Antenatal Ultrasonography

Category: Others/ Misc

Presentation Description

Everything a Neonatologist / Paediatrician need to know about Antenatal Scans


Presentation Transcript

Antenatal Ultrasonography :

Antenatal Ultrasonography Manan Parikh

Antenatal Ultrasonography:

Antenatal Ultrasonography Use of ultrasonography for fetal & maternal assessment during pregnancy started in 1970s Done by Real Time Scanner Uses high frequency sound waves (3-5 MHz)

Antenatal Ultrasonography:

Antenatal Ultrasonography Techniques Transabdominal Transpelvic Transvaginal Types Standard Examination Limited Examination Specialized Examination

Antenatal Ultrasonography:

Antenatal Ultrasonography

Standard Examination:

Standard Examination Diagnosis & Confirmation of Pregnancy Single / Multiple Pregnancy – Amnionicity, Chorionicity Determination of Gestational age / EDD Assessment of Fetal size & growth Diagnosis of Fetal malformation Placental Localization Liquor & AFI Anatomy survey of uterus & adnexa

First Scan : Dating Scan:

First Scan : Dating Scan Full bladder needed if Transabdominal Scan For better transmission of sound waves Pushes the intestinal loops outside the view It is Transpelvic USG Scan Done at around 7 weeks of gestation or as early as possible , if LMP is not clear, missed period Vaginal bleeding in early 1 st Trimester

First Scan What to see:

First Scan What to see G-Sac : Gestational Sac Y-Sac : Yolk Sac Fetal Pole Fetal Pulsations CRL: Crown Rump Length MSD : Mean S ac Diameter

G - Sac:

G - Sac First identifiable structure , imaged in 1 st Scan Gestational sac is visible by 4½ week (5-8 wks) Increase by 1mm/day Note the no. of G-sac, Site of G-sac (Uterine/Ectopic) G-Sac is not round – Average of Length, Width, Depth is calculated  Mean Sac Diameter (MSD) Dating of EDD: Accuracy +/- 7 Days

Slide 11:

G - Sac

Yolk Sac:

Yolk Sac Visible at 5 weeks of gestation (7-11 wks) It decreases in size & disappear as the placental circulation established Size of Y-Sac is Important Y-sac > 5-6 mm @ 10 wks --- Large Y-Sac : Adverse outcome Absence of Y-Sac + Presence of Embyo @ 8 wks : Fetal Demise Y-Sac is not used for dating

Yolk Sac:

Yolk Sac

Fetal Pole:

Fetal Pole Visible at 5½ - 6 weeks It is visible as a WHITE DOT in a G-Sac Not used for dating Absence of Fetal Pole P/o Early scan / Blighted ovum Repeat scan, after 2 wks, is indicated

Fetal Pulsations:

Fetal Pulsations Visible at 6 – 8 weeks of gestation It is the indicator of Fetal cardiac activity Fetal HR varies acc to gestational age Fetal HR < 90 @ 8 wks : High risk of miscarriage

Slide 17:

Repeat USG After 7 – 10 days For confirmation

Crown Rump Length : CRL:

Crown Rump Length : CRL Distance from the tip of the Head (Crown) to the bottom of the Buttocks (Rump) M easurement of Fetal Length from the tip of the cephalic pole to the tip of the caudal pole Fetus should be at rest, assuming normal curvature EDD is set by accurately measuring CRL Most accurate method for Dating / Gest. age Accuracy: +/- 5 days

MSD & CRL, Importance:

MSD & CRL, Importance MSD ~ 20 mm: Yolk sac should be visible MSD ~ 25 mm: Fetal pulsations should be visible Chromosomal Anomalies, e.g. Trisomy 18, Tripoidy can reduce the CRL (MSD – CRL) < 5 mm ---- Healthy pregnancy (MSD – CRL) > 5 mm ---- Prone to Abortion, Despite of normal HR


Important When initial EDD is accurately calculated from CRL, and if subsequent scans show different EDD…… Initial EDD should not be changed…. Consider that Fetus is not growing at expected rate

Second Scan:

Second Scan Full bladder not needed It is Transabdominal USG Scan Done around 11 – 14 weeks of gestation Mainly done To confirm findings of First scan USG soft markers for congenital anomalies (esp Down’s Syndrome)

