Protein mobility and GABA-induced conformational changes in GABA(A) receptor pore-lining M2 segment.

Protein movements underlying ligand-gated ion channel activation are poorly understood. Here we used disulfide bond trapping to examine the proximity and mobility of cysteines substituted for aligned GABAA receptor alpha1 and beta1 M2 segment channel-lining residues in resting and activated receptors. With or without GABA, disulfide bonds formed at alpha1N275C/beta1E270C (20') and alpha1S272C/beta1H267C (17'), near the extracellular end, suggesting that this end is more mobile and/or flexible than the rest of the segment. Near the middle of M2, at alpha1T261C/beta1T256C (6'), a disulfide bond formed only in the presence of GABA and locked the channels open. Channel activation must involve an asymmetric rotation of two adjacent subunits toward each other. This would move aligned engineered cysteines on different subunits into proximity and allow disulfide bond formation without blocking conduction. Asymmetric rotation of M2 segments is probably a common gating mechanism in other ligand-gated ion channels.

Improvement in outcomes of multifetal pregnancy reduction with increased experience.

OBJECTIVE: This study was undertaken to evaluate a decade of data on multifetal pregnancy reductions at centers with extensive experiences. STUDY DESIGN: A total of 3513 completed cases from 11 centers in 5 countries were analyzed according to year (before 1990, 1991-1994, and 1995-1998), starting and finishing numbers of embryos or fetuses, and outcomes. RESULTS: With increasing experience there has been a considerable improvement in outcomes, with decreases in rates of both pregnancy loss and prematurity. Overall loss rates in the last few years were correlated strongly with starting and finishing numbers (starting number > or =6, 15.4%; starting number 5, 11.4%; starting number 4, 7.3%; starting number 3, 4.5%; starting number 2, 6.2%: finishing number 3, 18.4%; finishing number 2, 6.0%; finishing number 1, 6.7%). Birth weight discordance between surviving twins was increased with greater starting number. The proportion of cases with starting number > or =5 diminished from 23.4% to 15.9% to 12.2%. The proportion of patients >40 years old increased in the last 6 years to 9.3%. Gestational age at delivery did not vary with increasing maternal age but was inversely correlated with starting number. CONCLUSION: Multifetal pregnancy reduction outcomes at our centers for both losses and early prematurity have improved considerably with experience. Reductions from triplets to twins and now from quadruplets to twins carry outcomes as good as those of unreduced twin gestations. Patient demographic characteristics continues to change as more older women use assisted reproductive technologies. In terms of losses, prematurity, and growth, higher starting numbers carry worse outcomes.

Aerotolerance and peroxide resistance in peroxidase and PerR mutants of Streptococcus pyogenes.

Survival in aerobic conditions is critical to the pathogenicity of many bacteria. To investigate the means of aerotolerance and resistance to oxidative stress in the catalase-negative organism Streptococcus pyogenes, we used a genomics-based approach to identify and inactivate homologues of two peroxidase genes, encoding alkyl hydroperoxidase (ahpC) and glutathione peroxidase (gpoA). Single and double mutants survived as well as the wild type under aerobic conditions. However, they were more susceptible than the wild type to growth suppression by paraquat and cumene hydroperoxide. In addition, we show that S. pyogenes demonstrates an inducible peroxide resistance response when treated with sublethal doses of peroxide. This resistance response was intact in ahpC and gpoA mutants but not in mutants lacking PerR, a repressor of several genes including ahpC and catalase (katA) in Bacillus subtilis. Because our data indicate that these peroxidase genes are not essential for aerotolerance or induced resistance to peroxide stress in S. pyogenes, genes for a novel mechanism of managing peroxide stress may be regulated by PerR in streptococci.

Selective termination for structural, chromosomal, and mendelian anomalies: international experience.

