Update on new developments in the study of human teratogens

BACKGROUND AND METHODS

The purpose of this annual article is to highlight and briefly review new and significant information on agents that may be teratogenic in pregnant women. Various sources of on-line and printed information are given.

RESULTS

The following topics have been discussed: 1) lithium medication: decreased estimate of risk; 2) cigarette smoking and genotype as contributors to oral-facial clefts and clubfoot; 3) trimethoprim; 4) methimazole syndrome?; 5) glucocorticoids and oral-facial clefts; 6) binge drinking; 7) fetal valproate syndrome; and 8) carbamazepine.

CONCLUSIONS

We have highlighted several maternal exposures during pregnancy that are associated with small but increased rates of birth defects, generally only a few cases per 1,000 infants. These exposures include cigarette smoking, and treatment with lithium, trimethoprim, methimazole, or corticosteroids. This weak teratogenic effect was usually identified by the linkage of an uncommon treatment with an unusual birth defect outcome. The use of modern epidemiologic techniques, especially prospective multicenter studies that provide increased numbers, has helped to strengthen the evidence for these associations. We discuss how teratogenic risks that are small in comparison to the background risk can be presented to at-risk women and their doctors. We have briefly listed some elements that might be used in prioritizing further studies of suspected teratogenic exposures. Various existing methods for expressing the strength of evidence for human teratogenicity are also given.

A history of the Teratology Society

BACKGROUND

The 39-year history of the Teratology Society is reviewed. An abbreviated history is outlined in table form, along with listings of the Warkany Lectures, the postgraduate courses, and officers of the Society.

METHODS

A year-by-year description of the events, including the scientific and social content of the annual meetings and changes in the business of the Society, is given, in many cases using comments from the past presidents. The valuable and unique diversity of the members is discussed and illustrated, presenting the disciplines and main research area of the presidents. The number of submitted abstracts and the various categories are tabulated, averaging the number and type over four periods. Within the past 10 years, a significant increase in the number of abstracts dealing with epidemiology and developmental biology is evident. The Society's development is compared with that of a human, and the question is asked: Have we reached the maturational stage of old age or senescence, or is the Society still maturing gracefully? This question needs further discussion by all the members.

RESULTS

During the past 40 years, we have developed the scientific basis to prevent birth defects caused by rubella, alcoholism, and folate deficiency, as well as many other prenatal exposures.

CONCLUSIONS

We must now engage in the political battles to obtain the resources needed to conduct further research and to implement the prevention programs, as well as to provide care and rehabilitation for persons with birth defects.

Mitochondrial ultrastructure in embryos after implantation

Information on the morphology of mitochondria during embryogenesis is scattered in the literature, but there appears to be a consistent pattern. During early organogenesis, the embryo is in a state of relative hypoxia associated with a major decrease in terminal electron transport system activity and a marked increase in anaerobic glycolysis. Ultrastructural studies of a 14-somite monkey embryo and day 10 and 12 rat embryos, together with a review of the literature, led us to determine that this hypoxic stage is characterized by vesiculation of the mitochondrial inner membranes, or cristae. Starting in the late morula stage and continuing during early postimplantation embryogenesis, the cristae increase but appear tubular or vesicular. After the end of neurulation, and with the onset of vascular perfusion of embryonic tissues, the cristae gradually become lamellated; by the limb bud stage they appear more mature. We suggest that new cristae derive from blebs of the inner mitochondrial membrane and that with maturation these blebs collapse, giving them a lamelliform appearance. The delamellated state of the cristae might inactivate oxidative phosphorylation to protect the embryo from toxic respiratory end-products that could accumulate in an embryo before there is vascular perfusion. Consistent with this hypothesis, mitochondrial diameters in the developing heart of monkey and rat embryos were approximately twice those found in skin and neural tube.

Ultrastructural study of mitochondria and their cristae in embryonic rats and primate (N. nemistrina)

Information on the morphology of mitochondria during embryogenesis is scattered in the literature but there appears to be a developmental pattern characterized by vesiculation of the mitochondrial cristae. During early organogenesis, the embryo is in a relative state of hypoxia and this is associated with decrease of terminal electron transport system activity and a marked increase in glycolysis. Ultrastructural studies of a 14 somite monkey embryo, and day 10 and 12 rat embryos, along with a review of the literature led us to determine that this hypoxic stage is characterized by vesiculation of the mitochondrial cristae. Starting in the late morula stage and continuing during early postimplantation embryogenesis the cristae increase and appear tubular or vesicular. After the end of neurulation, and with onset of vascular perfusion, the cristae gradually become lamellated and by the limb bud stage appear more mature. We suggest that new cristae form from blebs of the inner mitochondrial membrane and that subsequently with maturation these blebs collapse giving them a lamelliform appearance. The delamellated state of the cristae may protect the embryo from toxic respiratory end-products of oxidative respiration which could accumulate in an embryo lacking vascular perfusion. In the heart of monkey and rat embryos, the mitochondria had diameters which were approximately twice those found in skin and neural tube.

