Arteriovenous nonesterified fatty acids and glycerol differences in the umbilical cord at term and their relationship to fetal metabolism

Transferred maternal fatty acids stimulate fetal adipogenesis and lead to neonatal and adult obesity

The prevalence of adult and childhood obesity are increasing. Most of the human newborn's body fat accumulates in the last half of intrauterine life. Fat in the fetus was thought to be mostly synthesized from glucose, but now it is commonly accepted that the bulk of it is the product of placental transfer of maternal fatty acids. Transported fatty acids originate in maternal plasma "free" fatty acids, fatty acids hydrolyzed from maternal plasma triglycerides, and the poly-unsaturated fatty acid component of maternal phospholipids. Glucose remains an important precursor of alpha-glycerol phosphate, to which most transported fatty acids are eventually esterified. Maternal plasma lipids are elevated in late pregnancy and even more in obese and diabetic pregnant women. This accelerates the placental transport of fatty acids. The hypothesis presented in this paper rests on the observations that the exponential increase in fat tissue in the human embryo's body occurs in time to parallel the increase of lipids in the mother's blood and depends on the chemical affinity of the transcription factor PPAR gamma to fatty acids and on fatty acid stimulation of adipocyte generation from precursor cells. The hypothesis asserts that transported maternal fatty acids activate the transcription factors in the fetus and initiate conversion of the mesenchymal stem cells into adipocytes. In obese and diabetic mothers, the higher plasma lipids facilitate increased placental fatty acid transfer. This will increase adipocyte generation and, through this, the prevalence of babies with increased fat cell size and number. Babies born with increased adipose tissue cellularity will have greater probability of growing up to become obese adolescents and adults. These newborns, whose obesity is hyperplastic as well as hypertrophic, as adults will have difficulty losing weight through diet and exercise or will regain the lost weight more quickly than others without these characteristics. Accordingly, increased placental fatty acid transfer and accelerated adipocyte generation may explain not only neonatal obesity, but some aspects of the adult obesity epidemic also. It is therefore recommended that prevention of fetal fat cell hyperplasia, by lowering maternal plasma lipids in mid and late pregnancy, should be attempted in pregnancies at risk for macrosomia.

Umbilical venous–arterial plasma composition differences suggest differential incorporation of fatty acids in NEFA and cholesteryl ester pools

The developing fetus requires an adequate supply of fatty acids, in particular PUFA, for optimal growth and development. Little is known about the transfer of fatty acids by the placenta into the fetal circulation. However, the molecular form in which fatty acids are transferred into the fetal circulation may influence their metabolism and hence their availability to specific tissues. The aim of the present study was to determine which lipid pools in the fetal circulation become enriched in fatty acids from the placenta by comparing the fatty acid compositions of individual lipid pools between umbilical venous (UV) and umbilical arterial (UA) plasma. Plasma from the UV and UA was collected after delivery from ten uncomplicated pregnancies, and the fatty acid composition of each lipid class was determined by GC. Total NEFA concentration in the UV was twofold higher than in the UA (P < 0·05) due to enrichment in 16 : 0, 16 : 1n-7, 18 : 1n-9, 18 : 1n-7, 18 : 2n-6, 20 : 3n-6, 20 : 4n-6, 24 : 0 and 22 : 6n-3. Total cholesteryl ester concentration was twofold higher in the UV than in the UA (P < 0·05) due to enrichment in 16 : 0, 16 : 1n-7, 18 : 0, 18 : 1n-9, 18 : 1n-7, 18 : 2n-6 and 20 : 4n-6. There were no significant UV–UA differences in the total concentration or composition of TAG or phosphatidylcholine. The present study demonstrates differential enrichment across the placenta of fatty acids into specific lipid pools in the fetal circulation. Such partitioning may facilitate supply of individual fatty acids to specific fetal tissues.

Carbohydrate solution intake during labour just before the start of the second stage: a double-blind study on metabolic effects and clinical outcome

OBJECTIVE

To study the effects of oral carbohydrate ingestion on clinical outcome and on maternal and fetal metabolism.

