Is there a sea change ahead for obstetrics and gynecology?

A number of beneficial sociocultural reforms have occurred throughout our society, including a new work/family balance. This change, and a number of others, are challenging the dynamic balance within our specialty. We must advocate for appropriate social, political, and economic interventions that will realistically mesh with the health care needs of our nation, while preserving that which is best about the culture of American medicine.

Pulse pressure and risk of preeclampsia: a prospective study.

OBJECTIVE: To find whether pulse pressure, a measure of arterial compliance, is associated early in pregnancy with increased risk of developing preeclampsia. METHODS: In a prospective cohort of 576 nulliparas, we examined blood pressures throughout pregnancy and at 6-8 weeks postpartum. Measurements during weeks 7-15, 16-24, and 25-38 of gestation were pooled to find averages for each period. Outcomes assessed were gestational hypertension and preeclampsia. Logistic regression analysis was used to develop relative risks and 95% confidence intervals. RESULTS: We confirmed 34 (5.9%) cases of preeclampsia, 32 (5.6%) cases of gestational hypertension, and 510 normotensive women. Mean systolic and diastolic blood pressures and mean arterial pressures were elevated throughout pregnancy in women who developed hypertensive disorders of pregnancy compared with normotensive women. Pulse pressure at 7-15 weeks was significantly higher in women who developed preeclampsia (45 +/- 6 mmHg) than in those who developed gestational hypertension (41 +/- 7 mmHg, P =.03) and normotensive women (41 +/- 8 mmHg, P =.01). Examined in tertiles, increasing pulse pressure was associated with increasing risk of developing preeclampsia (P for trend =.01) but not gestational hypertension (P for trend =.95). After adjustment for potential confounders, a 1-mmHg rise in early pregnancy pulse pressure was associated with a 6% (95% confidence interval: 1, 10) increase in risk for developing preeclampsia but not gestational hypertension (relative risk: 1%; 95% confidence interval: -1, 6). Beyond 15 weeks' gestation, differences between groups diminished, but women with any hypertensive disorder had higher pulse pressures than women with uncomplicated pregnancies. CONCLUSION: Elevated pulse pressure, indicating poor arterial compliance, was evident early in pregnancies of women who subsequently developed preeclampsia.

Intrapartum maternal fever and neonatal outcome.

OBJECTIVE: Much of fever during term labor may not be infectious but rather a consequence of the use of epidural analgesia. Therefore, we investigated the association of elevated maternal intrapartum temperature with neonatal outcome when the infant does not develop an infection. METHODS: We studied 1218 nulliparous women with singleton, term pregnancies in a vertex presentation and spontaneous labor. Women were excluded if their temperature was >99.5 degrees F at admission for delivery, if they were diabetic or had an active genital herpes infection or if their infant developed a neonatal infection, had a congenital infection, or had a major malformation. Maximum intrapartum temperature was categorized as: 101 degrees F. RESULTS: During labor, 123 women (10.1%) developed a fever >100.4 degrees F; 62 (5.1%) women had a maximum temperature of 100.5 degrees F to 101 degrees F and 61 (5.0%) women had a maximum temperature >101 degrees F. Of febrile women, 97.6% had received epidural analgesia for pain relief. Infants of women developing a fever >100.4 degrees F were more likely to have a 1-minute Apgar score <7 (22.8% for >100.4 degrees F vs 8.0% for afebrile) and to be hypotonic after delivery (4.8% for >100.4 degrees F vs.5% for afebrile). Compared with infants of afebrile women, infants whose mothers' maximum temperature was >101 degrees F were more likely to require bag and mask resuscitation (11.5% vs 3.0%) and to be given oxygen therapy in the nursery (8.2% vs 1.3%). We also found a higher rate of neonatal seizure with fever (3.3% vs.2%), but the number of infants with seizure was small (n = 4). All associations remained essentially the same after controlling for confounding in logistic regression analyses. CONCLUSIONS: Intrapartum maternal fever, particularly if >101 degrees F, was associated with a number of apparently transient adverse effects in the newborn. Larger studies are needed to investigate the association of intrapartum fever with neonatal seizures and to determine whether any lasting injury to the fetus may occur.

