Should the definition of preeclampsia include a rise in diastolic blood pressure of >/=15 mm Hg to a level <90 mm Hg in association with proteinuria?

OBJECTIVE

This study was undertaken to compare baseline characteristics and pregnancy outcomes between normotensive women who did and those who did not have a rise in diastolic blood pressure of >/=15 mm Hg in association with proteinuria.

STUDY DESIGN

We studied 4302 healthy nulliparous women from the Calcium for Preeclampsia Prevention trial who were delivered at >/=20 weeks' gestation. We selected as the study group normotensive women who developed proteinuria within 7 days of a rise in diastolic blood pressure of >/=15 mm Hg with respect to baseline on 2 occasions 4 to 168 hours apart. Baseline blood pressure was the mean of measurements at 2 clinic visits before 22 weeks' gestation. Other normotensive women used for comparison were those who did not develop gestational hypertension or a rise in diastolic blood pressure of >/=15 mm Hg in association with proteinuria.

RESULTS

Except for greater weight (P <.001), body mass index (P <.001), and systolic blood pressure (P =.05) the baseline characteristics of the 82 women with a rise in diastolic blood pressure of >/=15 mm Hg in association with proteinuria did not differ significantly from those of the other normotensive women. Although they had a greater rate of weight gain (P <.005), larger babies (P =.06), and a 2-fold increase in abdominal delivery (P <.001), there was little other evidence of adverse pregnancy outcomes among these women.

CONCLUSION

During normotensive pregnancy a rise in diastolic blood pressure of >/=15 mm Hg in association with proteinuria appears to be benign and is not a useful clinical construct.

Pregnancy outcomes in healthy nulliparas who developed hypertension. Calcium for Preeclampsia Prevention Study Group

OBJECTIVE

To determine maternal and perinatal outcomes in nulliparas with pregnancy-associated hypertension or preeclampsia.

METHODS

We conducted (and reported elsewhere) a randomized, double-masked, placebo-controlled trial calcium supplementation of 4589 healthy nulliparas assigned at 13-21 weeks' gestation. This well-defined and characterized data set provided an opportunity to detail more precisely adverse maternal, fetal, and newborn outcomes in women who developed hypertension among a prospective series of healthy nulliparas.

RESULTS

Of 4302 women observed to or beyond 20 weeks' gestation, 1073 (24.9%) developed mild or severe pregnancy-associated hypertension or preeclampsia. One hundred sixteen women of the 1073 with hypertension (10.8%) and 336 of the 3229 without hypertension (10.4%) were delivered before 37 weeks' gestation. Fetal and neonatal mortality were similar in those groups; however, selected maternal and newborn morbidities were significantly greater in women with hypertension. Significantly increased maternal morbidities included increased cesarean deliveries, abruptio placentae, and acute renal dysfunction; and significantly increased perinatal morbidities included respiratory distress syndrome, ventilatory support, and fetal growth restriction. Adverse outcomes were highest in women with severe pregnancy-associated hypertension or preeclampsia.

CONCLUSION

Hypertension, especially severe hypertension, was associated with an appreciable increase in important maternal and perinatal morbidity but not perinatal mortality.

The puzzling association between smoking and hypertension during pregnancy

OBJECTIVE

The object of this study was to examine the association between maternal smoking and hypertension during pregnancy.

STUDY DESIGN

We used data from the Collaborative Perinatal Project, a large prospective cohort study that collected detailed information on blood pressure, proteinuria, smoking, and placental morphologic and histologic characteristics. A total of 9651 healthy primigravid women without chronic hypertension who had been enrolled in the study at the first or second trimester (average 18 weeks' gestation) and had had >/=3 prenatal visits were included. Gestational hypertension was defined as diastolic blood pressure >/=90 mm Hg on 2 occasions from 24 weeks' gestation to 2 weeks post partum. Preeclampsia was defined as gestational hypertension plus >/=2 urine samples containing >/=1+ protein according to dipstick measurement during the same gestational period.

