less than 0.01). In the patients studied on room air before receiving methadone, fetal breathing movements were significantly decreased from those of the control group, 4.7% +/- 1.2% (p less than 0.01), with a further decrease when studied after receiving methadone, 1.3% +/- 0.7%. Fetal breathing movements did increase significantly in response to 5% carbon dioxide both before and after receiving methadone; however, in both instances the incidence was significantly less that that of the control group. The findings of the present study on methadone subjects demonstrate that abnormal function of the respiratory control network is evident in utero, which may be predictive of subsequent neonatal respiratory development.     

Intrauterine breathing movements and fetal presentation

Fetal breathing movements in 14 twin pregnancies were examined with ultrasonic technique. The twin fetuses I in cephalic presentation showed a significantly higher percentage of apnea and periodic breathing compared with twin fetuses II. No such difference was found in twin pairs with Twin ti in breech presentation. Also in the control group of 27 singleton pregnancies, the fetuses in cephalic presentation had a higher incidence of apnea and periodic breathing than those in breech presentation. The position of the fetus seems to be decisive for the character of the breathing movements before birth.     

Maternal smoking and fetal breathing movements

Pregnant, habitually smoking women were studied during the last trimester when smoking a standard cigarette, smoking a nontobacco cigarette, or chewing a piece of chewing gum containing 2 or 4 mg. of nicotine. The effects of the experimental interventions were followed on the concentration of nicotine and the percentage of car?yhemoglobin (COHb) in maternal blood, on the amount and pattern of the fetal breathing movements, and on the maternal heart rate, breathing rate, and blood glucose level. The maternal blood concentration of nicotine was increased by the standard cigarette, the 4 mg. nicotine chewing gum, and the 2 mg. nicotine chewing gum in descending order. The COHb percentage in maternal blood was increased by the standard cigarette and to a lower degree by the nontobacco cigarette. A significant increase of apnea and periodic breathing movements in the fetus followed the smoking of a standard cigarette; a similar but nonsignificant change occurred in a dose-related way after the 4 mg. and the 2 mg. chewing gum. The maternal heart rate was positively correlated to the level of blood nicotine. Nicotine appears to be partly responsible for the transient reduction of the fetal breathing movements occurring after smoking one standard cigarette. The suppression of the fetal breathing movements in utero poses the question whether iterated maternal smoking might influence the prenatal assessment of fetal maturity using determination of pulmonary surfactants in the amniotic fluid.     

Relation between fetal heart rate accelerations, fetal movements, and fetal breathing movements

The presence of fetal heart rate (FHR) accelerations is considered a sign of fetal well-being. Fetal body and breathing movements, as visualized by real-time ultrasound, were correlated to FHR accelerations in 16 high-risk pregnancies. The association between FHR accelerations (greater than 15 beats/min lasting 15 sec or more) and the different fetal behavioral states is described.     

Effect of amniotomy on fetal breathing movements

Fetal breathing movements were recorded by real-time ultrasound before and after artificial rupture of the membranes. Fifteen normal pregnancies between 39 and 41 weeks gestation were studied. A significant increase in breathing incidence and maximum breathing rate was observed in the first 10 minutes after amniotomy.     

Cigarette smoking and fetal breathing movements.

Cigarette smoking caused a reduction in the incidence of fetal breathing movements in normal and abnormal pregnancies. The size of the reduction varied, being greatest in small-for-dates pregnancies and pregnancies complicated by fetal distress in labour and least in pre-eclamptic pregnancies. The fall in the amount of fetal breathing movements was significantly related to the rise in maternal plasma nicotine after smoking but was unrelated to the rise in barboxyhaemoglobin. Smoking non-nicotine (herbal) cigarettes produced increases in carboxyhaemoglobin concentrations similar to those observed after smoking tobacco cigarettes, and was not associated with a fall in the incidence of fetal breathing movements. Chewing gum containing nicotine produced rises in plasma nicotine concentration similar to those observed after smoking tobacco cigarettes and was associated with a significant reduction in the incidence of fetal breathing movements. Hence nicotine appeared to be the factor in cigarette smoke responsible for the reduction in the incidence of fetal breathing movements. Nicotine was present in the cord blood of infants whose mothers smoked. The possible mechanism by which nicotine caused a reduction in the incidence of fetal breathing movements and its possible relevance to the detrimental effects of smoking on the fetus are considered.     

Fetal breathing movements and fetal distress.

Twenty-seven pregnancies were monitored by antenatal cardiotocographs, daily fetal movement counts and an assessment of fetal breathing activity by real time scanning, and the results of these tests were related to the development of fetal distress during the first stage of labour. The proportion of time during which fetal breathing movements were present, determined over only a short period of time, was found to be a useful predictor of fetal behaviour during a labour.     

Maternal hypoxemia and fetal breathing movements.