Routine ultrasound screening in low-risk pregnancies: imperatives for further study.

The benefits of screening ultrasonography in low-risk pregnancies are uncertain and require further investigation. As researchers organize future trials, however, they will need to define clearly the structure and content of the screening ultrasound examination and explicitly detail those outcomes considered important. Such studies must examine the effectiveness of screening sonography in comparison with and in the context of other available prenatal tests and screens. Until studies showing efficacy are available, screening ultrasound in low-risk pregnancies should be considered only when patients, guided by clinicians, consider the potential benefits to be of value.

The changing pattern of prenatal care utilization in the United States, 1981-1995, using different prenatal care indices.

CONTEXT: Two measures traditionally used to examine adequacy of prenatal care indicate that prenatal care utilization remained unchanged through the 1980s and only began to rise slightly in the 1990s. In recent years, new measures have been developed that include a category for women who receive more than the recommended amount of care (intensive utilization). OBJECTIVE: To compare the older and newer indices in the monitoring of prenatal care trends in the United States from 1981 to 1995, for the overall population and for selected subpopulations. Second, to examine factors associated with receiving intensive utilization. DESIGN: Cross-sectional and trend analysis of national birth records. SETTING: The United States. SUBJECTS: All live births between 1981 and 1995 (N=54 million). MAIN OUTCOME MEASURES: Trends in prenatal care utilization, according to 4 indices (the older indices: the Institute of Medicine Index and the trimester that care began, and the newer indices: the R-GINDEX and the Adequacy of Prenatal Care Utilization Index). Multiple logistic regression was used to assess the risk of intensive prenatal care use in 1981 and 1995. RESULTS: The newer indices showed a steadily increasing trend toward more prenatal care use throughout the study period (R-GINDEX, intensive or adequate use, 32.7% in 1981 to 47.1 % in 1995; the Adequacy of Prenatal Care Utilization Index, intensive use, 18.4% in 1981 to 28.8% in 1995), especially for intensive utilization. Women having a multiple birth were much more likely to have had intensive utilization in 1995 compared with 1981 (R-GINDEX, 22.8% vs 8.5%). Teenagers were more likely to begin care later than adults, but similar proportions of teens and adults had intensive utilization. Intensive use among low-risk women also increased steadily each year. Factors associated with a greater likelihood of receiving intensive use in 1981 and 1995 were having a multiple birth, primiparity, being married, and maternal age of 35 years or older. CONCLUSIONS: The proportion of women who began care early and received at least the recommended number of visits increased between 1981 and 1995. This change was undetected by more traditional prenatal care indices. These increases have cost and practice implications and suggest a paradox since previous studies have shown that rates of preterm delivery and low birth weight did not improve during this time.

The association of fetal sex with the rate of cesarean section.

OBJECTIVE: Our purpose was to evaluate the rate of cesarean deliveries according to fetal sex. STUDY DESIGN: We evaluated method of delivery, indication for cesarean section, and infant outcome according to fetal sex in 2439 low-risk nulliparous women in spontaneous labor. Crude odds ratios and 95% confidence intervals were calculated. Confounding was controlled with use of logistic regression. RESULTS: The overall cesarean section rate was 13.2% among 1246 women carrying male fetuses compared with 9.6% among 1193 women carrying female fetuses (odds ratio 1.4, 95% confidence interval 1.1 to 1.8). There was a 30% increase in cesarean sections for failure to progress (odds ratio 1.3, 95% confidence interval 1.0 to 1.8) and a 70% increase in those for fetal distress (odds ratio 1.7, 95% confidence interval 1.0 to 3.0). When adjusted for gestational age and fetal size, male fetal sex no longer predicted the risk of cesarean delivery for failure to progress (adjusted odds ratio 1.04, 95% confidence interval 0.8 to 1.4) but continued to predict the risk of cesarean section for fetal distress (adjusted odds ratio 2.2, 95% confidence interval 1.3 to 4.0). Among infants delivered by cesarean section for fetal distress, males were more than three times as likely than females to have an Apgar score < or = 7 at both 1 and 5 minutes. CONCLUSION: Increased cesarean deliveries for failure to progress among women with male fetuses is related to the larger size of males, whereas the increase for fetal distress is not, and may relate to other developmental differences between male and female fetuses.