RESULTS

After we controlled for prepregnancy body mass, age, socioeconomic status, and race, both past smoking and smoking during pregnancy were associated in a dose-response pattern with reduced risks of gestational hypertension and preeclampsia. For women who smoked >/=10 cigarettes/d the relative risks with respect to women who had never smoked were 0.6 (95% confidence interval, 0.4-0.9) for gestational hypertension and 0.5 (95% confidence interval, 0.4-0.7) for preeclampsia. This protective effect was observed both for mild and severe gestational hypertension and for preeclampsia. The more and the longer a woman had smoked previously, the lower was her risk of development of hypertension during pregnancy. This association could not be explained by confounding factors, by changes in placental morphologic or histopathologic characteristics, by maternal net weight gain, or by elevated liver enzyme bioactivity.

CONCLUSION

Smoking is associated with a reduced risk of hypertension during pregnancy. The protective effect appears to continue even after cessation of smoking. Further basic research on this issue is warranted.

Maternal serum paraxanthine, a caffeine metabolite, and the risk of spontaneous abortion

BACKGROUND

Whether the consumption of caffeine during pregnancy increases the risk of spontaneous abortion is controversial. Prior studies have determined caffeine consumption by questionnaire. We used a biologic marker, such as serum paraxanthine, a metabolite of caffeine, to measure the dose of caffeine.

METHODS

In a nested case-control study, we measured serum paraxanthine in 591 women who had spontaneous abortions at less than 140 days' gestation and in 2558 matched women from the same clinic who gave birth to live infants at 28 weeks' gestation or later and who had serum drawn on the same day of gestation as the women who had abortions. The women were enrolled in the Collaborative Perinatal Project during the period from 1959 to 1966, and serum paraxanthine was measured over 30 years later.

RESULTS

A total of 487 women who had spontaneous abortions (82 percent) and 2087 controls (82 percent) had quantifiable serum paraxanthine concentrations. However, the mean serum paraxanthine concentration was higher in the women who had spontaneous abortions than in the controls (752 vs. 583 ng per milliliter, P<0.001). The odds ratio for spontaneous abortion was not significantly elevated in the women who had serum paraxanthine concentrations of 1845 ng per milliliter or lower, corresponding to the 95th percentile of the matched women. However, the adjusted odds ratio for spontaneous abortion among women with serum paraxanthine concentrations higher than 1845 ng per milliliter, as compared with women who had concentrations below 50 ng per milliliter, was 1.9 (95 percent confidence interval, 1.2 to 2.8).

CONCLUSIONS

Only extremely high serum paraxanthine concentrations are associated with spontaneous abortion. This suggests that moderate consumption of caffeine is unlikely to increase the risk of spontaneous abortion.

Maternal calcium supplementation and fetal bone mineralization

OBJECTIVE

To determine the effect of maternal calcium supplementation during pregnancy on fetal bone mineralization.

METHODS

Healthy mothers with early ultrasound confirmation of dates and singleton pregnancies were enrolled in a double-masked study and randomized before 22 weeks' gestation to 2 g/day of elemental calcium or placebo until delivery. Maternal dietary intake at randomization and at 32-33 weeks' gestation was recorded with 24-hour dietary recalls. Dual-energy x-ray absorptiometry measurements of the whole body and lumbar spine of the neonates were performed before hospital discharge.

RESULTS

The infants of 256 women (128 per group) had dual-energy x-ray absorptiometry measurements during the first week of life. There were no significant differences between treatment groups in gestational age, birth weight, or length of the infants, or in the total-body or lumbar spine bone mineral content. However, when bone mineral content was analyzed by treatment group within quintiles of maternal dietary calcium intake, total body bone mineral content (mean +/- standard error of the mean) was significantly greater in infants born to calcium-supplemented mothers (64.1+/-3.2 versus 55.7+/-2.7 g in the placebo group) in the lowest quintile of dietary calcium intake (less than 600 mg/day). The effect of calcium supplementation remained significant after adjustment for maternal age and maternal body mass index and after normalization for skeletal area and body length of the infant.

CONCLUSION

Maternal calcium supplementation of up to 2 g/day during the second and third trimesters can increase fetal bone mineralization in women with low dietary calcium intake. However, calcium supplementation in pregnant women with adequate dietary calcium intake is unlikely to result in major improvement in fetal bone mineralization.

