Birth weight as a predictor of brachial plexus injury.

OBJECTIVE: To examine the relationship between birth weight and brachial plexus injury and estimate the number of cesareans needed to reduce such injuries. METHODS: All 80 neonatal records coded for brachial plexus injury from October 1985 to September 1993 at the Brigham and Women's Hospital in Boston, Massachusetts, were studied along with linked maternal files. Birth weight, method of delivery, presence or absence of shoulder dystocia, and any diagnosis of maternal gestational or nongestational diabetes were abstracted. Data for the group with brachial plexus injury were compared with data for live-born infants without this injury during the same period. The sensitivity and specificity of birth weight as a predictor of brachial plexus injury were calculated. Further, the number of cesarean deliveries necessary to prevent a single brachial plexus injury was estimated using various weight cutoffs (4000, 4500, and 5000 g) for elective cesarean delivery. RESULTS: Among 77,616 consecutive deliveries, there were 80 brachial plexus injuries identified, for an incidence of 1.03 per 1000 live births. The incidence of brachial plexus injury increased with increasing birth weight, operative vaginal delivery, and the presence of glucose intolerance. In the group of women without diabetes, between 19 and 162 cesarean deliveries would have been necessary to prevent a single immediate brachial plexus injury. Among women with diabetes, between five and 48 additional cesareans would have been required. CONCLUSION: Although birth weight is a predictor of brachial plexus injury, the number of cesarean deliveries necessary to prevent a single injury is high at most birth weights. Because of the large number of cesarean deliveries needed to prevent a single brachial plexus injury in infants born to women without diabetes, it is difficult to recommend routine cesarean delivery for suspected macrosomia in these women.

Cost-effectiveness of strategies used in the evaluation of pregnancies complicated by elevated maternal serum alpha-fetoprotein levels.

OBJECTIVE: To perform a cost-effectiveness analysis of various protocols used in the diagnostic evaluation of pregnancies complicated by elevated levels of maternal serum alpha-fetoprotein (MSAFP). METHODS: The variables incorporated in this model were the prevalence of relevant fetal anomalies; the sensitivity and specificity of MSAFP at 2.0 or 2.5 multiples of the median (MoM); and the sensitivity, specificity, cost, and safety of targeted ultrasound and amniocentesis. We expressed the cost-effectiveness of each strategy as the total cost of the diagnostic evaluation divided by the number of anomalous fetuses identified, yielding the cost per identified anomalous fetus. RESULTS: In a hypothetical cohort of 100,000 singleton pregnancies, a strategy of targeted ultrasound for MSAFP of at least 2.0 MoM detected 90 of 110 structurally abnormal fetuses, without iatrogenic fetal loss, at a cost of $5700 per anomalous fetus. A strategy of amniocentesis with karyo-type determination for MSAFP of at least 2.5 MoM detected 15 additional abnormal fetuses (87 structural abnormalities, ten autosomal aneuploidies, and eight sex chromosomal aneuploidies), with nine iatrogenic fetal losses, at an incremental cost of $46,100 per anomalous fetus. CONCLUSION: The increased cost and iatrogenic fetal loss rate may not justify the increased diagnostic yield of amniocentesis as compared with ultrasound in the evaluation of pregnancies complicated by elevated MSAFP.

Improved birth weight table for neonates developed from gestations dated by early ultrasonography.

Most previously published tables of birth weight percentiles as a function of gestational age have been derived from neonates with imprecise gestational dating. In order to improve the accuracy of neonatal birth weight percentiles, we developed a birth weight table based on measurements from a group of neonates who had accurate gestational dating by prenatal first trimester ultrasonography. By matching a database of obstetrical ultrasonograms over a 5 year period to birth records at our institution, 3718 newborn infants with gestational dating by first trimester ultrasonography were identified. Statistical smoothing and regression techniques were applied to gestational age at birth and birth weight data to develop a table for the 10th, 50th, 90th, and other weight percentiles for 25 weeks of gestation onward. The weight table developed from our population has lower 50th and 90th percentile weights, and narrower 10th to 90th percentile ranges, at 25 to 35 weeks than in prior tables. At 39 to 43 weeks, our 10th, 50th, and 90th percentile weights are higher than those in previous tables. Our weight table for newborn infants, based on measurements from neonates with accurate dating, permits improved assignment of weight percentiles for gestational age and more accurate diagnosis of growth disorders in fetuses and neonates.

Lateral ventricular atrium: larger in male than female fetuses.

