Risk of Stillbirth and Infant Death Stratified by Gestational Age
Gestational Age
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Transcript of Gestational Age
ESTIMATION OF
GESTATIONAL AGE
By: Anushya Jayendran
OBJECTIVES
• Definitions of important terminology
• Methods of determination of gestational age
• Importance of determination of gestational age
TERMINOLOGY
• Gestational Age– Refers to the length of pregnancy after the first
day of the last menstrual period (LMP) and is usually expressed in weeks and days.
• Conceptional Age– Refers to the true fetal age and refers to the
length of pregnancy from the time of conception.
DETERMINATION OF GESTATIONAL AGE
DETERMINATION OF GESTATIONAL AGE
History Taking
Physical Examination Investigation
DETERMINATION OF GESTATIONAL AGE
HISTORY TAKING
Date of Fruitful Coitus
Date of Last Normal Menstrual
Period(Naegele’s Formula)
Date of Quickening
HISTORY TAKING
• Date of Fruitful Coitus– 266 days are to be added to the date of single
fruitful coitus – Accuracy is up to 50% within 7 days on either side– Advantages: Useful and extremely accurate when
used in cases of assisted reproduction, particularly in IVF
– Disadvantages: Not practicable except when pregnancy occurs in instances of sudden death or absence of the husband or rape
HISTORY TAKING• Date of Last Normal Menstrual Period
– This follows Naegele’s Rule: EDD is 280 days from the LNMP in a patient with a regular cycle of 28 days and where ovulation occurs in midcycle
– Accuracy is up to 50% within 7 days on either side– If the interval of cycles is longer, the extra days are to be added
and if the interval is shorter, the lesser days are to be subtracted to get the EDD
– Advantages: Easy to calculate in a patient who is certain of LNMP– Disadvantages: 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)
HISTORY TAKING
• Date of Quickening– A rough idea about the probable date of delivery
can be deduced by adding 22 weeks in primigravidae and 24 weeks in multiparae to the date of quickening
– Advantage: Can be used as an estimation in the absence of other more reliable methods
– Disadvantages: Inaccurate as every patient is different and values used are based on an average
DETERMINATION OF GESTATIONAL AGE
PHYSICAL EXAMINATION
Uterus
Size of Uterus
Height of the Uterus
Cervix From Vaginal Examination
Fetus
Palpation of Fetal Parts
Auscultation of Fetal Heart Rate
Lightening
Size of Fetus
PHYSICAL EXAMINATION
• Uterus– Size of Uterus
• Can be assessed by vaginal examination• Is most accurate prior to 12 weeks• Corresponds with the Period of Amenorrhoea• Disadvantages: Size can be misleading in the
presence of multiple pregnancy, uterine fibroids, or a full bladder
– Height of the Uterus• Refers to the Symphysial-Fundal-Height (SFH)• Corresponds with the Period of Gestation
(POG)• Advantages: Accurate in cases of normal
pregnancy• Disadvantages: Inaccurate in cases of fetus
which are small for gestational age or pregnancies with inadequate liquor
PHYSICAL EXAMINATION
• Cervix– From Vaginal Examination• If the cervix becomes shorter and dilated, the labour is
fairly not far off• More accurately assessed using the Bishop’s score• Advantages: Extremely accurate when used to monitor
the progress of labour• Disadvantages: Can only be used to assess pregnancy in
the later part. Labour may start even with long and closed cervix
BISHOP SCORE
• Scoring– Cervical Dilation
• Cervix dilated < 1 cm: 0• Cervix dilated 1-2 cm: 1• Cervix dilated 2-4 cm: 2• Cervix dilated > 4 cm: 3
– Cervical Length (Effacement)• Cervical Length > 4 cm (0% effaced): 0• Cervical Length 2-4 cm (0 to 50% effaced): 1• Cervical Length 1-2 cm (50 to 75% effaced): 2• Cervical Length < 1 cm (>75% effaced): 3
BISHOP SCORE
• Scoring (Cont.)– Cervical Consistency
• Firm cervical consistency: 0• Average cervical consistency: 1• Soft cervical consistency: 2
