Prenatal ultrasonography is a common procedure in many countries. It is an accurate technique for determining gestational age, number of fetuses, fetal cardiac activity, and placental location. In addition, many congenital structural anomalies and significant abnormalities in fetal growth can be identified. However, whether all obstetrical patients should undergo ultrasound screening and whether such screening improves pregnancy outcome is controversial.
Many countries have developed local guidelines for the practice of prenatal ultrasonography and most offer at least one mid-trimester ultrasound examination as part of standard prenatal care, although worldwide obstetric practice varies. In the United States, the American College of Obstetricians and Gynecologists (ACOG) supports the use of ultrasound when there is a specific medical indication and advises against nonmedical use of prenatal ultrasonography (eg, to accommodate parental curiosity about fetal sex or parental desire to view and/or obtain an image of the fetus). ACOG also stated that the benefits and limitations of ultrasonography should be discussed with all patients, and performance of the procedure is reasonable in patients who request it. In addition, a 2006 workshop organized by the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) reached a consensus that “all fetuses should have a screening ultrasonogram for the detection of fetal anomalies and pregnancy complications”.
An evidence-based discussion of the application of ultrasound to an unselected obstetric population as a screening tool will be presented here. The use of prenatal ultrasonography for specific obstetrical indications is reviewed separately. CRITERIA FOR A GOOD SCREENING TEST — In general, a good screening test should be safe, have high sensitivity and specificity, ideally take only a few minutes to perform, require minimum preparation by the patient, and be inexpensive. It should identify individuals with an important disease or condition and be cost-effective, allowing for control of health care costs by identifying disease early and treating before the consequences of the disease are overwhelming. (See RATIONALE FOR ROUTINE SCREENING PRENATAL ULTRASOUND — It is hypothesized that routine use of ultrasound in all pregnancies will prove beneficial since adverse outcomes may occur in pregnancies without risk factors and clinical conditions that place the fetus at high risk may not be detected by clinical examination. The primary objective is to obtain information that will enable delivery of optimal antenatal care and thus the best possible outcomes for mother and fetus. However, the benefit of such prenatal sonographic screening on neonatal outcomes remains unproven.
BENEFITS OF ROUTINE PRENATAL ULTRASOUND EXAMINATION — Compared to no prenatal ultrasound examination or ultrasound examination in selected patients, routine ultrasound examination improves:
● Estimation of gestational age
● Identification of multiple gestation
● Identification of congenital anomalies
Better estimate of gestational age/delivery date — Determination of the expected date of delivery (EDD) is essential in obstetrics so that misdiagnosis (and inappropriate intervention) of pre-viable, preterm, and post term pregnancy can be avoided. As more focus is placed on reducing late preterm birth and early term birth, more accurate estimation of EDD takes on increasing importance. Ample evidence has accumulated that routine ultrasound examination results in more accurate assessment of the EDD than last menstrual period (LMP) dating or physical examination, even in women with regular and certain menstrual.
The benefits of ensuring the most accurate estimation of gestational age/delivery date include a reduction in intervention for post-term pregnancy, reduction in diagnosis of fetal growth restriction, and reduction in use of tocolysis. More accurate estimation of EDD may also reduce planned cesarean delivery before 39 weeks of gestation resulting from misdiagnosis of gestational age.
Reduction in intervention for post term pregnancy — Ultrasound-based determination of EDD reduces intervention for post term pregnancy. In a 2015 Cochrane review of 11 trials of routine/revealed ultrasound versus selective/concealed ultrasound before the 24th week of pregnancy, routine use of early ultrasound and the subsequent adjustment of the EDD led to a significant reduction in induction of labor for post term pregnancy. Although these trials showed that ultrasound determination of EDD as late as 24 weeks can reduce the number of pregnancies eventually diagnosed as post term, as well as scans performed at 10 to 18 weeks, a randomized trial looking specifically at the timing of the examination demonstrated that first trimester ultrasound examination in a low-risk population was more effective than second trimester ultrasound examination in decreasing post term pregnancy.
