Are there ethnic disparities in risk of preterm birth among infants born with congenital heart defects?

BACKGROUND: Birth defects and preterm birth (PTB) are leading causes of infant morbidity and mortality in the United States. Infants with birth defects are more likely to be born preterm (<37 weeks), yet the roles of maternal ethnicity and fetal growth in this relationship are unclear. This study aimed to assess the risk of PTB among non-Hispanic (NH) Black, NH-White, and Hispanic infants with congenital heart defects (CHD), adjusting for fetal growth. METHODS: Florida Birth Defects Registry data were used to conduct a retrospective cohort study on 14,319 live-born infants with CHDs born January 1, 1998 to December 31, 2002. ORs and 95% CIs were computed for each growth category (small-for-gestational age [SGA], appropriate-for-gestational-age [AGA], and large-for-gestational-age [LGA]) by ethnicity and adjusted for maternal and infant covariates using logistic regression. RESULTS: After adjusting for potential confounders, SGA and AGA NH-Black infants with CHDs had increased risk of PTB compared to NH-White infants with CHDs (OR 1.79; 95% CI: 1.40, 2.30 and OR 1.89; 95% CI: 1.68, 2.13, respectively). Hispanic SGA, AGA, and infants with CHDs had no increased risk of PTB compared to NH-White infants. CONCLUSIONS: The increased risk of PTB among SGA and AGA NH-Black infants with CHDs is not explained by the overall disparities in risk of PTB between NH-Blacks and NH-Whites. Additional studies are needed to determine the specific subtypes of CHD for which these relationships are present and if these findings are seen among infants with other birth defects.     

Rapid recovery of fat mass in small for gestational age preterm infants after term

Background

Preterm small for gestational age (SGA) infants may be at risk for increased adiposity, especially when experiencing rapid postnatal weight gain. Data on the dynamic features of body weight and fat mass (FM) gain that occurs early in life is scarce. We investigated the postnatal weight and FM gain during the first five months after term in a cohort of preterm infants.

Methodology/Principal Findings

Changes in growth parameters and FM were prospectively monitored in 195 infants with birth weight ≤1500 g. The infants were categorized as born adequate for gestational age (AGA) without growth retardation at term (GR−), born AGA with growth retardation at term (GR+), born SGA. Weight and FM were assessed by an air displacement plethysmography system. At five months, weight z-score was comparable between the AGA (GR+) and the AGA (GR−), whereas the SGA showed a significantly lower weight.The mean weight (g) differences (95% CI) between SGA and AGA (GR−) and between SGA and AGA (GR+) infants at 5 months were −613 (−1215; −12) and −573 (−1227; −79), respectively. At term, the AGA (GR+) and the SGA groups showed a significantly lower FM than the AGA (GR−) group. In the first three months, change in FM was comparable between the AGA (GR+) and the SGA groups and significantly higher than that of the AGA (GR−) group.The mean difference (95% CI) in FM change between SGA and AGA (GR−) and between AGA (GR+) and AGA (GR−) from term to 3 months were 38.6 (12; 65); and 37.7 (10; 65). At three months, the FM was similar in all groups.

Conclusions

Our data suggests that fetal growth pattern influences the potential to rapidly correct anthropometry whereas the restoration of fat stores takes place irrespective of birth weight. The metabolic consequences of these findings need to be elucidated.     

Can the fall in Avon's sudden infant death rate be explained by changes in sleeping position?

