First trimester ultrasound measurements are optimal when estimating GA because of limited variability in fetal size due to IUGR [ 3 ]; ultrasound estimates in our study are likely influenced by IUGR, which would underestimate GA and may bias results. In low- and middle-income countries, however, first trimester ultrasound measurements are typically not feasible and previous studies have demonstrated the accuracy of second trimester ultrasound estimates of GA [ 29 ].
Despite being considered gold standard, it is important to recognize that ultrasound estimates of GA are not direct measurements of pregnancy duration and, similar to other GA estimation methods, are subject to some error [ 3 ]; importantly, studies have established the improved accuracy of ultrasound estimates of GA compared with other methods [ 3 , 9 — 11 ]. As ultrasound measurements are frequently not available in low- and middle-income countries, it is important to identify alternative methods that provide accurate estimates of GA.
Our findings provide information regarding the utility of LMP-based estimates of GA compared to Farr examination estimates, and the level of accuracy compared to ultrasound estimates. Discordance between LMP-based and clinically estimated gestational age: implications for research, programs, and policy. Public Health Rep. Conceptualization, measurement, and use of gestational age. Clinical and public health practice.
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Champaign: Human Kinetics Publishers; Google Scholar. Cogill B. Anthropometric Indicators Measurement Guide. The definition of some external characteristics used in the assessment of gestational age in the newborn infant. Dev Med Child Neurol. The value of some external characteristics in the assessment of gestational age at birth. Ultrasound based gestational age estimation in late pregnancy. Forming inferences about some intraclass correlation coefficients. Psychol Methods.
Intraclass correlations: uses in assessing rater reliability. Psychol Bull. Lin LI. A concordance correlation coefficient to evaluate reproducibility. Measuring agreement in method comparison studies. Stat Methods Med Res. Patterns of fetal growth based on ultrasound measurement and its relationship to small for gestational age birth in rural Vietnam.
Assessment of gestational age in the Cameroonian newborn infant: a comparison of four scoring methods. J Trop Pediatr. Dating gestational age by last menstrual period, symphysis-fundal height, and ultrasound in urban Pakistan. Int J Gynaecol Obstet. First- and second-trimester ultrasound assessment of gestational age. Download references. The authors thank O. The authors also thank the Reviewers for their thoughtful feedback to help improve the manuscript. Funding for this research was provided by the Mathile Institute for the Advancement of Human Nutrition and the Micronutrient Initiative.
Deputy was supported in part by U. Data are available on the Additional file 1 submitted together with the manuscript. NPD contributed to developing the research question, conducting the statistical analysis, and drafting and revising the manuscript. HP a day to-day project field director, participated in field supervision, carried out data collection and provided inputs for manuscript. SN participated in field organization and provided inputs for manuscripts.
All authors contributed in the development, review and approval of the final manuscript. A dating scan is an ultrasound examination which is performed in order to establish the gestational age of the pregnancy.
Most dating scans are done with a trans-abdominal ultrasound and a fullish bladder. If the pregnancy is very early the gestation sac and embryo will not be big enough to see, so the transvaginal approach will give better pictures. For transvaginal ultrasound you can have an empty bladder. By 6 to 7 weeks gestation the developing baby is clearly seen on trans-vaginal ultrasound and the heartbeat can be seen at this early stage 90 to beats per minute under 6 to 7 weeks, then to beats per minute as the baby matures.
By 8 weeks gestation the baby and its heartbeat can be detected relatively easily with trans-abdominal and trans-vaginal examination. This is presuming that the pregnancy is actually at this stage of development. Sometimes a trans-vaginal examination shows that your pregnancy is less advanced than expected. Ultrasounds performed during the first 12 weeks of pregnancy are generally within 5 days of accuracy. The most accurate time is between 8 and 11 weeks gestation.
This is because the baby is growing so quickly that there is a big difference in size from week to week. Also, the baby cannot bend and twist too much yet, so the length of the body is fairly constant at these gestations.
However, the accuracy of the ultrasound examination is always dependent on the position of the uterus, how much tissue the probe needs to penetrate, the size of the baby, the skill of the sonographer and the quality of the equipment.
This is why at Ultrasound Care we use the latest equipment, and all our sonographers are highly skilled. If the last menstrual period is not known or is unreliable, or the dating scan differs from the last menstrual period dating by more than 5 days the EDD from the early dating scan is used.
Bear in mind, that even women with regular 28 day menstrual cycles do not always ovulate on day 14 of the cycle, so your due date may change according to your date of conception. As the baby gets bigger, it starts to express its individual growth potential.
The size of the baby correlates less and less with its age as time goes on. For example, a baby with cm tall parents is likely to be longer than a baby with cm tall parents. After 28 weeks, the ultrasound may be off by three weeks or more in predicting a due date. Thus, later in pregnancy, ultrasound measurements are more valuable for evaluating the baby's growth over time compared with earlier measurements than they are for predicting a due date.
Get diet and wellness tips to help your kids stay healthy and happy. Diagnostic accuracy of ultrasound above and below the beta-hCG discriminatory zone. Obstet Gynecol. Estimating the date of confinement: Ultrasonographic biometry versus certain menstrual dates.
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