Maternal hyperthermia as a possible cause of anencephaly

Nanomedicines for Improved Management of Ectopic Pregnancy: A Narrative Review

Ectopic pregnancy (EP) - the implantation of an embryo outside of the endometrial cavity, often in the fallopian tube - is a significant contributor to maternal morbidity and leading cause of maternal death due to hemorrhage in first trimester. Current diagnostic modalities including human chorionic gonadotropin (hCG) quantification and ultrasonography are effective, but may still misdiagnose EP at initial examination in many cases. Depending on the patient's hemodynamic stability and gestational duration of the pregnancy, as assessed by history, hCG measurement and ultrasonography, management strategies may include expectant management, chemotherapeutic treatment using methotrexate (MTX), or surgical intervention. While these strategies are largely successful, expectant management may result in tubal rupture if the pregnancy does not resolve spontaneously; MTX administration is not always successful and may induce significant side effects; and surgical intervention may result in loss of the already-damaged fallopian tube, further hampering the patient's subsequent attempts to conceive. Nanomaterial-based technologies offer the potential to enhance delivery of diagnostic imaging contrast and therapeutic agents to more effectively and safely manage EP. The purpose of this narrative review is to summarize the current state of nanomedicine technology dedicated to its potential to improve both the diagnosis and treatment of EP.

Review of Evidence for Environmental Causes of Uveal Coloboma

Uveal coloboma is a condition defined by missing ocular tissues and is a significant cause of childhood blindness. It occurs from a failure of the optic fissure to close during embryonic development,and may lead to missing parts of the iris, ciliary body, retina, choroid, and optic nerve. Because there is no treatment for coloboma, efforts have focused on prevention. While several genetic causes of coloboma have been identified, little definitive research exists regarding the environmental causes of this condition. We review the current literature on environmental factors associated with coloboma in an effort to guide future research and preventative counseling related to this condition.

Risk Factors of Anencephaly: A Case-Control Study in Dessie Town, North East Ethiopia

Introduction

Anencephaly is a form of neural tube defect, which develops when the cranial neuropore is unable to close. It is one of the fatal anomalies of the neural tube. Although most of the causes of anencephaly are unknown, multiple risk factors are associated with this defect. Therefore, this study aimed to investigate the incidence and associated risk factors of anencephaly in Dessie town, in the north eastern region of Ethiopia.

Methods

An institution-based unmatched case-control study was conducted. Sociodemographic characteristics of pregnant women were collected with a structured questionnaire and clinical data were recorded during an ultrasound examination. Data were entered into Epi Info 7 and analyzed by SPSS version 20. Binary logistic regression was applied to detect the associations between risk factors and the occurrence of anencephaly.

Results

The incidence of anencephaly was 3.3/1000 pregnancies. The multivariate logistic regression model indicated that maternal age between 26 and 30 years and khat chewing during pregnancy were significantly associated with anencephaly (OR 0.13, 95% CI 0.02-0.97, p=0.046; and OR 3.571, 95% CI 1.06-12.06, p=0.04, respectively). Exposure to typhus and typhoid and the use of antihypertensive drugs during early pregnancy were also significantly correlated as anencephaly risk factors. Furthermore, spina bifida simultaneously occurred with anencephaly significantly (p<0.05).

Conclusion

It is suggested that exposure to risk factors such as khat chewing during pregnancy may predispose to the development of anencephaly.

Heat stress and fetal risk. Environmental limits for exercise and passive heat stress during pregnancy: a systematic review with best evidence synthesis

OBJECTIVE

Pregnant women are advised to avoid heat stress (eg, excessive exercise and/or heat exposure) due to the risk of teratogenicity associated with maternal hyperthermia; defined as a core temperature (T_core) ≥39.0°C. However, guidelines are ambiguous in terms of critical combinations of climate and activity to avoid and may therefore unnecessarily discourage physical activity during pregnancy. Thus, the primary aim was to assess T_core elevations with different characteristics defining exercise and passive heat stress (intensity, mode, ambient conditions, duration) during pregnancy relative to the critical maternal T_core of ≥39.0°C.

DESIGN

Systematic review with best evidence synthesis.

DATA SOURCES

EMBASE, MEDLINE, SCOPUS, CINAHL and Web of Science were searched from inception to 12 July 2017.

STUDY ELIGIBILITY CRITERIA

Studies reporting the T_core response of pregnant women, at any period of gestation, to exercise or passive heat stress, were included.

RESULTS

12 studies satisfied our inclusion criteria (n=347). No woman exceeded a T_core of 39.0°C. The highest T_core was 38.9°C, reported during land-based exercise. The highest mean end-trial T_core was 38.3°C (95% CI 37.7°C to 38.9°C) for land-based exercise, 37.5°C (95% CI 37.3°C to 37.7°C) for water immersion exercise, 36.9°C (95% CI 36.8°C to 37.0°C) for hot water bathing and 37.6°C (95% CI 37.5°C to 37.7°C) for sauna exposure.

CONCLUSION

The highest individual core temperature reported was 38.9°C. Immediately after exercise (either land based or water immersion), the highest mean core temperature was 38.3°C; 0.7°C below the proposed teratogenic threshold. Pregnant women can safely engage in: (1) exercise for up to 35 min at 80%-90% of their maximum heart rate in 25°C and 45% relative humidity (RH); (2) water immersion (≤33.4°C) exercise for up to 45 min; and (3) sitting in hot baths (40°C) or hot/dry saunas (70°C; 15% RH) for up to 20 min, irrespective of pregnancy stage, without reaching a core temperature exceeding the teratogenic threshold.

No 129-L'exercice physique pendant la grossesse et le postpartum

OBJECTIF

Énoncer une directive canadienne visant à informer les fournisseurs de soins obstétricaux des répercussions, pour la mère, le fœtus et le nouveau-né, des exercices de conditionnement aerobique et musculaire pendant la grossesse. RéSULTATS ATTENDUS: Effets sur la morbidité maternelle, fœtale et néonatale et mesures de la forme physique maternelle.

PREUVES

Une recherche sur MEDLINE des articles, publiés en anglais de 1966 à 2002, appartenant aux catégories suivantes : études sur le conditionnement aérobique et musculaire chez des femmes ne faisant pas jusque-là d'exercice et chez des femmes actives avant leur grossesse, ainsi que des études sur les répercussions du conditionnement aérobique et musculaire sur les issues précoces et tardives de la grossesse ou sur les issues néonatales; rapports de synthèse et méta-analyses portant sur l'exercice pendant la grossesse.