OBJECTIVE--To examine the impact of changing practice with regard to infant sleeping position on mortality from the sudden infant death syndrome. DESIGN--A population based study of all infants dying suddenly and unexpectedly during February 1990 to July 1991, and two groups of controls; one comprising every 125th baby born to Avon residents and the other comprising pairs of infants matched to each index case for age, neighbourhood, and date of study. Information about sleeping position was collected at home visits soon after the index baby''s death or, for the population based controls, on several occasions in the first six months of life. The design was comparable to that of an earlier study of the same population. SETTING--County of Avon. SUBJECTS--35 infants who died suddenly and unexpectedly (32 of the sudden infant death syndrome), 70 matched controls, and 152 population based controls. RESULTS--The prevalence of prone sleeping in the matched controls was much lower than that found in an earlier study in Avon (28% (18/64) 1990-1 v 58% (76/131) 1987-9; p less than 0.001) and was comparable with the prevalence in population based controls (29%). This would be expected to lead to a reduction in the incidence of the sudden infant death syndrome to 2.0/1000 live births (95% confidence interval 1.8/1000 to 2.5/1000). The actual mortality fell from 3.5/1000 in 1987-9 to 1.7/1000. CONCLUSION--The fall in mortality can be almost entirely accounted for by the reduction in prone sleeping, suggesting a causal relation exists between them. Side and supine positions confer protection but the side position is unstable and the infant may roll prone. We therefore recommend supine as the safest sleeping position for babies.     

Increased sympathetic and decreased parasympathetic cardiovascular modulation in normal humans with acute sleep deprivation.

Cardiovascular autonomic modulation during 36 h of total sleep deprivation (SD) was assessed in 18 normal subjects (16 men, 2 women, 26.0 +/- 4.6 yr old). ECG and continuous blood pressure (BP) from radial artery tonometry were obtained at 2100 on the first study night (baseline) and every subsequent 12 h of SD. Each measurement period included resting supine, seated, and seated performing computerized tasks and measured vigilance and executive function. Subjects were not supine in the periods between measurements. Spectral analysis of heart rate variability (HRV) and BP variability (BPV) was computed for cardiac parasympathetic modulation [high-frequency power (HF)], sympathetic modulation [low-frequency power (LF)], sympathovagal balance (LF/HF power of R-R variability), and BPV sympathetic modulation (at LF). All spectral data were expressed in normalized units [(total power of the components/total power-very LF) x 100]. Spontaneous baroreflex sensitivity (BRS), based on systolic BP and pulse interval powers, was also measured. Supine and sitting, BPV LF was significantly increased from baseline at 12, 24, and 36 h of SD. Sitting, HRV LF was increased at 12 and 24 h of SD, HRV HF was decreased at 12 h SD, and HRV LF/HF power of R-R variability was increased at 12 h of SD. BRS was decreased at 24 h of SD supine and seated. During the simple reaction time task (vigilance testing), the significantly increased sympathetic and decreased parasympathetic cardiac modulation and BRS extended through 36 h of SD. In summary, acute SD was associated with increased sympathetic and decreased parasympathetic cardiovascular modulation and decreased BRS, most consistently in the seated position and during simple reaction-time testing.     

Mitochondrial DNA depletion in small- and large-for-gestational-age newborns

Objective: To investigate whether mitochondrial DNA (mtDNA) content may be associated with clinical features, anthropometric variables, and laboratory findings in both extremes of abnormal fetal growth: small and large size for gestational age. Research Methods and Procedures: Eighty‐eight pregnant women and their infants were included in a cross‐sectional study. According to the offspring birthweight, normalized by sex and gestational age, there were 57 newborns with appropriate weight for gestational age (AGA) and 31 with abnormal weight for gestational age: 17 small for gestational age (SGA) and 14 large for gestational age (LGA). mtDNA quantification using nuclear DNA as a reference was measured by a real‐time quantitative polymerase chain reaction method. Results: The mothers’ pregestational BMI was associated with the weight of their offspring: SGA infants had lean mothers (BMI, 21.4 ± 0.7), and LGA infants had overweight mothers (BMI, 26.7 ± 1.4) in comparison with AGA infants (BMI, 23.0 ± 0.7) (p < 0.003). Newborn leptin levels were associated with birthweight after adjustment for sex and gestational age (SGA, 7.0 ± 1.1 ng/mL; AGA, 15.2 ± 1.6 ng/mL; and LGA, 25.6 ± 4.1 ng/mL) (p < 0.002). Conversely, mtDNA/nuclear DNA ratio was significantly lower in both extremes of abnormal fetal growth, SGA (18 ± 6) and LGA (9 ± 2), at birth in comparison to AGA‐weight infants (28 ± 4) (p < 0.03). Discussion: Our findings show that mtDNA content is decreased in newborns with abnormal weight in comparison with AGA infants. On the basis of a cumulative body of evidence, we speculate that mtDNA depletion is one of the putative links between abnormal fetal growth and metabolic and cardiovascular complications in later life.     

