Assessment of gestational age
• Measured from last (normal) menstrual period (LNMP or LMP) by convention
• Average length of pregnancy is 280 days or 10 lunar months, 40 weeks from LMP (38 weeks from ovulation/conception)
• Determine estimated date of delivery (EDD) using Naegle’s rule:
--• EDD = LMP + 9 calendar months + 7 days; or
--• EDD = LMP – 3 calendar months + 7 days
--• based on a 28-30 day menstrual cycle; adjust according to cycle length
--• Or by using a gestation wheel or gestational calculator applications for handheld devices
• Ultrasound: accurate within 5 days in the first trimester, 1-2 wks in second trimester, 2-3 weeks in third trimester
• Bimanual or abdominal examination: uterine fundus will be at the symphysis at 12 weeks (bimanual examination), between symphysis and umbilicus at 16 wks, at umbilicus at 20 wks, at xyphoid at term
• Measurement of symphysis-fundal height (SFH): measurement in centimetres roughly equal to GA in weeks (between 20-36 wks)