Influence of time at which oxytocin is administered during labor on uterine activity and perinatal death in pigs

Oxytocin is extensively used to induce or augment uterine contractions, especially to facilitate the third stage of labor in humans. Administration of oxytocin to parturient sows reduces duration of labor whereas mortality of the offspring may remain unchanged. This study aimed to evaluate whether time of administration of oxytocin during parturition may alter the uterine response and fetal outcomes. Two hundred parturient sows were randomly assigned to intramuscularly receive either saline solution (control group) or oxytocin 0.083 IU/kg immediately after the delivery of the 1st, 4th or 8th piglet (groups O-1, 0-4 and 0-8, respectively). Uterine effects and fetal outcomes were registered in all groups. The duration of labor was 20-40 min shorter (P < 0.0001) and time interval between babies was reduced by 3-5 min (P < 0.0001) in the three groups receiving oxytocin. The duration and intensity of contractions, meconium-stained piglets and intrapartum deaths decreased as time at which oxytocin administered during labor was increased. In group 0-8, we observed approximately 70% less meconium-stained piglets and intrapartum deaths than in the control group. In conclusion, oxytocin administered at early phases of parturition to sows may increase duration and intensity of uterine contractions as well as adverse fetal outcomes.     

Cardiac output during labour.

Serial measurements of cardiac output and mean arterial pressure were performed in 15 women during the first stage of labour and at one and 24 hours after delivery. Cardiac output was measured by Doppler and cross sectional echocardiography at the pulmonary valve. Basal cardiac output (between uterine contractions) increased from a prelabour mean of 6.99 l/min to 7.88 l/min at greater than or equal to 8 cm of cervical dilatation as a result of an increase in stroke volume. Over the same period basal mean arterial pressure also increased. During uterine contractions there was a further increase in cardiac output as a result of increases in both stroke volume and heart rate. The increment in cardiac output during contractions became progressively greater as labour advanced. At greater than or equal to 8 cm of dilatation cardiac output increased from a basal mean of 7.88 l/min to 10.57 l/min during contractions. There were also further increases in mean blood pressure during contractions. One hour after delivery heart rate and cardiac output had returned to prelabour values, though mean arterial pressure and stroke volume remained raised. By 24 hours after delivery all haemodynamic variables had returned to prelabour values. Haemodynamic changes of the magnitude found in this series are of considerable clinical relevance in managing mothers with complicated cardiovascular function.     

Effect of short-term hypothyroidism on reproduction in the bitch

Hypothyroidism in bitches has been reported to cause a variable interestrus interval, infertility, abortion, and stillbirth. The objective of this study was to evaluate the effect of experimentally induced hypothyroidism in bitches on fertility, pregnancy, parturition, and neonatal health. Eighteen healthy multiparous bitches were used; hypothyroidism was induced (by radioiodine administration) in nine bitches and the remaining nine served as untreated controls. After breeding, bitches were evaluated for pregnancy, fetal resorption, gestation length, litter size, duration and strength of uterine contractions (during parturition), interval between delivery of pups, viability of pups at birth, periparturient survival, and weight of pups at birth through 4 weeks of age. Bitches were bred a median of 19 weeks after induction of hypothyroidism. All bitches became pregnant and delivered term litters. There was no difference in the interestrus interval, litter size, or gestation length between hypothyroid and control bitches. Duration of uterine contractions was longer, but contraction strength was weaker in hypothyroid than control bitches; however, the interval between delivery of pups was not affected. Periparturient puppy mortality was significantly higher in litters from hypothyroid bitches. Viability scores and weight at birth were significantly lower in pups from hypothyroid bitches than controls. There was no difference between groups in pup weight gain during the first 4 weeks, in the interval from birth to the eyes opened, or to the onset of walking. Although hypothyroidism of relatively short duration did not affect fertility, it prolonged parturition and reduced pup survival in the periparturient period.     

