Final Weeks Of Gestation Research Articles

Transcriptomic Signatures of the Foetal Liver and Late Prenatal Development in Vitrified Rabbit Embryos.

Assisted reproduction technologies (ARTs) are generally considered safe; however, emerging evidence highlights the need to evaluate potential risks in adulthood to improve safety further. ART procedures like rederivation of embryos by vitrification differ from natural conditions, causing significant disparities between in vitro and in vivo embryos, affecting foetal physiology and postnatal life. This study aims to investigate whether hepatic transcriptome and metabolome changes observed postnatally are already present in foetal livers at the end of gestation. This study compared fresh and vitrified rabbit embryos, finding differences between foetuses obtained by the transfer of fresh and vitrified embryos at 24 days of gestation. Rederived embryos had reduced foetal and liver weights and crown-rump length. However, the offspring of vitrified embryos tended to be born with higher weight, showing compensatory growth in the final week of gestation (59.2 vs. 49.8 g). RNA-Seq analysis revealed 43 differentially expressed genes (DEGs) in the foetal liver of vitrified embryos compared to the fresh group. Notably, downregulated genes included BRAT1, CYP4A7, CYP2B4, RPL23, RPL22L1, PPILAL1, A1BG, IFGGC1, LRRC57, DIPP2, UGT2B14, IRGM1, NUTF2, MPST, and PPP1R1B, while upregulated genes included ACOT8, ERICH3, UBXN2A, METTL9, ALDH3A2, DERPC-like, NR5A2-like, AP-1, COG8, INHBE, and PLA2G4C. Overall, a functional annotation of these DEGs indicated an involvement in lipid metabolism and the stress and inflammatory process or immune response. Thus, our results suggest that vitrification and embryo transfer manipulation induce an adaptive response that can be observed in the liver during the last week of gestation.

Lacticaseibacillus rhamnosus Probio-M9 may be vertically transmitted from mother to infant during lactation based on faeces metagenomics

Probiotics exert beneficial effects on the host. This study aimed to investigate whether maternally ingested Lacticaseibacillus rhamnosus Probio-M9 during pregnancy could access and colonize the infant gut. This study recruited one pregnant woman, who ingested Probio-M9 daily from 35 weeks of gestation to delivery. Feces of the mother-infant pair were regularly collected from one month before delivery to 6 months of infant’s age for metagenomic sequencing. Probio-M9 genomes were mappable to all infant fecal samples, suggesting the ingested probiotics could be vertically transmitted from mother to infant. Infant- or mother-specific differential metabolic pathways were found between the maternal and infant’s gut microbiome, implicating apparent differences in the intestinal metagenomic potential/function between the mother and the infant. In conclusion, maternal ingestion of Probio-M9 during the final weeks of gestation could deliver to the infant gut. The findings provided novel insights into shaping infant’s gut microbiota.

Hormonal and immunological responses of Holstein dairy cows from late lactation to the dry period and from the dry period to early lactation

Parturition and dry-off are challenging events for dairy cows partially due to changes in endocrine responses. The aim of this experiment was to evaluate blood concentrations of cortisol and prolactin and their effects on proliferation of peripheral blood mononuclear cells (PBMC) with or without stimulation by common immune cell mitogens (lipopolysaccharide [LPS], and concanavalin A [ConA]) of multiparous dairy cows from late lactation to the dry period and from the dry period to early lactation. Two groups of cows were enrolled: cows from late lactation to the dry period enrolled at 8 d before dry-off (LTD, n = 6, days in milk at dry-off = 332 ± 41 d) and cows from the dry period to early lactation enrolled at 7 d before expected calving date (DTL, n = 7). Blood was collected on d -8, 3, 7, and 15 relatives to dry-off for LTD cows, and on d -7, 3, 7, and 21 relatives to calving for DTL cows to analyze circulating stress hormones and to isolate PBMC. The PBMC were stimulated in vitro with prolactin (PRL), hydrocortisone (HDC), LPS, ConA, PRL + LPS, PRL + ConA, HDC+LPS, and HDC + ConA to assess proliferative responses. Plasma cortisol and PRL concentrations of LTD and DTL cows were not affected by time. Regardless of time, addition of HDC reduced PBMC proliferation stimulated by LPS, but PRL had no effect. No time effect was observed for proliferation of PBMC collected from LTD cows, but PBMC collected at 21 d after calving had higher proliferative responses to LPS and ConA than those from late dry period or early lactation. In conclusion, results from this experiment confirmed the lower PBMC proliferation during the transition period from the final week of gestation to early lactation and suggested that cows transitioning from late lactation to dry period maintained unchanged cell-mediated immune function.

