Lmp vs ultrasound dating
Read terms. Pettker, MD; James D. Goldberg, MD; and Yasser Y. This document reflects emerging clinical and scientific advances as of the date issued and is subject to change.SEE VIDEO BY TOPIC: How to Calculate Your Due Date by Ultrasound (Week 6-2)
When LMP and Ultrasound Dates Don’t Match: When to Redate?
Initially, the estimated date of delivery EDD is generally calculated based on the first day of the last menstrual period LMP and may later be modified when an ultrasound US scan is performed.
According to the International Society of Ultrasound in Obstetrics and Gynecology, clinical decisions should preferably be based on the EDD by US 1 , and based on first trimester ultrasound, if performed. The most frequently used formula for pregnancy dating in Sweden today is based on fetal biparietal measurements during the second trimester US scan, and this formula can be used to predict the day of delivery with a standard deviation SD of 8 days 2 , 3 , 4. A minority of clinics perform first trimester pregnancy dating, with increasing practice during the last decade 2 , 5.
Before , the combined information from measurement of the biparietal diameter and femur length were generally used 5. Although the US-based method is superior to the LMP-based method in most pregnancies, some maternal and fetal characteristics, such as the sex of the fetus, may influence the precision of the US-based estimate, and this lack of precision may be associated with adverse perinatal outcomes 9 , 10 , 11 , 12 , The discrepancy between dating methods and its association with pregnancy-related outcomes has been investigated in a few studies, but these have included a small study size or a limited number of perinatal outcomes 9 , 10 , The aim of this large population-based Swedish register study was to assess whether the discrepancy between LMP-based and US-based EDD is associated with a series of adverse pregnancy, delivery, and neonatal outcomes.
This register-based cohort study included all singleton births, live or stillborn, in Sweden, from to , with valid documentation of the EDD based on both LMP and US, and a discrepancy between estimates of 20 days or less. According to a study of the 59 clinics in Sweden that provided obstetric and antenatal care, pregnancy dating was based on a routine US examination performed between gestational weeks 16—20 in 52 clinics, and on a US examination performed at 10—15 weeks in three clinics 5.
There was no available information on an individual basis concerning the day when the pregnancy dating by US was performed.
All data were retrieved from the national Medical Birth Register and the Swedish Patient Register, in which information is prospectively recorded and of good quality 15 , 16 , All births with a live-born infant, irrespective of gestational age GA , were recorded in the Medical Birth Register during the entire study period. The fetus was therefore larger than expected when dated by US, and the EDD was changed to an earlier date.
A large discrepancy was defined as below the 10 th percentile large negative discrepancy and above the 90 th percentile large positive discrepancy in the discrepancy distribution. The reference category was defined as a discrepancy within 2 days of the median.
The remaining pregnancies were defined as a small negative or small positive discrepancy Fig. Delivery outcomes were included if adverse outcomes were expected to be more frequent among large infants at birth because a larger fetal size may be apparent at the time of the dating scan: prolonged second stage of labor , O Neonatal outcomes were included as outcomes related to growth deviations that may be present at the time of the dating scan.
To check for any association with the discrepancy between dating methods to infant size at birth, we included small for gestational age SGA and large for gestational age LGA.
SGA and LGA were defined as more than two SDs from the expected mean birth weight for fetal sex according to ultrasound-based GA, which reflects the clinical practice in Sweden, and is equivalent to below and above the second to third percentile In model 2, fetal sex was added to the first model with female as the reference category.
In model 3, a diagnosis of diabetes mellitus or preeclampsia recorded during the current pregnancy was added as a covariate to those included in model 2.
NNT should in this context be interpreted as number needed to follow up more closely to possibly detect the specific adverse outcome. Statistical analyses were performed using R statistical software version 3.
Informed consent was not possible, as it is normally not allowed in national register studies, because contacting individuals would interfere with personal integrity and the ethical board solely granted access to de-identified data. A negative discrepancy between dating methods was associated with lower odds than expected for all adverse delivery outcomes related to large infants, except for shoulder dystocia.
The effect estimates for cesarean section were slightly lower in models 2 and 3 when there was a large positive discrepancy. The highest effect estimates were found for intrauterine fetal death, SGA at birth, and neonatal death in cases of a large negative discrepancy.
The largest effect estimate was found for neonatal death: OR 2. In cases of positive discrepancy , the odds were lower for intrauterine fetal death limited to small positive discrepancy and SGA.
NNT was 96, i. Most importantly, a large negative discrepancy was associated with higher odds for neonatal and intrauterine fetal death, as well as SGA. A positive discrepancy was associated with adverse delivery outcomes related to large infant size. A reported association between a negative discrepancy and subsequent preeclampsia was confirmed in this population-based study In women with preeclampsia, the reason for a negative discrepancy may be early growth restriction In women with diabetes, the association with negative discrepancy may reflect longer menstrual cycles, because women with an irregular menstrual cycle have an increased risk of developing diabetes mellitus Another plausible explanation is restricted intrauterine growth in the first half of diabetic pregnancies along with catch-up growth in late pregnancy, as reported for some women with type 1 diabetes The odds for adverse delivery outcomes varied according to the magnitude and direction of discrepancy between methods.