Association of epidural analgesia with cesarean delivery in nulliparas.

OBJECTIVE: To evaluate whether epidural analgesia during the first stage of labor is associated with an increased risk of cesarean delivery. METHODS: The association of epidural analgesia and cesarean delivery was examined in a retrospective study of 1733 low-risk, term nulliparas with singleton infants in vertex presentations, in which labor began spontaneously. To evaluate the effect of epidural analgesia on cesarean deliveries, independent of other factors influencing the use of epidural analgesia, we used propensity scores to create five subgroups (quintiles) of women who, based on characteristics discernible at admission, appeared equally likely to receive epidural analgesia. Multivariate logistic regression analysis was used to control for confounding. RESULTS: Overall, the cesarean rate among women receiving epidural analgesia was 17% (168 of 991), compared with 4% (30 of 742) among those who did not receive epidural analgesia. An increased cesarean rate among women receiving epidural analgesia was present in all propensity quintiles. In an adjusted logistic regression analysis, women receiving epidural analgesia were 3.7 times more likely to undergo a cesarean (95% confidence interval 2.4, 5.7). The greatest increase in cesarean risk was noted when epidural analgesia was administered earlier in labor, but there was a more than twofold increase regardless of the dilation and station at administration of epidural analgesia. CONCLUSIONS: Epidural analgesia may increase substantially the risk of cesarean delivery. Although the causal nature of this association remains open to debate, prenatal care providers should routinely discuss the risks and benefits of epidural analgesia with women during their pregnancies so that they can make informed decisions about the use of pain relief during labor.

Antepartum screening in the office-based practice: findings from the collaborative Ambulatory Research Network.

OBJECTIVE: To examine utilization patterns of four antepartum screening tests by office-based obstetricians. METHODS: The population surveyed was the Collaborative Ambulatory Research Network, a voluntary subset of 550 ACOG fellows from 130 practices participating in data collection regarding ambulatory practices. Responses from self-administered questionnaires concerning screening for hepatitis B, gestational diabetes, neural tube defects, and trisomy 21 were analyzed. RESULTS: Hepatitis screening was performed by all practices with 95% (2750 of 2886) of women tested; however, only 55% (six of 11) of at-risk newborns received treatment. For gestational diabetes screening, 94% (116 of 124) administer a 50-g glucose load to all parturients, regardless of risk factors, two-thirds initiate further testing for a 1-hour post-load glucose of 140 mg/dL or greater, and 34% do so at lower glucose levels (130-135 mg/dL). For neural tube defect screening, 92% (95 of 103) offer maternal serum alpha-fetoprotein (MSAFP) screening although when results are elevated, further recommendations are varied. For women under 35 years of age, 84% (87 of 103) offer serum screening for trisomy 21 risk, most (68%) with double or triple (MSAFP, hCG, and estriol) markers. For women over 35 years, a majority (87%) offer serum screening, although half do so only if amniocentesis is declined for age risk alone. The relatively high initial positive rate and poor specificity of serum screening were underappreciated by a large number of respondents. CONCLUSION: Increased initial and continuing education of antenatal care providers is warranted if these screening tools are to perform optimally within office practices.

Uterine arcuate artery Doppler and decidual microvascular pathology in pregnancies complicated by type I diabetes mellitus.

The objective was to correlate Doppler indices from the uterine arcuate arteries with an analysis of the decidual vascular histology in patients with type I diabetes. Pulsed wave Doppler was used to sample the uterine arcuate artery system beneath the placenta within 8 days of delivery in 47 patients with type I diabetes mellitus. A placental pathologist, without knowledge of either clinical outcome or Doppler information, classified the histological appearance of the decidual arteries as normal, type A (hyalinization, mural thickening), or type B (fibrinoid necrosis, atherosis, thrombosis). Patients were then grouped according to the histology of the decidual arteries. An analysis of variance (ANOVA) of the systolic/diastolic (S/D) ratios (log. S/D) showed significant variation (p < 0.025). A multiple range comparison test showed that patients with normal or only mildly abnormal (type A) vessels had similar values, whereas those with severe vasculopathy (type B) had significantly higher S/D ratios (p < 0.05). The study confirmed a relationship between arcuate artery Doppler indices and downstream decidual vascular pathology.