Programming effects of late gestation heat stress in dairy cattle.

The final weeks of gestation represent a critical period for dairy cows that can determine the success of the subsequent lactation. Many physiological changes take place and additional exogenous stressors can alter the success of the transition into lactation. Moreover, this phase is pivotal for the final stage of intrauterine development of the fetus, which can have negative long-lasting postnatal effects. Heat stress is widely recognised as a threat to dairy cattle welfare, health, and productivity. Specifically, late gestation heat stress impairs the dam's productivity by undermining mammary gland remodelling during the dry period and altering metabolic and immune responses in early lactation. Heat stress also affects placental development and function, with relevant consequences on fetal development and programming. In utero heat stressed newborns have reduced birth weight, growth, and compromised passive immune transfer. Moreover, the liver and mammary DNA of in utero heat stressed calves show a clear divergence in the pattern of methylation relative to that of in utero cooled calves. These alterations in gene regulation might result in depressed immune function, as well as altered thermoregulation, hepatic metabolism, and mammary development jeopardising their survival in the herd and productivity. Furthermore, late gestation heat stress appears to exert multigenerational effects, influencing milk yield and survival up to the third generation.

The effect of prenatal temperature and PM2.5 exposure on birthweight: weekly windows of exposure throughout the pregnancy

BACKGROUND AND AIM: Birthweight is a strong predictor of normal growth, healthy development, and survival. Several studies have found associations between temperature, fine particulate matter (PM2.5), and birth weight. However, the relevant timing of exposures varies between studies and is yet unclear. Therefore, we assessed the difference in term birthweight (TBW) associated with weekly exposure to temperature and PM2.5 throughout 37 weeks of gestation. METHODS: We included all singleton live term births in Massachusetts, U.S between 2004 and 2015 (n=712,438). Weekly PM2.5 and temperature predictions were estimated on a 1 km grid from satellite-based models. We utilized a distributed lag nonlinear model (DLNM) to estimate the difference in TBW associated with weekly exposures to PM2.5 and temperature simultaneously from the last menstrual period to 37 weeks of gestation. RESULTS:We found a nonlinear association with temperature exposure. We observed positive differences in TBW associated with rises of colder temperatures (2.6g increase, 95% CI 0.1g; 5.1g, for one ºC increase from -4 ºC) and negative difference in TBW associated with rises of warmer temperatures (7.9g decrease, 95% CI -11.2g; -4.6g, for one ºC increase from 23 ºC). Temperature effects were larger in the first and final weeks of gestation. We observed a negative difference in TBW associated with PM2.5 exposure. Overall, one µg/m3 increase in prenatal exposure was associated with 3.9g lower TBW (95% CI -5.0g; -2.9g). PM2.5 effects were larger in the final weeks of gestation. CONCLUSIONS:We found heat and PM2.5 exposure to be related to lower TBW. Our findings suggest that women are more susceptible to both exposures towards the end of pregnancy. Susceptibility to heat was higher in the initial weeks of pregnancy as well. These critical windows of susceptibility can be communicated to pregnant women during routine prenatal visits to increase awareness and target interventions to reduce exposures. KEYWORDS: birthweight, temperature, air pollution, birth outcomes