Better detection of aneuploidy — Serum screening protocols are dependent upon accurate estimation of gestational age. The majority of abnormal tests recalculated based on corrected EDD are normal. Thus, routine ultrasound estimation of gestational age may reduce the number of women who have anxiety caused by false positive results in serum screening.
In addition to gestational age determination, the combination of sonographic nuchal translucency measurement and maternal serum analyte assessment in the first trimester can detect over 90 percent of fetuses with Down syndrome, as well as some fetuses with other aneuploidies.
Risk assessment for fetal aneuploidy using cell-free DNA in maternal blood is not dependent on precise determination of gestational age.
Better identification of multiple gestation — A major benefit of routine ultrasound screening is early, reliable identification of twin pregnancies. In women who do not undergo routine ultrasound examination, a significant number of twin pregnancies are not recognized until the third trimester or delivery.
In the 2015 Cochrane review of trials of routine ultrasound before the 24th week of pregnancy described above, multiple gestation was diagnosed earlier in routinely scanned pregnancies and ultrasound in early pregnancy significantly reduced the failure to detect multiple pregnancy by 24 weeks of gestation (RR 0.07, 95% CI 0.03-0.17; 7 trials, 295 patients). In the Routine Antenatal Diagnostic Imaging with Ultrasound Study (RADIUS), of over 15,000 gravidas (the largest trial in the Cochrane review), women who did not have a routine second trimester ultrasound examination had 38 percent of twin pregnancies unrecognized until after 26 weeks of gestation and 13 percent of twins were not diagnosed until delivery. There were no twin pregnancies missed on ultrasound examination.
Similar findings were reported by the Helsinki trial, a prospective randomized trial of 9310 women, of which 4691 underwent screening ultrasound between 16 and 20 weeks. All twin pregnancies were detected before 21 weeks of gestation in the screened group, versus 76.3 percent in the control group. Moreover, the perinatal mortality rate (PMR) of twins in the screened group was 27.8/1000 compared with 65.8/1000 in the control group, although these were small numbers and did not reach statistical significance. Retrospective series have also suggested improved neonatal outcomes with early diagnosis of twin pregnancy.
Better detection of congenital anomalies — The ability of routine ultrasound screening to detect fetal anomalies in an unselected population is highly controversial. Over 30 studies have evaluated this question, and numerous reviews have attempted to summarize them critically. In the 2015 Cochrane review of trials of routine ultrasound before the 24th week of pregnancy described above, performance of routine/revealed early pregnancy ultrasound significantly increased detection of fetal abnormalities before 24 weeks of gestation (RR 3.46, 95% CI 1.67-7.14; 2 trials, 387 patients) . A number of factors (eg, gestational age at examination, type of malformation, number of ultrasounds performed, operator experience, quality of equipment, population characteristics) affect detection rates, and were not addressed in the meta-analys.
The largest trials and studies comparing second trimester screened and unscreened pregnancies are reviewed below (only RADIUS was included in the Cochrane review).
● Helsinki Trial — The Helsinki Trial, performed from 1986 to 1987, randomly assigned 4691 women to screening ultrasound at 16 to 20 weeks to look for fetal anomalies and compared their outcome to 4619 controls who underwent ultrasound examination if obstetrically indicated. Ultrasounds were performed at one of two hospitals, 95 percent of all pregnant women in the Helsinki metropolitan area agreed to participate, and only four women were lost to follow-up (but mortality data were complete). Seventy-seven percent of women in the control group underwent ultrasound examination sometime during pregnancy. Routine second trimester ultrasound screening resulted in:
● Significantly increased detection of fetal anomalies. The rate of detection of malformations was 36 percent in the City Hospital and 77 percent at the University Hospital.