OBJECTIVE: Our purpose was to evaluate the outcomes of selective termination for fetal anomalies at 8 centers with the largest known experiences worldwide. STUDY DESIGN: Outcomes in 402 cases of selective termination in pregnancies with dizygotic twins from 8 centers in 4 countries were analyzed by year, gestational age at procedure, and indication. Reductions of fetuses were as follows: 2 to 1, n = 345; 3 to 2, 39; >/=4 to 2 or 3, n = 18. Potassium chloride was used in all procedures. RESULTS: Selective termination resulted in delivery of a viable infant or infants in >90% of cases. Loss up to 24 weeks occurred in 7.1% of cases in which the final result was a singleton fetus and in 13.0% of cases in which the final result was twins. Loss was 6.6% as a result of structural abnormalities, 7.0% for chromosomal abnormalities, and 10% for mendelian abnormalities (difference not statistically significant). Loss rates for procedures were as follows: 9-12 weeks, 5.4%; 13-18 weeks, 8.7%; 19-24 weeks, 6.8%; and >/=25 weeks, 9.1% (difference not statistically significant). Mean gestational age at delivery was 35.7 weeks. No differences were seen in outcomes by maternal age. The rate of very early premature deliveries has fallen in recent years. There were no known cases of disseminated intravascular coagulation or serious maternal complications. CONCLUSION: (1) Selective termination, in the most experienced hands, can be technically performed in all 3 trimesters with good outcomes in >90% of cases. (2) The previously observed increase in second- versus first-trimester losses has diminished. (3) Third-trimester procedures, where legal, can be performed with a good outcome for the surviving fetus.

Location of a high affinity Zn2+ binding site in the channel of alpha1beta1 gamma-aminobutyric acidA receptors.

Zn2+ inhibits currents through gamma-aminobutyric acid (GABA)A receptors. Its affinity depends on the subunit composition; alpha1beta1 receptors are inhibited with high affinity (IC50 = 0.54 micro M). We sought to identify the residues that form this high affinity Zn2+ binding site. beta1His267 aligns with alpha1Ser272, a residue near the extracellular end of the M2 membrane-spanning segment that we previously demonstrated to be exposed in the channel. The Zn2+ affinity of alpha1beta1 H267S was reduced by 300-fold (IC50 = 161 micro M). Addition of a histidine at the aligned position in alpha1 creates a receptor, alpha1S272Hbeta1, that should have five channel-lining histidines; the Zn2+ affinity was increased 20-fold (IC50 = 0.025 micro M). Shifting the position of the histidine from the beta1 subunit to the aligned position in alpha1 with the two mutants alpha1S272Hbeta1H267S reduced the affinity (IC50 = 26 micro M) compared with wild-type. We infer that the high affinity Zn2+ binding site involves beta1His267 from at least two subunits. For two histidines to interact with a Zn2+ ion, the alpha carbons must be separated by <13 A. This limits the separation of the subunits and provides a constraint on the possible quaternary structures of the channel. The ability of a divalent cation to penetrate from the extracellular end of the channel to beta1His267 implies that the charge-selectivity filter, the structure that discriminates between anions and cations, is located at a more cytoplasmic position than beta1His267; this is consistent with our previous work that showed that positively charged sulfhydryl-specific reagents reacted with an engineered cysteine residue as cytoplasmic as alpha1T261C.

An actin monomer binding activity localizes to the carboxyl-terminal half of the Saccharomyces cerevisiae cyclase-associated protein.

The Saccharomyces cerevisiae adenylyl cyclase complex contains at least two subunits, a 200-kDa catalytic subunit and a 70-kDa cyclase-associated protein, CAP (also called Srv2p). Genetic studies suggested two roles for CAP, one as a positive regulator of cAMP levels in yeast and a second role as a cytoskeletal regulator. We present evidence showing that CAP sequesters monomeric actin (Kd in the range of 0.5-5 microM), decreasing actin incorporation into actin filaments. Anti-CAP monoclonal antibodies co-immunoprecipitate a protein with a molecular size of about 46 kDa. When CAP was purified from yeast using an anti-CAP monoclonal antibody column, the 46-kDa protein co-purified with a stoichiometry of about 1:1 with CAP. Western blots identified the 46-kDa protein as yeast actin. CAP also bound to muscle actin in vitro in immunoprecipitation assays and falling ball viscometry assays. Experiments with pyrene-labeled actin demonstrated that CAP sequesters actin monomers. The actin monomer binding activity is localized to the carboxyl-terminal half of CAP. Together, these data suggest that yeast CAP regulates the yeast cytoskeleton by sequestering actin monomers.

Efficacy of second-trimester selective termination for fetal abnormalities: international collaborative experience among the world's largest centers.