VALEURS

Les résultats recueillis ont été revus par la Société des obstétriciens et gynécologues du Canada (Comité de la pratique clinique - obstétrique), avec la participation de la Société canadienne de physiologie de l'exercice, et ils ont été classés suivant les critères d'évaluation des preuves établis par le Groupe de travail canadien sur l'examen de santé périodique.

RECOMMANDATIONS

VALIDATION: Cette directive a été approuvée par le Comité de pratique clinique - obstétrique de la SOGC, par le Comité exécutif et par le Conseil de la SOGC, ainsi que par le Conseil d'administration de la Société canadienne de physiologie de l'exercice. PARRAINé PAR: la Société des obstétriciens et gynécologues du Canada et par la Société canadienne de physiologie de l'exercice.

Fever in pregnancy and the risk of congenital malformations: a cohort study

Background

In a variety of animal species, hyperthermia in pregnancy has been recognized as teratogenic. Hyperthermia interferes with protein synthesis via heat-shock proteins, which can entail membrane disruption, cell death, vascular disruption, and placental infarction. This can induce severe fetal malformations or death. Fever during pregnancy, especially during embryogenesis, has also been associated with congenital malformations in human offspring.

The purpose of this large cohort study of clinically recognized pregnancies was to investigate whether fever during first trimester was associated with an increased risk of congenital malformations in the offspring.

Methods

The Danish National Birth Cohort is a population-based cohort of 100,418 pregnant women and their offspring recruited in 1996 to 2002. Information on fever during pregnancy was collected prospectively by means of two telephone interviews.

The study population comprised the 77,344 pregnancies enrolled in the Danish National Birth Cohort where self-reported information on fever during first trimester of pregnancy was available. Pregnancy outcomes were identified through linkage with the National Patient Registry. Congenital malformations within the first three and a half years of life were categorized according to EUROCAT’s classification criteria. Logistic regression models were used to estimate the associations between fever in first trimester and overall congenital malformations and congenital malformations by subgroups.

Results

Eight thousand three hundred twenty-one women reported fever during first trimester (10.8%) and 2876 infants were diagnosed with a congenital malformation (3.7%). Fever during first trimester did not affect the risk of overall fetal congenital malformation (OR 0.99, 95% CI 0.88–1.12). The subgroup analyses indicated slightly higher risk of congenital anomalies in the eye, ear, face and neck (OR 1.29, 95% CI 0.78–2.12) and in the genitals (OR 1.17, 95% CI 0.79–1.12), whereas lower risk of malformations in the nervous system (OR 0.47, 95% CI 0.21–1.08), the respiratory system (OR 0.56, 95% CI 0.23–1.29) and in the urinary subgroup (OR 0.58, 95% CI 0.35–0.99) was suggested, the latter constituting the only statistically significant finding.

Conclusions

Overall, this study did not show any association between maternal fever in pregnancy and risk of congenital anomalies.

Interaction between the SLC19A1 gene and maternal first trimester fever on offspring neural tube defects

BACKGROUND

Many studies have indicated that the reduced folate carrier gene (SLC19A1) is associated with an increased risk of neural tube defects (NTDs). However, the interaction between the SLC19A1 gene variant and maternal fever exposure and NTD risk remains unknown. The aim of this study was to investigate whether the risk for NTDs was influenced by the interactions between the SLC19A1 (rs1051266) variant and maternal first trimester fever.

METHODS

We investigated the potential interaction between maternal first trimester fever and maternal or offspring SLC19A1 polymorphism through a population-based case-control study. One hundred and four nuclear families with NTDs and 100 control families with nonmal newborns were included in the study. SLC19A1 polymorphism was determined using polymerase chain reaction-restricted fragment length polymorphism.

RESULTS

Mothers who had the GG/GA genotype and first trimester fever had an elevated risk of NTDs (adjusted odds ratio, 11.73; 95% confidence interval, 3.02-45.58) as compared to absence of maternal first trimester fever and AA genotype after adjusting for maternal education, paternal education, and age, and had a significant interactive coefficient (γ = 3.17) between maternal GG/GA genotype and first trimester fever. However, there was no interaction between offspring's GG/GA genotype and maternal first trimester fever (the interactive coefficient γ = 0.97) after adjusting for confounding factors.

CONCLUSION

Our findings suggested that the risk of NTDs was potentially influenced by a gene-environment interaction between maternal SLC19A1 rs1051266 GG/GA genotype and first trimester fever. Maternal GG/GA genotype may strengthen the effect of maternal fever exposure on NTD risk in this Chinese population.

Hyperthermia: malformations to chaperones

Hyperthermia has been known to induce malformations in numerous animal models as well being associated with human abnormalities. This was apparent particularly when the hyperthermia exposure was during the early stages of neural development. Although it was recognized relatively early that these exposures induced cell death, the specific molecular mechanism of how a brief heat exposure was translated in to specific cellular functions remains largely unknown. While our understanding of the events that govern how cells react to heat, or stresses in general, has increased, there is much that remains undiscovered. In this brief review, animal and clinical observations are outlined as are some of the scientific explorations that were undertaken to characterize, define, and better understand the morphological, biochemical, and molecular effects of hyperthermia on the developing embryo.

Maternal fever during early pregnancy and the risk of oral clefts

An increased risk of birth defects after hyperthermic exposures has been confirmed in animal studies, but population studies have yielded inconsistent results. Oral clefts are a common birth defect and have been associated with these exposures in some of these studies. In this study, data from the National Birth Defects Prevention Study was used to evaluate the association of maternal report of febrile illness in early pregnancy and the risk of oral clefts. All oral cleft cases born between 1997 and 2004 were compared with nonmalformed controls born in the same geographical region during the same time period. Mothers reporting febrile illness during pregnancy were stratified by fever grade and antipyretic use. Logistic regression models were used to generate crude and adjusted odds ratios for exposure to fever and association with each oral cleft phenotype. The dataset included 5821 controls, 1567 cases of cleft lip with or without cleft palate (CL+/-P) and 835 cases of cleft palate only. A modestly increased risk was observed for isolated CL+/-P (odds ratio, 1.28; 95% confidence interval, 1.01-1.63). Stratification by fever grade (body temperature <101.5 degrees or > or =101.5 degrees F) did not yield significant differences in risk. Risk estimates were higher among women who reported a fever, but did not take antipyretics to control their fever, particularly for nonisolated compared with isolated oral clefts. This finding suggests that adequate control of fever may diminish the deleterious effects of fever in cases of oral cleft.