This observation suggests that a discrepancy between methods sometimes reflects deviating fetal growth instead of imprecision in the LMP-based estimate 26 , 27 , Adjusting for SGA or LGA, or excluding these covariates from the analyses, changed the effect estimates only marginally.
In contrast to an earlier study 29 , a positive discrepancy was not associated with an increased risk for cesarean section. A higher risk for adverse neonatal outcomes observed for pregnancies with a negative discrepancy has been described previously in part of the same study population; from a shorter time-period and with fewer neonatal outcomes evaluated 9. In the current study, a negative discrepancy was also associated with birth asphyxia and SGA.
Associations between discrepancy and the outcomes SGA and LGA will always be biased as they are defined by the US method, using fetal size as a proxy for age. Another consequence of underestimated GA is that labor will not be induced within the optimal pregnancy duration, as indicated by other studies 4 , 9.
In this study, adjusting for SGA or LGA in the analyses had only a minor effect on the increased odds for intrauterine fetal death and neonatal death, although US-based underestimation of SGA may have diluted this effect 3. However, excluding SGA and LGA reduced the effect estimates for intrauterine or neonatal death in cases of large negative discrepancy.
This result suggests that continued decelerating or accelerating of fetal growth may contribute to the association of a discrepancy between methods with these neonatal outcomes. The latter may indicate incorrect recording of the LMP or catch-up growth after initially slower fetal growth, which may occur in diabetic pregnancies The strengths of this study are the large population-based study population and the use of information from national registers, with almost complete coverage and with prospectively collected information of high validity.
The results are consistent with previous studies, but also add new knowledge because more outcomes were assessed. We also used four separate models for additional adjustments to control for possible confounding variables.
One limitation was the lack of valid information regarding the regularity of menstrual cycles and when the US examinations were performed. Malformations that resulted in termination of pregnancy or fetal death before viability were not included in the study because these were not recorded on an individual level in the national health registers.
The prevalence of adverse outcomes may have been underestimated because some events or diagnoses might not have been recorded; however, assuming no association with the discrepancy categories, this should only have diluted the observed associations 16 , Our findings that discrepancy between the two pregnancy dating methods is associated with adverse perinatal outcomes may be useful in clinical practice for identifying pregnancies at risk of adverse outcomes. Although any discrepancy between methods may reflect an erroneous EDD estimated by LMP; it could also be a risk indicator for adverse outcomes.
As a large negative discrepancy was the strongest risk indicator for intrauterine and neonatal death, and was also strongly associated with SGA at birth, pregnancies with large discrepancies may benefit the most from additional and close follow-up to lower the risk of perinatal mortality.
Identifying discrepancies between dating methods may be a cost-effective way to select pregnancies that would benefit from closer monitoring 3 , 4 , 31 , 32 , The number of pregnancies with large discrepancy between dating methods are expected to be smaller if pregnancy dating had been based predominately on first-trimester instead of second-trimester ultrasound examinations, as the variability in growth is less pronounced in early pregnancy 1 , 37 , However, no comparison between first trimester based on crown-rump-length or biparietal diameter and second trimester pregnancy dating could be performed in this study, as the vast majority of pregnancies included were dated at a second trimester ultrasound examination and in accordance with clinical routines during the study period.
Also, the time-points of pregnancy dating by US were not recorded in the national registers during the timespan of the study. Information on date and fetal measurements are now included in national registers and will be possible to retrieve for future studies with a similar study design as this one, when data is available for large enough birth cohorts. These results support the hypothesis that a smaller or larger than expected fetal size based on the date of the LMP may in some cases reflect decelerated or accelerated early fetal growth, which could later lead to size-related adverse perinatal outcomes.
Even though pregnancy dating by US is generally more accurate than that by LMP, discrepancy between methods — and especially large negative discrepancy — should be noted because it may be associated with increased risks of adverse perinatal outcomes. Salomon, L. ISUOG practice guidelines: performance of first-trimester fetal ultrasound scan. Ultrasound in Obstetrics and Gynecology. Saltvedt, S. Ultrasound dating at 12—14 or 15—20 weeks of gestation? A prospective cross-validation of established dating formulae in a population of in-vitro fertilized pregnancies randomized to early or late dating scan.
Ultrasound Obstet Gynecol. Gardosi, J. Maternal and fetal risk factors for stillbirth: population based study. Morken, N. Perinatal mortality by gestational week and size at birth in singleton pregnancies at and beyond term: a nationwide population-based cohort study.
BMC Pregnancy and Childbirth. Chervenak, F. How accurate is fetal biometry in the assessment of fetal age? American Journal of Obstetrics and Gynecology. Sladkevicius, P. Ultrasound dating at 12—14 weeks of gestation. A prospective cross-validation of established dating formulae in in-vitro fertilized pregnancies.