OBJECTIVE: Our goal was to develop the most comprehensive database possible to counsel patients about selective termination for fetal abnormalities, because no one center has sufficient data to assess much more than crude loss rates. STUDY DESIGN: A total of 183 completed cases of selective termination from 9 centers in 4 countries were combined (169 twins, 11 triplets, 3 quadruplets). Variables included indications, methods, (potassium chloride, exsanguination, air embolus), gestational age at procedure, pregnancies lost (< or = 24 weeks), gestational age at delivery, and neonatal outcome. RESULTS: Indications for selective termination were 96 chromosomal, 76 structural, and 11 mendelian. Selective termination was technically successful in 100% of cases. In 23 of 183 (12.6%) miscarriage occurred before 24 weeks; 2 of 37 (5.4%) occurred when the procedure done at < or = 16 weeks and 21 of 146 (14.4%) when it was done thereafter. Air embolization had a higher loss rate: 10 of 24 (41.7%) compared with 13 of 156 (8.3%) by potassium chloride (chi 2 = 117, p < 0.0001). Three cases of selective termination performed in monochorionic pregnancies all resulted in pregnancy loss. Among 183 potentially viable deliveries, 7 occurred before 28 weeks, 19 at 29 to 32 weeks, 41 at 33 to 36 weeks, and 93 at > or = 37 weeks. Gestational age at delivery was not influenced by the technique used or the indication but was negatively correlated with gestational age at the time of selective termination. No coagulopathy or ischemic damage was observed in survivors. There was no maternal morbidity. CONCLUSIONS: (1) Selective termination in experienced hands for a dizygotic abnormal twin is safe and effective when done with potassium chloride. A total of 83.8% of viable deliveries occurred after 33 weeks and only 4.3% at 25 to 28 weeks. (2) Gestational age at the procedure correlated positively with loss rate and inversely with gestational age at delivery; this emphasizes the need for early diagnosis in multifetal pregnancies. (3) Coagulopathy tests are probably unnecessary.

Color Doppler identification of a pericardial effusion in the fetus.

The aim of the study was to determine whether color Doppler identifies abnormal fluid within the pericardial space of the fetal were referred for heart. Second- and third-trimester fetuses diagnostic ultrasound. The four-chamber view of the fetal heart was imaged with real-time ultrasonography and examined for the presence or absence of separation of the pericardium from the epicardium, which extended from the atrioventricular junction toward the apex of the ventricle. To examine the pericardial space, the color Doppler maximal velocity was set at low Nyquist limits (0.08-0.24 m/s). In each fetus the transducer was angled so that the axis of the interventricular septum was parallel or tangential to the ultrasound beam to optimize the color Doppler recording. The control group consisted of 50 fetuses (16-38 weeks of gestation) who did not demonstrate evidence of pericardial effusion when examined with real-time ultrasound. Second- and third-trimester fetuses were selected from our database who demonstrated a pericardial effusion identified with real-time ultrasound. Color Doppler signals were not identified within the pericardial space in the 50 control fetuses. Fetuses with a pericardial effusion identified with real-time ultrasound demonstrated color Doppler within the pericardial space which was opposite to the direction of blood entering and exiting the ventricles. Color Doppler enhanced the detection of a pericardial effusion in the second-trimester fetus when the axis of the heart was and third-parallel or tangential to the ultrasound beam, which is suboptimal for real-time imaging. Color Doppler provides a new method to identify a pericardial effusion in the fetus during the second and third trimesters of pregnancy and complements the real-time examination.

Simultaneous Doppler recording of the pulmonary artery and vein: a new technique for the evaluation of a fetal arrhythmia.

We describe a new technique to evaluate cardiac rhythm using color and pulsed Doppler ultrasonography to identify and record pulmonary arterial and venous waveforms. Fifty fetuses were examined during the second and third trimesters of pregnancy. Simultaneous pulsed Doppler recording of the pulmonary artery and vein was obtained in 100% of fetuses between 15 and 40 weeks' gestation. Atrial systole was identified from the pulmonary vein and was manifested by an interruption of venous flow. Ventricular systole was manifested by a sharp peak that returned toward the baseline before it continued through the duration of systole as a lower-velocity waveform. This technique has the following advantages: (1) the lung parenchyma is easily accessible, irrespective of fetal position; (2) the pulmonary arteries and veins are adjacent to each other as they enter and exit the lung, thus making it easy to simultaneously obtain Doppler recordings of these vessels; (3) the pulsed Doppler waveform has an appearance similar to an electrocardiogram.

Fetal echocardiography: factors that influence imaging of the fetal heart during the second trimester of pregnancy.