Cardiac autonomic balance in small-for-gestational-age neonates

The cardiac sympathetic nervous system is one putative key factor involved in the intrauterine programming of adult cardiovascular disease. We therefore analyzed cardiac autonomic system activity in small for gestational age (SGA) neonates. Heart rate variability (HRV) from 24-h ECG recordings were analyzed for time-domain and frequency-domain parameters in 27 SGA neonates [median 261 (240-283) days of gestation] compared with 27 appropriate for gestational age (AGA) neonates [median 270 (239-293) days of gestation]. In addition, salivary alpha-amylase levels were analyzed during resting conditions and in response to a pain-induced stress event in 18 SGA [median 266 (240-292) days of gestation] and 34 AGA [median 271 (240-294) days of gestation] neonates. Overall HRV was not significantly different in SGA neonates compared with AGA neonates (SD of all valid NN intervals: P = 0.14; triangular index: P = 0.29), and the sympathovagal balance [low frequency (LF)/high frequency (HF)] was similar (P = 0.62). Parameters mostly influenced by sympathetic activity did not reveal significant differences: (SD of the average of valid NN intervals: P = 0.27; average of the hourly means of SDs of all NN intervals: P = 0.66, LF: P = 0.83) as well as vagal tone-influenced parameters were unaltered (average of the hourly square root of the mean of the sum of the squares of differences between adjacent NN intervals: P = 0.59; proportion of pairs of adjacent NN intervals differing by >50 ms: P = 0.93; HF: P = 0.82). Median resting levels for alpha-amylase were not significantly different in SGA neonates (P = 0.13), and a neonatal stress stimulus revealed similar stress response patterns (P = 0.29). HRV and salivary alpha-amylase levels as indicators of cardiac autonomic activity were not altered in SGA neonates compared with AGA neonates. Thus, it appears that the intrauterine activation of the sympathetic system in SGA fetuses does not directly persist into postnatal life, and neonatal sympathovagal balance appears to be preserved.     

Greater sensitivity of the vestibulosympathetic reflex in the upright posture in humans.

Otolith organs have been shown to activate the sympathetic nervous system in the prone position by head-down rotation (HDR) in humans. To date, otolithic stimulation by HDR has not been comprehensively studied in the upright posture. The purpose of the present study was to determine whether otolithic stimulation increases muscle sympathetic nerve activity (MSNA) in the upright posture. It was hypothesized that stimulation of the otolith organs would increase MSNA in the upright posture, despite increased baseline sympathetic activation due to unloading of the baroreceptors. MSNA, arterial blood pressure, heart rate, and degree of head rotation were measured during HDR in 18 volunteers (23 +/- 1 yr) in different postures. Study 1 (n = 11) examined HDR in the prone and sitting positions and study 2 (n = 7) examined HDR in the prone and 60 degrees head-up tilt positions. Baseline MSNA was 8 +/- 4, 15 +/- 4, and 33 +/- 2 bursts/min for prone, sitting, and head-up tilt, respectively. HDR significantly increased MSNA in the prone (Delta4 +/- 1 and Delta105 +/- 37% for burst frequency and total activity, respectively), sitting (Delta5 +/- 1 and Delta43 +/- 12%), and head-up tilt (Delta7 +/- 1 and Delta110 +/- 41%; P < 0.05). Sensitivity of the vestibulosympathetic reflex (%DeltaMSNA/DeltaHDR; degree of head rotation) was significantly greater in the sitting and head-up tilt than prone position (prone = 74 +/- 22; sitting = 109 +/- 30; head-up tilt = 276 +/- 103; P < 0.05). These data indicate that stimulation of the otolith organs can mediate increases in MSNA in the upright posture and suggest a greater sensitivity of the vestibulosympathetic reflex in the upright posture in humans.     