The teratogenicity of N(omega)-nitro-L-ariginine methyl ester (L-NAME), a nitric oxide synthase inhibitor, in rats

Exposure of gravid rats to the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) in drinking water or by implanted osmotic minipumps significantly elevates maternal blood pressure, reducing uteroplacental perfusion. Administration by either route causes fetal growth retardation, but oral exposure also causes hind limb reduction malformations. The present study employed both oral and intraperitoneal routes to determine the period of sensitivity to developmental toxicity, dose-response, and possible fetotoxic mechanisms. Hind limb hemorrhage occurred only in litters from dams exposed to oral doses of 1 to 2 mg/mL from gestational days 15 through 17. In contrast to oral exposure, single intraperitoneal injections caused both fore and hind limb reductions at doses of 25 mg/kg and above administered on gestational day 16 and later. Many other exposures that reduce uteroplacental perfusion have been associated with vascular disruptive dysmorphogenesis. These exposures include phenytoin, calcium channel inhibitors, cocaine, and uterine vascular clamping. Limb hemorrhage induced by these exposures is usually limited to distal structures, typically phalanges, and the incidence of affected fetuses rarely exceeds 50%. By contrast, hemorrhage caused by L-NAME frequently involves entire limbs, extending into adjacent flank in severe instances, and 100% of fetuses from treated dams may be affected. The basis of this difference and the differing defect patterns associated with the various routes of exposure are unclear, but the generation of reactive oxygen species during resumption of normal perfusion may play a role in this vascular disruption.

Uterine contraction in the development of Möbius syndrome

We report a patient with Möbius syndrome. The birth defect in this child is probably the result of both vasoconstriction and uterine contractions brought on by ergotamine taken during the sixth week of pregnancy. We propose that vasoconstrictive or mechanical effects, or both, of abortifacient drugs such as ergotamine and misoprostol may account for other cases of Möbius syndrome, and we suggest that uterine contraction from any cause, at about the sixth or seventh week of pregnancy, may cause this birth defect. Further observational studies are needed to verify this hypothesis.

Glucose absorption and utilization by rat embryos

There is little doubt that glucose plays a significant nutritional role in early somite embryos. The high glucose utilization of anaerobic glycolysis drops as the activity of the Kreb's cycle and terminal electron transport increase. Concurrently, maturation of mitochondrial cristae and dependence on oxygen supply are taking place. The neuroepithelium of the early somite rat embryo responds in vitro during culture by microvilliar lengthening when exposed to glucose levels of 50 mg/dl or more. At lower glucose concentrations both in whole embryo culture and inside the closed neural tube the microvilli are shorter. Lengthening of the microvilli at room temperature is produced only by d-glucose and 2-deoxyglucose, two hexoses that are absorbed and phosphorylated. Cytochalasin D which disrupts actin polymerization causes ballooning of the microvilli. A role of this microvillar elongation in degenerative changes seen in uncontrolled diabetes and on function of the immune system is proposed. The amniotic cavity is one major portal of entry for glucose during the early somite embryo stage. The 7-fold increase in volume of the amniotic cavity after day 10 allows the rat embryo to convert its axis from dorsal to ventral flexion.

Assessment of reproductive disorders and birth defects in communities near hazardous chemical sites. I. Birth defects and developmental disorders

Members of the workgroup on birth defects and developmental disorders discussed methods to assess structural anomalies, genetic changes and mutations, fetal and infant mortality, functional deficits, and impaired fetal and neonatal growth. Tier 1 assessments for all five adverse reproductive outcomes consist of questionnaires and reviews of medical records rather than laboratory testing of biologic specimens. The work-group members noted a role for neurodevelopmental testing and for limited genetic studies, such as karyotyping in Tier 2 assessments. Emerging methodologies to identify chromosomal aberrations, DNA adducts, and repair inhibition were reserved for Tier 3.

Neural plate microvillus lengthening in rat embryos grown in various concentrations of glucose and further studies of the mechanism

Glucose is an important cellular nutrient, and in the early embryo, which is dependent mostly on anaerobic glycolysis, it is even more essential. Based on tissue culture cells in which glucose utilization has become membrane-limited, a concept has been developed that the tip of the microvilli is the entrance compartment for glucose and that the shaft sets up a diffusion barrier. An increase in length of the microvillus is associated with decreased entry of phosphorylated hexose into the cells. Our previous findings of lengthening of the microvilli of the neural plate cells after 40 min exposure to glucose at room temperature have been extended to a 17 hr whole embryo culture system. In cultures where the final concentration of glucose was 20 and 24 mg/dl there was embryonic death. In those cultures ending with 29-137 mg/dl of glucose the embryos developed normally. Those grown in dialyzed serum supplemented with B vitamins and glucose grew equally as well as those in whole rat serum. Somite numbers attained did not change with increasing glucose concentration but a modest increase in micromoles of glucose used per embryo was found, suggesting the presence of another source of energy at lower glucose concentrations. The average glucose utilization per gram of protein per hour was 844 mumol in these day 9.5-10 embryos and this compares to 733 mumol previously found using uniformly labeled 14C glucose on day 10.3. Lactate production averaged 85% of the glucose utilized. Pyruvate did not support growth in the absence of glucose.(ABSTRACT TRUNCATED AT 250 WORDS)