OBJECTIVE: The four-chamber view of the heart is an important component of the ultrasonographic examination of the fetus. However, during the second trimester of pregnancy the fetal heart cannot always be imaged in every patient. The purpose of this study was to ascertain the rate of successful imaging of the fetal heart during the second trimester and to determine factors that may influence imaging. METHODS: Seven hundred and nine second trimester fetuses were examined and an attempt was made to obtain the four-chamber and outflow tract views of the heart. Analysis included multiple logistic regression models of the main effects and interactions of ten candidate variables. RESULTS: The four chambers and outflow tracts were imaged in 643 fetuses (90.7%) and not imaged in 66 (9.3%). Fifty-two of 709 patients (7.3%) had had previous surgery. In the 52 patients with a history of previous surgery, the heart could not be imaged in 18 (34%). Six hundred and fifty-seven patients (92.7%) did not have previous surgery. Of this group, the fetal heart could not be imaged in 48 (7.3%). In only one fetus in which the heart could not be imaged was it because of fetal position. Three independent risk factors that influenced imaging of the fetal heart were gestational age, maternal adipose tissue thickness, and previous lower abdominal surgery. Increasing gestational age increased the probability of imaging the heart, whereas increasing adipose tissue thickness and a history of previous surgery decreased the probability of imaging the heart. COMMENTS: When the fetal heart cannot be imaged during the second trimester, these factors should be identified. Using data from this study, the gestational age at which the highest probability of imaging the heart can be determined if the thickness of the adipose tissue and a history of lower abdominal surgery are known.

Monocyte monolayer assay as a predictor of severity of hemolytic disease of the fetus and newborn.

The monocyte monolayer assay (MMA), an in vitro model of in vivo antibody-mediated red blood cell destruction, was previously reported to predict the severity of hemolytic disease of the fetus and newborn accurately when only Rh antibodies and antigen-positive babies were studied. We studied 33 women whose serum contained antibodies with the potential to cause erythroblastosis fetalis; 7 of the 33 women had antibodies other than Rh. None of the babies of the ten women who had consistently negative test results required intrauterine or neonatal transfusions. False-positive MMA results were sometimes found when the fetus was antigen negative. Although the predictive value of a negative MMA was 100%, the efficiency of the MMA was no better than that of the antibody titer. Because of the lack of advantage of the MMA as well as the time and expense it requires, we cannot recommend the general clinical application of this test at this time.

Ductus venosus index: a method for evaluating right ventricular preload in the second-trimester fetus.

This study was designed to examine ventricular preload by measuring the ductus venosus index during the second trimester of pregnancy. A total of 137 women were entered into the study. Each fetus was examined with real-time, color and pulsed Doppler ultrasound. The color Doppler maximal velocity setting was adjusted so that the umbilical vein was homogeneous in color, did not demonstrate aliasing, and filled the venous lumen. The pulsed Doppler gate was placed within the ductus venosus in all subjects. Color Doppler identified a turbulent flow velocity within the ductus venosus which was not present in the umbilical vein, hepatic vein or inferior vena cava. The ductus venosus pulsed Doppler waveform demonstrated flow velocity from the umbilical vein to the heart during ventricular systole, the rapid filling phase of ventricular diastole, and atrial systole. However, flow velocity was decreased during atrial systole compared to ventricular systole and the rapid filling phase of diastole. The ductus venosus index was computed from the Doppler waveform of the ductus venosus at points consistent with ventricular and atrial systole ((ventricular systole - atrial systole)/ventricular systole). Regression analysis demonstrated a significant (p = 0.001) relationship between the ductus venosus index and gestational age (ductus venosus index = 75.5757 - 7.25484 x weeks gestation), standard error of the estimate = 7.21959; R = -0.451. One fetus with a hypoplastic left atrium and ventricle demonstrated a normal ductus venosus index. Two fetuses, one with pulmonary atresia and the second with severe cardiovascular dysfunction, demonstrated an abnormal ductus venosus index associated with absent flow velocity during atrial systole. This was associated with notching in the umbilical vein. The ductus venosus index is an angle-independent measurement from which right ventricular preload may be evaluated.

Screening for Down syndrome with the femur length/biparietal diameter ratio: a new twist of the data.