Paternal contribution to small for gestational age babies: a multicenter prospective study

Our aims were to investigate whether men who fathered small for gestational age (SGA) infants themselves had lower birthweight, were more likely to be obese, have central adiposity and elevated blood pressure in adult life compared with men who fathered non-SGA infants. A total of 2,002 couples participating in the Screening for Pregnancy Endpoints (SCOPE) study were enrolled in early pregnancy and pregnancy outcome data collected prospectively. SGA was defined as birthweight <10th customized centile, obesity as BMI ≥30 kg/m(2), central adiposity as waist circumference >102 cm. Logistic regression was used to compare rates of obesity, and central adiposity between men who fathered SGA infants compared with those with non-SGA infants and the final model was adjusted for maternal and paternal confounders. The men who fathered an SGA infant (209 (10.4%)) themselves had lower mean birthweight (3,291 (530) g vs. 3,472 (584) g, P < 0.0001), were more likely to be obese (50 (24.8%) vs. 321 (18.3%), adjusted odds ratio (OR) 1.50, 95% confidence interval 1.05-2.16, adjusted for maternal and paternal factors) and to have central adiposity (52 (25.1%) vs. 341 (19.2%), adjusted OR 1.53, 95% confidence interval 1.06-2.20) compared with men who fathered a non-SGA infant. Elevated paternal blood pressure was not associated with SGA. In conclusion, we report a novel relationship between paternal obesity/central adiposity and birth of an SGA infant, which appears to be independent of maternal factors associated with fetal growth restriction.     

Risk Factors and Adverse Perinatal Outcomes among Term and Preterm Infants Born Small-for-Gestational-Age: Secondary Analyses of the WHO Multi-Country Survey on Maternal and Newborn Health

Background

Small for gestational age (SGA) is not only a major indicator of perinatal mortality and morbidity, but also the morbidity risks in later in life. We aim to estimate the association between the birth of SGA infants and the risk factors and adverse perinatal outcomes among twenty-nine countries in Africa, Latin America, the Middle East and Asia in 359 health facilities in 2010–11.

Methods

We analysed facility-based, cross-sectional data from the WHO Multi-country Survey on Maternal and Newborn Health. We constructed multilevel logistic regression models with random effects for facilities and countries to estimate the risk factors for SGA infants using country-specific birthweight reference standards in preterm and term delivery, and SGA’s association with adverse perinatal outcomes. We compared the risks and adverse perinatal outcomes with appropriate for gestational age (AGA) infants categorized by preterm and term delivery.

Results

A total of 295,829 singleton infants delivered were analysed. The overall prevalence of SGA was highest in Cambodia (18.8%), Nepal (17.9%), the Occupied Palestinian Territory (16.1%), and Japan (16.0%), while the lowest was observed in Afghanistan (4.8%), Uganda (6.6%) and Thailand (9.7%). The risk of preterm SGA infants was significantly higher among nulliparous mothers and mothers with chronic hypertension and preeclampsia/eclampsia (aOR: 2.89; 95% CI: 2.55–3.28) compared with AGA infants. Higher risks of term SGA were observed among sociodemographic factors and women with preeclampsia/eclampsia, anaemia and other medical conditions. Multiparity (> = 3) (AOR: 0.88; 95% CI: 0.83–0.92) was a protective factor for term SGA. The risk of perinatal mortality was significantly higher in preterm SGA deliveries in low to high HDI countries.

Conclusion

Preterm SGA is associated with medical conditions related to preeclampsia, but not with sociodemographic status. Term SGA is associated with sociodemographic status and various medical conditions.     