The effect of prenatal temperature and PM2.5 exposure on birthweight: Weekly windows of exposure throughout the pregnancy

BackgroundBirthweight is a strong predictor of normal growth, healthy development, and survival. Several studies have found associations between temperature, fine particulate matter (PM2.5), and birth weight. However, the relevant timing of exposures varies between studies and is yet unclear. Therefore, we assessed the difference in term birthweight (TBW) associated with weekly exposure to temperature and PM2.5 throughout 37 weeks of gestation. MethodsWe included all singleton live term births in Massachusetts, U.S between 2004 and 2015 (n = 712,438). Weekly PM2.5 and temperature predictions were estimated on a 1 km grid from satellite-based models. We utilized a distributed lag nonlinear model (DLNM) to estimate the difference in TBW associated with weekly exposures from the last menstrual period to 37 weeks of gestation. ResultsWe found a nonlinear association with prenatal temperature exposure. Larger effects were observed in warmer temperatures, where higher temperatures were negatively associated with TBW. Temperature effects were larger in the first and final weeks of gestation. We observed a negative difference in TBW associated with PM2.5 exposure. Overall, a 1 µg/m3 increase in prenatal exposure was associated with 3.9 g lower TBW (95% CI −5.0 g; −2.9 g). PM2.5 effects were larger in the final weeks of gestation. ConclusionWe found heat and PM2.5 exposure to be related to lower TBW. Our findings suggest that women are more susceptible to both exposures towards the end of pregnancy. Susceptibility to heat was higher in the initial weeks of pregnancy as well. These critical windows of susceptibility can be communicated to pregnant women during routine prenatal visits to increase awareness and target interventions to reduce exposures.

Progestogen metabolites for use in pregnancy monitoring of 13-lined ground squirrels (Ictidomys tridecemlineatus).

This research was conducted to discover whether pregnancy prediction is possible in female 13-lined ground squirrels (TLGS; a small hibernating ground squirrel named for their number of stripes). Pregnancy status in this species, we postulated, could be anticipated by generating profiles for individuals via a non-invasive technique known as fecal endocrine hormone profiling. Fecal samples were collected from 13 females thrice weekly for 4 weeks post-hibernation in the breeding season of 2016. Fecal samples were then processed and run through an assay known as an ELISA giving concentrations of hormone metabolites excreted through feces. We then set these samples against time points to develop a profile for each female. We have ascertained that elevated progesterone (potential pregnancy) can be detected by a commercially available assay kit. Understanding hormone patterns in animals gives researchers a better idea of best husbandry practices, including breeding in managed care.

Gestational Age and the Cord Blood Lipidomic Profile in Late Preterm and Term Infants

Background: Lipid metabolism is vital to fetal development and cardiometabolic health and the final weeks of gestation are known to be a time of intense metabolic activity. New techniques such as lipidomics allow investigation of a complex lipidomic profile in infants. Objectives: This research aimed to (1) describe variations in lipidomic profile in late preterm and term infants and (2) compare variations to an adult lipidomic profile with known clinical implications. Methods: The Barwon Infant Study (n = 1,074) is a population-derived pre-birth cohort study. The lipidomic profile of cord blood was measured by liquid chromatography-mass spectrometry in 225 participants and the association between gestational age and lipidomic profile was investigated using multiple linear regression adjusting for birth weight, exposure to labour, and infant sex. Patterns of association with gestational age across the lipidomic profile were compared with associations between body mass index (BMI) and lipidomic profile observed among adults in the San Antonia Family Heart Study (n = 994). Results: Gestational age was independently associated with the abundances of 39% of lipid species. Variations in the lipidomic profile with increasing gestational age were comparable to some variations observed in association with increasing BMI among adults. Conclusion: There is a strong relationship between gestational age and the cord blood lipid profile at birth, providing further evidence for the importance of metabolic changes of late gestation. A number of the variations in the lipid profile with increasing gestational age are analogous to differences observed in the adult lipid profile with an increasing BMI.

