Your Baby Ultrasound: What You’ll See - Kaiser Permanente
Accurate dating of pregnancy is important to improve outcomes and is a research and public health imperative. As soon as data from the LMP, the first accurate ultrasound examination, or both are obtained, the gestational age and the EDD should be determined, discussed with the patient, and documented clearly in the medical record. For the purposes of research and surveillance, the best obstetric estimate, rather than estimates based on the LMP alone, should be used as the measure for gestational age.
The American College of Obstetricians and Gynecologists, the American Institute of Ultrasound in Medicine, and the Society for Maternal-Fetal Medicine recognize the advantages of a single dating paradigm being used within and between institutions that provide obstetric care. Table 1 provides guidelines for estimating the due date based on ultrasonography and the LMP in pregnancy, and provides single-point cutoffs and ranges based on available evidence and expert opinion.
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Second Trimester. And you're due for a detailed ultrasound, generally between weeks 18 to 20 of pregnancy, which will give you a good, long look at your baby. What to expect at your exam This ultrasound, called an anatomy scan, lasts 20 to 45 minutes if you're having one baby, longer if you're having multiples. We designed a retrospective cohort study of all women delivered beyond 37 weeks gestational age from January 1, to December 31, at Moffitt-Long Hospital affiliated with the University of California, San Francisco (UCSF) in order to compare women who experienced a first trimester ultrasound (OBUS12 - less than or equal to 12 weeks gestation) to those who experienced a second Cited by: Pregnancy Dating: Key points Ultrasound is consistently more accurate than relying on patient recall for menstrual dating Routine ultrasound in the first or second trimester reduces inductions for post term pregnancies A woman’s self-knowledge and awareness of her internal functions, including ovulation, can be very accurate. However.
Committee Opinion No. American College of Obstetricians and Gynecologists. Obstet Gynecol ;e Women's Health Care Physicians. As soon as data from the last menstrual period LMPthe first accurate ultrasound examination, or both are obtained, the gestational age and the EDD should be determined, discussed with the patient, and documented clearly in the medical record.
Introduction An accurately assigned EDD early in prenatal care is among the most important results of evaluation and history taking. Clinical Considerations in the Second Trimester Using a single ultrasound examination in the second trimester to assist in determining the gestational age enables simultaneous fetal anatomic evaluation. Ultrasonography dating in the second trimester typically is based on regression formulas that incorporate variables such as the biparietal diameter and head circumference measured in transverse section of the head at the level of the thalami and cavum septi pellucidi; the cerebellar hemispheres should not be visible in this scanning plane the femur length measured with full length of the bone perpendicular to the ultrasound beam, excluding the distal femoral epiphysis the abdominal circumference measured in symmetrical, transverse round section at the skin line, with visualization of the vertebrae and in a plane with visualization of the stomach, umbilical vein, and portal sinus 8 Other biometric variables, such as additional long bones and the transverse cerebellar diameter, also can play a role.
Conclusion Accurate dating of pregnancy is important to improve outcomes and is a research and public health imperative. Fetal Imaging Workshop Invited Participants. Obstet Gynecol ;- A comparison of recalled date of last menstrual period with prospectively recorded dates. J Womens Health Larchmt ;- Comparison of pregnancy dating by last menstrual period, ultrasound scanning, and their combination. Am J Obstet Gynecol ; Last menstrual period versus ultrasound for pregnancy dating.
Int J Gynaecol Obstet ; First trimester ultrasound screening is effective in reducing postterm labor induction rates: a randomized controlled trial. Am J Obstet Gynecol ;- Ultrasound for fetal assessment in early pregnancy.
Cochrane Database of Systematic ReviewsIssue 7. Predicting delivery date by ultrasound and last menstrual period in early gestation. New charts for ultrasound dating of pregnancy and assessment of fetal growth: longitudinal data from a population-based cohort study. Ultrasound Obstet Gynecol ;- First- and second-trimester ultrasound assessment of gestational age. Am J Obstet Gynecol ; First- vs second-trimester ultrasound: the effect on pregnancy dating and perinatal outcomes.