Aortic Intima-Media Thickness and Aortic Diameter in Small for Gestational Age and Growth Restricted Fetuses

ObjectiveThe objective of this study is to measure aortic intima-media thickness (aIMT) and aortic diameter (AD) in appropriate for gestational age (AGA) fetuses, small for gestational age (SGA) fetuses, and intrauterine growth restricted (IUGR) fetuses.MethodsCase-control study performed between June 2011 and June 2012. Forty-nine AGA fetuses, 40 SGA fetuses, and 35 IUGR fetuses underwent concomitant measurement of aIMT and AD at a mean gestational age of 34.4 weeks.ResultsMedian aIMT was higher in fetuses with IUGR (0.504 mm [95%CI: 0.477-0.530 mm]), than in SGA fetuses (0.466 mm [95% CI: 0.447–0.485 mm]), and AGA fetuses (0.471 mm [95% CI: 0.454-0.488 mm]) (p = 0.023). Mean AD was significantly lower in fetuses with IUGR (4.451 mm [95% CI: 4.258–4.655 mm]), than in AGA fetuses (4.74 mm [95% CI: 4.63-4.843 mm]) (p = 0.028).ConclusionsGrowth restricted fetuses have a thicker aortic wall than AGA and SGA fetuses, which possibly represents preclinical atherosclerosis and a predisposition to later cardiovascular disease.     

Interaction between bedding and sleeping position in the sudden infant death syndrome: a population based case-control study.

OBJECTIVE--To determine the relation between sleeping position and quantity of bedding and the risk of sudden unexpected infant death. DESIGN--A study of all infants dying suddenly and unexpectedly and of two controls matched for age and date with each index case. The parents of control infants were interviewed within 72 hours of the index infant''s death. Information was collected on bedding, sleeping position, heating, and recent signs of illness for index and control infants. SETTING--A defined geographical area comprising most of the county of Avon and part of Somerset. SUBJECTS--72 Infants who had died suddenly and unexpectedly (of whom 67 had died from the sudden infant death syndrome) and 144 control infants. RESULTS--Compared with the control infants the infants who had died from the sudden infant death syndrome were more likely to have been sleeping prone (relative risk 8.8; 95% confidence interval 7.0 to 11.0; p less than 0.001), to have been more heavily wrapped (relative risk 1.14 per tog above 8 tog; 1.03 to 1.28; p less than 0.05), and to have had the heating on all night (relative risk 2.7; 1.4 to 5.2; p less than 0.01). These differences were less pronounced in the younger infants (less than 70 days) than the older ones. The risk of sudden unexpected death among infants older than 70 days, nursed prone, and with clothing and bedding of total thermal resistance greater than 10 tog was increased by factors of 15.1 (2.6 to 89.6) and 25.2 (3.7 to 169.0) respectively compared with the risk in infants of the same age nursed supine or on their side and under less than 6 tog of bedding. CONCLUSIONS--Overheating and the prone position are independently associated with an increased risk of sudden unexpected infant death, particularly in infants aged more than 70 days. Educating parents about appropriate thermal care and sleeping position of infants may help to reduce the incidence of the sudden infant death syndrome.     

nCPAP improves abnormal autonomic function in at-risk-for-SIDS infants with OSA.

We evaluated cardiovascular autonomic control and arousability during sleep in infants with obstructive sleep apnea (OSA) before and after 10 +/- 4 (mean +/- SD) days of treatment with nasal continuous positive airway pressure (nCPAP). Six OSA infants and 12 age-matched control infants were studied with polygraphic sleep studies at the age of 13 +/- 4 wk. During the study, 45 degrees head-up tilt tests were performed in slow-wave and rapid eye movement sleep. Blood pressure (BP) and heart rate (HR) were continuously monitored. All OSA infants had decreased initial BP and HR responses, followed by hypotension in two and hypertension in two. OSA infants displayed higher arousal thresholds in response to the tilt in rapid eye movement sleep (P < 0.005) and higher baseline HR (P < 0.05) than controls. nCPAP treatment normalized BP and HR responses as well as arousal thresholds to tilting and stabilized HR levels. OSA in infants may be linked with cardiovascular autonomic control disturbances and decreased arousability during sleep. These defects are improved by control of OSA with nCPAP.     

