It's ALL About Dates, DOC
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Transcript of It's ALL About Dates, DOC
Max Brinsmead MB BS PhMay 2015
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
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
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
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
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
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 datesThis assessment needs to be performed by
an experienced person
Dates are CERTAIN when...
The patient attends for antenatal care at <16 weeks gestation and dates are confirmed by UltrasoundThis assessment needs to be performed by
an experienced service
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
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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