Staurosporine does not prevent adrenergic-induced situs inversus, but causes a unique syndrome of defects in rat embryos grown in culture

Staurosporine, an alkaloid isolated from Streptomyces species, is commonly used as a protein kinase C (PKC) inhibitor in animal investigations. In the present study, we used this compound to determine whether alpha 1-adrenergic stimulation-induced situs inversus in rats is mediated by PKC. Embryos were explanted at 8 A.M. on day 9 of gestation. Those with a neural groove but with no visible neural folds (Stage 11a) were selected and were cultured in medium containing various concentrations of staurosporine with or without 50 microM of phenylephrine, an alpha 1-adrenergic agonist. At 10 A.M. on day 11 of gestation, embryos were examined for situs inversus and other abnormalities. Staurosporine, tested at 0.0001, 0.001, 0.01, 0.1, 0.375, and 0.5 microM (lethal concentration), did not block phenylephrine-induced situs inversus at any concentration. However, staurosporine alone produced situs inversus at concentrations above 0.1 microM. At 0.5 and 1.0 microM, staurosporine also caused cyst-like lesions projecting dorsally from the mesencephalon that we named "mesencephalic vesicles" and the formation of secondary somites. To confirm and further examine these unique effects of staurosporine both grossly and histologically, we conducted additional experiments using staurosporine from another source. Embryos were explanted between 6 A.M. and 9 P.M. on day 9 of gestation and were placed in one of the following groups according to their stage of development: 10b, 11a, 11b, 11c, 12/s1-2, 12/s3-4, and 12/s5-6. Embryos were then cultured with various concentrations of staurosporine. Those cultured from Stage 11a exhibited similar lesions to those seen in the initial experiment but at somewhat higher concentrations of staurosporine. Embryos cultured from Stage 10b showed a similar pattern of lesions as seen at Stage 11a, except that higher concentrations of staurosporine were required to cause mesencephalic vesicles and secondary somites formation. Embryos cultured from Stage 11b showed similar effects to those cultured from younger stages except that maximum incidences of situs inversus were much lower. Those cultured from Stage 11c showed similar dose-response to those cultured from Stage 11b except that the incidence of secondary somites formation was much higher. In addition, in approximately 40% (n = 25) of embryos treated with greater than 1.0 microM of staurosporine, the growing end of the allantois did not reach the chorion and remained unattached in the exocoelomic cavity.(ABSTRACT TRUNCATED AT 400 WORDS)

Growth parameters in mid-trimester fetal Turner syndrome

Growth failure is a consistent finding at birth in infants with Turner syndrome. However, the time of onset and pattern of growth deficiency is unknown. To determine the presence of growth failure in the second trimester in fetuses with Turner syndrome, second trimester fetuses that had a complete autopsy at the Central Laboratory for Human Embryology at the University of Washington were studied. A control group of specimens with normal findings was selected and compared with a study group with Turner syndrome documented by karyotype. Footlength and crown-rump length were measured directly with a ruler and femur, tibia, fibula, humerus, ulna and radius were measured from X-rays. Crown-rump length was used as the indicator of gestational age. Statistical comparisons between the normal and study groups were performed by multiple regression. Long bone measurements were made on 105 normal and 13 Turner fetuses. Footlength and the six long bones showed evidence of statistically significant growth failure. Fetuses with 45,X/46,XX mosaic Turner syndrome may demonstrate a lesser degree of growth retardation, at least for footlength, than those with a 45,X karyotype, but small numbers limited the analysis. We conclude that the growth failure consistently demonstrated in newborns with Turner syndrome begins early in gestation and is well-established by mid-pregnancy.

Volume and glucose concentration of rat amniotic fluid: effects on embryo nutrition and axis rotation

In order to pursue our previous studies of the changes in neural tube microvilli produced by glucose, we developed a micro method of measuring glucose concentration in the very small volumes of amniotic fluid during neurulation. The volume of amniotic fluid was found to increase nearly 10-fold during major neurulation (day 10 to day 11 in the rat). This increase in volume and our repeated observations that physical removal of the restraining amnion initiates embryonic rotation leads us to propose that the growth of the amniotic cavity is essential for conversion from the ventral- to dorsi-flexion of the embryonic axis. Amniotic fluid volume continues to increase until day 18 but dropped by day 20. A method for glucose determination was developed using the color reaction on glucose oxidase indicator paper. The intensity of the color was analyzed with a color scanner. Amniotic glucose was 27.1 +/- 1.6 mg/dl on day 10 and continued in this range with some fluctuation until day 20 when it decreased. We isolated days 10, 11, and 16 embryonic sites from their decidua and incubated them at 0 degrees C and 38 degrees C while measuring glucose concentration. The glucose concentration did not show significant decrease at 0 degrees C on day 10 or 11 or on day 16 at 38 degrees C. At 38 degrees C the day 10 embryo amniotic fluid glucose disappeared after 22 minutes and the day 11 amniotic fluid glucose was gone in 34 minutes. These depletion times were statistically different. The magnitude of glucose depletion on day 10 was shown by calculation to be approximately 323 mumoles/gm protein per hour which is a substantial portion of the glucose utilized by the embryo as determined in previous experiments (731 mumoles/gm protein per hour). This model may serve as a way to study glucose utilization by embryos after their exposure to various teratogens.