Effect of empty uterine space on birth intervals and fetal and placental development in pigs

A substantial loss of embryos occurs between Days 30 and 40 of pregnancy in the pig under crowded intrauterine conditions, but it is not clear whether this loss affects the growth of adjacent conceptuses. Birth intervals are known to increase with decreasing litter size, but the factors responsible are unknown. Two possibilities are that increased birth weight associated with reduced litter size and the empty uterine space and resulting constricted uterine regions that occur in pigs with small litters may impair piglet delivery. To address these, pregnant gilts were laparotomized on Day 35 of pregnancy and one or two fetuses were manually crushed through the uterine wall on the ovarian or cervical end of each uterine horn to create an empty uterine space behind or in front of the litter of piglets, respectively, in relation to the route of delivery from the uterus. A subset of gilts was slaughtered at 105 days of gestation to confirm that the empty uterine spaces were successfully created and to determine their effects on placental and fetal weights of adjacent conceptuses. At slaughter, the lengths of all externally visible empty constricted regions of the uterus were measured. The uterine horns were opened and the lengths of each placenta were measured from the umbilicus toward the ovary and toward the cervix to assess whether placentas developed symmetrically, and then each fetus and placenta was weighed. Fetal crushing successfully created constricted empty uterine regions on the ovarian and cervical ends of the uterine horns. Ovarian-side placental lengths were greater than cervical-side for conceptuses adjacent to fetuses crushed on the ovarian end of the horn. Cervical-side placental lengths were greater than ovarian-side for conceptuses adjacent to fetuses crushed on the cervical end. Both placental and fetal weights were greater (10% and 6%, respectively, P<0.05) for conceptuses adjacent to crushed fetuses compared to nonadjacent conceptuses. Remaining gilts were farrowed to determine the effect of litter size, average birth weights, and treatment on birth intervals of piglets, which were monitored using 24-h video surveillance. The negative association between number of piglets born alive and average birth interval was confirmed and was not explained by litter size-induced reduction in litter average birth weights. Birth intervals and stillbirth rate did not differ between cervically- and ovarian-treated gilts. These results indicate that conceptus loss on Day 35 of gestation can benefit the growth of adjacent placentas and fetuses, but the benefit is small. Increased average birth weight and the presence of empty uterine space that occurs when litter size is reduced does not fully explain the effect of litter size on birth intervals.     

Respiratory Stimulants in Treatment of Perinatal Asphyxia

The effects of two analeptic drugs—taloximine and ethamivan—have been studied in asphyxiated fetal and newborn rabbits. In primary apnoea ethamivan reduced the time before the onset of gasping, while during gasping taloximine increased the gasp rate. In secondary apnoea neither drug initiated respiration, though most animals could be resuscitated by using intermittent positive pressure respiration. From these results it is suggested that analeptic drugs have no place in obstetric or neonatal departments.     

Fetal viability and fetal growth after prolonged uterine contractions induced by progesterone withdrawal in late pregnancy in rats.

The hypothesis that sustained uterine contractile activity is the direct cause of fetal death after progesterone withdrawal in late pregnancy in rats was investigated. Pregnant rats were subjected to progesterone withdrawal on day 15 of pregnancy by injecting 2 mg mifepristone (RU 486) kg-1 or by ovariectomy with oestradiol replacement (200 ng day-1). Uterine contractile activity (force and frequency) at 4 h, but not at 2 h, in rats injected with mifepristone was significantly higher than in rats injected with vehicle. The contractile activity in mifepristone-treated rats remained higher than in control rats, at 12, 24 and 48 h. Fetal viability 36 h after mifepristone injection, when uterine contractions had lasted for 32 h, was not significantly different from fetal viability in rats injected with vehicle, but at 42 h after mifepristone injection, fetal viability was significantly reduced. In ovariectomized rats, uterine contractile activity at 12, 24, 36 and 48 h, but not at 8 h, was significantly greater than in ovariectomized rats with progesterone replacement (4 mg day-1). Fetal viability at 42 h after the operation, when uterine contractions had lasted for 30 h, was not significantly reduced, but it was significantly reduced at 48 h. When ovariectomized rats had been left to develop uterine contractions for a period before progesterone was injected, deprivation of progesterone and prolonged uterine contractions for about 30 h did not reduce fetal viability or fetal growth determined on day 18, but it did so 3 days later, on day 21. Administration of 5 mg isoxuprine kg-1 twice a day, which suppressed uterine contractions, improved fetal viability in ovariectomized rats at the earlier stage, but not at the later stage. Nevertheless, isoxuprine did improve fetal growth at the later stage in these ovariectomized rats. It is concluded that increased uterine contractile activity sustained for 32 h or less does not reduce fetal viability, but longer periods of contraction may be the cause of fetal death.     