Resolving discrepancies between a meta-analysis and a subsequent large controlled trial

CONTEXT

A recent meta-analysis found calcium supplementation to be highly effective in preventing preeclampsia but a large National Institutes of Health trial (Calcium for Preeclampsia Prevention [CPEP]) found no risk reduction due to calcium in healthy nulliparous women.

OBJECTIVES

To resolve discrepancies between the results of the meta-analysis and the CPEP trial and to assess the role of effect heterogeneity in the discrepancies.

DATA SOURCES

Literature search of English-language articles published prior to July 10, 1997, the date of publication of the CPEP trial, using MEDLINE and by a manual search of bibliographies of published articles.

STUDY SELECTION

Trials were included if they reported data on preeclampsia and calcium supplementation. Fourteen trials were systematically evaluated for differences in study design and patient populations. One trial was excluded because its results were reported after publication of the major CPEP results.

DATA EXTRACTION

The sample size and number of subjects who developed preeclampsia in the calcium supplementation group vs a control group were recorded and analyzed on an intent-to-treat basis. Each author independently extracted the data.

DATA SYNTHESIS

Substantial heterogeneity existed across trials (P = .001). After stratifying studies by the presence of a placebo-controlled group and by high-risk and low-risk populations, the conclusions of the meta-analysis of placebo-controlled trials enrolling a low-risk population (relative risk, 0.79; 99% confidence interval, 0.44-1.42; P = .30) were compatible with the conclusions of the CPEP trial that calcium supplementation does not prevent preeclampsia in healthy nulliparous women. In contrast, the data implied a strong beneficial calcium effect (relative risk, 0.19; 99% confidence interval, 0.08-0.46; P = .001) in healthy high-risk subject populations. However, only 225 women were analyzed and because of inconsistent data, these results remain equivocal.

CONCLUSIONS

Further studies are needed to establish the efficacy of calcium for preeclampsia prevention in healthy high-risk populations. A single summary measure does not adequately describe the findings of a meta-analysis when the observed effects in individual studies differ substantially. In such settings the primary focus should be to identify and incorporate pertinent covariates that reduce heterogeneity and allow for optimum treatment strategies.

Prostacyclin and thromboxane changes predating clinical onset of preeclampsia: a multicenter prospective study

CONTEXT

An imbalance in vasodilating (prostacyclin [PGI2]) and vasoconstricting (thromboxane A2 [TxA2]) eicosanoids may be important in preeclampsia, but prospective data from large studies needed to resolve this issue are lacking. Because most trials using aspirin to reduce TxA2 production have failed to prevent preeclampsia, it is critical to determine whether eicosanoid changes occur before the onset of clinical disease or are secondary to clinical manifestations of preeclampsia.

OBJECTIVE

To determine whether PGI2 or TxA2 changes occur before onset of clinical signs of preeclampsia.

DESIGN, SETTING, AND PARTICIPANTS

Multicenter prospective study from 1992 to 1995 of subjects from the placebo arm of the Calcium for Preeclampsia Prevention Trial. Women who developed preeclampsia (n = 134) were compared with matched normotensive control women (n = 139).

MAIN OUTCOME MEASURES

Excretion of urinary metabolites of PGI2 (PGI-M) and TxA2 (Tx-M) as measured from timed urine collections obtained prospectively before 22 weeks', between 26 and 29 weeks', and at 36 weeks' gestation.

RESULTS

Women who developed preeclampsia had significantly lower PGI-M levels throughout pregnancy, even at 13 to 16 weeks' gestation (long before the onset of clinical disease); their gestational age-adjusted levels were 17% lower than those of controls (95% confidence interval [CI], 6%-27%; P=.005). The Tx-M levels of preeclamptic women were not significantly higher overall (9% higher than those of controls; 95% CI, -3% to 23%; P=.14). The ratio of Tx-M to PGI-M, used to express relative vasoconstricting vs vasodilating effects, was 24% higher (95% CI, 6%-45%) in preeclamptic women throughout pregnancy (P=.007).