DESIGN

Prospective, double-blind, randomised study.

SETTING

Leyenburg Hospital, The Hague, The Netherlands.

POPULATION

Two hundred and two nulliparous women.

METHODS

In labour, at 8 to 10 cm of cervical dilatation, the women were asked to drink a solution containing either 25 g carbohydrates or placebo. In a subgroup of 28 women, metabolic parameters were measured.

MAIN OUTCOME MEASURES

Number of instrumental deliveries, fetal and maternal glucose, free fatty acids, lactate, pH, Pco2, base excess/deficit and beta-hydroxybutyrate.

RESULTS

Drinking a carbohydrate-enriched solution just before starting the second stage of labour did not reduce instrumental delivery rate (RR 1.1, 95% CI 0.9-1.3). Caesarean section rate was lower in the carbohydrate group, but the difference did not reach statistical significance (1% vs 7%, RR 0.2, 95% CI 0.02-1.2). In the carbohydrate group, maternal free fatty acids decreased and the lactate increased. In the umbilical cord there was a positive venous-arterial lactate difference in the carbohydrate group and a negative one in the placebo group, but the differences in pH and base deficit were comparable.

CONCLUSION

Intake of carbohydrates just before the second stage does not reduce instrumental delivery rate. The venous-arterial difference in the umbilical cord suggested lactate transport to the fetal circulation but did not result in fetal acidaemia.

The effects of oral carbohydrate administration on fetal acid base balance

AIMS

Little evidence-based data are available on the effects of eating and drinking during labor. Intravenous glucose administration has been related to fetal metabolic acidosis. The question is, whether oral intake of carbohydrates effects the fetal acid-base balance.

METHODS

In a double blind, prospective placebo controlled study 100 nulliparous women were randomized at 8-10 cm of cervical dilatation. All women were asked to drink 200 cc of either a carbohydrate solution (containing 25 grams carbohydrates) or placebo. In all women, both arterial and venous umbilical cord pH, pCO2, pO2, HCO3- and base excess/deficit were assessed. In a subgroup of women, whose deliveries were complicated by mild signs of fetal distress, clinical outcome and acid-base status was described separately.

RESULTS

Fetal arterial umbilical cord pH were identical: 7.20 +/- 0.07 in the placebo group and 7.20 +/- 0.08 in the carbohydrate group and the base excess -6.6 +/- 2.8 versus 6.6 +/- 3.7. In the women with mild signs of fetal distress, no differences were observed as well.

CONCLUSIONS

Oral carbohydrate intake during labor seems to be safe regarding the fetal acid-base balance. Further study on the maternal and fetal metabolic parameters is essential to give a more complete picture.

Fetal and maternal energy metabolism during labor in relation to the available caloric substrate

AIM

To discuss maternal and fetal metabolic events during labor and the possible role of glucose administration.

RESULTS

The oxidative pathway covers the largest part of the energy demand of labor, although in the second stage or, in polysystolic labor, the non-oxidative pathway becomes important as well. Glucose is the main maternal energy source, but the rise in ketobodies, even during normal labor, suggests a relative shortage. In the first stage of labor, a combination of a respiratory alkalosis, and to a lesser extent, a metabolic acidosis, result in a rise in the maternal pH. In the second stage of labor, the maternal pH decreases due to an increasing metabolic acidosis. Glucose is also the main fetal energetic fuel. In fetal hypoxia, lactate is produced, which in most cases is transferred to the maternal circulation. High maternal lactate concentrations, however, may interfere with this process. Furthermore, fetal hyperglycemia may lead to an increased fetal lactate production.

CONCLUSIONS

Maternal hyperglycemia, may lead to an increase in maternal and fetal lactate production resulting in metabolic acidosis. Unlike high dosage intravenous glucose administration, it is not likely that oral intake of carbohydrates leads to maternal and fetal hyperglycemia and subsequently to metabolic acidosis, but studies are rare.