● A significant reduction in the PMR (4.6/1000 versus 9.0/1000 in controls) because elective termination of anomalous fetuses resulted in fewer fetal and neonatal deaths due to congenital anomalies.
● RADIUS Trial — The RADIUS trial was the first randomized trial of routine obstetrical ultrasound screening in the United States. It included over 15,000 women randomly assigned to either screening ultrasounds at both 15 to 22 weeks and 31 to 35 weeks or to ultrasound for obstetrical indications only. Forty five percent of the control group had at least one ultrasound. Routine second trimester ultrasound screening resulted in:
● Significantly increased detection of fetal anomalies (34.8 versus 11 percent in controls). Of these anomalies, one-half were detected prior to 24 weeks of gestation in the screened group (16.6 percent of the total cohort of anomalous fetuses). As noted in the Helsinki trial, detection rates were significantly higher in tertiary facilities.
● No improvement in any perinatal outcome under study, including mortality, preterm birth, birth weight, and neonatal morbidity (retinopathy of prematurity, bronchopulmonary dysplasia, need for mechanical ventilation, necrotizing enterocolitis, intraventricular hemorrhage).
● No increase in the number of abortions performed for fetal anomalies, which was the same in both groups.
● No improvement in survival among anomalous fetuses. Antenatal detection of fetal anomalies did not improve survival over that with postnatal diagnosis.
● Eurofetus study — The Eurofetus study of 1999 is the largest study of routine ultrasonographic examination in unselected population. Women were routinely scanned by trained sonologists at 18 to 22 weeks in 61 centers across Europe. Major findings were:
● The sensitivity for detection of all anomalies was 56.2 percent.
● The detection rate was higher for major (73.7 percent) than for minor (45.7 percent) anomalies, and higher for anomalies of the central nervous system (CNS, 88.3 percent) and the urinary tract (88.5 percent) than for cardiac abnormalities (38.8 percent of major cardiac and 20.8 percent of minor cardiac anomalies were detected).
● Overall, 44 percent of anomalies and 55 percent of severe anomalies were detected before 24 weeks. Cardiac defects and cleft lip/palate were diagnosed later in pregnancy than abnormalities of the CNS, urinary tract, or musculoskeletal systems.
● The rate of live births for mothers carrying fetuses with anomalies was lower than that of mothers carrying fetuses with no detected anomalies because many pregnancies with anomalous fetuses were electively terminated.
Factors affecting detection rates — Several important factors need to be considered when analyzing these data: prevalence of anomalies, characteristics of the population, the setting in which the ultrasound was performed, and study design.
● Prevalence of anomalies — Detection rates for anomalies are dependent upon the prevalence of each anomaly in the population studied, and prevalence is highly dependent upon the quality of follow-up achieved. For example, how thoroughly were aborted fetuses, stillbirths, and neonates examined for presence of anomalies? Were autopsies and x-rays performed when appropriate? Were neonates examined by a physician with additional expertise in dysmorphology? How many neonates underwent noninvasive studies with incidental discovery of a congenital anomaly? Some anomalies are not diagnosed until early childhood; was there examination of pediatric records to identify these children?
The table shows that anomaly prevalence rates reported in the literature range from 0.3 to 3.2 percent . Studies with low prevalence rates likely represent incomplete follow-up, thus detection rates and published sensitivities are not necessarily reliable. The last column in the table corrects for the differing prevalence rates and standardizes sensitivity rates for each study. The adjusted overall cumulative sensitivity becomes 40 percent, with the Eurofetus detection rate climbing to almost 70 percent.
● Population characteristics — Characteristics of the population studied also affect both detection rates and the applicability of data to other populations. For example, two of the RADIUS trial's main inclusion criteria were that the patients have private obstetrical care and that they be indifferent to the possibility of termination of pregnancy. In fact, after all exclusions, only 28 percent of the eligible women actually participated in the study. One consequence of these selection criteria is that women who wished to undergo ultrasound examination, including those who might consider termination in the event of fetal anomaly, did not elect to participate. Thus, the observation that 71 percent of women with ultrasound-detected anomalies prior to 24 weeks decided to continue their pregnancies is not generalizable to an unselected population of pregnant women.