Delineation of a multiple congenital abnormality syndrome in the offspring of pregnant women affected with high fever-related disorders: a population-based study

Our previous study showed an association between high fever-related maternal diseases during the second and/or third gestational months and a higher risk of multiple congenital abnormalities (MCA) in the population-based large dataset of the Hungarian Case-Control Surveillance of Congenital Abnormalities. The objective of our analysis is to attempt the delineation of the spectrum of the characteristic component defects of an MCA syndrome associated with high fever-related maternal diseases. Of 1349 cases with MCA without recognized genetic and teratogenic syndromes in the total dataset, 181 had a possible association with influenza, common cold with secondary complications, tonsillitis and recurrent orofacial herpes with high fever in the second and/or third gestational months. At the evaluation of component defects in these 181 MCA cases, an association was found between the components of the so-called two schisis-type defects, such as neural-tube defects and orofacial cleft, in addition to microphthalmos, neurogenic limb contractures, and indeterminate sex (i.e. maldevelopment of male external genital organs, such as hypoplasia of the penis and pseudohermaphroditism). In addition, previous findings that showed an association between high fever and facial anomalies (micrognathia and midfacial hypoplasia), microcephaly and defects of external ears, were confirmed in our dataset. Thus, we delineated the maternal high fever-related MCA syndrome, including the above component defects and this MCA syndrome was identified in 38 MCA (21.0%) among 181 MCA babies born to mothers with high fever-related diseases. In the total dataset of 1349 MCA, 2.8% of cases can be associated with high fever.

The influence of the environment and other exogenous agents on spontaneous abortion risk

It is estimated that close to 30% of all pregnancies end in spontaneous abortion. Although about 60% of spontaneous abortions are thought to be due to genetic, infectious, hormonal, and immunological factors, the role of the environment remains poorly understood. Pregnancy involves a delicate balance of hormonal and immunological functions, which may be affected by environmental substances. Many toxic substances that are persistent in the environment and accumulate in the fatty tissues may disrupt this equilibrium. This overview addresses known risk factors for spontaneous abortions and examines the role, if any, that environmental factors (chemical and physical) may play in the etiology of this adverse health outcome.

High fever-related maternal diseases as possible causes of multiple congenital abnormalities: a population-based case-control study

BACKGROUND

Multiple congenital abnormalities (MCAs) represent the most severe category of structural birth defects; therefore, we decided to evaluate the possible etiological factors for MCAs.

METHODS

The population-based large data set of the Hungarian Case-Control Surveillance of Congenital Abnormalities (1980-1996) was evaluated.

RESULTS

We compared the data of 1,349 cases with MCAs, 2,405 matched population controls without any defect, and 21,494 malformed controls with isolated congenital abnormalities. An association was found between a higher risk for MCAs and high fever-related influenza, common cold with secondary complications, tonsillitis, and recurrent orofacial herpes (adjusted ORs with 95% CIs: 2.3, 1.8-2.9). However, the risk for MCAs was reduced by antifever drug therapy (adjusted OR with 95% CI: 1.6, 0.9-2.9).

CONCLUSIONS

An association was found between high fever-related maternal diseases and a higher risk for MCAs; however, a certain portion of these MCAs is preventable by antifever therapy.

Review: Hyperthermia and fever during pregnancy

An episode of hyperthermia is not uncommon during pregnancy. The consequences depend on the extent of temperature elevation, its duration, and the stage of development when it occurs. Mild exposures during the preimplantation period and more severe exposures during embryonic and fetal development often result in prenatal death and abortion. Hyperthermia also causes a wide range of structural and functional defects. The central nervous system (CNS) is most at risk probably because it cannot compensate for the loss of prospective neurons by additional divisions by the surviving neuroblasts and it remains at risk at stages throughout pre- and postnatal life. In experimental animals the most common defects are of the neural tube, microphthalmia, cataract, and micrencephaly, with associated functional and behavioral problems. Defects of craniofacial development including clefts, the axial and appendicular skeleton, the body wall, teeth, and heart are also commonly found. Nearly all these defects have been found in human epidemiological studies following maternal fever or hyperthermia during pregnancy. Suggested future human studies include problems of CNS function after exposure to influenza and fever, including mental retardation, schizophrenia, autism, and cerebral palsy.

Parental heat exposure and risk of childhood brain tumor: a Children's Oncology Group study

Medulloblastoma (MB) and primitive neuroectodermal tumor (PNET) are histologically similar brain tumors that occur mostly in children. As part of a comprehensive case-control study of MB/PNET, this study explored parental exposure to heat and electromagnetic fields as potential risk factors. Parents of 318 cases (<6 years of age at diagnosis in 1991-1997 and registered with the Children's Cancer Group) and 318 controls selected by random digit dialing were interviewed. In univariate analyses, moderately strong associations were observed for mother's sauna use close to conception (odds ratio = 3.8, 95% confidence interval (CI): 1.0, 13.7) or in the first trimester (odds ratio = 3.6, 95% CI: 0.7, 17.3) and for father's exposure in the 3 months before the pregnancy to sauna (odds ratio = 2.4, 95% CI: 1.3, 4.5), electric blanket (odds ratio = 2.0, 95% CI: 0.9, 4.3), or any heat source (for higher exposure: odds ratio = 2.5, 95% CI: 1.4, 4.6). In multivariate models, father's sauna use and father's exposure to any heat source were associated with MB/PNET in a dose-response fashion (for high exposure: odds ratio = 3.4, 95% CI: 1.2, 9.7, and odds ratio = 2.1, 95% CI: 1.1, 4.3, respectively). This new observation regarding paternal exposure to heat just prior to the index pregnancy deserves consideration in future animal and human studies of MB/PNET.

Risks of hyperthermia associated with hot tub or spa use by pregnant women

There are a limited number of human studies linking hot tub or spa use during early pregnancy to increased risks for neural tube defects (NTDs) or spontaneous abortion. However, these data can be considered in the context of human studies that have demonstrated an association between high maternal fever in early pregnancy and NTDs. In addition, there is a large volume of animal literature suggesting that, regardless of the heat source, an elevated core maternal temperature at or above the threshold of 2 degrees C over baseline, as well as timing and duration of exposure, are the critical factors in conferring risk. Therefore, the potential for hot tub or spa use to increase core maternal body temperature to risky levels and thus increase the risk for NTDs is likely. A woman who knows or who may not yet be aware that she is pregnant should be advised of the recommended limits of exposure. She should also be aware of the possible variability in hot tub or spa temperature readings and be able to accurately monitor maximum water temperature in the hot tub or spa so that her body temperature can be maintained below 38.9 degrees C.