Longitudinal profiles of relaxin and progestagens during pregnancy, pregnancy loss and false pregnancy in the killer whale (Orcinus orca)

The circulating pattern of immunoreactive relaxin and progestagens based on monthly and gestational stage (early, mid, late) profiles were determined during pregnancies that resulted in live calves (LIVE, n = 30), stillbirths (STILLB, n = 3), abortions (ABORT, n = 5) and presumptive false pregnancies (FALSE, n = 8), and during the follicular (n = 34) and luteal phase (n = 58). Monthly LIVE relaxin concentrations steadily increased during gestation, but values did not significantly exceed those of the luteal phase until 9 months prior to parturition, peaking during the final month at 2356 ng/ml. Relaxin surged (P < 0.05) during the final week of gestation (36,397 ng/ml), undergoing a 3 and 9-fold increase compared with concentrations in the preceding two weeks, respectively. Monthly relaxin production did not differ among each reproductive state with the exception of months-13–16 where concentrations were higher (P < 0.001) for STILLB than LIVE. Relaxin concentration was reduced (P < 0.0001) by 849% in placental versus maternal serum collected within 1 day of labor. Mid- and late-pregnancy progestagen concentrations were lower for FALSE (P < 0.001) compared with STILLB and LIVE. Late pregnancy progestagen concentrations were reduced for FALSE (P < 0.05) and ABORT (P < 0.02) compared with LIVE and STILLB. Monthly progestagen production in ABORT tended to be lower than LIVE across a range of gestational months (Months 2, 7, 8, 11) but this difference only became significant during months 14 and 15. Results indicate that relaxin is primarily produced by the CL during pregnancy, and that concentrations could not be used to differentiate from non-pregnant females until the final 6 months of gestation. In addition, as would be expected from a primarily CL product, relaxin cannot be used to detect abnormal pregnancies. Conversely, progestagens, which are produced by both the placenta and CL can be used to differentiate FALSE from normal pregnancy and may be useful indicators of fetal health in the killer whale.

Effects of sleep restriction during pregnancy on the mother and fetuses in rats

The present study aimed to analyze the effects of sleep restriction (SR) during pregnancy in rats. The following three groups were studied: home cage (HC pregnant females remained in their home cage), Sham (females were placed in tanks similar to the SR group but with sawdust) and SR (females were submitted to the multiple platform method for 20h per day from gestational days (GD) 14 to 20). Plasma corticosterone after 6days of SR was not different among the groups. However, the relative adrenal weight was higher in the SR group compared with the HC group, which suggests possible stress impact. SR during pregnancy reduces the body weight of the female but no changes in liver glycogen, cholesterol and triglycerides, and muscle glycogen were detected. On GD 20, the fetuses of the females submitted to SR exhibited increased brain derived neurotrophic factor (BDNF) in the hippocampus, which indicates that sleep restriction of mothers during the final week of gestation may affect neuronal growth factors in a fetal brain structure, in which active neurogenesis occurs during the deprivation period. However, no changes in the total reactive oxygen species (ROS) in the cortex, hippocampus, or cerebellum of the fetuses were detected. SR females showed no major change in the maternal behavior, and the pups' preference for the mother's odor on postpartum day (PPD) 7 was not altered. On GD 20, the SR females exhibited increased plasma prolactin (PRL) and oxytocin (OT) compared with the HC and Sham groups. The negative outcomes of sleep restriction during delivery could be related, in part, to this hormonal imbalance. Sleep restriction during pregnancy induces different changes compared with the changes described in males and affects both the mother and offspring.

Normal Doppler Reference Values of the Pericallosal Artery.