In this respect, data from the Helsinki trial, which included 95 percent of women in the area, more reliably describe the consequences of detecting fetal anomalies antenatally. The Helsinki trial reported that birth rates of anomalous fetuses were low due to termination of many of these pregnancies.
Another important aspect of the RADIUS trial is that approximately 85 percent of the population ultimately had an identifiable indication for ultrasound. Seventy percent of women were excluded prior to randomization, primarily because potential indications for ultrasound examination were present, and 50 percent of the remaining (enrolled) patients developed indications during the trial.
●Setting — The setting in which the ultrasound is performed significantly affects detection rates. Factors relating to the setting involve the equipment available, as well as the skill and experience of the examiners. Both the RADIUS trial and the Helsinki trial showed that examinations performed in hospital or tertiary care settings identified more anomalies than those performed in office-based or community centers and ultrasound was more effective when performed by experienced operators. A review by the German Institute for Quality and Efficiency in Health Care (IQWiG) also noted that higher qualifications or greater experience of examiners and superior device quality were associated with higher detection rates for fetal abnormalities.
It is important to note that the RADIUS and Helsinki trials were both performed in the 1980s when ultrasound technology was still new. Since that time, the technology has evolved dramatically, which could enhance the diagnostic efficacy of less experienced sonologists and sonographers.
●Study design — Studies are designed and powered to detect differences in their main outcome variables. Investigators choose study outcomes based upon their clinical significance and relevance to the question at hand. The endpoints chosen by the investigators of the RADIUS trial were associated with prematurity, rather than with anomalies and their consequences. RADIUS was not powered to detect differences in secondary outcome measures associated with the diagnosis of anomalies, such as impact on immediate survival, long-term neonatal outcomes in anomalous fetuses, and economic and social implications. In fact, the survival rate for infants with acute life-threatening anomalies was higher in the screened group (75 percent) than in the unscreened group (52 percent). Although this was not statistically significant, this was likely due to the very small sample size.
Other investigators have found that patients with cardiac anomalies and specifically hypoplastic left heart and transposition of the great arteries have better outcomes when the diagnosis is made prenatally rather than postnatally. The data regarding long-term outcome for prenatally diagnosed anomalies of the renal system are conflicting and limited.
First trimester screening — Detection of fetal anomalies in the first trimester is limited by the small size of the fetus and ongoing fetal development, which can result in later development of markers suggestive of an underlying abnormality (eg, hydramnios related to esophageal atresia). Nevertheless, ultrasound technology is rapidly progressing and assessment of fetal anatomy in the first trimester is becoming more widely available.
A 2013 systematic review of the accuracy of ultrasonography at 11 to 14 weeks of gestation for detection of fetal structural anomalies included 19 observational studies, approximately 78,000 fetal anatomy examinations, and 996 postnatally-confirmed malformed fetuses. The overall detection rate for fetal structural anomalies was 51 percent, but detection rates for specific abnormalities varied widely from 0 to 100 percent. For example, no cases of renal agenesis were detected in this gestational age range, fewer than 50 percent of cases of spina bifida were detected, more than 50 percent of cases of omphalocele, gastroschisis, and tetralogy of Fallot were detected, and 100 percent of anencephalic fetuses were detected. Detection of anomalies was more likely if there were multiple anomalies, both abdominal and vaginal ultrasound examination was performed, or the woman was at high risk. Although there was considerable heterogeneity among these studies, the findings affirm both the potential benefits and limitations of the first trimester fetal anatomic survey. Most women will need a second trimester survey to provide a more reliable assessment of fetal anatomy.