Reversed circulation in acardiac fetuses is associated with anatomic inversions in the aortic wall

Blood vessel anatomy is probably related to hemodynamic factors which change during development. This principle has been postulated as the basis for differences in the numbers of elastic lamellae in the tunica media of the proximal and distal human aorta. Recent studies of human fetuses at varying stages confirmed that the number of elastin lamellae in the aortic wall varied along its length (spatially) and with age (temporally). These findings suggest that hemodynamic influences during prenatal development induce structural changes in the aortic wall. Acardiac fetuses provide a model for studying the effects of hemodynamic changes on the structure of elastic arteries because blood flow through the aorta in such fetuses is reversed and greatly reduced. Also, analysis of the vascular structure of acardiac fetuses would further define the characteristic features of this congenital disorder. In the present study, we have examined the gross and histological anatomy of the aorta from seven acardiac fetuses. In each case, the microscopic architecture of the aorta was deranged and the normal proximal-distal differences in arterial caliber and number of elastin lamellae were reversed. In the proximal aorta, medial lamellar units were thin, fragmented, and irregular. In some segments, only traces of medial lamellar units existed. We believe that these anatomic abnormalities represent degenerative or dysplastic responses to reversed flow and pressure gradients in the aorta. These findings are consistent with the hypothesis that aortic wall structure is influenced by hemodynamic factors during development.

Glucose causes lengthening of the microvilli of the neural plate of the rat embryo and produces a helical pattern on their surface

Prominent microvilli have been observed on the surface of neural plates in the embryos of many species. Since glucose is the main source of energy for embryos before neural tube closure and the onset of vascular circulation, it was of interest to study the relationship between these microvilli and glucose utilization in the neural plate. By applying microdrops of amniotic fluid to chemstrips, which colorimetrically measure glucose by glucose oxidase reaction, we determined that day 10 rat amniotic fluid glucose level was 31.6 +/- 1.6 mg/dl. On day 10 and within about 20 min from removal of the decidual sites, no glucose was found in the amniotic fluid. By use of a scanning electron microscope, the microvilli of the day 10 neural plate were found to have a 10-fold increase in length during a 40-min exposure to Hanks' solution at 21-23 degrees C. Similarly exposed embryos in Hanks' without glucose did not have microvillus elongation. However, under whole embryo culture conditions at 38 degrees C no extension of the microvilli was found. In the closed neural tube of the day 10 embryo, the microvilli were stubby and did not elongate with glucose exposure. Similarly, day 11 and 14 embryos had short microvilli which did not elongate with direct exposure to glucose at 21-23 degrees C. The short microvilli on the surface of the closed neural tube on day 11, 14, and 16 were associated with low glucose concentrations in the neural tube fluids. By use of a field emission scanning electron microscope, the surfaces of the microvilli in the extended position were seen to be covered by a right-handed helical array of globular objects the size of large molecules. The findings support the hypothesis that microvillar length may modulate glucose uptake. Shortening is associated with low concentrations of glucose in closed neural tubes, and lengthening occurs at glucose exposures of 100 mg/dl.

Intestinal ganglioneuroblastoma in a 22-week fetus

The clinical history and autopsy findings of a 22-week fetus with intestinal ganglioneuroblastoma, cardiac anomalies, omphalocele, and ileal atresia are presented. Ganglioneuroblastoma was confined to the large intestine and was not suspected prenatally despite ultrasonographic examination. Although enteric ganglia share neural crest lineage with other sites of congenital neuroblastoma, this is the first report of a primary intestinal ganglioneuroblastoma in a fetus or child. Various hypotheses are discussed to explain the coexistence of cardiac malformation and congenital neuroblastoma in this fetus and other cases in the literature. It is hypothesized that other malformations evident in this fetus were caused by the tumor, possibly as teratogenic effects of neuroblastoma-derived catecholamines during embryogenesis.

Twin fetuses with abnormalities that overlap with three midline malformation complexes

Twin fetuses aborted at an estimated gestational age of 145 days were concordant for oral, facial, skeletal, and central nervous system malformations. The twins were discordant for other anomalies including cardiac defects, polydactyly, and malrotated short bowel. The combination of malformations observed overlaps with that of the oral-facial-digital syndrome, hydrolethalus syndrome, and Pallister-Hall syndrome. The problem of phenotypic overlap between these syndromes is discussed.