Maternal influenza during pregnancy and risk of congenital abnormalities in offspring

BACKGROUND

The teratogenic effect of influenza viruses is currently being debated, and we examined the large population-based data set of the Hungarian Case-Control Surveillance of Congenital Abnormalities (HCCSCA) to study the possible association between maternal influenza and various congenital abnormalities (CAs).

METHODS

The 1980-1996 HCCSCA includes 22,843 newborns or fetuses with CAs, and 38,151 matched controls (newborn infants without any abnormalities).

RESULTS

In the case group, 1328 (5.8%) mothers had influenza at some time during their pregnancies compared to 1838 (4.8%) mothers in the control group (adjusted prevalence odds ratios [PORs], 1.3; 95% confidence interval [CI], 1.2-1.4). In the calculation of the adjusted PORs, the use of antifever drugs and maternal employment status were considered. When cases and their matched controls were compared, there was a higher prevalence of maternal influenza during the second and/or third month of pregnancy for the group of newborns with cleft lip +/- palate (adjusted POR, 3.2; 95% CI, 2.0-5.3), neural-tube defects (adjusted POR, 1.9; 95% CI, 1.1-3.3), and cardiovascular malformations (adjusted POR, 1.7; 95% CI, 1.3-2.3). However, a direct teratogenic effect from influenza viruses appears to be unlikely, and we suggest that the higher prevalence of the CAs indicated above can be explained mainly by fever, because this risk was reduced by the use of antifever drugs. Periconceptional folic acid supplementation also showed some preventive effect for these CAs.

CONCLUSIONS

The indirect teratogenic effect of maternal influenza during pregnancy may be restricted by appropriate medical treatment (e.g., antifever drugs) and periconceptional folic acid supplementation.

Marshall J. Edwards: Discoverer of maternal hyperthermia as a human teratogen

In a series of animal studies performed over a career spanning 40 years at the University of Sydney, Professor Marshall J. Edwards investigated the hypothesis that maternal hyperthermia during gestation can be teratogenic to the developing fetus. He is one of few investigators to have discovered a known human teratogen primarily through animal studies. In 1970 he earned his Ph.D. from the University of Sydney, writing a doctoral thesis entitled "A Study of Some Factors Affecting Fertility of Animals with Particular Reference to the Effects of Hyperthermia on Gestation and Prenatal Development of the Guinea-Pig." He went on to prove that hyperthermia-induced malformations in animals involve many organs and structures, particularly the central nervous system. Other defects include craniofacial anomalies, heart defects and hypodactyly, cataracts and coloboma, kyphoscoliosis, renal anomalies, dental agenesis, and abdominal wall defects. In a series of carefully planned and executed experiments, he demonstrated that the type of defect is related to the timing of the hyperthermic insult, and analyzed the underlying mechanisms. Cell death, membrane disruption, vascular disruption, and placental infarction were all implicated in causing embryonic damage. This special article reviews the scientific discoveries and personal philosophy of Marshall J. Edwards, the discoverer of maternal hyperthermia as a human teratogen.

Maternal hyperthermia and the risk for neural tube defects in offspring: systematic review and meta-analysis

BACKGROUND

In animals, excessive core body temperatures have been documented to cause malformations; neural tube defects (NTDs) are among the most frequently reported. In humans, data are inconclusive and often conflicting. The objective of our report is to determine the risk for neural tube defects associated with maternal hyperthermia in early pregnancy.

METHODS

We conducted a systematic review and meta-analysis to evaluate available evidence on this topic in humans. MEDLINE, EMBASE, references from published reports, and biologic abstracts from meetings were searched for relevant studies. Reviewers evaluated all the retrieved articles and extracted the relevant data. Individual and summary odds ratios and relative risks were calculated using the Mantel-Haenszel method.

RESULTS

Fifteen studies, reporting on 1,719 cases and 37,898 noncases, were included in the meta-analysis. The overall odds ratio for neural tube defects associated with maternal hyperthermia was 1.92 (95% confidence interval = 1.61-2.29). When analyzed separately, the 9 case-control studies had an odds ratio of 1.93 (1.53-2.42). The summary relative risk for the 6 cohort studies was 1.95 (1.30-2.92).

CONCLUSIONS

Maternal hyperthermia in early pregnancy is associated with increased risk for neural tube defects and may be a human teratogen.

The effect of fever, febrile illnesses, and heat exposures on the risk of neural tube defects in a Texas-Mexico border population

BACKGROUND

Hyperthermia produces neural tube defects (NTDs) in a variety of animal species. Elevated maternal body temperatures may also place the developing human embryo at risk. We examined the relation between maternal hyperthermia and the development of NTDs in a high-risk Mexican-American population.

METHODS

Case-women were Mexican-American women with NTD-affected pregnancies who resided and delivered in any of the 14 Texas counties bordering Mexico, during 1995-2000. Control-women were randomly selected from study area residents delivering normal live births, frequency-matched to cases by hospital and year. Information on maternal fevers, febrile illnesses, exposures to heat generated from external sources, and hyperthermia-inducing activities was gathered through in-person interviews, conducted about six weeks postpartum.

RESULTS

The risk effect (OR) associated with maternal fever in the first trimester, compared to no fever, was 2.9 (95% CI, 1.5-5.7). Women taking fever-reducing medications showed a lower risk effect (OR, 2.4; 95% CI, 1.0-5.6) than those who did not (OR, 3.8; 95% CI, 1.4-10.9). First-trimester maternal exposures to heat devices such as hot tubs, saunas, or electric blankets were associated with an OR of 3.6 (95% CI, 1.1-15.9). Small insignificant effects were observed for activities such as cooking in a hot kitchen (OR, 1.6; 95% CI, 1.0-2.6) and working or exercising in the sun (OR, 1.4; 95% CI, 0.9-2.2).

CONCLUSIONS

Maternal hyperthermia increases the risk for NTD-affected offspring. Women intending to become pregnant should avoid intense heat exposures, carefully monitor and manage their febrile illnesses, and routinely consume folic acid supplements.