Prevention of preterm birth — A 2013 Cochrane review did not find sufficient evidence to recommend routine cervical length screening of all pregnant women however, the trials did not have a clear protocol for management of women based on cervical length and included heterogeneous populations. Based on a meta-analysis of five trials of progesterone treatment of women with asymptomatic mid trimester cervical shortening, cervical length screening for all singleton pregnancies in the mid trimester coupled with treatment of women found to have a short cervix is a reasonable approach.
In a 2012 practice bulletin, the American College of Obstetricians and Gynecologists (ACOG) neither mandated universal routine cervical length screening in women without a prior preterm birth nor recommended against such screening. However, in women undergoing obstetrical ultrasound examination, ACOG has recommended that the cervix be examined when clinically appropriate and technically feasible. In 2011, the Society of Obstetricians and Gynecologists of Canada (SOGC) concluded that routine transvaginal cervical length assessment was not indicated in women at low risk.
UNPROVEN OR UNCLEAR BENEFIT OF ROUTINE SCREENING
Better diagnosis of deficient growth and improvement in perinatal outcome — An early ultrasound examination serves as a key baseline against which later examinations are compared for the evaluation of fetal growth. The assessment of appropriate fetal or neonatal size is based upon the expected weight for gestational age. If gestational age is overestimated, then an appropriately grown fetus/neonate may be incorrectly classified as growth restricted or small for gestational age (SGA). However, in the 2015 Cochrane review of trials of routine/revealed ultrasound versus selective/concealed ultrasound before the 24th week of pregnancy described above, routine use of early ultrasound did not result in a significant reduction in diagnosis of SGA (relative risk [RR] 1.05, 95% CI 0.81-1.35; three trials, n = 17,105.
The value of universal rather than selective ultrasound examination in late pregnancy to screen for fetal growth restriction is unclear. Although early identification of growth-restricted fetuses allows for closer surveillance and earlier intervention in case of fetal decompensation, a 2015 Cochrane review of controlled trials of routine ultrasound >24 weeks versus no/concealed/selective ultrasound >24 weeks of gestation found routine ultrasound did not improve detection of neonates with birth weight <10th percentile (RR 0.98, 95% CI 0.74-1.28; four trials, n = 20,293) or decrease perinatal mortality (RR 1.13, 95% CI 0.58-2.19; six trials, n = 28,133).
Subsequently, a prospective cohort study (Pregnancy Outcome Prediction study) specifically addressed this issue in a population of unselected nulliparous women with singleton gestations who underwent routine early ultrasonography for pregnancy dating. Women who agreed to participate (n = 4512) were scheduled to undergo serial ultrasound examinations at about 20, 28, and 36 weeks of gestation, but findings from the research component of these ultrasound scans (utero placental Doppler, biometry, estimated fetal weight [EFW]) were masked from both the women and their providers. About half of the women eventually underwent clinically indicated third-trimester ultrasound examinations. Universal sonography in the third trimester almost tripled the detection of infants subsequently born SGA compared with clinically indicated sonography (57 versus 20 percent); however, universal ultrasound over diagnosed SGA more often than clinically indicated ultrasound (positive predictive value 35 versus 50 percent).
The study also evaluated whether universal antenatal screening for SGA improved perinatal outcome. Among fetuses with EFW <10th percentile, only those with abdominal circumference growth velocity at the lowest decile were at increased risk for neonatal morbidity. Umbilical artery pulsatility index in the highest decile did not distinguish between SGA infants at low risk and high risk of neonatal morbidity.
Assessment of placental position, fetal presentation, amniotic fluid volume, macrosomia — Although ultrasound examination late in pregnancy can diagnose clinically important placental abnormalities (eg, placenta previa, placenta accreta), fetal malpresentation, disorders of amniotic fluid volume (oligohydramnios, polyhydramnios), and excessive fetal growth, a 2015 Cochrane review found no evidence that a policy of routine late pregnancy ultrasound screening for these conditions results in better maternal, fetal, or neonatal outcomes than performance of ultrasound when indicated by clinical findings or high-risk factors.