Asymmetric development of mitochondrial activity in rat embryos as a determinant of the defect patterns induced by exposure to hypoxia, hyperoxia, and redox cyclers in vitro

Previous study has shown that midorganogenesis-stage rat embryos exposed to strong redox cyclers under moderate hypoxia in vitro develop severe necrotic defects on the right side. Similar effects can be produced by exposure to severe hypoxia alone. Studies presented here indicate that exposure to severe but survivable hyperoxia induces comparable necrotic degeneration on the left sides of all embryos. We hypothesize that the basis of these axially asymmetric defects is relatively precocious mitochondrial maturity on the left side of the embryo. In order to investigate this hypothesis, we compared mitochondrial oxygen utilization (NADH oxidase activities) on either side of rat embryos between days 11 and 14 of gestation. Activities were consistently higher on the left side during this period and significantly higher on day 11. We also found that the asymmetric embryotoxicity induced by niridazole, a strong redox cycler, could be attenuated by prior culture under hyperoxic conditions. We propose that mitochondrial immaturity on the right results in inadequate energy generation under hypoxic conditions, either directly or as a result of redox cycling. On the other hand, necrosis associated with hyperoxic conditions results from "leakage" of superoxide from functionally mature mitochondria on the left side.

Brain hemorrhages in cocaine-exposed human fetuses

Autopsies of 4 fetuses exposed to maternal cocaine are reported. Brain examination revealed hemorrhages in 3 of the fetuses involving the germinal matrix. The hemorrhages resembled subependymal germinal matrix hemorrhages seen as postnatal complications in premature infants with idiopathic respiratory distress syndrome. One of the placentas had sonographic evidence of abruption which could not be confirmed pathologically. The findings are discussed in light of reports of neurobehavioral deficits and other congenital anomalies in children and animals exposed to cocaine in utero. Speculations about the pathophysiologic events leading to these findings are made.

Sirenomelia associated with a "vanishing twin"

A case is presented of twin gestation in which one gestational sac was completely resorbed and the remaining twin was subsequently found to be sirenomelic. First-trimester prenatal ultrasound examination demonstrated a second gestational sac that disappeared 2 weeks later. The sonographic features that led to the diagnosis of sirenomelia in the remaining fetus included severe renal dysgenesis, persistently apposed lower extremities, and absence of fibulae. Postmortem examination, including angiographic studies of the fetus, revealed caudal dysgenesis and a single umbilical artery that arose from the abdominal aorta. Sirenomelia occurs more frequently in twin gestations than in singletons. This case suggests that the association between twinning and sirenomelia may be greater than is currently recognized. Two hypotheses are given to explain this association.

Fetal coronary thrombosis as a cause of single ventricular heart

A fetus weighing 947 g was autopsied after prenatal echocardiographic diagnosis of a single ventricular heart. At autopsy a single ventricle was present with a pear-shaped scar in the area presumed to represent the right ventricle. A small stoma from the single ventricle connected to the scar and the pulmonary outflow was obstructed. The left coronary artery was occluded and on histologic examination recanalization was seen. A chromatographic peak which closely eluted with the cocaine metabolite, benzoylecognine, was identified in fetal urine. We postulate that coronary spasm following possible cocaine exposure could have produced an infarct which destroyed the right ventricle. It is possible that this fetal pathology may be one mechanism that leads to single ventricle hearts.

Growth failure in second-trimester fetuses with trisomy 21

Growth failure in the Down syndrome is common postnatally, but is thought to be less consistent in fetuses and newborns. We describe the growth of individual organs in 53 second-trimester abortuses with trisomy 21 and compare the organ weights to organ weights from 432 spontaneously aborted, but otherwise normal control specimens. Using multiple regression analysis, we found body weight to be the most significant predictor of all organ weights in normal fetuses; therefore, this variable was used to generate the regression lines to which the organ weights of trisomic specimens were compared. All trisomic fetal organs were found to be small, with an abnormal karyotype being a significant predictor of low organ weight. However, the effect on individual organs was variable, with some organs differing only minimally from the controls. Placental weights were not affected by fetal trisomy. This study demonstrates the presence of well-established, although variably severe, growth retardation in second-trimester fetuses with Down syndrome.

Size of the fetal adrenal in bilateral renal agenesis

Bilateral renal agenesis is a fetal malformation incompatible with extrauterine life. Accurate prenatal diagnosis is essential for patient counseling. False-negative diagnoses have been reported and were attributed to the sonographic misidentification of apparently hypertrophied fetal adrenal glands as fetal kidneys. To study the relationship between renal agenesis and adrenal size, we reviewed autopsy records from 11 affected fetuses that had undergone careful autopsy and organ weight determination in our laboratory. Anomalies of distant structures were present in five affected fetuses. A sonographic diagnosis of adrenal hypertrophy had been made in two cases. In four of 11 fetuses, the glands had taken on a flattened discoid appearance. The autopsy records of 240 normal fetuses were similarly reviewed, and regression lines were generated for adrenal weight based on foot length and crown-rump length. The adrenal weights from affected fetuses were well within normal limits when compared with these normal regression lines and with organ weight standards from the literature. We conclude that adrenal hypertrophy is not a common finding in this syndrome and that the reported false-negative diagnoses are more likely attributable to a change in adrenal shape rather than a true increase in adrenal mass.