Physical exposures during pregnancy and congenital cardiovascular malformations

Congenital cardiovascular malformations (CCM) cause substantial neonatal morbidity and mortality. Known risk factors for CCM explain only 10-20% of all cases. Few studies have examined mothers' physical exposures during pregnancy and the risk of CCM in their offspring. This study examined the association between exposures to extreme temperatures, prolonged standing, and heavy lifting during early pregnancy and risk of CCM in offspring. Using a case-control study design, 502 cases and 1066 controls were drawn from the population of all liveborn infants born between January 1988 and June 1991 to mothers living in 14 counties in New York State. Cases were identified from a population-based registry of congenital malformations. Controls were randomly selected from birth certificate records. Interviews were conducted by telephone, using a structured questionnaire. Exposure estimates were based on women's self-reports of conditions in the residence and workplace. Eighty-three per cent of the mothers were white, and 66% were between 25 and 34 years old. After adjusting all results for known risk factors and confounding variables, we found no significant increased risk of CCM in subjects whose mothers reported being exposed during early pregnancy to extreme heat (OR = 1.13, 95% CI 0.59, 2.19), nor to extreme cold (OR = 1.19, 95% CI 0.66, 2.15). Mothers who reported ever using a hot tub, hot bath, or sauna during early pregnancy had no increased risk of CCM in their offspring (OR = 0.88, 95% CI 0.65, 1.18). Performing heavy lifting during early pregnancy did not increase the risk of CCM in offspring (OR = 0.80, 95% CI 0.57, 1.11). Prolonged standing during early pregnancy was not associated with an increased risk of CCM in children (OR = 1.03, 95% CI 0.82, 1.28). Thus if these maternal exposures have an adverse effect, it is unlikely to involve CCMs.

Neural tube defects

Defects of development of the neural tube can result in a number of seemingly different malformations. Understanding the abnormal embryology helps one understand the malformations and their surgical treatments. The clinical presentations and the follow-up of these patients require attention to various end organs besides the nervous system. For most of these conditions, long-term follow-up is necessary regardless of initial treatment. A decline in function is not a part of the natural history of these malformations and requires prompt evaluation and treatment.

An evaluation of maternal illnesses in the origin of neural-tube defects

OBJECTIVE

The objective of the study was to estimate risk of acute and chronic maternal diseases during pregnancy in the origin of neural-tube defects.

MATERIALS AND METHODS

Mothers with neural-tube defect fetuses/newborns (the NTD group), controls without any congenital defects (the normal control group) and controls with other defects (the other CA control group) were compared in the population-based data set of the Hungarian Case-Control Surveillance of Congenital Abnormalities, 1980-1996. Of 1,202 cases with neural tube defects, 559 (49.8%) and 229 (19.1%) had mothers with one or more acute and chronic diseases, respectively. Of 38,151 mothers in the normal control group 14,004 (36.7%) and 8,328 (21.8%) had mothers with one or more acute or chronic diseases, respectively. Of 22,475 mothers in the other CA control group, 8,999 (40.0%) and 3,793 (16.9%) were affected with one or more acute or chronic maternal diseases, respectively. The prevalence of these diseases was evaluated in the 2nd months of gestation, however, if diseases occurred in the 1st month and continued in the 2nd month were also included.

RESULTS

There was a potential recall bias between the NTD group and the normal control group, but not between the NTD group and the other CA control group.

CONCLUSIONS

We suggest that maternal fever is a possible cause of neural-tube defects. Thus, these fevers should be treated with antipyretics during pregnancy. Among chronic maternal diseases, the possible association of migraine-headache, on the one hand and neural tube defects (particularly anencephaly) on the other hand cannot be excluded.

Genetic dissection of hyperthermia-induced neural tube defects in mice

BACKGROUND

Maternal hyperthermia has been shown to induce neural tube defects (NTD) in humans and in experimental animal systems. We report the first genetic dissection of maternal hyperthermia-induced NTD in mice.

METHODS

After maternal exposure on E8.5 to 43 degrees C water bath for 10 min, we observed exencephaly frequencies among E15.5-17.5 fetuses from the following crosses and backcrosses, SWV/Fnn(SWV)xSWV, C57BL/6J(C57)xC57, SWVxC57 (F1), F1xSWV and SWVxF1.

RESULTS

The fetuses with maternal hyperthermia exposure developed exencephaly in a strain-dependent manner and the exencephaly frequencies among the above crosses were 46.2, 14.3, 13.6, 11.3, and 27.0%, respectively, expressed over total live fetuses. The fetal death rates were 47.3, 24.6, 37.1, 4.3, and 35.5%, respectively, expressed over total implants.

CONCLUSION

The data demonstrate that a single fetal genetic locus, plus a maternal effect, have likely caused the strain differences in the susceptibility to hyperthermia-induced exencephaly. A maternal effect alone may have caused the higher prenatal mortality rates in the SWVxF1 cross versus the reciprocal cross. Analysis of gender ratios among those affected from these crosses excludes an X- or Y-linked effect in causing the higher numbers of affected females.

Joint SOGC/CSEP Clinical Practice Guideline: Exercise in Pregnancy and the Postpartum Period

Objective: To design Canadian guidelines advising obstetric care providers of the maternal, fetal, and neonatal implications of aerobic and strength-conditioning exercises in pregnancy. Outcomes: Knowledge of the impact of exercise on maternal, fetal, and neonatal morbidity, and of the maternal measures of fitness. Evidence: MEDLINE search from 1966 to 2002 for English-language articles related to studies of maternal aerobic and strength conditioning in a previously sedentary population, maternal aerobic and strength conditioning in a previously active population, impact of aerobic and strength conditioning on early and late pregnancy outcomes, impact of aerobic and strength conditioning on neonatal outcomes, as well as for review articles and meta-analyses related to exercise in pregnancy. Values: The evidence collected was reviewed by the Society of Obstetricians and Gynaecologists of Canada (SOGC Clinical Practice Obstetrics Committee) with representation from the Canadian Society for Exercise Physiology, and quantified using the evaluation of evidence guidelines developed by the Canadian Task Force on the Periodic Health Exam.Recommendations:1. All women without contraindications should be encouraged to participate in aerobic and strength-conditioning exercises as part of a healthy lifestyle during their pregnancy. (II-1,2B)2. Reasonable goals of aerobic conditioning in pregnancy should be to maintain a good fitness level throughout pregnancy without trying to reach peak fitness or train for an athletic competition. (II-1,2C)3. Women should choose activities that will minimize the risk of loss of balance and fetal trauma. (III-C)4. Women should be advised that adverse pregnancy or neonatal outcomes are not increased for exercising women. (II-1,2B)5. Initiation of pelvic floor exercises in the immediate postpartum period may reduce the risk of future urinary incontinence. (II-1C)6. Women should be advised that moderate exercise during lactation does not affect the quantity or composition of breast milk or impact infant growth. (I-A)Validation: This guideline has been approved by the SOGC Clinical Practice Obstetrics Committee, the Executive and Council of SOGC, and the Board of Directors of the Canadian Society for Exercise Physiology. Sponsors: This guideline has been jointly sponsored by the Society of Obstetricians and Gynaecologists of Canada and the Canadian Society for Exercise Physiology. Key words: fetus, neonate, outcomes, aerobic, strength

Exercise in pregnancy and the postpartum period

OBJECTIVE

To design Canadian guidelines advising obstetric care providers of the maternal, fetal, and neonatal implications of aerobic and strength-conditioning exercises in pregnancy.