Doppler ultrasound screening
Umbilical artery —The application of Doppler to obstetrical ultrasound provides information on function in addition to form. Doppler velocimetry of the fetal circulation is used to assess vascular impedance, especially in the setting of suspected growth restriction. Multiple trials have evaluated the use of Doppler ultrasound as a screening tool in low-risk women. These have consistently found neither maternal nor fetal benefit, which is in contrast to the proven benefit in high-risk pregnancies.
In a 2015 Cochrane review including 5 trials involving 14,185 women, routine fetal and umbilical artery Doppler ultrasound examination in low-risk or unselected populations did not result in increased antenatal, obstetric, and neonatal interventions, and no overall differences were detected for substantive short-term clinical outcomes such as perinatal mortality, neonatal morbidity, stillbirth, birthweight, preterm birth, or cesarean delivery.
Uterine artery — Although meta-analyses show that uterine artery Doppler analysis can predict women at increased risk of preeclampsia, we and most experts do not recommend these studies for screening purposes. Close clinical monitoring for preeclampsia is already a major component of prenatal care; improved identification of women at increased or decreased risk of a disease that cannot be prevented and has no treatment other than delivery is unlikely to improve maternal or fetal outcome. Furthermore, the false positive rate of this test is quite high, leading to excessive patient anxiety and health care costs. Further research is needed before screening with uterine artery Doppler can be recommended.
Safety issues — The safety of obstetric ultrasound is well established and is reviewed in detail elsewhere.
Resource utilization — The overall effect of routine screening on the health care system has yet to be determined. A small number of reports have analyzed the cost-benefit ratio of screening low-risk women with obstetrical ultrasound. The value (ie, utility) that individual patients place on birth, or avoidance of birth, of a child with an unsuspected anomaly needs to be incorporated into any cost-benefit equation of this issue, but is not routinely assessed, nor are such values easily assigned in monetary terms.
The authors of the Routine Antenatal Diagnostic Imaging with Ultrasound Study (RADIUS) trial concluded that routine ultrasound was not cost-effective and that offering the procedure would place a burden on health care systems. However, the authors neglected to take into consideration all outcome measures in the study. As an example, although overall perinatal mortality was not changed, there was a significantly higher rate of detection of anomalies in the screened group. The study was not powered to analyze what effect this detection rate had on secondary outcomes, namely utilization of abortion services or reduction in the neonatal costs for pregnancies that were not continued. In addition, the trial found a significant reduction in induction for post term pregnancy and in the use of tocolysis, but these effects were not evaluated in the cost analysis. The cost analysis also did not account for the societal costs of the ultrasounds performed on the patients who did not qualify for randomization.
Because of these criticisms, investigators not involved in the RADIUS study performed a complex cost-benefit analysis of routine second-trimester ultrasound using data from the RADIUS trial and taking into consideration all of the findings of the trial. Costs were estimated for each type of fetal anomaly and projected for the follow-up each would need in neonatal life, and savings from decreased use of tocolysis and decreased diagnosis of post term pregnancy were calculated. This analysis concluded that routine ultrasound screening was associated with significant savings, but only if the ultrasonography was performed in tertiary care centers, where experience and efficiency were greatest.
The Helsinki Trial also addressed the use of antenatal care services in its trial of routine ultrasound screening. Ultrasound screening slightly, but significantly, increased the number of routine antenatal visits (12.9 versus 12.6). However, it also reduced the need for specialist services, primarily by improving the accuracy of gestational age estimation and removing questions regarding pregnancy dating. There were no differences in hospital admissions.