Placental transfer of essential fatty acids in humans: venous-arterial difference for docosahexaenoic acid in fetal umbilical erythrocytes

Docosahexaenoic acid [22:6(n-3); 22:6(4,-7,10,13,16,19) (DHA)] is required in quantity by the developing nervous system of the fetus. This need could be met through synthesis of DHA from linolenic acid in the fetus or through placental transfer of DHA directly. To study the placental transfer of n-3 fatty acids, we obtained umbilical and maternal blood samples from 26 healthy women and infants at parturition and measured the fatty acid composition and content of both plasma and erythrocytes. A striking finding was a considerable venous-arterial difference for DHA in the umbilical erythrocytes as a proportion of total fatty acids and in absolute concentration. This difference of 2.2 micrograms per billion erythrocytes was 6 times larger than the difference in fetal plasma, when the plasma and erythrocyte concentrations were normalized to whole blood. Most other erythrocyte fatty acids showed a similar trend. In umbilical plasma, significant venous-arterial differences were found for 16:0, 16:1, 18:2, and total saturated fatty acids. There was a similar trend for most other plasma fatty acids. Compared with maternal blood, fetal plasma and erythrocytes had higher levels of 20:4 and DHA and lower levels of 18:2 and 18:3(n - 3) fatty acids as a proportion of total fatty acids. These results suggest that erythrocytes play a major role in the necessary transport of the essential fatty acid DHA into the fetus.

High arachidonic acid levels in the cord blood of infants of mothers on vegetarian diets

1. Maternal and umbilical cord plasma samples were collected from forty-seven Asian women, twenty-eight life-long vegetarians and seventeen non-vegetarians, during delivery of their babies. The concentrations and fatty acid profiles of the plasma free fatty acid and triacylglycerol fractions were determined. 2. There were no significant differences between the levels of free fatty acid and triacylglycerol in either maternal or cord plasma from vegetarian compared with non-vegetarian Asian women. The fatty acid profiles of the lipid fractions in the two groups were similar. Total plasma free fatty acid levels in the maternal circulation correlated with umbilical cord levels. 3. The levels of linoleic acid in the maternal plasma free fatty acid fraction of the Asian women were much higher than previous reports on mixed populations of European women. In the Asian women arachidonic acid concentrations in both maternal and umbilical circulations were over four times higher than those reported for women unselected for race and diet.

The transfer of free fatty acids across the human placenta

Thirty-three matched maternal venous and umbilical cord vein and artery plasma samples were obtained at elective caesarean section and the concentrations of the individual free fatty acids determined. The maternal levels were 1.009 (SEM 0.043) and the umbilical vein-artery difference was 0.036 (SEM 0.011) mmol/l. There was a significant correlation between the mean concentration in maternal venous blood and the vein-artery difference for myristic, palmitic, stearic, linoleic and docosahexaenoic acids but not for oleic acid. When arachidonic acid concentration in the fetus was high, then the vein-artery difference was negative (flow to the placenta), when it was low, the difference was positive (flow to the fetus). Thus whilst there appears in general to be a flow of fatty acid to the fetus dependent on maternal free fatty acid concentrations, the transfer of arachidonic acid is largely determined by other factors. The reasons why oleic acid does not behave like the other fatty acids is not clear.

Metabolic events in infants of diabetic mothers during first 24 hours after birth. II. Changes in plasma lipids

Changes in plasma glycerol (FG), free fatty acids (FFA) and triglyceride (TG) were studied in 24 normo- and 8-hypoglycemic infants of diabetic mothers (IDM). In both groups a normal rise in plasma FG 2 hours after birth was found indicating unimpaired lipolysis. The rise in plasma FFA, however, was only about 50% of normal in normoglycemic IDM and about 25% of normal in hypoglycemic IDM. The rise in plasma TG was normal in normoglycemic and about 70% of normal in hypoglycemic IDM. The 2 hour rise in plasma FFA correlated with the 2 hour concentration of insulin and glucose, whereas the rise in plasma FG and TG did not. Maternal plasma FFA correlated with fetal FFA retention (umbilical vein minus artery (V-A) FFA concentrations). No correlations were found between maternal plasma FFA values and birth-weights nor between umbilical V-A FFA concentrations and birth-weights.