OBJECTIVE: To attempt to detect the presence of a gender difference in the size of the fetal lateral ventricular atrium. METHODS: The width of the lateral ventricular atrium was measured sonographically on 543 consecutive fetuses scanned at 17-40 weeks, with a normal structural survey and documented gender assignment. Lateral ventricular measurements of male and female fetuses were compared. RESULTS: The mean width (+/- S.D.) of the lateral ventricular atrium for the entire study population of 543 fetuses was 6.5 +/- 1.4 mm. The measurement was 6.7 +/- 1.3 in male and 6.3 +/- 1.4 in female fetuses (P < 0.001). The atrial measurements were > or = 8.5 mm in 10% of the male and 7% of the female fetuses (P > 0.05, NS). CONCLUSION: Male fetuses have slightly larger cerebral lateral ventricles than female fetuses.

Can the presumed risk of autosomal trisomy be decreased in fetuses of older women following a normal sonogram?

Previous studies showed that a sonographic scoring system can be used to identify women under age 35 who are at an increased risk for a fetal autosomal trisomy. We propose to use the same scoring system to select women over age 35 who are at a decreased risk of a fetal autosomal trisomy because the ultrasonogram is normal. We reviewed the sonographic scores of 97 trisomic and 694 normal control fetuses from two previously published consecutive series designed to identify women at increased risk for an affected fetus. Using the same scoring index in this study, we calculated the sensitivity and specificity of a score = 0 zero for identifying fetuses with autosomal trisomy. We then applied Bayes' theorem to determine the probability of an autosomal trisomy at various maternal ages, given a sonographic score of 0. Of the 97 fetuses with an autosomal trisomy, 83 had a score of > or = 1, for a sensitivity of 86% (95% CI 77-92%). Of the 694 control fetuses with normal karyotype, 606 had a score of 0, for a specificity of 87% (95% CI 83-89%). A 42 year old woman's probability of an autosomal trisomy if the sonographic score is 0 becomes equivalent to the age-specific probability for a 35 year old woman. Using the lower limit of the CIs for sensitivity and specificity, we calculated that the probability of having a fetus with an autosomal trisomy falls from 18.8 in 1000 to 5.3 in 1000 for a 40 year old woman with a sonographic score of 0.(ABSTRACT TRUNCATED AT 250 WORDS)

Closure of the cerebellar vermis: evaluation with second trimester US.

PURPOSE: To evaluate with sonography the normal development of the fetal cerebellum in the second trimester. MATERIALS AND METHODS: The study included all patients undergoing second trimester genetic amniocentesis who had structurally normal fetuses, in whom the posterior fossa was adequately seen and in whom the karyotype was later determined to be normal. Views of the cerebellum were obtained prospectively, and the inferior vermis was determined to be open or closed at the time of the initial scan. Follow-up was obtained by means of subsequent scans and review of the pediatric record. RESULTS: Of 897 fetuses that met the inclusion criteria, 147 had an open vermis at initial scanning. At 14 weeks gestation, 56% of fetuses had an open vermis, decreasing to 23% at 15 weeks and 6% at 17 weeks. In utero follow-up sonograms were obtained in 79% of fetuses with an initially open vermis and demonstrated closure in all but one fetus. The remaining 21%, without sonographic follow-up, were normal as newborns. CONCLUSION: The prenatal diagnosis of Dandy-Walker variant should not be made before 18 weeks gestation because the development of the cerebellar vermis may be incomplete at that time.

Isolated choroid plexus cysts in the second-trimester fetus: is amniocentesis really indicated?

Choroid plexus (CP) cysts have been associated with trisomy 18, although most fetuses with CP cysts are normal. Since many fetuses with trisomy 18 have other sonographic abnormalities, the necessity of obtaining a karyotype for all fetuses with isolated CP cysts remains controversial. The authors prospectively studied 234 second-trimester fetuses with sonographically discovered CP cysts. Two hundred twenty of them had no other sonographic findings. None of these 220 normal fetuses had evidence of aneuploidy at amniocentesis or an anomaly at birth. Fourteen fetuses had major anomalies detected in utero: 11 had trisomy 18, one had triploidy, and two had normal karyotypes but were structurally abnormal. While size and bilaterality of the CP cysts were not helpful in predicting aneuploidy, the meticulous anatomic survey of fetuses with CP cysts allowed successful identification of all aneuploid fetuses. These data show that the yield of abnormal karyotypes in fetuses with isolated CP cysts is low and may not justify the risk of amniocentesis.

Absence of need for amniocentesis in patients with elevated levels of maternal serum alpha-fetoprotein and normal ultrasonographic examinations.