OUTCOMES

Knowledge of the impact of exercise on maternal, fetal, and neonatal morbidity, and of the maternal measures of fitness.

EVIDENCE

MEDLINE search from 1966 to 2002 for English-language articles related to studies of maternal aerobic and strength conditioning in a previously sedentary population, maternal aerobic and strength conditioning in a previously active population, impact of aerobic and strength conditioning on early and late pregnancy outcomes, and impact of aerobic and strength conditioning on neonatal outcomes, as well as for review articles and meta-analyses related to exercise in pregnancy.

VALUES

The evidence collected was reviewed by the Society of Obstetricians and Gynaecologists of Canada (SOGC Clinical Practice Obstetrics Committee) with representation from the Canadian Society for Exercise Physiology, and quantified using the evaluation of evidence guidelines developed by the Canadian Task Force on the Periodic Health Exam.

RECOMMENDATIONS

1. All women without contraindications should be encouraged to participate in aerobic and strength-conditioning exercises as part of a healthy lifestyle during their pregnancy. (II-1,2B) 2. Reasonable goals of aerobic conditioning in pregnancy should be to maintain a good fitness level throughout pregnancy without trying to reach peak fitness or train for an athletic competition. (II-1,2C) 3. Women should choose activities that will minimize the risk of loss of balance and fetal trauma. (III-C) 4. Women should be advised that adverse pregnancy or neonatal outcomes are not increased for exercising women. (II-1,2B) 5. Initiation of pelvic floor exercises in the immediate postpartum period may reduce the risk of future urinary incontinence. (II-1C) 6. Women should be advised that moderate exercise during lactation does not affect the quantity or composition of breast milk or impact infant growth. (I-A) VALIDATION: This guideline has been approved by the SOGC Clinical Practice Obstetrics Committee, the Executive and Council of SOGC, and the Board of Directors of the Canadian Society for Exercise Physiology.

SPONSORS

This guideline has been jointly sponsored by the Society of Obstetricians and Gynaecologists of Canada and the Canadian Society for Exercise Physiology.

Fever in pregnancy and risk of fetal death: a cohort study

BACKGROUND

Hyperthermia acts as a teratogen in some animals where it can induce resorption of the fetus and fetal death. Fever during pregnancy, especially in the period of embryogenesis, is also suspected as being a risk factor for fetal death in human beings. We did a large cohort study in Denmark to investigate this possibility.

METHODS

We interviewed 24040 women who were recruited in the first half of pregnancy to the Danish National Birth Cohort Study, and obtained information on the number of fever incidents during the first 16 weeks of pregnancy. For each fever episode, the highest measured body temperature, duration of incident, and gestational age were recorded. Outcomes of pregnancies were identified through linkage with the Civil Registration System and the National Discharge Registry. Cox's regression with time-dependent variables was used to estimate the relative risk of fetal death, taking delayed entry into account.

FINDINGS

1145 pregnancies resulted in a miscarriage or stillbirth (4.8%). During the first 16 pregnancy weeks 18.5% of the women experienced at least one episode of fever. However, we found no association between fever in pregnancy and fetal death before or after adjustment for known risk factors of fetal death (relative risk 0.95 [95% CI 0.80-1.13]). This finding was consistent irrespective of measured maximum temperature, duration and number of fever incidents, or the gestational time of the fever incident, and was observed for fetal death in all three trimesters of pregnancy.

INTERPRETATION

We found no evidence that fever in the first 16 weeks of pregnancy is associated with the risk of fetal death in clinically recognised pregnancies.

Thermal environment and human birth weight

Human birth weight is known to be influenced by several factors, including maternal energy supply, maternal stature, disease status, smoking status and gestation length. This article proposes that the thermal environment may be a further factor influencing birth weight. Experimental animal studies demonstrate clear effects of thermal stress on placental function and birth weight, but may have limited relevance for humans due to between-species differences in pregnancy physiology. Observational studies suggest an inverse relationship between environmental temperature and birth weight within and between human populations. Variation in maternal size, body fatness, pregnancy weight gain and heat production is predicted to influence maternal thermoregulatory capacity, as are the size and composition of the foetus. These associations generate the hypothesis that low birth weight in hot environments may in part represent an adaptation to environmental heat stress.

Neurodevelopment of children exposed in utero to treatment of maternal malignancy

Cancer is the second most common cause of death during the reproductive years, complicating approximately 1/1000 pregnancies. The occurrence of cancer during gestation is likely to increase as a result of a woman's tendency to delay childbearing. Improved diagnostic techniques for malignancies increases detection of cancer during pregnancy. Malignant conditions during gestation are believed to be associated with an increase in poor perinatal and fetal outcomes that are often due to maternal treatment. Physicians should weigh the benefits of treatment against the risks of fetal exposure. To date, most reports have focused on morphologic observations made very close to the time of delivery with little data collected on children's long-term neurodevelopment following in utero exposure to malignancy and treatment. Because the brain differentiates throughout pregnancy and in early postnatal life, damage may occur even after first trimester exposure. The possible delayed effects of treatment on a child's neurological, intellectual and behavioural functioning have never been systematically evaluated. The goal of this report was to summarize all related issues into one review to facilitate both practitioners' and patients' access to known data on fetal risks and safety.

Genetic basis of susceptibility to environmentally induced neural tube defects

Neural tube defects (NTDs) are among the most common of all human congenital defects, with multifactorial etiologies comprising both environmental and genetic components. Several murine model systems have been developed in an effort to elucidate genetic factors regulating expression of NTDs. Strain-dependent differences in susceptibility to teratogenic insults and altered patterns of gene expression observed within the neuroepithelium of affected embryos support the hypothesis that subtle genetic changes can result in NTDs. Since several affected genes are folate-regulated, transgenic knockout mice lacking a functional folate receptor were developed. Nullizygous embryos died in utero with significant morphological defects, supporting the critical role of folic acid in early embryogenesis. While epidemiological studies have not established an association between polymorphisms in the human folate receptor gene and NTDs, it is known that folate supplementation reduces infant NTD risk. Continued efforts are therefore necessary to reveal the mechanism by which folate works and the nature of the gene(s) responsible for human NTDs.