Second Scan What to see:

Second Scan What to see No. of Fetus If Multiple Gestation…….. Amnionicity, Chorionicity Presentation of all fetuses IUGR USG soft markers Fetal Nasal Bone Nuchal Thickness

USG Soft Markers:

USG Soft Markers Fetal Nasal Bone Absence of Fetal nasal bone / Flat face is associated with Down’s Syndrome

USG Soft Markers:

USG Soft Markers Nuchal Thickness Thickness at the nape of the neck when fetus is in sagital section & fetal head in neutral position I ncreased Nuchal Thickness > 3 mm @ 14 weeks / > 6 mm @ 20 weeks, associated with high risk of Turner’s syndrome, Down’s Syndrome & other Cong. Anomalies It is due to edema at nape of neck due to obstructed fluid drainage

USG Soft Markers:

USG Soft Markers

Important :

Important Absent Nasal Bone + Increased Nuchal Thickness Indication for Chorionic Villous sampling

Third Scan : Anomaly Scan:

Third Scan : Anomaly Scan Full bladder usually not needed It is Transabdominal USG Scan Done around 18 – 20 Wks Mainly done for Assessment of fetal anomalies Fetal Biometry Placental Information Amniotic fluid / AFI

Anomaly Scan : 10 Point Check:

Anomaly Scan : 10 Point Check 1. Skull Bone & Brain Normally skull should be all around brain without big gaps 2. Spine 3 raws of rosette Without something bulging out

Anomaly Scan : 10 Point Check:

Anomaly Scan : 10 Point Check 3. Chest Heart not shifted Exclude Diaphragmatic Hernia 4. Chambers of Heart All 4 chambers should be seen Rhythmic regular heart beats See Aortic Arch & Pulmonary Artery 5. Stomach & Diaphragm Diaphragm as a line separating chest & abdomen

Anomaly Scan : 10 Point Check:

Anomaly Scan : 10 Point Check 6. Abdomen Abdominal Circumference at Umbilical cord insertion, All organ normally aligned 7. Urinary Bladder Full bladder / AFI Normal No cyst @ kidney site Normal Genitourinary System

Anomaly Scan : 10 Point Check:

Anomaly Scan : 10 Point Check 8. Limbs & Feet Normal orientation Easy to see in early scans 9. Sex Identification After 14 wks 10. Fetal Activity Limb / Trunk movements Reaction to sound Co- ordinated Movements : Finger sucking, Fisting, Eye opening

Anomalies Detected @ Anomaly Scan:

Hydrocephalus Anencephaly Meningomyelocele Achondroplasia Dwarfism Spina Bifida Exomphalos Gastroschisis Duodenal Atresia Fetal Hydrops Cleft Lip / Palate Cardiac Abnomalities Anomalies Detected @ Anomaly Scan

Fetal Biometry:

Fetal Biometry Measurements & Calculations Use: Early Pregnancy: Gestational age assessment Later Part: Fetal size & growth Normogram available for each parameter

Fetal Biometry : Parameters:

Fetal Biometry : Parameters BPD : Biparietal Diameter HC : Head Circumference FL : Femur Length HL : Humerus Length AC : Abdominal Circumference CI : Cephalic Index HC / AC Ratio FL / BPD Ratio EFW : Effective Fetal Weight

Biparietal Diameter:

Biparietal Diameter Reflects Brain growth Measured as early after 13 th wk for accurate dating Most accurate when head shape is ovoid Distance b/w 2 sides of the head from inner edge to outer edge While measuring, Falx cerebri --- midline Thalami positioned on either side of falx Septum pellucidum anteriorly

Head Circumference:

Head Circumference Inaccurate for dating Difficult to measure Useful when Flat head / Abnormal Shaped Head Brachycephaly (Round Head) : BPD overestimates Dolicocephaly (Elongated Head) : BPD underestimates

Cephalic Index:

Cephalic Index Ratio b/w 2 axis of fetal head (BPD & FOD) Useful in abnormal shaped head N : 75 – 85% <75% - Flat Head If Cephalic index is abnormal, Use HC for dating, as BPD may give wrong estimation

Femur Length:

Femur Length Femur : Largest Bone, Least movable, Easy to image Reflects Longitudinal growth Most accurate for dating after 14 weeks Measure In longitudinal axis When both ends are blunt Femur parallel to probe In Dwarfism: FL fall by 4-5 weeks HL: Not routinely, Short HL – High sensitivity for Trisomy 21

Abdominal Circumference:

Abdominal Circumference Reflects Fetal growth, Weight, Size Measured in late part of Pregnancy Not used for dating While measuring, In Transaxial view of fetal abdomen At the level of stomach & liver Portal vein in umbilical region If IUGR / Macrosomia – Serial monitoring required

Calculated Parameters:

Calculated Parameters HC / AC Ratio In c/o IUGR To know Symmetric / Asymmetric IUGR FL / BPD Ratio N : 76 +/- 6 % FL/BPD : High : Microcephaly FL/BPD : Low : Hydrocephalus / Short limb dysplasia

Effective Fetal Weight:

Effective Fetal Weight Polynomial equation combining BPD, FL & AC Calculated by computer software / Charts Accuracy: +/- 250 gm EFW = (1.4×BPD×FL×AC) + 200 BPD, FL, AC in cm, EFW in gm Can’t be used accurately in Fetal Macrosomia, IUGR, skeletal dysplasia, Hydrocephalus

Slide 50:

Ultrasound Predictors of Gestational Age Parameter Timing Accuracy G-Sac 5 weeks +/- 7 days CRL 7 – 13 weeks +/- 5 days BPD 12 -26 weeks +/- 10 days HC 12 -26 weeks +/- 10 days FL 12 -26 weeks +/- 14 days AC 12 -26 weeks +/- 10 days BPD 27 – 42 weeks +/- 2-3 weeks HC 27 – 42 weeks +/- 2-3 weeks FL 27 – 42 weeks +/- 2-3 weeks AC 27 – 42 weeks +/- 2-3 weeks

Gestational Age assessment in Multiple Gestation:

Gestational Age assessment in Multiple Gestation During last 10 weeks Decrease growth of twin fetuses Head & Abdomen growth rates decreases Femur continues to grow normally throughout HC, BRD, AC : Not reliable FL : Most accurate for Gestational age assessment


Important When various USG parameters predicts different Gestational age……. Fetus should be further evaluated Small FL : Short limb defect Large BPD : Hydrocephalus Small AC : Asymmetric IUGR Large AC : Macrosomia Use Ratio : Cephalic Index, HC/AC, FL/BPD

Placental Localization:

Placental Localization Requires Full bladder Determine S ite of placenta & lower edges Umbilical cord insertion Placental abnormalities may be due to IUGR, Diabetes, Fetal hydrops , Rh Isoimunization . Any part of placenta @ upper turn of uterine fundus + Fetal head applied to cervix….. Rules out Placenta previa

Slide 54:

If USG done with Full Bladder & Placenta is not in upper segment

Slide 55:

Placental Maturity Grade Timing Chorionic Plate Calcification 0 Late 1 st Trimester Early 2 nd Trimester Smooth No indentation Absent 1 Mid 2 nd Trimester Early 3 rd Trimester (18 – 29 weeks) Mild Indentation Small, Diffuse Calcification 2 Late 3 rd Trimester (30 – 39 weeks ) Larger Indentation Larger Calcification 3 Post dates > 39 weeks Complete indentation through Basilar Plate creating Cotyledons More Calcification If Grade 3 maturity ---- < 36 weeks ……. High chances of Placental Abruption Placental Dysmaturity ….. P/o IUGR, Smoking, Chronic HT, SLE, Diabetes

Amniotic Fluid:

Amniotic Fluid Measured in all 4 quadrants around fetus at the deepest portion Amniotic Fluid Index (AFI) < 6 cm : Oligohydramnios 6 – 9 cm : Low Normal 10 – 20 cm : Normal 20 – 24 cm : High Normal > 25 cm : Polyhydramnios

Amniotic Fluid:

Amniotic Fluid If abnormal AFI noted: Serial scans required Rule out IUGR (AFI – N in 2 nd T, Low AFI in 3 rd T) Cong Malformation Intestinal Atresia Anorectal Malformation Hydrops Renal Dysplasia (Low AFI in 2 nd T) Tracheoesophageal Fistula Spina Bifida

Other Uses of Antenatal USG:

Other Uses of Antenatal USG Amniocentesis Chorionic Villous Sampling Cordocentesis Umbilical cord blood sampling Fetal Therapy

Transvaginal Scan:

Transvaginal Scan Specially designed probes placed in vagina High Freq Soundwaves (5-7 MHz) Indications Obese Pt R/o Ectopic Pregnancy Early stage of pregnancy with suspicious anomalies Location of placenta doubtful Benefits Early Diagnosis of Ectopic Pregnancy Early detection of fetal anomalies Closer proximity to Uterus – Better Images

3D Ultrasound:

3D Ultrasound Transducer takes a series of images in thin slices & the computer processes these images & presents as 3 dimensional image 3D Scan Requires Special probes Software to accumulate & render images

3D Ultrasound : Benefits:

3D Ultrasound : Benefits Volumetric measurements are more accurate Better appreciation of fetal features Smaller defects (Cleft lip, Cleft Palate, Spina Bifida, Polydactyl) very well demonstrated More subtle features(Facial dysmorphism , Low set ears, Club foot) better assessed More effective diagnosis of Chromosomal Abnormalities Better maternal bonding to baby

Safety of USG:

Safety of USG USG rays are not ionizing radiations like Xray USG rays have no embyotoxic effects to fetus Physical Effects: Mechanical vibration Increased tissue temperature Usually not relevant

Slide 64:

Patient Characteristics to be kept in mind while interpreting USG Scan Thin Pt --- Clear images Obese Pt --- Difficult to get clear view More Liquor --- Very clear images Less Liquor --- Fuzzy images

Slide 65:

Single Parameter has Limited value, Combining all together gives better idea about Fetus

Slide 66:

Single Scan has no value Periodic Scans at definite intervals are more informative & valuable for Fetal management

Slide 67:

USG Scan should be interpreted Carefully Things which are visible, Might not be there

Slide 68:

USG can’t diagnose all malformations Normal reported Scan should never be interpreted with guarantee that baby will be completely normal

Slide 69:

Ultrasonography is the most POWERFUL tool for Fetal screening But Its power may be limited or even be dangerous in an inexperienced hands

Fetal Doppler:

Fetal Doppler First use of Doppler ultrasonography to study flow velocity in the fetal umbilical artery was reported in 1977


Basics Echoes from stationary tissues are the same from pulse to pulse. Echoes from moving objects exhibit slight differences in the time for the signal to be returned to the receiver. These differences can measured as Phase Shift

Slide 72:

pulse repetition frequency (T2 –T1) = Phase Shift with known flow angle, it can calculate flow velocity . T1 T2 T1 : time of omitted signal T2 : time of returned signal

Slide 73:

Freq. q The angle of insonation Flow velocity 3 2 1 Factors affecting Doppler 4. If a second pulse is sent before the first is received, the receiver cannot discriminate between the reflected signal from both pulses - Aliasing


Parameters End Diastolic Flow Resistive Index (RI) Pulsatality Index (PI) S/D Ratio

Fetal Doppler:

Fetal Doppler Fetal Umbilical Artery Middle Cerebral Artery Thoracic Aorta Umbilical Vein Ductus Venosus Maternal Uterine Artery

Umbilical Artery Doppler:

Umbilical Artery Doppler Reflects Placental insufficiency Measured at 5 cm from cord insertion for accurate results Gestational Age based Normogram available With increasing gestational age, Umbilical artery end diastolic flow increases Umbilical artery PI decreases

Slide 78:

UMBILICAL ARTERY FLOW characteristic saw-tooth appearance of arterial flow in one direction and continuous umbilical venous blood flow in the other.

Umbilical Artery Doppler:

Umbilical Artery Doppler



Abnormal UA End Diastolic Flow:

Abnormal UA End Diastolic Flow Umbilical artery End Diastolic Flow may be Decreased Absent Reverse It indicates increasing degree of Placental insufficiency with IUGR

Clinical Implication:

Clinical Implication Reduced / Absent UA End Diastolic flow If in Early Gestational Age: Increase fetal surveillance If in Late 2 nd / Early 3 rd Trimester: Maternal Glucocorticoids & planned Preterm delivery If Close to Term: Indication of Delivery

Reversal of UA End Diastolic flow:

Reversal of UA End Diastolic flow Indicates IU decompensation & adverse effect on developing brain Long term poor neurological outcome Termination of pregnancy might be the option