To provide the normal reference values of the Doppler flow of the pericallosal artery in relation to gestational age from 18 to 41 weeks of gestation. The pericallosal artery (PCA) was studied in 466 normal pregnancies. The pulsed Doppler evaluation of the pericallosal artery was done in A3 and A4 segments, and records from PI, RI and Vmax were studied. The resistance index of the pericallosal artery in A3/A4 segments exhibits a plateau from 18 to 31 weeks of gestation. After 31 weeks, a marked decrease becomes apparent. The pulsatility index of the pericallosal artery in A3/A4 segments shows a plateau until 36 weeks of gestation. During the final weeks of gestation, there is a decrease in the pulsatility index. Vmax exhibits a plateau for the maximal flow velocity in A3/A4 segments of the pericallosal artery from 18 to 28 weeks of gestation. After 28 weeks of gestation, there is a slight increase in Vmax. Normal reference values of the pericallosal artery might have an impact on clinical judgment during adaptive hemodynamic changes and regarding the progression of the fetal deterioration occurring in the presence of fetal hypoxia.

Diffusion tensor imaging for understanding brain development in early life.

The human brain rapidly develops during the final weeks of gestation and in the first two years following birth. Diffusion tensor imaging (DTI) is a unique in vivo imaging technique that allows three-dimensional visualization of the white matter anatomy in the brain. It has been considered to be a valuable tool for studying brain development in early life. In this review, we first introduce the DTI technique. We then review DTI findings on white matter development at the fetal stage and in infancy as well as DTI applications for understanding neurocognitive development and brain abnormalities in preterm infants. Finally, we discuss limitations of DTI and potential valuable imaging techniques for studying white matter myelination.

Influence of Panax ginseng on the offspring of adult rats exposed to prenatal stress.

The exposure of pregnant females to stress during a critical period of fetal brain development is an environmental risk factor for the development of schizophrenia in adult offspring. Schizophrenia is a group of common mental disorders of unclear origin, affecting approximately 1% of the global population, showing a generally young age at onset. In the present study, a repeated variable stress paradigm was applied to pregnant rats during the final week of gestation. The effects of an extract of Panax ginseng C.A. Meyer (PG) on rats exposed to prenatal stress (PNS) were investigated in terms of behavioral activity and protein expression analyses. In the behavioral tests, grooming behavior in a social interaction test, line-crossing behavior in an open-field test and swimming activity in a forced-swim test were decreased in the rats exposed to PNS compared with the non-stressed offspring; the changes in behavioral activity were reversed upon oral treatment with PG (300 mg/kg). Subsequently, western blot analysis and immunohistochemical analyses of the prefrontal cortex and hippocampus revealed that the downregulation of several neurodevelopmental genes which occurred following exposure to PNS was reversed upon treatment with PG. The current findings demonstrate that the downregulation of several genes following exposure to PNS may affect subsequent behavioral changes, and that these phenomena are reversed following treatment with PG during pregnancy. Our results suggest that oral treatment with PG reduces the incidence of psychiatric disorders, such as schizophrenia.

Abstracts of 53rd Symposium of the Society for the Study of Human Biology celebrating the Human Biology of Jim Tanner held at Corpus Christi College, Cambridge, 13–15 December 2011

PROFFERED PAPERSGrowth cessation is not the necessary norm during the final weeks of gestationAmanda Mummert1, Michelle Lampl1 & Philippe Jeanty21Department of Anthropology, Emory University, Atlanta, GA, USA2Women's Ultrasound, Nashville, TN, USABackground: The cessation of growth in late gestation is considered to be a universal consequence of maternal constraint, limited by non-genetic and non-pathological influences that impact the flow of nutrients from mother and placenta to fetus.Aim: To investigate fetal growth patterns during late gestation with serial Toshiba SAL 10A ultrasound.Subjects and methods: Ultrasound assessments of the head, limb and abdomen were made weekly on 46 fetuses from clinically uncomplicated pregnancies among middle class women from Belgium. Repeated measures regression investigated growth patterns; maternal and paternal height and weight were covariates.Results: Positive slopes for each variable were found with gestational age from 33 weeks. Maternal height had no significant effect on any parameter; maternal weight and BMI had positive effects on head and limb, and together with paternal height, positively predicted abdominal diameter. We find that, contrary to notions of growth restriction during the final weeks of gestation, growth of body parameters continues from 33 gestational weeks.Conclusion: These findings suggest that the idea of maternal constraint be revisited in light of evidence that the normal fetus does not experience growth cessation during the final weeks of gestation.