Cerebral oxygen consumption during asphyxia in fetal sheep

Cerebral blood flow and cerebral arteriovenous oxygen content difference were measured in 17 fetal sheep, and cerebral oxygen uptake was calculated. The measurements were made under control conditions and after profound fetal asphyxia induced of uterine blood flow for up to 90 min. In 14 of the fetal sheep, sequential measurements were made to examine hemodynamic changes and cerebral oxygen consumption at comparable intervals up to 36 min of asphyxia. These fetuses initially had elevated blood pressure and lowered heart rate became hypoxemic, hypercarbic, and acidotic. There was an initial decrease in cerebral oxygen consumption. Sequential measurements, however, showed a relative stability in this decreased oxygenation during 4 to 36 min of asphyxia despite a progressive metabolic acidosis. The cerebral fractional oxygen extraction remained unchanged despite a mean pH of 6.98 at 36 min. The calculated cerebral oxygen uptake during asphyxia in all 17 sheep was grouped according to whether the ascending aortic oxygen content was greater or less than 1.0 mmol/l. In the first group with mean ascending aortic oxygen content of 1.3 mmol/l, blood flow to the brain was increased and cerebral oxygen consumption was 85% of control. In the second group with mean arterial blood oxygen content of 0.8 mmol/l, there was a narrowing of the arteriovenous oxygen content difference, but no further increase in cerebral blood flow. Cerebral oxygen consumption was only 48% of control in this more asphyxiated group. We conclude that the degree of hypoxemia in the second group represents a point where physiologic mechanisms cannot compensate, and may be associated with neuronal damage.     

Canine fetal heart rate: Do accelerations or decelerations predict the parturition day in bitches?

Ultrasonography is a safe and efficient technique for monitoring fetal development and viability. One of the most important and widely used parameters to verify fetal viability is the fetal heart rate (HR). In human medicine, the fetal HR normally oscillates during labor in transient accelerations and decelerations associated with uterine contractions. The present study investigated whether these variations also occur in canine fetuses and its relationship to parturition. A cohort study was conducted in 15 pregnant bitches undergoing two-dimensional high-resolution ultrasonographic examination during the 8th and 9th week of gestation. Fetal HR was assessed in M-mode for 5 minutes in each fetus in all bitches. In addition, the bitches were monitored for clinical signs of imminent parturition. Associations between the HR, antepartum time, and delivery characteristics were evaluated with a Poisson regression model. Fetal HR acceleration and deceleration occurred in canine fetuses and predicted the optimal time of parturition. These findings can help veterinarians and sonographers better understand this phenomenon in canine fetuses.     

Use of an ultrasonic blood flow monitor for determining fetal viability in the rhesus monkey (Macaca mulatta). A preliminary study.

Ultrasonic stethoscopy proved to be a reliable and convenient technique for determing fetal viability in Macaca mulatta. Examinations, begun at day 150 of gestation in 33 monkeys and between days 32 and 58 in four other animals, were repeated at intervals of one to seven days. The earliest time of detecting blood flow in the fetal placenta was 42 days of gestation, fetal heart sounds geing discerned later. Three types of fetal cardiac rhythms were recognized: (1) a constant rate during most of pregnancy, (2) fluctuations associated with uterine contractions during labor, and (3) sudden transient bradycardia during violent rotations of the cephalically presented fetus.     

Comparison of nifedipine and diltiazem with salbutamol for prevention of preterm delivery in the ovariectomized, oestrogen-treated late pregnant rat

The ovariectomized, oestrogen-treated, late pregnant rat has been used to compare the ability of two calcium antagonists, diltiazem and nifedipine, with an agonist at beta-adrenoceptors, salbutamol, to prevent the development of uterine contractions, prolong gestation and maintain fetal survival in utero. Preterm delivery of the fetuses was not prevented in the animals infused with salbutamol (2 micrograms/kg/min), occurring at the same time, 30-40 h after ovariectomy, as in the saline-infused rats. The overall integral of uterine contractions was significantly reduced in the salbutamol-treated compared with the saline-treated animals due to decreased contractions after abortion. Both diltiazem (100 micrograms/kg/min) and nifedipine (3.1 and 6.2 micrograms/kg/min) produced significant inhibition of uterine contractions and in contrast to salbutamol prolonged gestation and improved fetal survival in utero as assessed at post mortem on Day 21. However, maternal survival was low (57%) with the higher dose of nifedipine, possibly reflecting the relaxant effect of this compound on vascular smooth muscle with consequent underperfusion of vital organs.     