Determinants of preterm delivery in low-risk pregnancies. The RADIUS Study Group.

From 14,948 low-risk singleton pregnancies, we calculated incidence, risk ratios, and attributable risks for characteristics associated with spontaneous and medically induced preterm delivery. There were 754 women who gave birth prior to 37 weeks of gestation (50.4/1000 deliveries). The greatest fraction of the incidence of prematurity among low-risk pregnancies was due to unknown factors associated with carrying a first live birth, regardless of preterm delivery mechanism (i.e., spontaneous labor, PROM, medical intervention), with population-attributable risk percents (PAR%) ranging from 16.0 to 30.5%. Other than nulliparity, male sex of the fetus accounted for the greatest fraction of spontaneous labor-induced prematurity incidence (PAR% = 13.6%), and maternal age greater than 30 years or a positive urine culture accounted for the greatest fraction of PROM-induced prematurity incidence (PAR% = 7.9 and 6.7, respectively). All other risk factors for either preterm labor or PROM accounted for less than 5% of the incidence. Three characteristics explained a large fraction of medically induced prematurity: women over 150 pounds at the onset of pregnancy (PAR% = 23.8), a > or = 2+ prenatal urine protein (PAR% = 18.7%), and cigarette smoking during the first trimester (PAR% = 8.6). Our results suggest known risk factors may explain only a small fraction of spontaneous preterm delivery incidence in low-risk pregnancies.

Outcome of singleton pregnancies with severe oligohydramnios in the second and third trimesters.

We evaluated the significance of severe oligohydramnios, or anhydramnios, in the second and third trimesters, by determining the range of etiologies as well as the differences in fetal and neonatal outcome. All prenatal ultrasound results on pregnancies found to have severe oligohydramnios over a 7.5-year period at 13-42 weeks' gestation were retrospectively collected. Follow-up results were obtained from review of medical records, autopsies and pathology reports. A total of 250 singleton pregnancies met the criteria of having severe oligohydramnios. A bimodal distribution in gestational age at diagnosis was seen, with more cases diagnosed at 13-21 weeks and at 34-42 weeks. Fetal abnormalities were present in 50.7% of those diagnosed with severe oligohydramnios in the second trimester and in 22.1% of those in the third trimester. There were 10.2% and 85.3% survivors when severe oligohydramnios was diagnosed in the second and third trimesters, respectively. The rate of aneuploidy was at least 4.4% for the entire singleton population. A bimodal distribution of pregnancies presenting with severe oligohydramnios represents two different naturally occurring populations in terms of both etiology and prognosis.

A clinical trial of active management of labor.

BACKGROUND: Active management of labor is a multifaceted program that, as implemented at the National Maternity Hospital in Dublin, is associated with a lower rate of cesarean delivery than the rate usually found in the United States. We conducted a randomized trial to evaluate the efficacy of this approach in lowering the rate of cesarean section among women delivering their first babies. METHODS: We randomly assigned 1934 nulliparous women at low risk of complications of pregnancy, before 30 weeks' gestation, to active management of labor or to a usual-care group. The components of active management were customized childbirth classes; strict criteria for the diagnosis of labor; standardized management of labor, including early amniotomy and treatment with high-dose oxytocin; and one-to-one nursing. A low-risk subgroup was defined as including women with full-term, uncomplicated pregnancies who spontaneously went into labor (the protocol-eligible subgroup). Women meeting these criteria who had been randomly assigned to the active-management group were admitted to a separate unit where their labor was managed by trained, certified nurse-midwives. RESULTS: There was no difference between groups in the rate of cesarean section either among all women (active management, 19.5 percent; usual care, 19.4 percent) or in the protocol-eligible subgroup (active management, 10.9 percent; usual care, 11.5 percent). In the protocol-eligible subgroup, the median duration of labor was shortened by 2.7 hours by active management (from 8.9 to 6.2 hours), and the rate of maternal fever was lower (7 percent vs. 11 percent, P = 0.007). The percentage of women in whom labor lasted longer than 12 hours was three times higher in the usual-care group than in the active-management group (26 percent vs. 9 percent, P < 0.001). CONCLUSIONS: Active management of labor did not reduce the rate of cesarean section in nulliparous women but was associated with a somewhat shorter duration of labor and less maternal fever.