The passage of fat emulsion across the human placenta

Six patients near term were given an intravenous infusion of a fat emulsion (Intralipid) a few hours before normal delivery or Caesarean section. Six other non-infused patients were studied as controls. Maternal venous and umbilical venous and arterial blood samples were taken at delivery and analyzed for individual fatty acid concentrations in triglyceride, free fatty acid (FFA) and phospholipid fractions. The emulsion, being rich in oleic and linoleic acids, affected the composition of the maternal triglycerides. The fetal lipids were also altered and the infusions resulted in large positive umbilical venous-arterial (v-a) differences in FFA and triglyceride fatty acid concentrations, but this was not the case for phospholipid concentrations. The fatty acids with the largest v-a differences were those prominent in the emulsion.

Cord blood hypertriglyceridaemia as an index of fetal stress: use of a simple screening test and results of further biochemical analysis

In this preliminary study, 120 cord blood samples were subjected to a simple on-the-ward triglyceride screening procedure and 15 were designated as being high and another 15 randomly selected as controls. All the samples were then subjected to detailed biochemical analysis for fatty acid profiles and/or concentrations of free fatty acids, triglycerides (TG), phospholipids, cholesterol esters and glycerol. Eleven of the samples designated 'high' were associated with one or more of the following clinical conditions: family history of ischaemic heart disease, maternal starvation, fetal distress, light-for-dates babies and excessive weight gain during pregnancy. There was an association between high TG levels and high glycerol levels. The fatty acid pattern of the TG was altered when at abnormally high concentration, in particular oleic acid was increased relative to the others, and this was associated with an increase in cholesterol ester oleic acid. The possible mechanisms resulting in cord hypertriglyceridaemia are discussed.

Metabolism during normal and diabetic pregnancy and its effect on neonatal outcome

Diurnal profile studies have been used to define the fetal carbohydrate and lipid substrate environment in normal and diabetic women during late pregnancy. In women with normal glucose tolerance the diurnal plasma glucose concentration was maintained within close limits (mean +/- S.D., 4.70 +/- 0.38 mmol/l) but in chemical and insulin-dependent diabetics there was a marked increase in both the mean diurnal glucose value and in the variability of the plasma glucose levels observed through the day (mean +/- S.D., 5.61 +/- 5.61 +/- 1.03 and 6.02 +/- 1.26 mmol/l respectively, P less than 0.01). No difference was observed between the peripheral insulin activity of the normal and chemical diabetic women, and the impaired glucose tolerance of the latter group was due to a deficient insulin response to goucose. The diurnal glucose variability, expressed as the standard deviation of the mean, was found to be inversely correlated with the residual C-peptide response in insulin-requiring diabetics. The mean diurnal plasma free fatty acid (FFA) concentration was slightly raised in chemical diabetic subjects compared to normal women (mean +/- S.D., 0.77 +/- 0.34 and 0.68 +/- 0.20 mmol/l respectively) but this difference was not significant. Insulin treatment produced a marked reduction in circulating FFA concentration, with a mean value in the insulin-dependent diabetic group of 0.45 +/- 0.11 mmol/l (P less than 0.001). Neonatal glucose assimilation during the first two hours of life correlated strongly with several functions of maternal carbohydrate tolerance. This was associated with higher plasma insulin concentrations at birth, and a marked tendency to hypoglycaemia in the infants of untreated chemical diabetic women. Impaired mobilization of triglyceride stores was also observed during the two hours after birth in the infants of diabetic women. This, however, appears to be due not to impaired lipolysis but to rapid re-esterification of FFA. These findings all indicate a state of functional hyperinsulinism in the infant of the diabetic women secondary to maternal hyperglycaemia.