Evaluation of newborn canine viability by means of umbilical vein lactate measurement, apgar score and uterine tocodynamometry

Newborn viability evaluation and early detection of fetal distress could contribute to reducing mortality at birth in canine species. High neonatal mortality rate in dogs is reported subsequent to complicated or uncomplicated whelping. Umbilical vein lactate and tocodynamometry could provide valuable clinical information to the obstetricians so that appropriate medical and surgical treatments or oxygen and warm administration can be properly and timely applied to mother and newborn pup. In humans, the fetal lactate level represents an objective indicator of fetal distress and a valid predictor of babies' survival. Fetal acidosis recognition by umbilical lactate (UL) measurement, APGAR score classification, and uterine activity monitoring during labour, can represent an advanced system in the evaluation of the canine newborn patient. The purpose of this study was to correlate UL levels with canine neonatal morbidity and mortality within 48 h of birth. We evaluated the relationship among neonatal parameters at birth (mucous membrane color, heart and respiratory rate, reflex irritability, mobility, suckling and vocalization, UL, weight, and temperature) with labour characteristics (uterine contractions recorded by the tocodynamometric system of Whelpwise™ Veterinary Perinatal Specialties®, delivery time, and pup presentation), in view to predict pup viability. We considered also vaginal parturition versus elective and emergency Caesarean section, and uterotonic drugs influence on delivery. Umbilical lactate concentration proved to be useful to predict canine neonatal mortality within 48 h of birth (P < 0.05). We identified 5 mmol/L of vein umbilical lactate concentration as the cut off value, allowing us to distinguish between healthy and distressed pups. Higher values of UL were related with distressed pups, whereas lower values characterized vigorous pups. Lactate concentrations lower than 5 mmol/L and APGAR scores higher than 9, related to mean delivery time of 105 min with effective uterine contractions (10 mm of Hg of strength or more, frequency from 4 to 12 contractions per hour, and 2-5 min in duration), should be considered good prognostic factors in canine labour and neonatology.     

Relation between fetal arterial PO2 and oxytocin-induced uterine contractions in pregnant sheep

The relation between oxytocin-induced type A uterine contractions and fetal arterial PO2, measured continuously with an intravascular oxygen electrode, was studied in nine chronically catheterized sheep during late pregnancy. Oxytocin provoked dose-related increases in intrauterine pressure (IUP) and decreases in fetal PaO2. There was a significant positive relationship between changes in IUP and the maximum decrease in fetal PaO2 (average r = 0.696, df = 92; P less than 0.001). We conclude that changes in uterine activity contribute to transient fetal hypoxemia, and that administration of exogenous oxytocin provides an experimental paradigm to examine the consequences of this relationship.     

Influence of upper respiratory tract on liquid flow to and from fetal lungs

The experiments were designed to determine the influence of the upper respiratory tract (URT) on liquid flow in the fetal trachea. This flow probably influences pulmonary distension, which is thought to be a major determinant of prenatal lung development. In six fetal sheep the URT could be bypassed by connecting the lower trachea, via an external flowmeter, to a cannula in the amniotic sac. In confirmation of our earlier findings, when the URT was in circuit, the mean rate of tracheal efflux was greater during episodes of fetal breathing movements (FBM) [mean 13.8 +/- 2.6 (SE) ml/h] than during apneic periods (mean 3.2 +/- 1.0 ml/h). When the URT was bypassed there was a reversal of net tracheal flow during FBM episodes (mean 19.6 +/- 5.6 ml/h toward the lungs); during apnea there was a much greater rate of efflux (mean 33.1 +/- 10.2 ml/h) than when the URT was in circuit. Nonlabor uterine contractions were associated with an increased rate of efflux during apnea only when the URT was bypassed. We conclude that during fetal life the URT imposes an essentially unidirectional flow of pulmonary liquid away from the lungs, preventing ingress of amniotic fluid and maintaining constancy of composition of liquid in the developing airways. By retarding outward flow during periods of apnea and thoracic compression and by preventing net influx during episodes of FBM, the URT has the probable effect of maintaining the volume and composition of liquid in the fetal airways within narrow limits.     

Sow level risk factors for early piglet mortality and crushing in organic outdoor production