Benefits and risks of sauna bathing

Although sauna bathing causes various acute, transient cardiovascular and hormonal changes, it is well tolerated by most healthy adults and children. Sauna bathing does not influence fertility and is safe during the uncomplicated pregnancies of healthy women. Some studies have suggested that long-term sauna bathing may help lower blood pressure in patients with hypertension and improve the left ventricular ejection fraction in patients with chronic congestive heart failure, but additional data are needed to confirm these findings. The transient improvements in pulmonary function that occur in the sauna may provide some relief to patients with asthma and chronic bronchitis. Sauna bathing may also alleviate pain and improve joint mobility in patients with rheumatic disease. Although sauna bathing does not cause drying of the skin-and may even benefit patients with psoriasis-sweating may increase itching in patients with atopic dermatitis. Contraindications to sauna bathing include unstable angina pectoris, recent myocardial infarction, and severe aortic stenosis. Sauna bathing is safe, however, for most people with coronary heart disease with stable angina pectoris or old myocardial infarction. Very few acute myocardial infarctions and sudden deaths occur in saunas, but alcohol consumption during sauna bathing increases the risk of hypotension, arrhythmia, and sudden death, and should be avoided.

Identification of a growth arrest specific (gas 5) gene by differential display as a candidate gene for determining susceptibility to hyperthermia-induced exencephaly in mice

Neural tube defects (NTDs) are among the most common congenital malformations, affecting approximately 1 per 1,000 liveborn infants in the United States [Nakano, 1973; Richards et al., 1972]. Maternal exposure to hyperthermia, either through recreational sources or due to an infectious agent, is thought to account for approximately 10% of observed NTD cases. The specific genes conferring susceptibility or resistance to hyperthermia-induced NTDs have not been identified. This study used differential display-polymerase chain reaction (DD-PCR) to characterize alterations in gene expression in the anterior embryonic neural tube of two highly inbred murine strains (SWV/Fnn, LM/Bc/Fnn) known to differ in their genetically determined susceptibility to heat-induced NTDs. Herein, we report the neural tube-specific differential expression of the growth arrest specific (gas 5) gene in the highly susceptible SWV/Fnn strain during neural tube closure (NTC). Although the expression of gas 5 did not appear to be altered by the teratogenic heat treatment, its spatial and strain-specific pattern of expression makes it an excellent candidate gene responsible for the observed genetic differences in NTD susceptibility between these two inbred murine strains.

Maternal fever and birth outcome: a prospective study

Although maternal fever has been implicated as a human teratogen in several studies, no prospective study has adequately addressed the full spectrum of birth outcomes following such exposure in pregnancy. The purpose of this study was to determine whether or not maternal fever is associated with an increased risk for structural malformations, prematurity, growth retardation, or pregnancy loss. Using a prospective cohort study design, we ascertained women who had called the California Teratogen Information Service and Clinical Research Program between 1979-1996 with questions regarding fever in a current pregnancy. Of these women, 115 who reported a fever of at least 38.9 degrees C lasting for at least 24 h (high fever group) and 147 women who reported a fever of either less than 38.9 degrees C or lasting less than 24 h (low fever group) were enrolled in the cohort. An additional 298 pregnant women who reported having no fever at any time in pregnancy were enrolled in a control group. All pregnancies were followed in a similar fashion, and outcomes were compared among the three groups. The combined prevalence of all major structural malformations was increased, but not significantly so, in the offspring of women who had a high fever in the first trimester of pregnancy compared to those with a lower fever or to controls (relative risk 1.80 for high fever group compared to controls; 95% confidence interval, 0.54, 6.03; relative risk 1.21 for low fever group compared to controls; 95% confidence interval, 0.36, 4.03). However, 2/34 or 5.9% of women who had a high fever during the critical period for neural tube closure carried fetuses with anencephaly compared to none in the low fever group or controls. Specific minor defects were found more frequently in the high fever group compared to controls and were consistent with the pattern of defects previously reported in a retrospective case series. In addition, stillbirth occurred more frequently in the high fever group compared to controls (2.6% vs. 0%). These data support the conclusion that high maternal fever early in pregnancy is a human teratogen. Women who experience fevers of 38.9 degrees C or higher for extended periods of time in the first month of pregnancy should be considered at increased risk for neural tube defects and should be provided appropriate counseling.

Teratogen update: gestational effects of maternal hyperthermia due to febrile illnesses and resultant patterns of defects in humans

This review has covered the pertinent literature concerning the teratogenic effects of hyperthermia in man and experimental animals. This is the first teratogen that was initially discovered in animals and then subsequently found to be a cause for concern in humans when similar patterns of defects were observed. Hyperthermia is a physical agent with a dose-response curve for abortions and malformations, but these effects can be mitigated in some circumstances by the heat shock response (HSR). We have reviewed the known functions of HSR and provided some insight into why embryos have some protection following an initial dose of heat, if it is sufficient to initiate the response. Thus, by reviewing the effects of hyperthermia in experimental animals, as well as malformative and protective mechanisms of teratogenesis, we have attempted to understand the effects of human hyperthermia teratogenesis.

Maternal illness, including fever and medication use as risk factors for neural tube defects

We investigated if selected maternal illnesses or medications used during the periconceptional period increased risk of having neural tube defect (NTD)-affected pregnancies. We used a population-based case-control study of fetuses and liveborn infants with NTDs among 1989-1991 California births. In-person interviews were conducted with mothers of 538 (88% of eligible) NTD cases and 539 (88%) nonmalformed controls, usually within 5 months of delivery. A maternal fever or febrile illness episode in the first trimester was associated with an increased risk for having a NTD-affected pregnancy, odds ratio (OR) = 1.91 (95% confidence interval, 1.35-2.72) for fever and OR = 2.02 (1.20-3.43) for febrile illness. Risk estimates were not substantially altered after adjustment for maternal age, race/ethnicity, education, vitamin use, and body mass index. Other reported illnesses were generally not associated with risks of 1.5 or greater, or were too infrequent to adequately estimate risk. An OR of 1.5 or greater was observed for maternal use of guaifenesin, OR = 2.04 (0.79-5.28), and an OR of 0.5 or less was observed for maternal use of calcium-containing medicines, OR = 0.38 (0.14-1.03). Our findings are consistent with previous reports that suggested elevated NTD risks from maternal fever. We could not discriminate, however, whether the increased risks observed for maternal fever were indicative of a causal relation or due to reporting bias. Our findings suggest that many of the illnesses common to reproductive-aged women and the medications commonly used to treat them during pregnancy, except, perhaps, for those illnesses that are febrile-related, do not appear to substantially contribute to the occurrence of NTDs in the population.