Esophageal sensation in premature human neonates: temporal relationships and implications of aerodigestive reflexes and electrocortical arousals

Electrocortical arousal (ECA) as an effect of visceral provocation or of its temporal relationships with aerodigestive reflexes in premature neonates is not known. We tested the hypothesis that esophageal provocation results in both esophageal reflex responses and ECAs during sleep and that ECAs are dependent on the frequency characteristics of esophageal neuromotor responses. We defined the spatiotemporal relationship of ECAs in relation to 1) spontaneous pharyngoesophageal swallow sequences and gastroesophageal reflux (GER) events and 2) sensory-motor characteristics of esophageal reflexes. Sixteen healthy premature neonates born at 27.9 ± 3.4 wk were tested at 36.8 ± 1.9 wk postmenstrual age. Ninety-five midesophageal and 31 sham stimuli were given in sleep during concurrent manometry and videopolysomnography. With stimulus onset as reference point, we scored the response latency, frequency occurrence and duration of arousals, peristaltic reflex, and upper esophageal sphincter contractile reflex (UESCR). Changes in polysomnography-respiratory patterns and esophageal sensory-motor parameters were scored by blinded observers. Significantly (for each characteristic listed, P < 0.05), swallow sequences were associated with arousals and sleep state changes, and arousals were associated with incomplete peristalsis, response delays to lower esophageal sphincter relaxation, and prolonged esophageal clearance. GER events (73.5%) provoked arousals, and arousals were associated with response delays to peristaltic reflexes or clearance, sleep state modification, and prolonged respiratory arousal. Midesophageal stimuli (54%) provoked arousals and were associated with increased frequency, prolonged latency, prolonged response duration of peristaltic reflexes and UESCR, and increased frequency of sleep state changes and respiratory arousals. In human neonates, ECAs are provoked upon esophageal stimulation; the sensory-motor characteristics of esophageal reflexes are distinct when accompanied by arousals. Aerodigestive homeostasis is defended by multiple tiers of aerodigestive safety mechanisms, and when esophageal reflexes are delayed, cortical hypervigilance (ECAs) occurs.     

Baroreflex control of muscle sympathetic nerve activity after 120 days of 6 degrees head-down bed rest

To examine how long-lasting microgravity simulated by 6 degrees head-down bed rest (HDBR) induces changes in the baroreflex control of muscle sympathetic nerve activity (MSNA) at rest and changes in responses of MSNA to orthostasis, six healthy male volunteers (range 26-42 yr) participated in Valsalva maneuver and head-up tilt (HUT) tests before and after 120 days of HDBR. MSNA was measured directly using a microneurographic technique. After long-term HDBR, resting supine MSNA and heart rate were augmented. The baroreflex slopes for MSNA during Valsalva maneuver (in supine position) and during 60 degrees HUT test, determined by least-squares linear regression analysis, were significantly steeper after than before HDBR, whereas the baroreflex slopes for R-R interval were significantly flatter after HDBR. The increase in MSNA from supine to 60 degrees HUT was not different between before and after HDBR, but mean blood pressure decreased in 60 degrees HUT after HDBR. In conclusion, the baroreflex control of MSNA was augmented, whereas the same reflex control of R-R interval was attenuated after 120 days of HDBR.     

