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It's ALL About Dates, DOC

Max Brinsmead PhD FRANZCOG May 2011. It's ALL About Dates, DOC. Determining an EDD. An accurate estimate of the “due date” is fundamental to obstetric decision making Use Naegele’s rule by adding 9m & 7d to first day of the LMP

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It's ALL About Dates, DOC

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  1. Max Brinsmead PhD FRANZCOG May 2011 It's ALL About Dates, DOC

  2. Determining an EDD • An accurate estimate of the “due date” is fundamental to obstetric decision making • Use Naegele’s rule by adding 9m & 7d to first day of the LMP • But this assumes that ovulation & conception occurred 14 days after that dates and will be wrong when... • Long and short cycles • Recent pregnancy and lactation • Hormone contraception • Needs 3 – 4 cycles to be reliable • Requires >6m after Depot to be reliable

  3. So the LMP must be a Normal Period • Occurring at the expected time • Of the expected amount • Some dates confused by early pregnancy bleeding • A few patients nominate the first missed period as their LMP • But some 30 – 50 % of patients are unsure of dates because... • They book too late • Or they deliberately falsify the date

  4. Many services rely on routine ultrasound to set an EDD • Resources may be limited • Must occur before 16 weeks to be reliable (NICE guidelines) • Ultrasound in the 3rd trimester has a very limited role in determining dates • And may be critically misleading if there is intrauterine growth restriction

  5. Quickening • For primigravida the mean is 19w • And for parous patients it is 17.4w • But the range is wide • 15 – 22 weeks for Primigravida • 14 – 22 weeks for Multigravida • Will be influenced by placental location • And obesity • And a few patients claim to never feel fetal movements

  6. Symphysis-Fundal Height • Offers the attraction of objectivity • The mean is equivalent to the weeks of gestation between 20 and 34 weeks • But the range is +/- 2 weeks • And most studies have concerned its role in screening for IUGR • Will be misleading when: • It is <20 cm (there is no data) • It is measured by inexperienced person • The uterus is large or small for dates

  7. Dates are RELIABLE when... • The patient is sure of her dates • She was cycling regularly and normally at the time of conception AND • Quickening correlates AND • Antenatal care commenced at <24w when uterine size correlated with those dates • This assessment needs to be performed by an experienced person

  8. Dates are CERTAIN when... • The patient attends for antenatal care at <16 weeks gestation and dates are confirmed by Ultrasound • This assessment needs to be performed by an experienced service

  9. Conversely... • If the patient is unable to provide a last menstrual period OR that date is suspect • OR • There is significant discrepancy between dates and quickening OR SFH <>3 cm than dates in weeks • AND • The SFH is <26 cm • Then ultrasound should be performed

  10. Uncertain Dates • If pregnancy dating is uncertain then this should be stated in all communication • A best estimate of the EDD (or B-EDD) is desirable • Based on whatever data is available • And stated always with its degree of error thus... • “Possibly 42w +/- 3 weeks based on an uncertain menstrual history and a date of quickening recorded at the first visit at 38 weeks” • “Possibly 32w +/- 3 weeks based on uterine size and history of quickening obtained today”

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