OBJECTIVE: The purpose of this study was to determine the value of discordant morphometric measurements as identifiers of Down syndrome by evaluating the relationship of biparietal diameter, femur length, biparietal diameter/femur length ratio, and cephalic index between a group of fetuses with trisomy 21 and a control population. STUDY DESIGN: Biometric measurements from 48 fetuses with trisomy were reviewed and compared with 107 normal fetuses of similar gestational age. Data were analyzed in 2-week gestational age intervals to determine the effect of gestational age on ultrasonographic detection of Down syndrome. Outcome measures were subject to least-squares linear regression and the t test for analysis. RESULTS: A positive relationship between abnormal morphometric measurements and fetuses with Down syndrome was detected but only during specific weeks of pregnancy. CONCLUSION: Although it appears that biometric measurements may be useful for Down syndrome, further study is needed before its widespread introduction into clinical practice.

Selective labor induction in postterm patients. Observations and outcomes.

Six hundred twenty-nine postterm patients with reliable dates were evaluated for expectant management. Patients with medical or obstetric complications, a Bishop score greater than 6 or abnormal antepartum testing were ineligible for such management. The incidences of macrosomia, fetal distress necessitating cesarean section and low five-minute Apgar scores were similar in patients with labor induction as compared to those managed expectantly. The cesarean section rate was significantly lower in patients who underwent induction for a Bishop score greater than 6 as compared to those followed expectantly (15% vs. 28%). The lowest cesarean section rate was seen in patients with Bishop scores greater than 8 (5%) versus 15% in patients with Bishop scores of 6-8.

The use of fetal echocardiography for predicting intrapartum fetal heart rate patterns in the post-term pregnancy.

One of the shortcomings of antepartum testing in the post-term pregnancy is that it does not identify the majority of fetuses who develop abnormal intrapartum fetal heart rate changes. The purpose of this study was to determine whether antenatal cardiovascular evaluation could aid in the identification of post-term fetuses at risk for intrapartum heart rate abnormalities. Seventy-five patients with a gestational age greater than 41 weeks underwent a non-stress test, amniotic fluid index and real-time assessment of the heart for the presence or absence of a pericardial effusion. M-mode measurements of the right ventricular inner dimension (RVID), left ventricular inner dimension (LVID), biventricular outer dimension (BVOD) and Doppler velocimetry of the umbilical artery (S/D) were performed. Group I (n = 32) had normal intrapartum heart rate tracings. Group II (n = 20) had abnormal intrapartum fetal heart rate tracings but did not undergo emergency delivery. Group III (n = 23) had abnormal intrapartum fetal heart rate tracings but underwent emergency delivery. When comparing Group I with Group II, the latter had significant differences for abnormal RVID, RVID/LVID ratio, and pericardial effusion. When comparing Groups I and III, there were significant differences for RVID, RVID/LVID ratio, pericardial effusion, BVOD, LVID and amniotic fluid index. Neither the non-stress test nor S/D predicted abnormal intrapartum fetal heart rate patterns. For prediction of abnormal intrapartum heart rate patterns, the sensitivities of the RVID (0.79), LVID (0.33), RVID/LVID ratio (0.72) and BVOD (0.63) were 1.7-4 times greater than the non-stress test (0.19) and the sensitivities of the RVID, RVID/LVID ratio and BVOD were 2 times greater than the amniotic fluid index (0.28). The positive (0.50-0.86) and negative (0.42-0.68) predictive values were similar for all groups. To predict emergency delivery associated with abnormal heart rate tracings, the sensitivities of the RVID (0.83), RVID/LVID ratio (0.70) and BVOD (0.65) were 2.5-3 times greater than the non-stress test (0.26) and 1.5 times greater than the amniotic fluid index (0.39). The positive (0.36-0.56) and negative (0.70-0.86) predictive values were similar. The presence of pericardial effusion had a higher sensitivity than the non-stress test and amniotic fluid index for predicting abnormal intrapartum heart rate patterns but not emergency delivery. Doppler velocimetry of the umbilical artery had a lower sensitivity than the non-stress test and amniotic fluid index for predicting intrapartum heart rate patterns as well as identifying the fetus needing emergency delivery. The results of this study would suggest that there is initially dilatation of the right ventricle which may be associated with abnormal intrapartum fetal heart rate patterns. However, when the left ventricle dilates, leading to cardiomegaly, there is a greater incidence of abnormal intrapartum fetal heart rate changes and associated emergency delivery. The amniotic fluid index appears to be a later finding for predicting abnormal intrapartum fetal heart rate changes.

Characteristics of ovarian follicular development in Norplant users.