Cardiovascular effects of partial sleep deprivation in healthy volunteers

Sleep deprivation is common in Western societies and is associated with increased cardiovascular morbidity and mortality in epidemiological studies. However, the effects of partial sleep deprivation on the cardiovascular system are poorly understood. In the present study, we evaluated 13 healthy male volunteers (age: 31 ± 2 yr) monitoring sleep diary and wrist actigraphy during their daily routine for 12 nights. The subjects were randomized and crossover to 5 nights of control sleep (>7 h) or 5 nights of partial sleep deprivation (<5 h), interposed by 2 nights of unrestricted sleep. At the end of control and partial sleep deprivation periods, heart rate variability (HRV), blood pressure variability (BPV), serum norepinephrine, and venous endothelial function (dorsal hand vein technique) were measured at rest in a supine position. The subjects slept 8.0 ± 0.5 and 4.5 ± 0.3 h during control and partial sleep deprivation periods, respectively (P < 0.01). Compared with control, sleep deprivation caused significant increase in sympathetic activity as evidenced by increase in percent low-frequency (50 ± 15 vs. 59 ± 8) and a decrease in percent high-frequency (50 ± 10 vs. 41 ± 8) components of HRV, increase in low-frequency band of BPV, and increase in serum norepinephrine (119 ± 46 vs. 162 ± 58 ng/ml), as well as a reduction in maximum endothelial dependent venodilatation (100 ± 22 vs. 41 ± 20%; P < 0.05 for all comparisons). In conclusion, 5 nights of partial sleep deprivation is sufficient to cause significant increase in sympathetic activity and venous endothelial dysfunction. These results may help to explain the association between short sleep and increased cardiovascular risk in epidemiological studies.     

Effect of maternal age and growth on placental nutrient transport: potential mechanisms for teenagers' predisposition to small-for-gestational-age birth?

Teenagers have an increased risk of delivering small-for-gestational-age (SGA) infants. Young maternal age and continued skeletal growth have been implicated as causal factors. In growing adolescent sheep, impaired placental development and nutrient transfer cause reduced birth weight. In human pregnancies, SGA is associated with reduced placental amino acid transport. Maternal growth has no effect on placental morphology or cell turnover, but growing teenagers have higher birth weight:placental weight ratios than nongrowing teenagers. We hypothesized that placental nutrient transporter activity would be affected by maternal age and/or growth status. Placentas from teenagers and adults were collected. Teenagers were defined as growing or nongrowing based on knee height measurements. System A amino acid transporter activity was quantified as sodium-dependent uptake of [(14)C]methylaminoisobutyric acid into placental fragments. Teenagers had lower placental system A activity than adults (P < 0.05). In adults, placental system A activity was lower in SGA infants than appropriate-for-gestational-age (AGA) infants (P < 0.05). In teenagers, AGA and SGA infants had lower placental system A activity than AGA infants born to adults (P < 0.05). Placental system A activity was higher in growing teenagers than in nongrowing teenagers (P < 0.001). Placental mRNA expression of system A transporter isoforms SLC38A1 and -2 was lower in teenagers than in adults (P < 0.05) but did not differ between growing and nongrowing teenagers. There was no difference in transporter protein expression/localization between cohorts. Teenagers have inherently reduced placental transport, which may underlie their susceptibility to delivering SGA infants. Growing teenagers appear to overcome this susceptibility by stimulating the activity, but not expression, of system A transporters.     

Sleeping position in infants over 6 months of age: implications for theories of sudden infant death syndrome

The aim of this study was to determine the prevalence of prone and supine sleeping in infants aged 0-12 months and relate this to changes in the number of cases of sudden infant death syndrome (SIDS) since 1985. Seventy-two babies, 38 male and 34 female, were followed for the first 18 months of life with regular home visits and sleeping position was recorded. In addition, data on the number of cases of SIDS in England and Wales between 1985 and 1995 were analysed. All babies slept supine for the first 5 months of life, but once they could turn over in their cots (mean age 7.34 months, range 5-11 months) the majority slept prone. By 11 months of age, 53 regularly slept prone (73%), 95% CI +/- 19.8%), while 11 slept supine, three adopted the side position and five varied from night to night. The number of cases of SIDS in infants aged 7-11 months has fallen significantly (P<0.0001) in a period in which the prevalence of prone sleeping, in that age group, has not changed. The most plausible explanation for this paradoxical result is that supine sleeping in the first 5 months of life reduces the absolute risk of SIDS in the second 6 months of life even though most babies are then sleeping prone. It is suggested that reduced exposure to nasopharyngeal bacterial superantigens in babies sleeping prone might explain this effect.     