CONCLUSIONS

Our results show that reduced PGI2 production, but not increased TxA2 production, occurs many months before clinical onset of preeclampsia. Aspirin trials may have failed because an increase in thromboxane production is not the initial anomaly. Future interventions should make correcting prostacyclin deficiency a major part of the strategy to balance the abnormal vasoconstrictor-vasodilator ratio present in preeclampsia.

Seasonal variation of semen quality and fertility

At many locations in the northern hemisphere human sperm counts are reduced during the summer. Experiments with rhesus monkeys suggest that such seasonal variation may be induced by an endogenous biological clock reset annually by changes in the length of daylight. Little is known about seasonal variation in human female reproductive function, although fecundity may be lower during the summer, as it is for men. Variation in fecundity could help explain seasonal patterns of birth in countries such as the United States, where there is a deficit of spring births. But the relationship to patterns of birth in Canada and Europe, where the birth rate is highest during late winter and spring, is unclear.

Myofibrillar protein structure and assembly during idiopathic dilated cardiomyopathy

A neutral protease, mekratin, active in human hearts at end stage idiopathic dilated cardiomyopathy (IDC), mediates the breakdown of cardiac myosin LC2. Myosin purified from IDC heart tissue forms unusually short synthetic thick filaments. Therefore, determination of filament length and mekratin distribution in IDC heart muscle were initiated. Native thick filaments were prepared directly from control and IDC tissues and analyzed. Also, paraffin-embedded tissue sections were stained with a fluorescently-labeled anti-protease antibody to establish its distribution in myocardial tissues. Control sections had only very weak, background levels of fluorescence whereas IDC sections stained intensely throughout, indicating a wide ranging distribution of the protease within the myocyte cytoplasm. SDS-PAGE revealed LC2 to be present in stoichiometric amounts in control but greatly reduced in IDC heart muscle. Native thick filaments from control myocardium were structurally stable. They had a median length of 1.65 microm with well-defined bare zones and displayed the 43 nm helical periodicity typical of the relaxed arrangement of myosin heads close to the filaments' shafts. In contrast, native IDC filaments were less stable, and had a median length of 0.9 microm. These filaments were highly disordered: they had no surface periodicity and myosin heads were positioned away from the filaments' shafts. The shorter, less stable, aperiodic thick filaments from IDC hearts appear to result from depletion of LC2 caused by increased activity of mekratin in the IDC myocardium.

The relationship between abnormal glucose tolerance and hypertensive disorders of pregnancy in healthy nulliparous women. Calcium for Preeclampsia Prevention (CPEP) Study Group

OBJECTIVE

The study's aim was to determine whether healthy nulliparous women with abnormal glucose tolerance during pregnancy are at increased risk for development of pregnancy-associated hypertension or preeclampsia.

STUDY DESIGN

A series of 4589 healthy nulliparous women from 5 university centers were evaluated prospectively to determine whether calcium supplementation would prevent preeclampsia. Pregnancy-associated hypertension was a diastolic blood pressure > or = 90 mm Hg on 2 occasions 4 hours to 1 week apart. Pregnancy-associated proteinuria was proteinuria > or = 1+ by dipstick testing on 2 occasions 4 hours to 1 week apart, proteinuria > or = 300 mg/24 h, a protein to creatinine ratio of > or = 0.35, or a single dipstick measurement of > or = 2+. Preeclampsia was defined as pregnancy-associated hypertension and pregnancy-associated proteinuria documented within 7 days of each other. Normal glucose tolerance was a plasma glucose level < 140 mg/dL 1 hour after a 50-g oral glucose challenge. Abnormal glucose tolerance was a plasma glucose level > or = 140 mg/dL 1 hour after a 50-g oral glucose challenge followed by a 3-hour 100-g oral glucose tolerance test yielding < 2 abnormal values. Gestational diabetes mellitus was a plasma glucose level > or = 200 mg/dL 1 hour after a 50-g oral glucose challenge in the absence of an oral glucose tolerance test or > or = 2 abnormal plasma glucose values in a 3-hour 100-g oral glucose tolerance test (> or = 105 mg/dL fasting, > or = 190 mg/dL at 1 hour, > or = 165 mg/dL at 2 hours, or > or = 145 mg/dL at 3 hours). For purposes of this study women with preeclampsia were excluded from the category of pregnancy-associated hypertension.