Fetal breathing movements (FBM) were observed daily using a real-time B-mode ultrasound method in a patient with sickle cell anemia in crisis. Observations were made on 2 occasions in the presence of maternal hypoxemia (PO2 less than or equal to 40 mmHg), and FBM were noted to be absent. Conversely, when maternal PO2 was 60 mmHg or greater, FBM were present 23--80% of the time. The FBM were reduced or absent within 90 minutes of maternal Demerol injection. These observations suggest that the human fetal response to hypoxemia may be similar to that observed under expermental conditions in the animal fetus.     

The predictive value of fetal breathing movements in the outcome of premature labour

Fetal breathing movements (FBM) were assessed in 28 pregnant women, presenting with uterine contractions before 34 weeks gestation. External tocometry was used to determine uterine contractions objectively. The first group consisted of 17 patients, treated by tocolytics after the ultrasound scanning showed absence of FBM. The second group comprised 11 patients with FBM present, who were observed only. In the first group nine women were delivered within 1 week, whereas in the second group no patient was delivered in that period, all of them being discharged. In patients with premature contractions the presence of FBM seems to indicate that the pregnancy will continue while absence of FBM foreshadows early delivery.     

The predictive value of fetal breathing movements in the outcome of premature labour

Summary. Fetal breathing movements (FBM) were assessed in 28 pregnant women, presenting with uterine contractions before 34 weeks gestation. External tocometry was used to determine uterine contractions objectively. The first group consisted of 17 patients, treated by tocolytics after the ultrasound scanning showed absence of FBM. The second group comprised 11 patients with FBM present, who were observed only. In the first group nine women were delivered within 1 week, whereas in the second group no patient was delivered in that period, all of them being discharged. In patients with premature contractions the presence of FBM seems to indicate that the pregnancy will continue while absence of FBM foreshadows early delivery.     

The predictive value of fetal breathing movements in the diagnosis of preterm labour

Summary. A real time ultrasound investigation was performed on 64 patients who presented in threatened preterm labour. Fetal breathing movements (FBM) were absent in 17 patients, all of whom were delivered within 56 h. FBM were present in 47 patients of whom five were delivered within 56 h from examination and four of these had spontaneous rupture of membranes and/or chorioamnionitis. In 33 the pregnancy continued for at least 1 week. Two of the fetuses with false negative results showed a distinct breathing pattern different from the rest of the study group. This suggests that pattern recognition of fetal breathing might improve the specificity of this investigation.     

The predictive value of fetal breathing movements in the diagnosis of preterm labour

A real time ultrasound investigation was performed on 64 patients who presented in threatened preterm labour. Fetal breathing movements (FBM) were absent in 17 patients, all of whom were delivered within 56 h. FBM were present in 47 patients of whom five were delivered within 56 h from examination and four of these had spontaneous rupture of membranes and/or chorioamnionitis. In 33 the pregnancy continued for at least 1 week. Two of the fetuses with false negative results showed a distinct breathing pattern different from the rest of the study group. This suggests that pattern recognition of fetal breathing might improve the specificity of this investigation.     

Simultaneous recording of fetal breathing movements and body movements in twin pregnancy

Fetal breathing and body movements were simultaneously evaluated in twin pregnancies in order to determine to what extent these activities occur in a synchroneous pattern in both twin fetuses and if fetal position, presentation or sex have an influence on their behavior. Thirty healthy pairs of twins at 34-37 weeks of gestation were studied. Twenty-six percent of fetal body movements and 49% of breathing movements occurred simultaneously in both fetuses. The overall total simultaneous fetal activity rate was 53.3%. The length of breathing movements and total activity (summation of breathing and body movements) of the fetuses positioned on the right side of the uterus were significantly longer than in fetuses positioned on the left side of the uterus (p = 0.002) and (p less than 0.0001) respectively. This was also true for subgroups where only fetuses in the same presentation or of the same sex were compared. It is concluded that the fetus positioned on the right side of the uterus is more active and that fetal sex or presentation had no significant effect on intrauterine fetal activity in twin pregnancies.     

Ultrasonographic patterns of fetal breathing movements in normal pregnancy

Objective: To assess through pregnancy fetal breathing movements (FBMs) patterns detected by M-mode and Doppler velocimetry technology. Methods: In this cross-sectional study FBMs were investigated in 1882 uncomplicated pregnancies over a 4-year period. Abdominal and thoracic wall movements of fetuses between 14 and 40 weeks of gestation were studied by M-Mode scan, and color Doppler velocimetry with spectral imaging analysis was used to investigate the presence of FBMs associated with nasal fluid flow velocity waveforms (NFFVWs). Results: Abdominal movements were observed in 19% of cases when gestation was less than 20 weeks and in 61% of cases when it was between 21 and 25 weeks; chest movements were significant after 21 weeks; and NFFVWs were detected at 22 weeks and increased progressively to 93% of cases at term. Conclusions: Fetal breathing movements are a complex phenomenon with a composite, progressive pattern of development during gestation.