BACKGROUND: Recent improvements in the accuracy of sonographic diagnosis of neural-tube and ventral-wall defects have raised a question about the wisdom of routinely offering amniocentesis to women who have elevated levels of maternal serum alpha-fetoprotein with a structurally normal fetus as determined by ultrasonography. METHODS: We reviewed the ultrasound findings in 51 consecutive fetuses with spina bifida, encephalocele, gastroschisis, or omphalocele that were delivered or aborted at a single hospital, to estimate the sensitivity of ultrasonography for these diagnoses. In all cases, the mothers had undergone prenatal sonography at one facility between 16 and 24 weeks after the last menstrual period. We used these data to calculate the probability of an affected fetus in a women with a given level of maternal serum alpha-fetoprotein and a normal sonogram. RESULTS: These four types of anomalies were correctly identified in all 51 cases, yielding a sensitivity of 100 percent (95 percent confidence interval, 94 to 100 percent). Using the lower limit of this confidence interval, we calculated that the probability of an affected fetus ranges from 0.01 to 0.15 percent for maternal serum alpha-fetoprotein levels ranging from 2.0 to 3.5 times the median, respectively. CONCLUSIONS: This level of risk is less than the reported risk of abortion due to amniocentesis and may lead some women with elevated levels of alpha-fetoprotein to decide not to proceed with amniocentesis.

Early amniocentesis for prenatal cytogenetic evaluation.

Early amniocentesis at 11-14 weeks gestation was evaluated in 100 consecutive patients to see how this technique compares with later amniocentesis. There were no complications as a consequence of the procedure or related pregnancy losses of chromosomally normal fetuses. Samples obtained from three (3%) patients showed insufficient cell growth; two of these patients elected a repeat procedure, which yielded a normal karyotype in each case. There were five abnormal karyotypes, one of which was a culture artifact; in the latter case, repeat amniocentesis at 15 weeks yielded a normal result. Of the 95 pregnancies with normal karyotypes, 94 were progressing normally at follow-up, and one patient elected pregnancy termination because of maternal indications. It appears that early amniocentesis may be an attractive alternative to traditional amniocentesis, in that it provides results at an earlier gestational age and may avoid certain disadvantages of chorionic villus sampling.

Interrelationships among atrial peptides, renin, and blood volume in pregnant rats.

To determine how changes in intravascular volume are sensed by atrial and renal volume receptors during pregnancy and the puerperium, circulating atrial natriuretic peptide (ANP) levels and plasma renin activity (PRA) were measured in conscious chronically catheterized rats on days 9-10, 15-16, 19-20, and 22 of pregnancy, on the first postpartum day, and in nonpregnant controls. Blood volume measured in a separate group of anesthetized rats increased progressively during pregnancy, and circulating ANP levels tended to decline, although not significantly below the nonpregnant value of 132 +/- 9 pg/ml (mean +/- SE). PRA remained similar to the nonpregnant value of 5.5 +/- 0.6 ng angiotensin I.ml-1.h-1 until day 22 of pregnancy, when it rose to 14.1 +/- 1.8 ng angiotensin I.ml-1.h-1 (P less than 0.001 vs. nonpregnant). In pregnant rats, PRA was suppressed after uninephrectomy and chronic administration of deoxycorticosterone and saline, demonstrating the ability of this hormonal system to respond appropriately to further increments in volume induced during pregnancy. On the first postpartum day plasma ANP rose to 268 +/- 26 pg/ml, and PRA fell to 3.6 +/- 0.4 ng angiotensin I.ml-1.h-1 (P less than 0.005 and P less than 0.05 vs. nonpregnant values, respectively). Thus it appears that the increased blood volume in normal pregnancy is not sensed by renal or atrial volume sensors, presumably because it is accommodated by an enlarged maternal vascular compartment. In the puerperium, however, due to the decreased size of the maternal vascular compartment, atrial and renal volume sensors recognize the intravascular volume as expanded.(ABSTRACT TRUNCATED AT 250 WORDS)

Electronic fetal heart rate monitoring: why the dilemma?

As medical technology becomes more and more complex, both the benefits and risks increase. Perhaps we have misled ourselves and, unwittingly, our patients into expecting the perfect outcome by complication-free care. As we learn more about the pathophysiology of disease it becomes apparent that our expectations are unrealistic. In addition, as clinicians we have become more sophisticated about the utility of clinical testing. We have learned that the predictive value of a test is related to its sensitivity and specificity, and to the prevalence of the disease in the population being tested. We have also seen that the prevalence of intrapartum asphyxia is low and the prevalence of hypoxic-ischemic encephalopathy perhaps even lower. Therefore, the positive predictive value for an ominous fetal heart rate pattern in a low-risk patient to be indicative of fetal asphyxia is probably quite low, even if confirmed by a low fetal scalp pH. In practical terms, a number of emergency cesarean sections will be done unnecessarily, at least in retrospect. Collectively, society is concerned about the high and rising cesarean section rate, although the individual patient "knows" that the "brain-damaged" infant can be prevented by intrapartum fetal heart rate monitoring and emergency section. The reality is that from the best studies available it has yet to be demonstrated that routine EFM in the low-risk patient has provided a benefit. We continue to imply a benefit by its widespread use and wonder why the dilemma. Should our patients expect less? Should the lawyers expect less? Even our experts can not agree. Good practice is our goal. We can accept nothing less.(ABSTRACT TRUNCATED AT 250 WORDS)