RESULTS

Calcium supplementation did not prevent pregnancy-associated hypertension or preeclampsia. Of 3689 women with complete glucose testing data, 227 (6%) had abnormal glucose tolerance and 81 (2%) had gestational diabetes mellitus. Compared with women with normal glucose tolerance, women with abnormal glucose tolerance were significantly older, had greater body mass index, and were more likely to be white non-Hispanic, to smoke, and to have private medical insurance. Among women with gestational diabetes mellitus, after adjustment for clinical center the relative risks of preeclampsia and of all hypertensive disorders were increased (relative risk 1.67, 95% confidence interval 0.92-3.05, and relative risk 1.54, 95% confidence interval 1.28-2.11, respectively). Risk ratios were not substantially reduced after further adjustment for race and body mass index (odds ratios 1.41 and 1.48, respectively). Even within the normal range, multivariate analysis demonstrated that the level of plasma glucose 1 hour after a 50-g oral glucose challenge was an important predictor of preeclampsia.

CONCLUSION

Even within the normal range, the level of plasma glucose 1 hour after a 50-g oral glucose challenge was positively correlated with the likelihood of preeclampsia. Women with gestational diabetes mellitus were at increased risk for hypertensive disorders during pregnancy after adjustment for clinical center, race, and body mass index, although the increase was not statistically significant. These findings suggest that insulin resistance may play a role in the pathogenesis of the hypertensive disorders of pregnancy.

Structural and functional responses of mammalian thick filaments to alterations in myosin regulatory light chains

The ordered array of myosin heads, characteristic of relaxed striated muscle thick filaments, is reversibly disordered by phosphorylating myosin regulatory light chains, decreasing temperature and/or ionic strength, increasing pH, and depleting nucleotide. In the case of light chain phosphorylation, disorder, most likely due to a change in charge affecting the light chain amino-terminus, reflects increased myosin head mobility, thus increased accessibility to actin, and results in increased calcium sensitivity of tension development. Thus, interactions between the unphosphorylated regulatory light chain and the filament backbone may help maintain the overall order of the relaxed filament. To define this relationship, we have examined the structural and functional effects of such manipulations as exchanging wild-type smooth and skeletal myosin light chains into permeabilized rabbit psoas fibers and removing regulatory light chains (without exchange) from such fibers. We have also compared the structural and functional parameters of biopsied fibers from patients with severe familial hypertrophic cardiomyopathy due to a single amino acid substitution in the regulatory light chains to those exhibited by fibers from normal relatives. Our results support a role for regulatory light chains in reversible ordering of myosin heads and suggest that economy of energy utilization may provide for evolutionary preservation of this function in vertebrate striated muscle.

Changes in interfilament spacing mimic the effects of myosin regulatory light chain phosphorylation in rabbit psoas fibers

The modulatory effect of myosin regulatory light chain phosphorylation in mammalian skeletal muscle, first documented as posttetanic potentiation of twitch tension, was subsequently shown to enhance the expression and development of tension at submaximal levels of activating calcium. Structural analyses demonstrated that thick filaments with phosphorylated myosin regulatory light chains appeared disordered: they lost the near-helical, periodic arrangement of myosin head characteristic of the relaxed state. We suggested that disordered heads may be more mobile than ordered heads and are likely to spend more time close to their binding sites on thin filaments. In this study we determined that the physiological effects of phosphorylation could be mimicked by decreasing the lattice spacing between the thick and the thin filaments, either by osmotic compression with dextran or by increasing the sarcomere length of permeabilized rabbit psoas fibers. Phosphorylation of regulatory light chains by incubation of permeabilized fibers with myosin light chain kinase and calmodulin, followed by low levels of activating calcium, potentiated tension development at resting or lower sarcomere lengths in the absence of dextran but had no additional effect on tension potentiation or development in fibers with decreased lattice spacing due to either osmotic compression or increased sarcomere length.