The effect of dietary selenium intake on numbers of T and B cells in C57BL/6 mice with chronic inflammation

Selenium (Se) as a nutrient has many beneficial functions related to its nutritional, biochemical and molecular properties. Se is important for adequate immune response. In this study dams were fed a Torula yeast Se depletion diet for the final week of gestation and through lactation. At 23 days, 47 pups were weaned to the depletion diet or to diets with 0.2, 2 or 4 mg/kg diet Se added as sodium selenate for 14 weeks. Four weeks before necropsy lipopolysaccharide (LPS) time‐release pellets (0 or 0.1μg/g body weight/d) pellets were implanted subcutaneously. At necropsy the bone marrow from femur was flushed with saline, labeled with fluorochrome conjugated primary antibodies (CD3, B220, and CD4) and analyzed by flow cytometry (FACS). LPS stimulation versus placebo increased numbers of T helper cells (1.7×106 vs 0.93×106), T cells (0.57×106 vs 0.31×106) and B cells (3.3×106 vs 2.5×106). In addition CD3+ cell numbers were greater with increasing Se intake (p&lt;0.03). Although the immune system is dependent upon production of oxidative molecules as a protection against microbial pathogens, benefits of Se also include protection from excessive damage by oxidative radicals. Further understanding of the mechanisms by which dietary Se affects these immune cell populations will contribute to knowledge of using Se supplementation to affect T cell mediated immune response. (Supported by Oklahoma Center for Advancement of Science &amp; Technology)

Head-turning asymmetries during kissing and their association with lateral preference

A head-turning bias to the right side is one of the earliest functional asymmetries in human development and is already present during the final weeks of gestation. To test whether head-turning preference is related to other lateral preferences in adults, kissing behaviour of participants towards a symmetrical doll was observed to assess their spontaneous head-turning preference. Additionally, participants’ individual handedness, footedness, and eye preference were determined using questionnaires. A significant difference in handedness and footedness, but not eye preference, was found between left- and right-kissers, with right-kissers showing a stronger right-sided bias than left-kissers. These results support the assumption that the head-turning bias in humans may be able to induce or enhance other asymmetries of perception and action.

Environmental prenatal stress alters sexual dimorphism of maternal behavior in rats

The prenatal external environment can affect fetuses, altering the maternal behavior that they express when mature. In the present study, environmental prenatal stress (EPS) was applied to pregnant rats in their final week of gestation, and when their female offspring reached maturity, the long latency effect of the stress on those offspring was ascertained on their induced maternal behavior (MB), accessory olfactory bulb (AOB) morphology and plasma levels of ACTH and corticosterone (Cpd B). EPS reduced: the percentage of these virgins that showed induced MB, their retrieval of foster pups, the time spent crouching, and the quality of nest building; it also increased the incidence of their cannibalism of foster pups. The EPS-treated females presented a male-like pattern of induced MB. They showed increased plasma levels of ACTH and Cpd B and increased numbers of mitral cells in the AOB. These findings provide evidence that stress applied to the pregnant rat produces long-lasting behavioral, neuroanatomical and hormonal alterations in the female offspring that can be observed when they reach maturity.