Middle Cerebral Artery Doppler:

Middle Cerebral Artery Doppler Most accessible to U/S imaging More than 80% of cerebral blood in MCA Using color flow imaging, the middle cerebral artery can be seen as a major lateral branch of the circle of Willis, running anterolaterally at the borderline between the anterior and the middle cerebral fossa

Middle Cerebral Artery Doppler:

Middle Cerebral Artery Doppler Average of both MCAs must be calculated for more precise result

Middle cerebral artery :

Middle cerebral artery The blood velocity increases with advancing gestation , & this is significantly associated with the decrease in PI

MCA Doppler :

MCA Doppler Useful in Fetal hypoxia Fetal Anemia Brain Sparing Effect In early stage of fetal adaptation to hypoxemia, Central redistribution of blood flow occurs as a reflex, to maintain blood flow to vital organs

Brain Sparing Effect:

Brain Sparing Effect In fetal adaptation to hypoxemia Increased blood flow to Brain, Heart & Adrenals Reduced flow to peripheral & placental vessels Chronic Fetal Hypoxemia Increased pCO2 Decreased pO2 ........…Leads to Cerebral Vasodilatation Increased cerebral arterial EDBF

Slide 89:

Increased EDBF In MCA In response to Fetal Hypoxia The first Doppler change to fetal hypoxemia is rising peak velocity in ductus venosum . It can not be measured by Doppler precisely because it is an angle related index. Earliest detectable change to Fetal hypoxia is… Increased EDBF in MCA

Fetal Adaptation to Hypoxemia:

Fetal Adaptation to Hypoxemia EDBF PI RI S/D Ratio Middle Cerebral Artery Decreased Increased Increased Increased Umbilical Artery Increased Decreased Decreased Decreased Stage Early stage of Fetal Hypoxemia Late Hypoxia

Fetal Anemia & MCA Doppler:

Flow velocity waveform in the fetal MCA in a severely anemic and normal fetus In fetal anemia , Peak systolic blood velocity is increased, EDBF is same PI & RI are increased Fetal Anemia & MCA Doppler

Thoracic Aorta Doppler:

PI of thoracic aorta is sum of all branches’ PI below it, specially both umbilical & femoral arteries . It means that increased impedance against umbilical artery causes increasing PI of thoracic aorta. Placental insufficiency causes acidosis & Acidosis causes peripheral arterial spasm & rises PI of femoral arteries, consequently increases thoracic aorta PI. If fetal acidosis has an intrinsic cause, it will be expected that femoral artery PI will be effected more than umbilical PI. Thoracic Aorta Doppler

Venous Doppler in IUGR:

Venous Doppler in IUGR Venous indices reflect : ventricular function Fetal hypoxia Myocardial lactic acidosis Decrease cardiac output secondary to myocardial dysfunction Venous Doppler Umbilical Vein Ductus Venosus

Venous Doppler:

Venous Doppler

Ductus Venosus Doppler:

Ductus Venosus Doppler Normal progression through pregnancy is for a decrease in proportion of blood flow from umbilical vein - 40 to 15% of total volume 2nd to 3rd trimester Increase in blood flow velocity with GA The first Doppler change to fetal hypoxemia is rising peak velocity in Ductus Venosus. It is difficult to measure & perform Doppler of Ductus Venosus

Ductus Venosus Doppler:

Ductus Venosus Doppler

Umbilical Vein Doppler:

Umbilical Vein Doppler 1 st Trimester: UV pulsatile blood flow 2 nd & 3 rd Trimester: UV continuous blood flow

Uterine Artery Doppler:

Uterine Artery Doppler Uterine artery Doppler studies reflect the resistance in the utero-placental circulation In conditions such as preeclampsia and fetal growth restriction abnormal uterine artery Doppler studies indicate inadequate placentation and have been correlated with histological evidence of defective replacement of spiral arteries by maternal trophoblast .

Uterine Artery Doppler:

Uterine Artery Doppler Abnormal uterine artery Doppler studies in the context of a growth restricted pregnancy suggest a maternal cause for the growth restriction

Uterine Artery Doppler:

Uterine Artery Doppler The best predictor of PIH is notch in the uterine artery & RI>58 % after 24 wks of gestation.

Slide 102:

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