Am J Obstet Gynecol ; Br J Obstet Gynaecol ;- Fetal crown-rump length: reevaluation of relation to menstrual age weeks with high-resolution real-time US. Radiology ; Gestational age in pregnancies conceived after in vitro fertilization: a comparison between age assessed from oocyte retrieval, crown-rump length and biparietal diameter. Ultrasound Obstet Gynecol ; Ultrasound dating at weeks of gestation.
A prospective cross-validation of established dating formulae in in-vitro fertilized pregnancies.
Accuracy of gestational age estimation by means of fetal crown-rump length measurement. Estimation of gestational age by transvaginal sonographic measurement of greatest embryonic length in dated human embryos.
Underestimation of gestational age by conventional crown-rump length dating curves. Obstet Gynecol ; New crown-rump length curve based on over pregnancies. Ultrasound Obstet Gynecol ; First, researchers should be encouraged to conduct studies of perinatal outcomes by gestational age among populations that are well dated or at least to consider dating in such studies by conducting subgroup analyses. As more of our patients undergo the nuchal translucency screening test, it remains to be seen whether such ultrasounds, commonly done at weeks of gestation, will provide adequate dating and studies comparing such dating to an early first trimester ultrasound should be conducted.
An important practice and policy question remains, whether in women who will not otherwise receive a first trimester ultrasound, the practice of a routine first trimester ultrasound is cost-effective with respect to pregnancy dating.
As in first trimester ultrasound, fetal heart rate (FHR) is easily measured in the second and third trimester using M-mode. The fetal heart is easily identified in the chest by its rapid contractions. The second trimester ultrasound is commonly performed between 18 and 22 weeks gestation. Historically the second trimester ultrasound was often the only routine scan offered in a pregnancy and so was expected to provide information about gestational age (correcting menstrual dates if necessary), fetal number and type of multipleCited by: 4. First trimester ultrasound is the most accurate time frame for pregnancy dating and can increase the accuracy of the EDD even if LMP is known Consider a pregnancy without a dating ultrasound prior to 22 0/7 weeks 'suboptimally dated’ (refer to Related ObG Topics below).
In order to conduct such a study considerations would include the benefits to women of improved dating as well as the cost savings of less antenatal testing and labor inductions in those women who were improperly dated. Such studies may be necessary to encourage insurance companies to provide reimbursement for more than one routine ultrasound in pregnancy similar to the care commonly provided in many European countries.
From the findings that the risk of perinatal complications are likely to be even higher than previously noted in women whose pregnancies progress to 41 weeks gestation and beyond, how should we respond? Considering the findings of a large randomized, control trial and a recent meta-analysis, it appears that induction of labor at 41 weeks gestation as compared to expectant management beyond 41 weeks actually leads to lower rates of cesarean deliveries and perinatal morbidity.
While our study did verify that first trimester ultrasound dating may lead to less misdiagnosis of postterm pregnancies, it is not without limitations. First, as a nonrandomized study, it is prone to confounding bias, particularly because women receiving a first trimester ultrasound may differ from those who did not.
In fact we did identify several potential confounders that differed between the two groups.
The second trimester scan is a routine ultrasound examination in many countries that is primarily used to assess fetal anatomy and detect the presence of any fetal anomalies. The second trimester extends from 13 weeks and 0 days to 27 weeks and 6 days of gestation although the majority of these studies are performed between 18 and 23 weeks. Trimester dating Hudson who has greatly improved our ability to compare the majority of pregnant you get trimester weeks is 5 days. In a first scan on the second trimester the ultrasound was to the pregnancy. Mean sac diameter measurements are subject to renew your first trimester. An ultrasound in the first trimester can give an accurate estimated date of confinement (EDC) to within days. Generally speaking, the earlier in your pregnancy the ultrasound is performed, the more accurate it will be at estimating your baby’s due date (technical factors such as the quality of the ultrasound image and the expertise of the sonographer will affect this accuracy).
However, the differences we found persisted even when controlling for these confounders utilizing multivariable analyses. Additionally, our study might be prone to further misclassification bias in the second trimester ultrasound group.
While we searched the medical record for evidence of early ultrasound, it may be that some of these women experienced an early ultrasound elsewhere that did not make it into the record at UCSF.
However, such misclassification would actually result in a bias towards the null effect, so any difference that we did identify would be larger. Another potential confounder is year of delivery as practice may have changed over time.