– Cervical Position• Posterior cervical position: 0• Middle or anterior cervical position: 1
– Zero Station Notation (presenting part level)• Presenting part at ischial spines -3 cm: 0• Presenting part at ischial spines -1 cm: 1• Presenting part at ischial spines +1 cm: 2• Presenting part at ischial spines +2 cm: 3
BISHOP SCORE• Modifiers
– Add 1 point to score for:• Preeclampsia• Each prior Vaginal Delivery
– Subtract 1 point from score for:• Postdates Pregnancy• Nulliparity• Premature or prolonged Rupture of Membranes
• Interpretation– Indications for Cervical Ripening with prostaglandins
• Bishop Score <5• Membranes intact• No regular contractions
– Indications for Labor Induction with Pitocin• Bishop Score >= 5• Rupture of Membranes
PHYSICAL EXAMINATION
• Fetus (Cont.)– Palpation of Fetal Parts
• Fetal parts are felt earliest by 20 weeks of gestation• Disadvantages: Extremely subjective and subject to the skill
of examiner
– Auscultation of Fetal Heart Rate• Heard earliest by 18-20 weeks of gestation using ordinary
Pinard Stethescope• Heard earliest by 10 weeks of gestation using Doppler
Ultrasound• Disadvantages: Extremely subjective and subject to the skill
of examiner
PHYSICAL EXAMINATION
• Fetus (Cont.)– Lightening
• Labour is likely to commence within 3 weeks of appearance of symptoms of lightening
• Disadvantages: Extremely subjective and can only be used to assess pregnancy in its later part
– Size of the Fetus• Change in uterine shape, volume of liquor amnii, hardening of the skull and
girth of the abdomen are of value in assessing he maturity of the fetus specially if the examinations are done by the same person at intervals
• Disadvantages: Extremely subjective and inaccurate in cases of Intrauterine Growth Restriction and fetuses which are Small for Gestational Age
DETERMINATION OF GESTATIONAL AGE
INVESTIGATIONS
Recording of Positive
Pregnancy TestUltrasonography Radiography
INVESTIGATIONS• Recording of Positive Pregnancy Test
– The date of the first positive pregnancy test result allows the calculation of a minimum GA.
– This depends on the sensitivity of the test. – For example, if the test was performed 4 weeks ago and the
test is known to return positive results as early as 1 week after conception, then the minimum conceptional age (CA) would be 5 weeks (GA, 5 + 2 = 7 wk of amenorrhea)
• Radiography– Based on x-ray findings– Corresponds to the appearance and density of ossification
centres in the upper end of the tibia (38-40 weeks) and lower end of femur (36-37 weeks)
INVESTIGATIONS
• Ultrasonography– First Trimester: Crown-Rump Length (CRL) is most accurate
(Variation: ± 5 days)– Second Trimester: Biparietal Diameter (BPD), Head Circumference
(HC), (AC) and Femur Length (FL) is more accurate. This is best done between week 12 and 20. (Variation: ± 8 days)
– Third Trimester: Less reliable. (Variation: ± 16 days)– In clinical practice, when the difference between the gestational
age determined by sonographic measurement and the menstrual age is less than 10 days, the EDD is derived from the LNMP is confirmed. When the difference is more than 10 days, the EDD should be based on ultrasonographic fetal biometry
IMPORTANCE OF DETERMINATION OF GESTATIONAL AGE
• Accurate determination of gestational age is fundamental to obstetric care and is important in a variety of situations:– Antenatal test results will be inaccurate and misleading
when the dates are inaccurate– Fetal growth assessment, either clinically or by ultrasound
evaluation, relies on accurate assessment of gestational age.• Fetal growth retardation or macrosomia may be missed owing to
errors in gestational age assignment.
– Interpretation of antenatal biophysical testing subjected to variation with gestational age as well.
REFERENCE
• 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
THE ENDThank You Very Much