Comparative analysis of extra-ventricular mitoses at early stages of cortical development in rat and human

Embryonic germinal zones of the dorsal and ventral telencephalon generate cortical neurons during the final week of gestation in rodent and during several months in human. Whereas the vast majority of cortical interneurons originate from the ventral telencephalon, excitatory neurons are locally generated within the germinal zone of the dorsal telencephalon, the future cerebral cortex, itself. However, a number of studies have described proliferating cells external to the ventricular and subventricular germinal zones in the developing dorsal telencephalon. In this study, we performed a comprehensive cell density analysis of such 'extra-ventricular proliferating cells' (EVPCs) during corticogenesis in rat and human using a mitotic marker anti-phospho-histone H3. Subsequently, we performed double-labelling studies with other mitotic and cell type specific markers to undertake phenotypic characterisation of EVPCs. Our findings show: (1) the densities of extra-ventricular H3-positive (H3+) cells were surprisingly similar in preplate stage rat and human; (2) extra-ventricular proliferation continues during mid-and late corticogenesis in rat and in early fetal human cortex; and (3) extra-ventricular cells appear to be mitotic precursors as they are not immunoreactive for a panel of early post-mitotic and cell type-specific markers, although (4) a subset of EVPCs are proliferating microglia. These data suggest that some aspects of early corticogenesis are conserved between rodent and human despite marked differences in the duration of neurogenesis and the anatomical organisation of the developing cerebral cortex.

Characteristics of Heart Period Variability in Intubated Very Low Birth Weight Infants with Respiratory Disease

Background: Heart period variability provides a measure of balance between the sympathetic nervous system (SNS) and parasympathetic nervous system (PNS). Since the PNS develops during the final weeks of gestation, premature infants have an overriding SNS. Spectral power analysis of heart period variability reveals two main frequency regions, the low frequency region (LF) representing primarily SNS activity and the high frequency region (HF) representing PNS activity. Objectives: To identify the characteristics of heart period power in the LF and HF regions in very low birth weight (VLBW) infants in the neonatal intensive care unit across gestational age groups and between sleep and awake states. Methods: Data were collected from 16 intubated and mechanically ventilated VLBW infants with respiratory disease. Using spectral analysis techniques, heart period power in the two main frequency regions was extracted. Results: HF power did not improve with gestational age as expected. LF power did increase with age, albeit nonsignificantly. LF and HF power were not significantly different between awake and sleep states. Conclusions: The results of this preliminary study suggest that PNS tone does not improve with gestational age in VLBW infants with respiratory disease. The intensive care environment may stimulate a sympathetic response in these infants and disrupt normal PNS development.

Adult hemoglobin levels at birth and risk of sudden infant death syndrome.

During the final weeks of gestation, infants normally begin a transition from the production of fetal to adult hemoglobin. Delayed or faulty transition to the production of adult hemoglobin might play a role in the etiology of sudden infant death syndrome (SIDS). To examine the association between adult hemoglobin levels measured at birth and the subsequent risk of SIDS. Cohort study of all infants born in California between March 1, 1990, and December 31, 1997, who were enrolled in the state's Newborn Screening Program and followed up during the first year of life to identify deaths attributed to SIDS. Population-based sample of 3.2 million infants. Risk of death attributed to SIDS. The study included 2425 infants whose deaths were attributed to SIDS. There was an inverse relationship between adult hemoglobin level, expressed as a percentage of total hemoglobin, and the subsequent incidence of SIDS. After adjustment for infant sex, race/ethnicity, length of gestation, maternal age, maternal education, maternal smoking, intrauterine growth restriction, and preeclampsia/eclampsia, the relative risks of SIDS for infants in the lower 4 quintiles of adult hemoglobin level were, in descending order, 1.12 (95% confidence interval [CI], 0.96-1.32), 1.38 (95% CI, 1.19-1.59), 1.55 (95% CI, 1.34-1.80), and 2.15 (95% CI, 1.87-2.47) compared with infants in the highest quintile. These findings suggest that infants with low levels of adult hemoglobin in the first hours after birth are at elevated risk of SIDS. Delayed maturation in production of adult hemoglobin may play a role in the etiology of some SIDS cases.