Postural baroreflex stimuli may affect EEG arousal and sleep in humans

Past research has shown that baroreceptor stimulation can induce sleep. The present study investigated whether the upright posture inhibits sleep by reducing baroreceptor firing. Twenty-eight men were each exposed to four conditions on separate days: 40 degrees head-up tilt with (TP) and without (TN) 45 mmHg positive pressure on the legs and the supine position with (SP) and without (SN) leg pressure. Heart rate and blood pressure changes indicated that baroreceptor firing was strongly reduced by TN and only mildly reduced by TP in 24 subjects. Baroreceptor effects of SP were unclear. SN and SP did not differ significantly in their effects on electroencephalogram (EEG) sleep. Among subjects who showed a normal baroreflex response to tilt, both TN and TP inhibited sleep, but TN caused a persistent elevation of EEG beta activity that did not occur in TP plus a greater delay in sleep onset. TN had no such arousing effects in four subjects who showed little or no baroreflex response to tilt. These results are consistent with the hypothesis that the fall in baroreceptor firing produced by the upright posture contributes to EEG arousal.     

Characteristics of the infant arousal response

Arousal is considered to be an importantresponse to a life-threatening stimulus. Recently, it has been shownthat the infant arousal response to an elevated inspiredCO₂ level occurs as a sequence ofevents involving presumptive brain stem responses before awakening (A. Lijowska, N. Reed, B. Chiodini, and B. T. Thach. Am.J. Respir. Crit. Care Med. 151: A151, 1995; A. S. Lijowska, N. W. Reed, B. A. Mertins Chiodini, and B. T. Thach.J. Appl. Physiol. 83: 219-228,1997). We wanted to further evaluate the relationship ofsubcortical reflexes to cortical arousal in infants. We used anonrespiratory (tactile) stimulus to elicit arousal in infants duringnon-rapid-eye-movement (NREM) and rapid-eye-movement (REM) sleep. Wefound that a tactile stimulus elicited an arousal sequence thatcommenced with a spinal withdrawal reflex, was followed by brain stemresponses (respiratory and startle responses), and ended in a corticalarousal. The entire pathway or part of it in the order of spinal tocortical responses could be elicited. REM and NREMresponses were similar except for significant differences in thelatencies of spinal and subcortical reflexes. These observations suggest that the infant arousal response to a tactile stimulus involvesa progression of central nervous system activation from the spinal tocortical levels. The different components of the arousal pathway may beimportant for an infant to respond appropriately to stimuli duringsleep without necessarily disturbing sleep.

     

Selenium status, birth weight,

Selenium (Se) is an essential nutritional element for humans. A low Se status has been documented in formula-fed small-for-gestational age (SGA) newborns in the first month of life. The aim of the study was to compare the nutritional selenium status in adequate-for-gestational age (AGA) and in SGA newborns in the first month of life in relation to feeding type. Se status was assessed by plasma and erythrocyte concentrations, determined by pulsed Zeeman effect-atomic absorption spectrophotometry. We studied 210 newborns divided in groups according to birth weight (129 AGA, 81 SGA ) and feeding type (breast milk, formula, mixed) in wk 1-4 of postnatal life. Erythrocyte Se levels are affected neither by feeding type nor by birth weight. Se plasmatic concentrations were lower in SGA than in AGA newborns. Significant differences in mean plasma concentrations were found between formula-fed and breast-fed (p=0.013) and between formula-fed and mixed-fed (p=0.006) SGA newborns. The difference was not significant in AGA neonates. Breast-fed SGA newborns consistently showed higher plasma Se concentrations than formula-fed newborns. Unless supplemented from birth, Se intake will be inadequate in bottle-fed SGA infants.