Brain growth in Down syndrome subjects 15 to 22 weeks of gestational age and birth to 60 months

We have found similarities of skull shape, brain growth and brain maturation in 17 DS and 10 non-DS (control) fetuses, ages 15-22 weeks of gestational age (Group A), and differences in 101 DS and 80 non-DS cases, from birth to 60 months (Group B). Postnatally, the gross neuropathological differences between DS and control brains are more distinct after 3-5 months of age. The anterior posterior diameter fronto-occipital length of the brain hemispheres is shortened and that is secondary to reduction of frontal lobe growth. Also flattening of occipital poles, narrowing of the superior temporal gyruses and generalized retardation of brain growth were common findings. Standard morphometric methods indicate changes from birth [Wisniewski et al. 1984, 1986, 1990]. The cerebral cortex of the DS cases had a 20-50% reduction of neurons since birth, mainly in the granular layers [Wisniewski et al. 1984, 1986, 1990]. Changes in brain weight with age were greater in the non-DS than in the DS cases, and greater in males than in females. CHD and GI malformations were associated with less brain weight in both DS and non-DS cases. We suggest that the prenatal retardation of neurogenesis begins after 22 weeks' gestational age. The postnatal retardation of brain growth is secondary to pre- and postnatal abnormalities in synaptogenesis.

Growth of linear parameters in trisomy 18 fetuses

Linear growth in fetuses with trisomy 18 has not been systematically described. We studied the relationship between long-bone, crown-rump, and foot length and gestational age in 17 postmortem fetal specimens with this syndrome. Long-bone and crown-rump lengths were compared with normal regression lines and foot length was compared with gestational age determined on the basis of menstrual dates. Correlation between foot length and menstrual dates was weak in trisomy 18. Gestational age predicted by crown-rump length was significantly lower than gestational age by menstrual dates. All long bones were significantly shortened and fell below normal regression lines for gestational age. The fetal femur/foot length ratio was reduced. Thus no endogenous measure of gestational age appears to exist in this aneuploidy, forcing reliance on menstrual dates. The observed pattern of growth alterations will likely preclude the development of a gestational age-dependent biometric screen for the prenatal detection of this syndrome.

Potential human teratogenicity of frequently prescribed drugs

Published data regarding the human teratogenic potential of 157 drug components that are frequently prescribed to outpatients in the United States were evaluated according to a protocol developed for TERIS, an automated clinical teratology resource. This protocol stipulates that a bibliographic search be performed on each agent, a brief narrative summary of the available teratologic information prepared, and a risk rating assigned. The ratings are determined by consensus of five clinical teratologists, who independently assess the magnitude of teratogenic risk associated with each agent under usual therapeutic conditions as "none," "minimal," "small," "moderate," "high," and "undetermined." Forty-nine percent of the components of these frequently prescribed drugs had insufficient published information available to assess the risk of human teratogenicity. Of the agents that could be rated, the teratogenic risk in usual therapeutic doses was considered to be minimal or less in 92.5%. Many of these agents have also been assigned Pregnancy Categories by the United States Food and Drug Administration (FDA) according to a system designed to provide therapeutic guidance. There was no more agreement than that expected by chance between TERIS ratings and the FDA Pregnancy Categories for 83 agents that were classified according to both systems. We believe that the FDA Pregnancy Categories should not be used to provide counseling regarding the risk of teratogenic effects to women who have taken medication during pregnancy. Such counseling should be based on a more comprehensive evaluation of the teratologic literature and clinical situation, but need not involve consideration of the therapeutic benefit of the agent.

Umbilical cord growth in human and rat fetuses: evidence against the "stretch hypothesis"

A total of 103 human fetuses between the 7th and 30th week of gestation were obtained from induced abortion (40 fetuses were normal and 63 were abnormal), and the umbilical cord length (UCL) was measured. The UCL increased almost linearly with gestational age among normal fetuses, contrary to the commonly held tenet that the UCL increases exponentially during the second trimester. When UCLs from the 63 abnormal fetuses were compared with those of normal fetuses, 15 fetuses were found to have short UCL and 10 fetuses to have long UCL. Among the 15 fetuses with short UCL, 6 had early amnion rupture syndrome. An unexpected finding among the 10 with long UCL was that 8 of them had oligohydramnios. It has been suggested that the UCL increases in response to tensile forces placed upon it ("stretch hypothesis"); however, our results are inconsistent with this hypothesis because fetuses with oligohydramnios should be less active and their umbilical cords be subject to less stress. In a separate experiment, we studied the normal development of the UCL in rat fetuses and observed an almost linear increase during the whole gestation similar to that seen in humans. This finding is also inconsistent with the "stretch hypothesis" because amniotic fluid volume decreases significantly from day 19 of gestation to term in rats.

Trisomy 13 in the fetus

A significant number of fetuses with trisomy 13 are spontaneously or voluntarily lost before birth; however, very few such fetuses have been systemically autopsied. In the present study, ten trisomy 13 fetuses of 130-305 mm in crown-rump length, estimated gestational age from 108 days to 239 days, were examined following either karyotype or ultrasonographic diagnosis and voluntary termination. Mean maternal age was 35.1 years. The spectrum of anatomical features was similar to that observed in neonates or older infants with trisomy 13, namely, holoprosencephaly, cyclopia, microphthalmia, cleft palate and lip, cardiac defect, polydactyly, and cystic kidney. Kidney weights were significantly increased above normal in eight of nine fetuses. Histologically, the cortex of these kidneys showed increased mitotic activity and blastemic appearance, which extended deep into the medullary areas. The weights and histology of other organs were normal except for slight increases in spleen weight.