Piglet mortality is a major problem in organic pig production affecting both farm economy and animal welfare. Knowledge is scarce on the risk factors of piglet mortality in Danish commercial organic pig production. The objectives of this study were to evaluate season, litter size, parity, sow body condition and stillborn littermates as risk factors for early piglet mortality and crushing of liveborn piglets from parturition until castration at day 3 to 5 postpartum (pp). The study was conducted over a 1-year period in nine commercial Danish organic pig herds practicing outdoor farrowing all year round. Data included recordings on 3393 farrowings with 50 284 liveborn piglets of which 14.8% died before castration. A subset of the dead piglets were collected and necropsied to identify crushed piglets. The average number of liveborn piglets per litter was 14.8 (SD=3.7) and the average time from parturition until castration was 4.1 (SD=1.7) days. A negative binomial regression analysis was used to model the effect of the predictive variables on the early piglet mortality accounting for different time periods from parturition to castration. An increase in maternal body condition score (BCS) and parity significantly increased the risk of dying between parturition and castration. Early mortality was found to be lowest during spring (March to May) and highest during summer (June to August). Being born into a litter with one or more stillborn littermates increased the risk of early mortality. The risk factors for crushing of piglets were evaluated using a logistic analysis. A significant effect of parity and litter size was found where the odds of at least one piglet in a litter with mortality was diagnosed as crushed increased with increasing parity and litter size. In conclusion, being born during summer (June to August), high parity and maternal BCS and stillborn littermates were found to be risk factors for piglet mortality between parturition and castration. In addition, parity and increasing litter size were found to be risk factors for crushing of piglets in litters with mortality.     

The use of oxytocin in liquid semen doses to reduce seasonal fluctuations in the reproductive performance of sows and improve litter parameters—a 2-year study

The objective of the present research was to eliminate seasonal fluctuations in year-round reproductive performance of sows and to improve litter parameters by administration of oxytocin into liquid semen insemination doses. A 2-year experiment was performed on crossbreed sows, Polish Large White × Polish Landrace, which were partitioned into two groups: control, insemination without any modification with 100 mL semen doses and oxytocin, insemination with 100 mL semen doses to which 5 IU of oxytocin was added just before insemination. A total of 10,486 inseminations were made. The farrowing rate and obtained litter parameters, including the effect of season, were analyzed. For each litter, the following factors were defined: average litter size, percentage of fetal death and mummified piglets, average piglet birth weight, percentage of piglet mortality, fecundity index, average number of piglets weaned, weaned piglet weight, and daily gain. Sows presented a positive reaction to the experimental factor. A statistically higher farrowing rate for oxytocin group in summer and autumn seasons was confirmed (P ≤ 0.01). Regardless of the season, a higher average litter size was observed in the oxytocin group with the most evident differences for winter, spring (P ≤ 0.01), and summer (P ≤ 0.05). The effect of oxytocin on the percentage of fetal death and mummified piglets born was not confirmed statistically except for winter. Analyzing the fecundity index, higher values were obtained for the oxytocin group in all seasons (P ≤ 0.01), including the lowest difference between groups for winter (51.43) and the highest for summer (100.61). A higher average birth piglet weight and weaned piglet weight were recorded for the oxytocin group in all seasons. The highest differences in birth piglet weight between groups were noted for spring (0.22 kg; P ≤ 0.01) and winter (0.17 kg; P ≤ 0.05) and in weaned piglet weight for winter and spring (0.58 kg and 0.52 kg; for both, P ≤ 0.01). The greatest daily gains were observed in the winter season (P ≤ 0.05) in favor of oxytocin. On the basis of the presented results, it should be noted that the use of oxytocin into insemination doses improves the farrowing rate and other parameters of the reproductive performance of sows. In the absence of negative effects, year-round insemination with oxytocin addition into seminal doses is recommended, which effectively improves the production performance and reduces the problem of seasonality in reproduction.     

Piglet and placental traits at term in relation to the estrogen receptor genotype in gilts

Liveborn piglets from gilts with estrogen receptor (ESR) genotype AA (95 AA-AA and 91 AA-AB piglets), AB (88 AB-AA, 118 AB-AB, and 37 AB-BB piglets), and BB (97 BB-AB and 89 BB-BB piglets) were compared after farrowing, to examine whether piglet ESR genotype (ESRp) nested within maternal ESR genotype (ESRm) affected placental traits at term, piglet birth weight, and growth until weaning. Furthermore, the relation of birth weight to various placental traits and the relations between placental traits were evaluated relative to ESR genotype. For this study, 62 Large White x Meishan F2 crossbred gilts (18 AA, 24 AB, and 20 BB) were used. The gilts belonged to a population in which the A allele is favorable for litter size. ESRp nested within ESRm did not affect placental length, weight, surface area and number of areolae. ESRp nested within ESRm affected amnion weight (AA-AA amnions were heavier than AA-AB, AB-AA and BB-AB amnions), placental weight after including placental surface area in the model (AA-AB placentae were lighter than AA-AA, AB-BB and BB-AB placentae), placental efficiency calculated as birth weight divided by placental weight (AB-AA placentae were less efficient than AA-AB placentae), and the relations of birth weight to placental weight and birth weight to number of areolae. The found differences imply an interaction of maternal and fetal ESR genotype on placental traits (especially weight and number of areolae) during fetal development. Furthermore, the found effects on placental and amnion weight might be the result of a difference in thickness or vascularization or both. The favorable ESR allele for litter size, i.e. the A allele, appears to be the unfavorable allele for pre-weaning piglet growth. Therefore, further research on ESR in relation to vascularization, weight and thickness of placentae. uterine size, endometrial gland development, and piglet growth is recommended.     

