Five dating methods: LMP, FH, US and their combinations, were assessed against the actual day of delivery (ADD).
The main outcome measures were: (i) the days between the ADD and estimated date of delivery in pregnancies where spontaneous labour occurred and the baby had a normal birth weight; (ii) the incidence of gestational age-related outcomes; and (iii) the influence of clinical variables on dating discrepancies. The accuracy of dating was similar for certain and uncertain LMP. US-based dating was most accurate (for 85% of predictions within 14 days) and similarly accurate at 20 - 24 weeks and at Pregnancy dating by US, including those in more advanced pregnancies than currently permitted, is recommended since all non-ultrasound-based estimations of gestational age were considerably less accurate.
Evidence: Published literature was retrieved through searches of Pub Med or MEDLINE and The Cochrane Library in 2013 using appropriate controlled vocabulary and key words (gestational age, ultrasound biometry, ultrasound dating).
Results were restricted to systematic reviews, randomized control trials/controlled clinical trials, and observational studies written in English. Searches were updated on a regular basis and incorporated in the guideline to July 31, 2013.
With today's modern equipment, we can obtain very reliable images and measurements of even very early pregnancies, sometimes even seeing a heartbeat as early as 5-6 weeks!
The most common misconception we encounter almost daily, has to do with how accurate ultrasounds are in fixing the EDC at different stages of pregnancy.
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The accurate determination of a patient's "due" date, referred to by doctors and midwives as the EDC (Estimated Date of Confinement) or EDD (Estimated Date of Delivery), is very important for a variety of reasons.
Ultrasonography (US) in the 1st, or early 2nd trimester, is highly reproducible8 and widely used for dating, since early biological variability of fetal biometry is minimal.9 In the past, certain LMP was used for dating as long as the GA was within 7, 10 or 14 days of the estimate of GA by US,10 but now 1st, or 2nd trimester, US is increasingly recommended as the single dating method because of its smaller error rate.1 14 The current policy in the Western Cape Province of South Africa (SA) provides for a routine US examination between 18 - 23 weeks of the clinically estimated GA for low-risk pregnancies since this reduces the number of presumptive post- and pre-term deliveries as well as the number of referrals to a higher level of care for suspected deviations in fetal growth.15 The approximately 34% of women who typically present at 23 weeks16 do not routinely receive US.
Pregnancy dating is based on a pragmatic guideline incorporating information from the LMP, FH and early US (if available).17 The accuracy of this guideline and the clinical value of late US-based GA dating have not been assessed. Okland I, Gjessing HK, Grøttum P, Eggebø TM, Eik-Nes SH. two traditional sample-based models: validation on 9046 ultrasound examinations.
Outcomes: To determine whether ultrasound dating provides more accurate gestational age assessment than menstrual dating with or without the use of ultrasound.