Nitrous oxide alters body laterality in rats

Seventy timed-pregnant Sprague-Dawley rats were exposed to either air (control) or 75% nitrous oxide (N2O) for 24 hours on day 8 of gestation. Four rats from each group were killed on days 11-16, 18, and 20, and laparotomy was performed. The viability of the embryos/fetuses was determined, as was the side of tail flexion on days 11 and 12, the direction from which the umbilical artery emerged from the body on days 13 and 14, the side of the body facing the placenta on days 15 and 16, and the side to which the aortic arch curved on days 18 and 20. Mean mortality rate in the control group was 8.9 +/- 6.1% (+/- S.D.), and there were no control embryos/fetuses with altered laterality except the 9% that faced left on day 16. In contrast, N2O treatment on day 8 of gestation resulted in significantly increased mortality (40.8 +/- 3.3%) beginning on day 14 of gestation and increased incidence of altered laterality overall (31.3%) and at all stages of development. The mechanisms underlying these events remain to be defined, as do the implications of our findings for pregnant surgical patients and occupationally exposed workers.

Human achondroplasia: defective mitochondrial oxidative energy metabolism may produce the pathophysiology

A summary is presented of previous studies by other investigators of human achondroplasia and dyschondroplastic animal models. In addition, studies previously reported from our laboratories are discussed, and they demonstrate that defective oxidative energy metabolism is present in mitochondrial preparations from achondroplastic human subjects and rabbits (ac/ac) with chondrodystrophy. The results of the studies support the hypothesis discussed fully in the manuscript that a partial defect in mitochondrial oxidative metabolism in achondroplastic subjects is expressed specifically in the growth plates of the long bones because this tissue has the lowest oxygen tension of any bodily organ undergoing active proliferation, thus leading to the achondroplastic phenotype in humans and the ac/ac rabbit. In the ac/ac rabbit phosphorylation at the cytochrome c oxidase region (site III) of the terminal respiratory system was shown to be absent in mitochondrial preparations from the livers of newborn ac/ac rabbits. Normal-appearing littermates did not exhibit the defect. Studies of mitochondrial preparations from human skin fibroblasts (grown in tissue culture) from normal human subjects and subjects with homozygous achondroplasia demonstrated that concentrations of cytochrome a3 were decreased approximately 80% in preparations from homozygous achondroplastic cells. Levels of cytochrome a3 in heterozygous achondroplastic cells were intermediate between the levels in normal cells and homozygous achondroplastic cells demonstrating the effects of gene dosage. Determination of total heme a (as the pyridine hemochromogen) in the normal and achondroplastic preparations from human subjects showed that the observed decrease in concentration of cytochrome a3 in the achondroplastic preparations was due to an absence of cytochrome a3 and not to a change in its absorbancy (extinction coefficient).

Congenital heart disease among spontaneous abortuses and stillborn fetuses: prevalence and associations

The prevalence, range, and associations of congenital heart disease (CHD) were studied among 400 spontaneous abortuses between 9 and 40 weeks' gestation. Fifty-two (13.0%) cases of CHD were detected. To minimize selection bias the specimens were grouped by external appearance and the prevalence expressed accordingly. CHD was detected in 21 (7.3%) of 289 externally normal and 31 (27.9%) of 111 externally abnormal fetuses. Ventricular septal defect (VSD) was the most frequent CHD found in isolation as well as in combination with extracardiac malformations. Seventy-five percent of isolated CHD was VSD. Forty (69.2%) of the 52 cases of CHD were associated with extracardiac malformations. Chromosomal syndromes were responsible for a minimum of 19.2% of the cases and suspected in up to 36.5%. The most frequent associations involved the musculoskeletal system, central nervous system, abdominal wall, and kidneys. In contrast, studies of liveborn infants have reported 70% of CHD as isolated defects, including many CHD infrequently seen among spontaneous abortuses. This suggests that fetuses with isolated CHD often survive to term, and CHD does not significantly affect the survival of the fetus in utero. Ventricular septum formation may be particularly susceptible to hemodynamic changes and may be indicative of an underlying pathologic condition that also leads to a spontaneous abortion.

Long-bone growth in fetuses with Down syndrome

Short stature is a well-recognized component of Down syndrome. The femur lengths of affected fetuses have been observed to be shorter than normal, with a ratio of actual to expected femur length of less than 0.91 indicating a high risk of trisomy. To further evaluate this finding we have determined the relationship between limb lengths and gestational age in 37 postmortem fetal specimens with trisomy 21. Control values were obtained from 174 normal fetuses. Measurements of the femur, tibia, fibula, humerus, radius, and ulna were made from roentgenograms or by direct measurement of the bone. Most measurements for each bone of the affected fetuses fell below the normal regression line for that bone, but only 3/37 femurs, 4/32 tibias, 5/32 fibulas, 9/32 humeri, 10/32 radii, and 7/32 ulnas fell more than 2 SDs below the mean. The ratios of actual to expected femur lengths were computed and six fetuses with Down syndrome (16.2%) had ratios less than 0.91. The bones of the extremities of fetuses with trisomy 21 are shorter than normal, but the differences are relatively small. The ratio of actual/expected femur lengths was a less efficient predictor of Down syndrome than were either maternal age or maternal serum alpha-fetoprotein tests. The upper extremity bones were shorter than normal more often than were the bones of the lower extremity, and this finding should be explored further in a prospective study.

