Expected Date of Delivery (EDD) Calculation

Methods for Calculating EDD

The expected date of delivery (EDD) is calculated as 280 days (40 weeks) from the first day of the last menstrual period (LMP), but this should be confirmed by early ultrasound dating, especially before 21 weeks of gestation, to ensure accuracy and avoid iatrogenic early term or preterm delivery, as recommended by the American College of Obstetricians and Gynecologists 1
For women with uncertain LMP, only those with first-trimester ultrasound dating should be used to establish the EDD, according to the American College of Obstetricians and Gynecologists 1

Accurate dating is critical to avoid iatrogenic early term or preterm delivery, particularly when considering elective interventions, as stated by the American College of Obstetricians and Gynecologists 1
Confidence in the EDD is imperative when considering elective interventions like induction of labor at 39 weeks, as recommended by the American College of Obstetricians and Gynecologists 1

For diet-controlled gestational diabetes, delivery is recommended at 38 weeks' gestation 2
For medication-dependent gestational diabetes, delivery is recommended by 39 weeks' gestation 2
For fetal growth restriction with normal Doppler studies, delivery is recommended at 38-39 weeks' gestation, as suggested by the American College of Obstetricians and Gynecologists 3, 4
For fetal growth restriction with abnormal Doppler studies, earlier delivery may be indicated based on the severity of findings, according to the American College of Obstetricians and Gynecologists 3, 4

Relying solely on LMP dating without ultrasound confirmation can lead to inaccurate EDD, especially in women with irregular cycles, as warned by the American College of Obstetricians and Gynecologists 1
Failing to document early ultrasound dating (before 21 weeks) may lead to uncertainty about gestational age later in pregnancy, as noted by the American College of Obstetricians and Gynecologists 1
Using different dating methods interchangeably without clear documentation can lead to confusion about the true gestational age, as cautioned by the American College of Obstetricians and Gynecologists 1

For Fetal Growth Restriction (FGR) with abnormal umbilical artery Doppler showing decreased diastolic flow, delivery is recommended at 37 weeks, as per the American College of Obstetricians and Gynecologists guidelines 5
For severe FGR with estimated fetal weight <3rd percentile, delivery is recommended at 37 weeks, regardless of Doppler findings, based on guidelines from the American College of Obstetricians and Gynecologists 5
For Intrahepatic Cholestasis of Pregnancy (ICP) with total bile acid levels <100 μmol/L, delivery is recommended between 36 0/7 and 39 0/7 weeks, with timing individualized based on bile acid levels, as suggested by the American College of Obstetricians and Gynecologists 6, 7, 8
For ICP with total bile acid levels ≥100 μmol/L, delivery is recommended at 36 0/7 weeks due to substantially increased stillbirth risk, according to the American College of Obstetricians and Gynecologists guidelines 6, 7, 8
For placenta accreta spectrum in stable patients, scheduled delivery at 34 0/7 to 35 6/7 weeks is preferred, as recommended by the American College of Obstetricians and Gynecologists 9

Antenatal corticosteroids must be administered if delivery will occur before 37 0/7 weeks and has not been previously given, as per guidelines from the American College of Obstetricians and Gynecologists 6, 7, 8