Kullinger, M. Maternal and fetal characteristics affect discrepancies between pregnancy-dating methods: a population-based cross-sectional register study.
Acta Obstet Gynecol Scand. Morin, I. Determinants and consequences of discrepancies in menstrual and ultrasonographic gestational age estimates.
Hoffman, C. Comparison of gestational age at birth based on last menstrual period and ultrasound during the first trimester. Paediatr Perinat Epidemiol. Skalkidou, A.
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 transducer and a fullish bladder. If the pregnancy is very early the gestation sac and fetus will not be big enough to see, so the transvaginal approach will give better pictures. Dating scans are usually recommended if there is doubt about the validity of the last menstrual period.
Metrics details. Assessing gestational age by ultrasound can introduce a systematic bias due to sex differences in early growth. This cohort study included data on 1,, births recorded in the Swedish Medical Birth Register. As expected, adverse outcomes were lower in the later time period, but the reduction in prematurity-related morbidity was less marked for male than for female infants.
20 Gestational age
Name the time in gestation when ultrasound is most accurate 2. Discuss the ACOG recommendations for redating a pregnancy based on trimester. Postgraduate Institute for Medicine PIM requires instructors, planners, managers and other individuals who are in a position to control the content of this activity to disclose any real or apparent conflict of interest COI they may have as related to the content of this activity. PIM is committed to providing its learners with high quality CME activities and related materials that promote improvements or quality in healthcare and not a specific proprietary business interest of a commercial interest. Faculty: Susan J. During the period from Dec 31 through Dec 31 , participants must read the learning objectives and faculty disclosures and study the educational activity. If you wish to receive acknowledgment for completing this activity, please complete the post-test and evaluation. In support of improving patient care, this activity has been planned and implemented by the Postgraduate Institute for Medicine and The ObG Project.
Predicting delivery date by ultrasound and last menstrual period in early gestation.
Metrics details. Accurate estimation of gestational age is important for both clinical and public health purposes. Estimates of gestational age using fetal ultrasound measurements are considered most accurate but are frequently unavailable in low- and middle-income countries. The objective of this study was to assess the validity of last menstrual period and Farr neonatal examination estimates of gestational age, compared to ultrasound estimates, in a large cohort of women in Vietnam.
Ultrasound examination in the first trimester allows accurate assessment of gestational age, and identifies and allows for appropriate care of women with multiple pregnancies. Methods used to assess gestational age include known date of ovulation, date of the last menstrual period LMP and diagnostic ultrasound. Diagnostic ultrasound is a sophisticated electronic technology, which uses pulses of high frequency sound to produce an image.
Methods for Estimating the Due Date
A podcast about pregnancy and drug use, Native people and tribal sovereignty. Medical professionals use a standard set of up to three methods to date pregnancies: last menstrual period, ultrasound, and a physical exam. That way, regardless of where they trained or where they practice, any two doctors dating a pregnancy will predict the same due date or gestational age. However, the timing of the actual delivery is not so predictable.SEE VIDEO BY TOPIC: DUE DATE - Usapang Due Date - EDD by LMP VS EDD by Ultrasound
You can calculate your due date by subtracting three months from the first day of your last menstrual period LMP and then add a week. Use our pregnancy calculator. A pregnancy is based on being days long, which is 40 weeks more like 10 months not 9! When we give you a due date we consider 37 to 42 weeks to be full-term, so even if your baby is born two weeks before your due date it is not considered premature. Because few women know the exact day they ovulated or conceived, an ultrasound done in the first trimester of pregnancy has been shown to the be the most accurate way to date a pregnancy.
How to Calculate Your Due Date
Pregnancy lasts an average of days 40 weeks from the first day of your last menstrual period LMP. Read our report on the 13 best pregnancy iPhone and Android apps of the year here. If you have regular day menstrual cycles, there are two ways to calculate your due date. The other way to calculate your due date is to use a pregnancy wheel. This is the method that most doctors use. The first step is locating the date of your LMP on the wheel.
An accurate assessment of gestational age is vital to population-based research and surveillance in maternal and infant health. However, the quality of gestational age measurements derived from birth certificates has been in question. Using the US public-use natality file, the authors examined the agreement between estimates of gestational age based on the last menstrual period LMP and clinical estimates in vital records across durations of gestation and US states and explored reasons for disagreement. Agreement between the LMP and the clinical estimate of gestational age varied substantially across gestations and among states.
How Doctors Date Pregnancies, Explained
Gestational age is a measure of the age of a pregnancy which is taken from the beginning of the woman's last menstrual period LMP , or the corresponding age of the gestation as estimated by a more accurate method if available. Such methods include adding 14 days to a known duration since fertilization as is possible in in vitro fertilization , or by obstetric ultrasonography. The popularity of using such a definition of gestational age is that menstrual periods are essentially always noticed, while there is usually a lack of a convenient way to discern when fertilization occurred.
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