Some Factors Influencing Pregnancy Rate and Subsequent Litter Size in Primiparous Sows

The pregnancy rate and the subsequent litter size were studied in 332 Swedish Yorkshire primiparous sows, fed according to a commercial Swedish feeding regime during lactation. The sows were weighed and backfat depth was recorded at the first farrowing, at weaning, and at mating. Oestrous detection was performed once daily after weaning, and the interval from weaning to first oestrus (IWO) was recorded. Blood samples for determination of plasma progesterone were drawn regularly after the first weaning. Statistical analyses were only performed on sows with an IWO of 3-8 days. Of these 206 sows were mated on their first (OE1 sows) and 87 sows on their second (87 OE2 sows) oestrus after weaning. The pregnancy rate was 85.4% for OE1 sows and 75.9% for OE2 sows (p=0.048). There was no significant difference in pregnancy rate between OE1 sows with an IWO of 3-5 days and OE1 sows with an interval of 6-8 days. OE2 sows with an IWO of 6-8 days, on the other hand, had a significantly lower pregnancy rate compared with OE2 sows with an interval of 3-5 days. The pregnancy rate in sows that lost more than 30 kg during the first lactation period did not differ from that of sows losing less than 30 kg. In sows with a first litter size of more than 9 piglets alive at birth, the pregnancy rate decreases significantly if mating is delayed until the second oestrus after weaning. OE2 sows had a significantly larger second litter size at birth than OE1 sows (+ 2.0). The litter size at six weeks did not, on the other hand, differ significantly (+ 0.4). There was a positive correlation between the IWO and 2nd litter size, although significant only for OE1 sows between the IWO and litter size alive at birth. In the OE1 group, sows losing 20 kg or less during lactation had significantly larger second litters at birth than the sows losing 21-30 kg, but not significantly larger than the sows losing more than 30 kg. One piglet more, at birth, in the first litter resulted in 0.25 piglet more in the second litter. For sows with a large first litter there was a low probability of also having a large second litter.     

The relationship of umbilical glucose uptake to uterine blood flow

In 30 experiments performed on 5 pregnant sheep, the rate of glucose transfer from the placenta to fetus via the umbilical circulation was measured while varying uterine blood flow by means of a cuff-type occluder and while maintaining a constant maternal glucose concentration by means of a 'glucose clamp'. Over the range of uterine blood flows obtained, there was no significant effect on the simultaneously measured umbilical blood flow. Fetal glucose uptake and arterial glucose concentration remained normal as the uterine blood flow rate decreased from 600 to 300 ml per min per kg of fetus. At blood flow rates less than 300 ml.min-1.kg-1, the fetal glucose uptake decreased and became negative in one instance while the arterial glucose concentration became variable and markedly increased in 2 animals. This increase in fetal glucose concentration was associated with a decrease in the uterine oxygen delivery rate, a decrease in fetal oxygen content and a decrease in fetal oxygen uptake. These observations support the concept that fetal glucose metabolism is altered by severe hypoxia and demonstrate that there is little effect of uterine blood flow on fetal glucose uptake in the normal physiological range.     

Stimulation of fetal hypothalamus induces uterine contractions in pregnant rats at term

The fetal brain is thought to have a role in the onset and progression of labor. Evidence also exists for fetal oxytocin release just before and during parturition. The present study examined whether activation of the fetal brain could induce uterine myometrial contractions through oxytocin receptors in the dam. Under urethane anesthesia, electrical stimulation of the hypothalamus of fetal rats that were still connected with the dams by an intact umbilical cord induced uterine contractions in term pregnant rats. Intraperitoneal injections of synthetic oxytocin in fetuses induced uterine contractions in the dams similar to those induced by electrical stimulation of the fetal hypothalamus. Maternal intravenous injections of an oxytocin antagonist immediately attenuated uterine contractions induced by fetal oxytocin injections and electrical stimulation of the fetal hypothalamus. These findings suggest the possibility that oxytocin released from the fetal hypothalamus is involved in parturition.