Serum cotinine concentration and self-reported smoking during pregnancy

Although during pregnancy there is a better correlation between maternal serum cotinine concentration and adverse outcome than between self-reported smoking and such an outcome, few studies of pregnancy have measured cotinine concentration to determine how much a woman smokes. This study assessed the accuracy of self-reported smoking during pregnancy by performing serum cotinine assays on 448 women registered in the Collaborative Perinatal Project (1959-1966). Based on the assumption that a serum cotinine concentration of >10 ng/ml represented active smoking, 94.9% of women who denied smoking and 87.0% of women who stated that they smoked (kappa=0.83) reported their status accurately. Among smokers, the correlation coefficient between cotinine concentration and number of cigarettes smoked per day was 0.44. Serum cotinine concentration correlated more strongly than self-reported smoking with infant birth weight (r=0.246 vs. 0.200). In conclusion, this study showed that pregnant women accurately reported whether they smoked, but cotinine concentration was a better measure than self-report of the actual tobacco dose received.

Stability of immunoglobulin E (IgE) in stored obstetric sera

OBJECTIVE

To determine the stability of immunoglobulin E levels in obstetric sera.

METHODS

AlaSTAT(R) and AlaTOP(R) (Diagnostic Products) were used to assay total and specific IgE levels in obstetric sera collected in Memphis, TN and Portland, OR. The samples were collected from the Collaborative Perinatal Project (CPP) between 1959 and 1965 and stored at -20 degrees C. The assay results were compared with IgE levels found in sera collected at the same locations for the Calcium for Pre-eclampsia Prevention Study (CPEP) and stored since 1992 at -70 degrees C. The samples were also assayed for cockroach (CR) and mouse urine specific IgE using the AlaSTAT(R) assay (Diagnostic Products).

RESULTS

Total IgE and specific IgE to CR and mouse urine were detectable in older and recent samples. The median total IgE for the recent and older Portland samples was 26 IU/ml and 65 IU/ml, respectively. The median total IgE was identical (40 IU/ml) in the recent and older Memphis samples.

CONCLUSION

Long-term storage does not diminish the ability to measure serum IgE. Levels of IgE in sera stored 32-37 years were equal to or greater than levels in sera stored for 5 years. reserved.

Serum caffeine and paraxanthine as markers for reported caffeine intake in pregnancy

PURPOSE

Previous studies of maternal caffeine use and pregnancy outcome have relied on self-reported use. Even if these were perfectly accurate, inter-individual differences in caffeine metabolism result in a relatively weak correlation between caffeine intake and serum concentration. The purpose of this study was to determine whether the serum concentration of caffeine or its primary metabolite, paraxanthine, obtained at an unknown time during working hours, is useful to distinguish between pregnant women who report consuming small and large amounts of caffeine.

METHODS

We selected from the Birmingham fetal growth study 60 women with normal pregnancy outcomes who reported consuming < or = 0.8 mg/kg/day of caffeine in a 24-hour dietary recall, 60 who consumed 0.81-2.5 mg/kg/day, 60 who consumed 2.51-5.0 mg/kg/day and 59 who consumed > or = 5.01 mg/kg/day. These women had serum drawn for storage during regular clinic hours on the same day as the recall interview. Caffeine and paraxanthine were measured in the stored serum using high performance liquid chromatography.

RESULTS

The weighted kappa coefficient between strata of caffeine intake and quartiles of serum paraxanthine was 0.58 among smokers and 0.53 among nonsmokers, versus 0.44 and 0.51, respectively, for quartiles of serum caffeine. The Pearson correlation coefficient between intake and paraxanthine was 0.50 for smokers and 0.53 for nonsmokers, and 0.37 and 0.51, respectively, for serum caffeine. These values are comparable to the correlation between reported smoking and serum cotinine in pregnancy.

CONCLUSIONS

The serum concentrations of paraxanthine, and to a lesser degree, caffeine are useful to distinguish between women with varying levels of caffeine intake.

Risk factors associated with preeclampsia in healthy nulliparous women. The Calcium for Preeclampsia Prevention (CPEP) Study Group

OBJECTIVE

Our goal was to identify risk factors for the development of preeclampsia in nulliparous women enrolled in a multicenter trial comparing calcium supplementation to a placebo.

