This document discusses how to determine a pregnant woman's expected date of delivery (EDD) and why accurate dating is important. It outlines four groups for determining EDD: 1) women with regular cycles based on last menstrual period, 2) women with irregular cycles based on ultrasound scans, 3) women conceiving through IVF based on embryo transfer date, and 4) women with multifetal pregnancies based on the larger fetus. The document emphasizes that the EDD determined early in pregnancy from last menstrual period or early ultrasound scans between 6-14 weeks is usually the most accurate. Subsequent scans may show different dates due to fetal growth variations, but the original EDD should not be changed. Accurate dating guides prenatal care

1. HOW TO FIND OUT CORRECT EDD ?
AND
WHY IS ACCURATE DATING OF
PREGNANCY SO IMPORTANT?
Dr. NISHEETH M. OZA

2. Dr. Nisheeth M. Oza
M.D., D.G.O., F.C.P.S., D.N.B., (M.N.A.M.S.) (OBGYN)
D.A., M.B.B.S., Dip. YAN
Obstetrician, Gynaecologist, Infertility Consultant,
FMF Certified Ultrasonographer (FMF ID 145907)
Licensed for Aneuploidy Screening NT, NB, DV, Cervix & PIH Screening.
Diploma in Yoga, Ayurveda & Naturopathy
Dr. Oza’s Hospital 87/7, Panvel 410206, Maharashtra India.
Email : drnmozas@gmail.com
Website : drozashospital.com
YouTube : DrOzaConnects

3. A lady who has conceived, is naturally eager to know when she would deliver.
She is given an EDD–Expected Date of Delivery, by her Doctor calculated from her LMP–Last
Menstrual Period. When an Ultrasonography scan is performed on her, the scan mentions some
EDD , which may be different from previously given EDD. When she undergoes subsequent
Ultrasonography scans, the reports may mention different EDD. Ultimately, the lady may get
confused and wonder as to which one is her correct EDD?
So Today, I am here to clarify the relevant facts and solve this puzzle.
Let us consider four different Groups of Patients.

4. Group I : A Lady with previous regular cycles of 28 days
& she remembers her LMP with surety (Good or Excellent dates) :
• Take 1st day of LMP + Add 280 days (i.e. 9 months and 7 days) => EDD.
• This is called as LMP derived EDD !
• One can reconfirm this by correlating with early ultrasonography scan
between 6 and 14 weeks.
• If this scan report EDD differs by less than 5 days, uphold LMP derived EDD.
• If this scan report EDD differs by more than 5 days, uphold USG derived EDD
& this is called ‘Corrected EDD’ .

5. GROUP II : A Lady with previous irregular cycles or who
does not remember her LMP with surity:
Consider assigning EDD according to Ultrasonography scan between 6 & 14
weeks.
A] Scan performed between 6 and 9 weeks from LMP: Measures Maximum
Length of Embryo.

6. B] Scan performed between 09 and 14 weeks from LMP :
• Measures CRL –Crown to Rump Length , i.e., from top of head to bottom of fetal spine.
• This can be called as Ultrasonography Scan derived EDD.

7. Group III: A LADY who has conceived with IVF [TEST TUBE BABY]
A] For Fresh Egg IVF :
Take date of ET [Embryo Transfer ] + Add 266 days –> EDD.
B] For Frozen Embryo IVF :
Take date of ET + add 266 days – Age of Embryo –> EDD
eg 1] If day 3 Frozen Embryo is transferred ,
Date of ET + 266 – 3 –> EDD.
2] If day 5 Blastocyst is transferred.
Date of ET + 266 – 5 –> EDD.
• This can be called as ET derived EDD.

8. Group IV: Lady with multifetal pregnancy, eg Twin pregnancy & if measurement
of both fetuses are different , EDD is assigned as per USG scan measurement
of ‘bigger in size’ fetus.
The most important point:
WHEN SUBSEQUENT ULTRASONOGRAPHY SCANS SHOW DIFFERENT EDD,
WHAT TO DO?
• I would like to explain why this may happen.
• Because the Ultrasonography Machine Software gives EDD based on then size of the fetus.
eg. If fetus is slow in its growth, Machine Software would mention a later date then actual EDD.
AND
If fetus is rapid in its growth, Machine Software would mention an earlier date than actual
EDD.
Both of these are incorrect.
REMEMBER: EDD ‘assigned’ in early pregnancy, from LMP & 6 to 14 weeks’ scan is the most
ACCURATE one & hence should NEVER be changed.

9. WHY is Accurate Dating of Pregnancy so important?
• Guides Timing of Surveillance Tests, eg Blood Tests, USG Scans.
• Guides Timing to administer certain Medications, eg for fetal lung maturity.
• Guides to Monitor Fetal Growth in High Risk cases, eg FGR, PIH, GDM, Twin
Pregnancy.
• Guides to consider Correct Timing to deliver the fetus at high risk eg FGR,
GDM, BOH (Previous Stillbirth).
• Helps to plan Special Newborn Care depending on GA and EFW.

10.  Having Assigned an EDD, will a lady deliver on the same date as EDD?
Let us know some Exceptions.
Lady who is likely to deliver earlier than EDD:
• If she had delivered in previous pregnancy earlier than EDD.
Cause may be : PTL, PPROM or Incompetent Cervix.
• If a lady is having any of the complicating conditions such as, Twin Pregnancy ,
Polyhydramnios (excess Amniotic Fluid), PIH, Diabetes, Placenta Previa.
• If lady consumes Tobacco in any form or consumes Alcohol or excess amount of Coffee.
Lady who is likely to deliver later than EDD :
• If she had delivered later than EDD in previous pregnancy.
• If she is Obese i.e. having high BMI.
• If she is Primigravida.

11. Thank You !