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)

Epidemiologic predictors of cesarean section in nulliparous patients at low risk. RADIUS Study Group. Routine Antenatal Diagnostic Imaging with Ultrasound Study.

OBJECTIVES: We sought to determine whether certain maternal and fetal characteristics influenced the risk of maternal- and fetal-indicated cesarean sections in pregnant women at low risk for adverse perinatal outcomes. STUDY DESIGN: From a cohort of 6393 low-risk nulliparous patients maternal and fetal indicated cesarean section rates with 95% confidence intervals were calculated and stratified by demographic, anthropometric, and clinical tests and measurements. The strongest risk factors were modeled by means of multiple logistic regression. RESULTS: Few risk factors distinguished maternal from fetal characteristics preceding cesarean delivery. Maternal age was associated with increased cesarean section risk in the tallest group of women only, and cesarean section rates decreased with increasing height, increased with higher prepregnancy weights, and was highest in women carrying male fetuses. Higher first prenatal visit diastolic blood pressure, increasing numbers of nonstress tests, > or = 2+ prenatal urine protein, late sonograms, geographic region, and practice type were statistically significant risk factors as well. Interestingly, results of prenatal visit tests and measurements contributed less to the prevalence of cesarean section than did age, fetal sex, and anthropometric parameters. However, the generalizability of these results is limited to low-risk (predominantly white) populations. CONCLUSIONS: Of the risk factors we were able to assess, a large proportion of the incidence of cesarean section in this population of nulliparous patients at low risk was attributable to age, sex of fetus, and anthropometric patient profiles.

The role of Doppler velocimetry in the structurally normal second-trimester fetus with elevated levels of maternal serum alpha-fetoprotein.

Umbilical and uterine artery velocimetry was performed in 199 second-trimester pregnancies undergoing sonographic examination for unexplained elevated levels of maternal serum alpha-fetoprotein in order to evaluate the efficacy of Doppler waveforms for the prediction of adverse perinatal outcome. A total of 169 pregnancies resulted in term deliveries of infants with appropriate growth for age, and 30 pregnancies (15%) had adverse outcomes, including preterm delivery, growth retardation and death. The umbilical artery systolic/diastolic ratio was not statistically different in the two groups (3.9 vs. 4.2, p = 0.16). The uterine artery systolic/diastolic ratio was slightly greater in the group with abnormal outcome (5.7) than in the group with normal outcome (3.3), but the difference was not significant (p = 0.11). Forty-six patients had uterine artery waveforms that exhibited an early diastolic notch. Of these, 31 had a grade 1 notch in which the lowest part of the notch was not greater than one half of the diastolic frequency shift. Fifteen patients had a severe or grade II notch in which the deepest part of the diastolic notch was less than half of the diastolic flow. In patients with either no diastolic or grade I uterine artery notch, the incidence of adverse outcomes was 23/184 (12.5%). In patients with a grade II notch, 7/15 (47%) had a poor outcome. The rate of adverse outcome in patients with a grade II notch was more than three times that observed in women without severe uterine notch, yielding a relative risk of 3.4 (95% CI 1.9-6.0). Thus, the presence of a grade II uterine artery notch on second-trimester sonographic evaluation is associated with an increased risk for adverse perinatal outcome over unexplained elevated levels of maternal serum alpha-fetoprotein.

A randomized trial of prenatal ultrasonographic screening: impact on the detection, management, and outcome of anomalous fetuses. The RADIUS Study Group.

