1

Associate Professor Dr

Hanifullah Khan

GESTATIONAL AGE & ESTIMATION OF DUE DATES

OBJECTIVES

• Importance of determination of gestational age

• Definitions of important terminology • Methods of determination of

gestational age • Proper estimation of GA & EDD

2

IMPORTANCE OF DETERMINATION OF GESTATIONAL AGE

• Accurate determination of the Expected Due Date (EDD) - one of the most important factors in early pregnancy assessment !

• Healthcare professionals must take great pains to determine accurate gestation & EDD during booking

3

Accurate dating is vital for

• the timing of appropriate antenatal care • scheduling & interpretation of tests • determining appropriate fetal growth • intervention purposes

prevention of preterm birth prevent postdates prevent comorbidities

• for research purposes4

Gestational age can be determined by

Clinical History

5

Ultrasound Scan

Physical Examination

CLINICAL HISTORY

6

Determining the gestational age

using clinical history

•Reliant on knowledge of accurate menstrual period

•1st day of LMP

•calculation based on Naegele’s rule

Naegele’s Rule: • EDD is 280 days from the

LNMP • Must be regular cycles for

this to be accurate • Accuracy is up to 50% within

7 days on either side

Inaccurate in patients in the following circumstances:-

• Oligomenorrhoea or polymenorrhagia (irregular cycles)

• Bleeding in the first trimester of pregnancy (implantation bleeding)

• Pregnancy following the use of oral contraceptives or intrauterine devices

• Pregnancy in the postpartum period (lactational amenorrhoea)

If the interval of cycles is longer than 28/7, the extra days are to be added and if the interval is shorter, the days are to be subtracted to get the EDD

7

Confirm by time of onset of pregnancy

symptoms

•Typically, these begin around 5+ weeks of gestation

•commonly include nausea, headache, loss of appetite etc..

Using dates, early pregnancy symptoms should occur about

5-6 weeks from the 1st day of the

LMP

8

Time of Quickening

Add 22/52 in primigravidae & 24/52

in multiparae to the date of quickening = EDD

!

Can be used as an estimation in the

absence of other more reliable methods

!

Inaccurate

9

PHYSICAL EXAMINATION

10

P/E augments history

•P / E b y i t s e l f i s inaccurate

•What it can do is to confirm the historical findings

•P/E is more helpful in later pregnancy

Height of the Uterus Refers to the Symphysio-Fundal-Height (SFH) Corresponds with the Period of Gestation (POG) Is widely influenced by the state of the pregnancy - may be smaller or larger than dates

11

Very late pregnancy

•If the gestation is uncertain late on..

•cervical assessment may indicate maturity

•as a component of the Bishop score, cervical assessment may help denote the likelihood of successful vaginal delivery

If the cervix becomes shorter and dilated, labour

is not far off This suggests a term

pregnancy but cannot date it conclusively

Cervical assessment !• cervical length, position and

consistency are most useful • a short, anterior and soft cervix is

usually present after 38 weeks maturity

• although cervical shortening & position may not change, changes in consistency almost always do

12

Ultrasound scanning

13

Ultrasonography

early pregnancy scans are the most accurate

for dating !

midtrimester scans are used for anomaly assessment

!3rd trimester

scans may assess liquor volume &

fetal weight accurately but are useless for

dating

Not all scans during pregnancy serve the same purpose

Crown-Rump Length (CRL)

14

Early Pregnancy Scan

•Termed as a scan done b e f o r e 1 4 w e e k s gestation

•The CRL is the desired measurement

•Accurate up to a day!

•All mothers should have this

It is crucial that the mother is questioned if a scan was done early in pregnancy

If so, she should be asked if the findings corresponded

to the LMP dates

In clinical practice, if the discrepancy between menstrual & u/s dates is < 7 days, the LMP dates should be employed (as

long as the periods are regular) !

If the discrepancy is more then the EDD should be based on

ultrasonographic fetal biometry

15

The EDD

16

Amongst all the methods for EDD assessment, a high quality ultrasound scan early in

pregnancy is the best estimate

Estimation of the EDD

EDD has traditionally been based on LMP!but this has been found to be unreliable

as about half of women cannot accurately recall the 1st day of their LMP,

have irregular menses and the timing of ovulation varies

17

Summary

18

Estimation of GA & EDD is usually dependant on history (LMP)

!GA & EDD should be confirmed by other historical features, physical exam and early ultrasound scan

!A high quality ultrasound measurement of the embryo or fetes within the 1st 14 weeks is the most accurate method of confirming GA & establishing EDD

!The GA & EDD should be documented clearly in the records as soon as confirmation is made via an accurate calculation of the LMP, u/s or both

19

REFERENCES• Konar H, D.C. Dutta’s Textbook of Obstetrics, 7th

Edition, New Central Book Agency, 2010 !

• Mongelli M and Gardosi J, Update 19 April 2010, Evaluation of Gestation, Emedicine.medscape.com, Extracted from: http://emedicine.medscape.com/article/259269-overview !

• New guidelines standardize pregnancy due date estimates. Medscape. Sep 25 2014

20

Thank You Very Much

21

Accurate!