Growth and behavioral changes in mice prenatally exposed to methylmercury and heat

Postnatal and behavioral changes in mice exposed prenatally to methylmercury and heat were investigated. Pregnant ICR mice were immersed in water at 37 degrees C or 42 degrees C for 10 min once or twice daily from day 12 through day 15 of gestation. Two hours after the heat exposure on day 12 of age, mice were injected s.c. with 5 mg Hg/kg of methylmercury (MeHg, as chloride) or saline. Prenatal exposure to heat significantly induced inactivity in an open field test (OPF) in males and retarded walking ability in both males and females. Prenatal exposure to MeHg caused significant inactivity in the OPF in females. Although heat did not enhance the effect of MeHg on physical growth or the behavior of pups and vice versa, there were some interactions between the effects of these two agents. Thus, the difference in walking ability in both sexes caused by heat was more distinctive in the saline-treated groups than in the MeHg-treated groups; the difference in locomotion in OPF caused by MeHg in females was more distinctive in the normothermic group than among the hyperthermic groups. The mechanisms underlying these behavioral changes need to be further examined.

Tympanic versus rectal thermometry in pregnant women

OBJECTIVE

To assess the accuracy of the tympanic membrane thermometer for use with pregnant women.

DESIGN

Cross-sectional descriptive study.

SETTING

A major medical center in the midwestern United States.

PARTICIPANTS

Thirty-three hospitalized, afebrile pregnant women.

MAIN OUTCOME MEASURES

Tympanic membrane thermometers and glass mercury thermometers were used to measure body temperature at the ear and rectum, respectively. The results were compared using two statistical methods: the Pearson correlation coefficient and a new technique suggested by Bland and Altman (1986).

RESULTS

Auditory canal temperature measured by a tympanic membrane thermometer correlated with rectal temperature as measured by a glass mercury thermometer (r = 0.38, p = 0.01). Thus, the tympanic membrane thermometer is acceptable for monitoring the body temperature of pregnant women. However, the device's estimation of rectal temperature is not clinically reliable.

CONCLUSIONS

Tympanic membrane thermometers, when applied with direct measures, are acceptable for use with pregnant women. It is not recommended that the rectal estimate mode be used with pregnant women.

Effects of MR exposure on axonal outgrowth in the sympathetic nervous system of the chick

The effects of MR exposure on the rate and specificity of sympathetic preganglionic axonal outgrowth were examined in the chick embryo. Embryos were exposed to a static magnetic field of 1.5 T for 6 hours, 64 MHz RF field pulses, and a switched magnetic field gradient of amplitude 0.6 G/cm for 4 hours. No significant difference in axonal outgrowth was observed between MR-exposed and control embryos. In addition, the distributions of several major extracellular matrix (ECM) molecules, laminin, fibronectin, and collagen IV, were examined. Immunostaining patterns of these ECM molecules during axonal outgrowth showed no difference between MR-exposed and control embryos. Our results suggest that the MR exposure conditions used in this study do not affect axonal outgrowth in the sympathetic nervous system of the chick.

Exercise at high temperature causes maternal hyperthermia and fetal anomalies in rats

Hyperthermia is thought to be a teratogen in many animal species and also in humans. It has been reported that hyperthermia caused by sauna, hot tub, or fever during the early stages of pregnancy is related to an increased risk for neural tube defects. During exercise, especially in hot conditions, body temperature can also rise to fairly high levels. Thus, we can surmise that hyperthermia induced by exercise can also cause fetal malformation. To investigate this hypothesis, pregnant rats at 9 days of gestation were divided into four groups. In the first group, the animals were made to swim for 30 minutes in water at a temperature of 40.5 degrees C. In the second group, they were restrained and immersed in water for the same time at the same temperature. In the third group, the rats were forced to swim in water at 36.0 degrees C. The fourth group were controls. The core temperature of the rats was measured during these procedures. On the 18th gestational day, fetuses were extracted by cesarean section. The elevation of maternal core temperature was significantly greater in the first group than in the other groups. In the first group, 69% of fetuses had various external anomalies. No anomalies were found in the other groups. Our results show that exercise in hot conditions caused the elevation of core temperature and resulted in fetal anomalies in rats.

Exercise guidelines for pregnant women

Despite remarkable improvements in high technologies and an increase in the number of studies related to exercise for pregnant women, the guidelines for maternal exercise remain contradictory. The effects of exercise in pregnant women and cardiovascular modifications due to pregnancy, and effects of maternal exercise on the fetal environment, including uterine and umbilical hemodynamic changes, are reviewed. Suggested future directions in this area of nursing science are discussed.

Exercise and pregnancy: a review

The effects of pregnancy on the maternal cardiorespiratory system include increases in oxygen consumption, cardiac output, heart rate, stroke volume, and plasma volume. The increase in oxygen reserve seen in early pregnancy is reduced later, suggesting that maternal exercise may present a greater physiologic stress in the third trimester. Evidence suggests that weight-bearing exercise produces a greater decrease in oxygen reserve than nonweight-bearing exercise. Furthermore, to maintain a heart rate below 140 beats per minute during pregnancy, the intensity of weight-bearing exercise must be reduced. Nonweight-bearing, water-based exercise results in smaller fetal heart rate changes and a lower maternal heart rate than the same exercise performed on land. Exercising in the supine position in late pregnancy has raised concerns because cardiac output in the supine position is lower than in the lateral position at rest, presumably because the gravid uterus partially obstructs the inferior vena cava. Sustained exercise produces a training effect on the mother, although reported associations between this effect and the experience of labor are not consistent. Short-term changes in fetal heart rate provide circumstantial evidence that physical activity can influence the fetus. Acute effects of exercise that can potentially affect the fetus include hyperthermia, changes in uteroplacental flow, reduced levels of maternal glucose, and increased uterine contractions. Moderate to high levels of sustained maternal exercise have been associated with reduced birthweight. Much research remains to be done on the effects of specific exercise regimens during pregnancy, the effects on previously sedentary women, and the long-term health consequences to the offspring of women who perform vigorous exercise during pregnancy.