OBJECTIVE: The objective of this randomized clinical trial was to test the hypothesis that ultrasonographic screening would significantly alter perinatal outcome as a result of the antenatal detection of fetal congenital malformations. STUDY DESIGN: Pregnant women without a specific indication for ultrasonography were randomly assigned to have either two screening sonograms (15 to 22 weeks and 31 to 35 weeks) or conventional obstetric care with ultrasonography used only as determined by the clinical judgment of the patient's physician. The frequency of birth defect detection in the screened and control populations was compared, as was the impact of discovery on pregnancy outcome. RESULTS: Major congenital malformations occurred in 2.3% of the 15,281 fetuses and infants in this study. Antenatal ultrasonography detected 35% of the anomalous fetuses in the screened group versus only 11% in the control population (relative detection rate 3.1; 95% confidence interval 2.0 to 5.1). Ultrasonography screening did not, however, significantly influence the management or outcome of pregnancies complicated by congenital malformations. Specifically, only 9 abortions were performed for anomalies among 7685 fetuses in the screened group whereas 4 pregnancies were terminated for fetal anomalies detected among 7596 control subjects. Ultrasonography screening also had no significant impact on survival rates among infants with potentially treatable, life-threatening anomalies despite the opportunity to take precautionary measures such as delivery in a tertiary center. CONCLUSIONS: Ultrasonography screening in a low-risk pregnant population had no significant impact on the frequency of abortion for fetal anomalies. Survival rates for anomalous fetuses were also unaffected by screening.

Is fetal hyperechoic bowel on second-trimester sonogram an indication for amniocentesis?

OBJECTIVE: To determine the clinical significance of hyperechoic bowel seen sonographically in second-trimester fetuses. METHODS: Fifty fetuses (0.6%) with echogenic bowel were identified sonographically from a population of 8680 consecutive second-trimester fetuses over 21 months. The fetal bowel was considered hyperechoic if its echogenicity was similar to that of surrounding bone. Follow-up was obtained through medical record review. RESULTS: Twenty-nine of 50 fetuses (58%) were normal; eight (16%) were aneuploid, including six Down syndrome, one trisomy 13, and one Turner syndrome. All eight fetuses with aneuploidy had sonographic anomalies in addition to the echogenic bowel. Eight of 50 fetuses (16%) were growth-retarded, and five others (10%) had normal karyotypes but are still undelivered. Among the eight growth-retarded fetuses, there were five intrauterine or neonatal deaths, one elective abortion, and two survivors. In addition, the six fetuses with Down syndrome and echogenic bowel represented 12.5% of all second-trimester Down syndrome fetuses karyotyped in our laboratory during the study period. Combining results from the present study (six Down syndrome fetuses) with three studies from the literature (21 additional Down syndrome fetuses), a total of 27 fetuses with echogenic bowel and Down syndrome were identified, 11 (40.7%) of whom had no other sonographic findings. We calculate that if 1,000,000 second-trimester fetuses were scanned, 5105 would have hyperechoic bowel as the only finding, of whom 71 would have Down syndrome and 5034 would not. The risk of Down syndrome in fetuses with isolated hyperechoic bowel is, therefore, 71 in 5105 or 1.4%. CONCLUSION: The finding of isolated hyperechoic bowel in the second trimester should prompt genetic counseling and consideration of karyotypic analysis.

Second trimester sonographically diagnosed placenta previa: prediction of persistent previa at birth.

OBJECTIVES: We sought to determine the natural history of second trimester sonographically diagnosed placenta previa, and to ascertain whether the position of the placenta with respect to the cervical os at second trimester sonography can accurately predict persistence of the placenta previa at term. METHODS: The study population included all women consecutively diagnosed by ultrasound with placenta previa between 14 and 20 weeks' gestation. Medical records of the patients requiring cesarean section were reviewed to determine the presence of placenta previa. We reviewed the second trimester sonogram of patients who underwent abdominal delivery for placental and nonplacental indications to determine whether the central (symmetrical) versus the partial (asymmetrial) position of the placenta with respect to the internal os predicted the presence of placenta previa at delivery. RESULTS: A total of 925 second trimester- patients were sonographically identified as having placenta previa. Two hundred and sixty seven patients underwent cesarean delivery, 43 of which had placenta previa (43/925 or 4.6%). Twenty-two of the 43 were asymptomatic without antepartum bleeding. Analysis of the second trimester position of the placenta revealed that symmetry of the placenta with respect to the internal os at second trimester scan had a sensitivity of 49% for prediction of placenta previa at birth. CONCLUSIONS: The degree of placental symmetry with respect to the internal os during the second trimester successfully predicted the previas most likely to persist at delivery with a sensitivity of 49% (95% CI 34-64) and specificity of 93%.