Daily transvaginal ultrasound (US) scanning of the ovaries to assess follicular development and daily blood sampling were performed on 19 Norplant (Leiras, Turku, Finland) subdermal contraceptive implant users who had regular menstrual cycles and on 10 normally cycling women. Three groups were identified in the implant users based on US finding. Six (31.6%) of the implant users had US findings that were consistent with a normal ovulatory pattern. However, their mean peak luteinizing hormone levels and peak midluteal phase progesterone (P) levels were significantly lower than control values. Eleven (57.9%) users had persistent follicles, and 2 users (10.5%) had no follicular development. These data suggest that after 2 to 4 years of use, about one third of Norplant users with regular bleeding patterns may ovulate but most have deficient luteal P levels. In this small study, the presence of persistent follicular enlargement in implant users was common.

Performing cytogenetic studies on ascitic, amniotic and hygroma fluid.

The importance of obtaining cytogenetic studies on antenatally diagnosed structural malformations is well recognized. In two cases, three fetal compartments were sampled, each resulting in successful cytogenetic studies. Fluid was obtained under ultrasound guidance from amniotic fluid, fetal ascites and cystic hygroma fluid. Fluid from the hygroma itself may be the easiest compartment to analyze.

Prognostic indicators of the resolution of nonimmune hydrops fetalis and survival of the fetus.

To delineate any possible prognostic indicators, we reviewed the ultrasonographic and nonmorphometric findings in 19 antenatally diagnosed cases of nonimmune hydrops fetalis in which it was chosen to continue the pregnancy. Thirteen fetuses died and six survived. Of all parameters examined, including associated anomalies, abnormal karyotype, location of serous fluid, anemia, and possible cause of nonimmune hydrops fetalis, the most sensitive prognostic indicator was the real-time-directed M-mode echocardiographic measurement of the biventricular outer dimension in diastole. All fetuses with biventricular outer dimensions greater than 95% died, whereas all but one with normal biventricular outer dimensions had resolution of nonimmune hydrops fetalis and survived. This was highly significant (p less than 0.001) with the predictive value of a normal biventricular outer dimension being 86% and the predictive value of an enlarged biventricular outer dimension being 100%.

Quantifiable polyhydramnios: diagnosis and management.

Little has been written regarding the ultrasonographic quantification of polyhydramnios or its subsequent management. Therefore, we designed this study to define polyhydramnios using the amniotic fluid index of greater than 2 SDs above the mean for late second- to third-trimester pregnancies, or 24 cm or greater. One hundred twelve nondiabetic women referred to Women's Hospital, Los Angeles County/University of Southern California Medical Center with the descriptive diagnosis of polyhydramnios made by experienced ultrasonographers were included in the study. There was poor correlation between these descriptions and fetal outcome. Twenty-six were qualitatively described as having severe, 29 as moderate, and 57 as mild polyhydramnios. Forty-nine of the 112 patients met our definition of significant polyhydramnios by having an amniotic fluid index of 24 cm or more. This particular definition allowed the inclusion of all fetuses with serious structural defects and/or death. Seven patients had an amniotic fluid index less than 24 cm, but with the traditional quantitative definition of one pocket of 8 cm or more; none of these patients had poor fetal outcome. These data appear to suggest that the use of descriptive definitions of polyhydramnios or a single fluid pocket of 8 cm or greater should be discarded in favor of using an amniotic fluid index of 24 cm or more. Once the diagnosis of polyhydramnios is made, the patient should have a detailed sonographic evaluation, be offered cytogenetic studies, and have antepartum surveillance.

Ultrasonographic estimation of fetal weight in the clinically macrosomic fetus.

The purpose of this study is to evaluate models for the prediction of birth weight in fetuses suspected of being macrosomic. A total of 141 patients with standard measurements of the head, abdomen, and femur were studied. Linear regressions were performed with single parameters, squares, and all possible cross products in the generation of models with log (birth weight) and birth weight as dependent variables. These models were then compared with a group of previously published equations. Clinically, all models performed poorly. However, two models were significantly less accurate in the prediction of birth weight (p less than or equal to 0.05). The best results were obtained by equations that used abdominal circumference and femur length measurements. There was no improvement in models that contained log (birth weight) or birth weight as dependent variables or models with complex variables such as squares or cross products of measured parameters. In conclusion, when evaluating patients at risk of macrosomia, the best estimates of fetal weight can be obtained by models that contain abdominal circumference and femur length.