Congenital defect rates among spontaneous abortuses: twenty years of monitoring

A 20-year study of 1,124 spontaneously aborted embryos and fetuses found 214 (19.0%) to have a localized defect or identifiable syndrome. No clear trend of change over time was noted. The rate is compared with other studies of spontaneously aborted specimens and is approximately ten times higher than in newborns. Forty (3.6%) had neural tube defects and 30 (2.7%) had a clinically recognized chromosomal phenotype. Fifteen had Turner's phenotype, four trisomy 18, and 11 triploidy. Amniotic bands occurred in eight. Two had bilateral renal agenesis. Thirty had some form of facial cleft.

Unexplained second trimester oligohydramnios: a clinical-pathologic study

The importance of oligohydramnios in the absence of fetal malformations has been recognized because of the associated high risk for adverse pregnancy outcome. Pathologic dissections were performed on four fresh fetuses whose mothers were identified by ultrasound as having oligohydramnios and had no clinical history or physical evidence of vaginal leakage of amniotic fluid. The fetuses were all normal except for hypoplasia of the lungs and varying degrees of Potter's facies. The kidneys were histologically normal but had increased weight. The more widespread use of ultrasound may have allowed us to detect an earlier stage of a previously present type of pregnancy failure.

Placental weights of normal and aneuploid early human fetuses

Placental and body weights were plotted for 252 normal human fetuses less than 600 gm and mean regressions and 95% prediction intervals were calculated. Placentas from 62 aneuploid fetuses were compared to these standards. Placenta to body weight ratios from 34 trisomy-21 fetuses were not reduced but those from 15 trisomy-18 fetuses were generally decreased. One of 5 trisomy-13 ratios was below the prediction interval. Among 7 triploid fetuses the ratios were above the normal interval in 3 and below normal in 4. Three of the triploids that were below were associated with a karyotype of 69,XXX and did not have hydatidiform degeneration. All 4 placentas with hydatidiform changes were abnormally large. All of the 7 triploids had 3-4 syndactyly and 3 had hydrocephalus.

Rat whole embryo culture: an in vitro model for testing nitrous oxide teratogenicity

The teratogenic effects of nitrous oxide (N2O) on postimplantation rat embryos were studied using a whole embryo culture system to separate the direct effects of N2O from those that are maternally mediated. A total of 100, 10-day-old rat embryos were cultured in either a control atmosphere (75% N2, 20% O2, and 5% CO2), or a N2O atmosphere (75% N2O, 20% O2, and 5% CO2). After 22 h of culture embryos were examined microscopically, and protein and DNA contents were determined. DNA content was significantly lower in the embryos exposed to N2O compared with the controls. Additionally, three malformed embryos and four embryos with left-sided tails were observed in the N2O group, whereas no abnormalities were observed in the control group. There were no differences in crown-rump length, somite numbers, limb bud index, and protein content between the two groups of embryos. The positive findings in this study indicate that whole embryo culture is useful for studying the mechanisms of N2O teratogenicity.

Fetal rhombencephalon: normal US findings

Using ultrasound (US), the authors examined 25 embryos that were 8-10 menstrual weeks old for gestational age and the presence of a small cystic structure (3-4 mm) in the posterior aspect of the cranium. This structure was seen in all embryos. The US images of an in vitro embryo at 8 weeks menstrual age were also evaluated for anatomic correlation. Analysis of these US images determined that the cystic structure was the open rhombencephalon or hindbrain. Follow-up US studies or postpartum clinical examinations of the 25 in utero embryos demonstrated no abnormal posterior cranial cystic structures or neurologic deficits. This first-trimester structure should be considered a normal finding, since it develops into the normally proportioned fourth ventricle after the 11th menstrual week.

Organ weight standards for human fetuses

Five hundred fifty-eight fresh human embryos and fetuses were obtained from the universities of Washington and Michigan following spontaneous loss, elective termination, or neonatal death within 2 days of delivery. The body weights ranged from 1.5 to 1500 g. Each of these autopsied specimens was morphologically normal. Specimens from diabetic or hypertensive mothers were not included. Correlations between fetal body weight and weights of adrenal, brain, kidney, liver, lung, spleen, and thymus were established. For analysis, regression curves were calculated as quadratic equations of best fit by the weighted least squares. The relation of the weights of brain, heart, and liver to body weight appeared linear. The ratios of thymus, spleen, and kidney to body weight were nonlinear and gradually increased. The ratios of lung and adrenal weights to body weight were also nonlinear and gradually decreased. Ninety-five percent prediction intervals were generated for each of the eight organs using a computerized statistical package. The results compare closely with smaller studies in the literature.