STUDY DESIGN

A total of 4589 women from five centers was studied. Analysis of risk factors for preeclampsia was performed in 4314 who carried the pregnancy to > 20 weeks. Baseline systolic and diastolic blood pressure, demographic characteristics, and findings after randomization were examined for the prediction of preeclampsia. Preeclampsia was defined as hypertension (diastolic blood pressure > or = 90 mm Hg on two occasions 4 hours to 1 week apart) and proteinuria (> or = 300 mg/24 hours, a protein/creatinine ratio > or = 0.35, one dipstick measurement > or = 2+ or two dipstick measurements > or = 1+ at an interval as specified for diastolic blood pressure).

RESULTS

Preeclampsia developed in 326 women (7.6%). The first analysis treated each risk factor as a categoric variable in a univariate regression. Maternal age, blood group and Rh factor, alcohol use, previous abortion or miscarriage, private insurance, and calcium supplementation were not statistically significant. Risk factors initially found to be significant were body mass index, systolic blood pressure, diastolic blood pressure, non-white race (African-American and other), clinical center, and smoking. Adjusted odds ratios computed with a logistic regression model revealed that body mass index (odds ratio 3.22 for > or = 35 kg/m2 vs < 19.8 kg/m2), systolic blood pressure (odds ratio 2.66 for > or = 120 vs < 101 mm Hg), diastolic blood pressure (odds ratio 1.72 for > or = 61 mm Hg vs < 60 mm Hg), and clinical center (odds ratio 1.85 for Memphis vs the other clinical centers) were statistically significant predictors of preeclampsia. Results of the final model fit revealed that preeclampsia risk increases significantly (p < 0.0001) with increased body mass index at randomization, as well as with increased systolic and diastolic blood pressure at randomization. Calcium supplementation had no effect on the risks posed by body mass index and blood pressure. Among risk factors developing after randomization, an abnormal results of a glucose screen (plasma glucose > or = 140 mg/dl 1 hour after a 50 gm glucose challenge) was not found to be associated with a significant risk of preeclampsia.

CONCLUSION

These risk factors should be of value in counseling women regarding preeclampsia and should aid in understanding the pathophysiologic characteristics of this syndrome.

Differences in myosin head arrangement on relaxed thick filaments from Lethocerus and rabbit muscles

Relaxed thick filaments from insect asynchronous flight muscle appear different from those of other striated muscles, both in sections and as separated, negatively-stained structures. Unlike relaxed filaments of scallops, chelicerate arthropods, or vertebrate striated muscle, all of which display a predominantly helical arrangement of surface myosin heads, insect asynchronous flight muscle filaments appear striped, with cross-striations or shelves at spacings of 14.5 nm. Using a bifunctional agent to cross-link the active sites of nearest-neighbour myosin heads we previously demonstrated that the helical arrays on the surfaces of scallop, arthropod, fish and frog filaments are produced by the association of two oppositely-oriented myosin heads, each of which originates from an axially sequential molecule within the same helical strand. The effect of similarly cross-linking nearest-neighbour heads with the bifunctional agent 3,3'-dithiobis[3'(2')-O-(6-propionylamino)hexanoyl]adenosine 5'-triphosphate in the presence of vanadate on the solubility of thick filaments separated from Lethocerus indirect flight muscle (an insect asynchronous flight muscle) and rabbit psoas muscle was examined. After incubation on high salt, treated rabbit filaments retained their length and surface myosin, while untreated filaments and those with severed cross-links dissolved, indicating that the myosin head arrangement on rabbit filaments is similar to those previously studied. Treated indirect flight muscles filaments, however, separated into distinct segments of variable lengths, usually multiples of 150 nm, while untreated filaments and those with severed cross-links dissolved completely. This implies that intermolecular associations on indirect flight muscles filaments most likely occur between circumferentially-adjacent heads within each crown, but originating from different helical strands. We interpret this difference in the relaxed orientations of splayed myosin heads on the two types of filament as reflecting a difference in functional requirements at the onset of, or during, contractile activity.