Evidence for fatty acid transfer across the human placenta

Lipid analysis of blood from umbilical artery and vein, experiments on artificially perfused human placentas, measurements of fetal blood triglyceride concentrations and the relative percentage of essential fatty acids in fetal adipose tissue are all consistent with the view that fatty acids cross the human placenta and that the flow to the fetus is influenced by maternal blood concentrations of free fatty acids and triglycerides.

The transfer of free fatty acids across the rabbit placenta

1. The passage of fatty acids across the placenta was studied in 28 day pregnant rabbits (i) by comparing the fatty acid distribution in plasma free fatty acids (FFA) of umbilical cord artery and vein with that in maternal plasma and (ii) by infusing the doe at a constant rate with labelled palmitic, linoleic or arachidonic acids. During the infusion maternal and foetal plasma FFA specific activities were measured. 2. The mean levels of all the fatty acids studied (from twelve to twenty carbon atoms) were similar in both the umbilical vein plasma and maternal arterial plasma FFA, except for arachidonic acid, which was higher in foetal blood. The relative distribution of the fatty acids in umbilical arterial plasma similar to that in the vein, but at lower concentrations. The mean cord venous-arterial difference for each fatty acid correlated positively with the mean maternal arterial levels, with the exception of arachidonic acid. 3. During the constant infusion experiments the specific activities of the fatty acids in the maternal and foetal circulating FFA pools rose rapidly during the first 4 min then rose only slowly. Palmitic and linoleic acids were cleared from the maternal circulation in a similar manner and crossed the placenta at similar rates. 4. The average foetal specific activity in plasma FFA reached 15% of the maternal level for both palmitate and linoleate. The figure for arachidonic acid was half that for palmitic acid infused at the same time. 5. It is concluded that (i) all the major fatty acids present in foetal adipose tissue cross the placenta, (ii) the net transport of each fatty acid depends in part on maternal concentrations, (iii) the rate of metabolism of palmitic and linoleic acids is the same and both cross the placenta at the same rate. Proportionately less foetal arachidonic acid is derived from maternal FFA, and (iv) the results suggest a second placental source of arachidonic acid and possibly also of otherfatty acids.

Carbohydrate and lipid metabolism during human labor: free fatty acids, glucose, insulin, and lactic acid metabolism during normal and oxytocin-induced labor for postmaturity

This investigation was performed to study the metabolism of the major body fuels (viz. glucose and free fatty acids), insulin, and lactic acid during the stress of human labor. In addition, the role of the normal placenta in the transport of these substances between mother and the fetus was evaluated by measuring them in the mother and cord blood at delivery. To study possible alterations of this role in the placenta which had exceeded the normal period of gestation, a second comparable group of women had labor induced with oxytocin 16-18 days beyond the expected date of delivery. A dramatic twofold increase in maternal plasma free fatty acids was observed during labor. There was a lesser but definite increase in blood glucose concentrations. No rise in serum insulin levels was noted which coincided with the changes in blood glucose. Lactic acid concentrations during the course of labor were variable from baseline but at delivery, the concentrations rose to very significant levels. Free fatty acids and blood glucose levels were significantly higher in the maternal than in the fetal side. A significantly positive correlation was noted between the maternal and cord blood values except for free fatty acids in the postmature group. No significant difference, nor a correlation was found between the two compartments in the insulin nor lactic acid levels. These results suggest that during human labor free fatty acids are the principal metabolic fuel. This increase in maternal free fatty acids may serve to spare glucose as a metabolic fuel in the fetus. The mechanism responsible for the increase maternal free fatty acid mobilization remains to be determined. It is not possible to discern any consistant alteration in placental function as a consequence of prolonged gestation.

Concentrations of free fatty acids in maternal and umbilical cord blood during elective Caesarean section

The concentration of free fatty acids was measured in blood taken from the umbilical artery and vein of 29 infants during elective Caesarean section and compared with levels in maternal venous blood. The mean venous-arterial (v-a) difference was 0.07 mEq/l. There was a direct and significant correlation between the umbilical v-a difference and maternal venous concentrations.