A cost-effectiveness analysis on the same data set suggested that second trimester screening with ultrasound is cost-effective, at least in a society with a publicly financed health system. The absolute cost per ultrasound was $86, which included the cost of equipment, staff, travel, and lost working time. When the costs of screening-induced examinations and procedures (repeat ultrasounds, amniocenteses, etc.) were added, the cost per ultrasound rose to $102. Cost savings were calculated based upon decreased utilization of health services and visits, and amounted to $182 per ultrasound, yielding a net saving of $80 per patient in the screened group. The gross cost of avoiding one perinatal death was $21,938, as based upon the decreased perinatal mortality rate (PMR) reported in that trial. Stated differently, if the malformation rate was 2.95/1000, and the cost per ultrasound was $102, the cost to identify a single fetus with a malformation was $34,620, a number which is much lower than the amount spent during the hospitalization of a neonate with a congenital anomaly. The Helsinki data cannot be directly applied to the United States health care system when one considers that costs in general are much greater in the United States. Importantly, this evaluation assumes the availability and acceptability of termination of pregnancy.
A randomized trial from an urban center in South Africa also looked at the costs of routine ultrasound screening and perinatal outcomes. The study group consisted of patients without risk factors for congenital anomalies referred for ultrasound at 18 to 24 weeks of gestation, while the control group had routine care only; both groups could be referred for additional scans as indicated. Women in the control group were more likely to be diagnosed with postdate pregnancies and undergo amniocenteses for confirmation of lung maturity; however, the overall incidence of major adverse perinatal outcomes was comparable in the two groups. Routine sonography was associated with increased costs that were not accounted for by improved outcomes.
A systematic review of studies examining cost and cost-effectiveness in screening ultrasound concluded that the available data were of poor quality and that data could not be summarized to draw useful conclusions. The authors commented specifically that charges were examined instead of costs, and maternal costs and long-term costs were not examined effectively. It is also important to emphasize that the data used in these cost analyses come from countries outside of the United States, and also from a different time period, factors that limit their generalizability to the contemporary United States population.
Ethical considerations — The ethical concept of autonomy guides the physician in providing patients with as much information as they need to make educated choices about their medical care. It implies a respect for patients' individual belief systems and patients' ability to choose among appropriate options in health care. Engaging patients in a thoughtful discussion of the benefits and limitations of routine ultrasound respects the concept of autonomy by providing patients with the information they need to make these choices.
However, moral dilemmas have emerged when healthy fetuses have been lost due to invasive diagnostic testing or pregnancy termination related to ultrasound findings of uncertain clinical significance.
Women's views — Ultrasound is very attractive to women because it provides early visual confirmation of pregnancy, contact with their babies, and enhances feeling of bonding between the woman and her baby. Although most examinations are reassuring about fetal well-being, anxiety can be heightened while waiting for the scan and when the scan shows a problem, especially when findings of uncertain clinical significance are noted.
●Routine early ultrasound is beneficial in an unselected population because of better estimation of gestational age resulting in significantly reduced frequency of labor induction for post term pregnancy.
●Routine early ultrasound examination can lead to earlier detection of clinically unsuspected fetal malformations (including aneuploidies) and earlier detection of multiple pregnancies. The Eurofetus trial likely approaches the most accurate sensitivity rates for ultrasound in the detection of anomalies (approximately 50 to 70 percent). One hundred percent of multiple gestations can be detected by ultrasound examination. These findings have not been shown to improve ultimate fetal outcome, although studies have lacked power to assess for secondary outcomes
●Improvements in technology, increasing experience, and refinements in visualization should make the detection of anomalies in the first trimester more efficient at a time when termination of pregnancy is possible and private
●If one screening ultrasound examination is performed, we agree with the recommendation of the American College of Obstetricians and Gynecologists (ACOG) that the optimal timing is at 18 to 20 weeks of gestation. This allows for good visualization of anatomy and is early enough to allow completion of prenatal diagnostic procedures (eg, fetal karyotype/microarray, additional imaging studies) while legal termination of pregnancy is possible, if desired. The ultrasound examination should be carried out by an experienced practitioner.