Second trimester dating ultrasound
However, we did not identify obvious changes in the practice of induction of labor during the time period of the study and we controlled for year of delivery in the multivariable analyses. In spite of these theoretical concerns, we believe that we have demonstrated that first trimester ultrasound dating leads to less misclassification with respect to gestational age.
The result of such improved dating is that fewer women are misdiagnosed as having a prolonged gestation. However, it also unmasks larger risks of perinatal complications in such women who do progress to and beyond 41 weeks of gestation.
Thus, these findings would suggest that women will benefit from a first trimester ultrasound to confirm or adjust pregnancy dating. Additionally, closer attention to the issue of pregnancies that progress beyond their due date should be paid by both clinicians and researchers in order to reduce the perinatal morbidity and mortality in term and postterm pregnancies.
However, before we support the practice of routine induction of labor or antenatal testing at 39 or 40 weeks of gestation, large prospective, randomized, controlled trials of such interventions should be conducted. Condensation: Women with first trimester ultrasounds are diagnosed with postterm pregnancies and experience postterm induction less often than those with a second trimester ultrasound.
Women's Health Care Physicians
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National Center for Biotechnology InformationU. Am J Obstet Gynecol. Author manuscript; available in PMC Dec Aaron B. Eugene Washington. Author information Copyright and License information Disclaimer. Correspondence: Aaron B. Copyright notice.Transvaginal Ultrasound - CHI Health
The publisher's final edited version of this article is available at Am J Obstet Gynecol. See other articles in PMC that cite the published article. Abstract Objective To examine the effect of first trimester obstetric ultrasound OBUS on the measurement of the effect of complications ascribed to postterm pregnancies.
Conclusion Our findings suggest that earlier obstetric ultrasound, which leads to better pregnancy dating, reduces the rate of estimated postterm pregnancies. Keywords: pregnancy dating, ultrasound, complications of pregnancy, post-term, post-dates.
Introduction Postterm pregnancy continues to be defined as one that progresses to and beyond 42 completed weeks, or days, of gestation.
Open in a separate window. Figure 1. Misclassification Bias and the Comparison Between Term and Postterm Pregnancies In the figure, note that due to misclassification bias in the poor dating group, the rate of complications is higher in the women diagnosed as term pregnancies due to the inclusion of postterm pregnancies and the rate of complications is lower in the women diagnosed as postterm pregnancies due to the inclusion of term pregnancies.
Materials and Methods We designed a retrospective cohort study of all women delivered beyond 37 weeks gestational age from January 1, to December 31, at Moffitt-Long Hospital affiliated with the University of California, San Francisco UCSF in order to compare women who experienced a first trimester ultrasound OBUS12 - less than or equal to 12 weeks gestation to those who experienced a second trimester ultrasound OBUS - 13 to 24 weeks gestation.
Results During the study period, there were 7, women who delivered at or beyond 37 completed weeks of gestation who had a documented ultrasound at or before 24 weeks gestation. Comment When we compared women who had undergone a first versus a second trimester ultrasound, those who had a first trimester ultrasound were less frequently diagnosed with a prolonged pregnancy beyond 41 weeks gestation or postterm pregnancy beyond 42 weeks gestation. Footnotes This study was presented at the Pacific Coast Obstetrical and Gynecological Society Meeting in Las Vegas, NV in October, Condensation: Women with first trimester ultrasounds are diagnosed with postterm pregnancies and experience postterm induction less often than those with a second trimester ultrasound.
References 1. American College of Obstetricians and Gynecologists. Washington, D. Post-Term Pregnancy. Obstet Gynecol. The Problem of Postterm Pregnancy.
Naeye RL. Causes of perinatal mortality excess in prolonged gestations. Am J Epidemiol. Complications of term pregnancies beyond 37 weeks of gestation. The impact of the interaction between increasing gestational age and obstetrical risk on birth outcomes: evidence of a varying optimal time of delivery.
J Perinatol. Neonatal complications of term pregnancies: rates increase in a continuous, not threshold fashion. Taipale P, Hilesmaa V. Comparison of pregnancy dating by last menstrual period, ultrasound scanning, and their combination. First trimester ultrasound screening is effective in reducing postterm labor induction rates: a randomized controlled trial.