Cross Sectional Anatomy introduction to Obstetrics hhholdorf

Let’s start with the LNMP NAGELE’s RULE To determine the due date EDC (estimated date of confinement) or EDD (expected date of delivery) using the last menstrual period (LMP or Last Normal Menstrual Period (LNMP): ECD= LMP – 3 months + 7 days About 280 days or 40 weeks.

Terminology G= Gravida (Gravity) means number of pregnancies P= Parity means number of deliveries Term= >37 weeks , < 42 weeks Preterm=20-37 weeks Post Term = >42 weeks Abortion <20 weeks Trimesters 1st 0 to 12 weeks 2nd 13 to 28 weeks 3rd >28 weeks

Harry’s Helpful Hints Ask the patient: When was your LMP…or LNMP? (This date does not have to match up with your Ultrasound findings, and quite often does not. How many times have you been pregnant, including this pregnancy? (Account for all pregnancies: i.e., still births, abortions, miscarries, twins, triplets) If pregnant before, were the births uneventful, and are the children in good health? Obtain the Gravid and Para numbers (G2 P1) Do you have any pre-existing conditions such as diabetes, high blood pressure, etc?

Scan-Assess (take a look around ) Fibroids, ovaries, fluid in PCDS? Is this an IUP? Is this a viable pregnancy? Does everything look ok? Singleton or multiples? Position of the baby-Breach, Cephalic, Transverse? Location of the Placenta-Low lying, placental previa, anterior, posterior, fundal, transverse? Check the LUS (Lower Uterine Segment-Cervical length).

Obtain measurements If 1st trimester-Gestational sac, CRL, nuchal translucency If 2nd or 3rd trimester BPD HC AC FL Others

Anatomy Head Chest-Heart Abdomen diaphragm Kidneys Stomach Pelvis Bladder Gender Spine-Transverse and Longitudinal C-spine D-Spine L/S spine

First-Trimester measurements 0 to 13 weeks

MEAN SAC DIAMETER (MSD) Established gestational age prior to visualization of an embryonic disc. Measure the length, height, and width of the inner to outer borders of the gestational sac MSD (mm) = Length (mm) + Height (mm) + Width (mm)/3 Mean sac size can be used to date an early pregnancy. A MEAN DIAMETER is calculated form three planar sections MSD (mm) + 30 = gestational age (days) A (MSD – CRL) < 5mm is associated with a high risk of SAB (Spontaneous Abortion)

IUGS with Double Sac sign

Abnormal Gestational Sac

Crown-rum length (CRL) measured until the 12th gestational week most accurate method of dating a pregnancy Sagittal measurement of the embryo or fetus from the top of the head to the bottom of the rump. Lower extremities are not included in the measurement. The embryo should always be seen sonographically when the gestational sac measures 16mm TV or 25 mm TA. The CRL is the most accurate method of dating a pregnancy sonographically, and is accurate within 3-5 days if measured properly. The correct measurement is from the top of the head to the bottom of the rump, excluding legs. The embryo grows at a rate of 1mm per day. ROT: CRL (mm) + 42 = GA (days)

CRL

Nuchal translucency The gestation should be 11 weeks 0 days to 13 weeks 6 days and the crown-rump length (CRL) should be a minimum of 45mm and a maximum of 84mm. Mid-Sagittal section of the fetus should be in a neutral position. Only the fetal head and upper thorax should be included in the image. Maximum thickness of the subcutaneous translucency between the skin and soft tissue Overlying the cervical spine is measured. Calipers are placed on the hyperechoic lines, NOT in the nuchal fluid. More than one measurement must be taken and the maximum one is to be recorded

Nuchal translucency exceeding 3mm is abnormal. A nuchal translucency scan measures the fluid filled area in the back of the neck between 11.5 to 13.5 weeks (CRL 45-84mm). The measurement can be used to calculate the risk that the fetus has Trisomy 21 or Trisomy 18 It is determined to be normal or abnormal based on the CRL of the fetus.

Normal Nuchal Translucency

Normal Nuchal Translucency

First Trimester assessment Is there an IUGS- Inter-uterine Gestational Sac? Implantation site in the fundus? Yolk sac? Does it look normal? Double Sac sign? If not, could be a pseudo-Gestational Sac of Is there an embryo? Does it look normal? Is there a heart beat? Does the embryo move? How many embryos? Twins, Triplets, more?

Two Critters

Second-Trimester measurements 14 to 27 weeks

Biparietal Diameter (BPD) Two-dimensional measurement Accurate predictor of gestational age before 20 weeks Measured in a plane that passes through the third ventricle and thalami Transverse axial plane is most common and includes the following landmarks Falx Cerebri Third Ventricle Thalamic Nuclei Cavum septi Pellucidi Atrium of each lateral ventricle

Measure perpendicular to the falx placing calipers from the outer margin of the upper Cranium to the inner margin of the lower cranium. Measurement of the Biparietal diameter can be obtained from the head circumference plane. Axial measurement performed at the level of he thalami and Cavum septum Pellucidum Calipers are placed “outer-to-outer” (leading edge to leading edge) First measurable between 10-12 weeks For the exact BPD, the angle of insonation should be 90 degrees.

Biparietal Diameter BPD

Head Circumference Three-dimensional measurement Reliable measurement independent of cranial shape Measure in plane that must include the Cavum septum Pellucidi and the tentorial hiatus. Measured parallel to the base of the skull, placing he calipers on the outer margins of the cranium. Measurement of the head circumference cannot always be obtained from the BPD plane.

Measured at the same level as BPD Circumference should NOT include scalp echoes When Occipital-frontal (OFD) measurements are used in conjunction with BPD, OFD should be measured outer edge to outer edge. More accurate than BPD when the feat head is dolichocephalic or brachycephalic

HC-Outer to Outer BPD Outer to inner

Cephalic Index Three-dimensional measurement Devised to determine the normality of the fetal head shape Normal cephalic index is approximately 78% Abnormal when less than 74% or greater than 83% Defines head shape, and is determined by dividing BPD by OFD (occipital-frontal Diameter) Normal range is 0.70 – 0.86 (70% to 86%) In cases of Dolichocephaly (CI < 70% or Brachycephaly (CI > 86%) the BPD is eliminated from estimation of gestational age.

Cephalic Index

Abdominal Circumference Three-dimensional measurement Predictor of fetal growth, not gestational age Most difficult measurement to obtain Cross-Sectional measurement slightly superior to the cord insertion at the junction of the left and right portal veins (hockey stick sign) or demonstrates a short length of the umbilical vein and the left portal vein Place calipers on the outer margins of the skin edge.

Measured at a level to include the fetal liver Preformed at the level of the stomach and portal sinus of umbilical vein Reflects fetal growth through fetal liver size Measurement is taken along skin line to include soft tissue and subcutaneous fat Least reliable measurement in establishing gestational age due to significant genetic and physiologic variations in size after 25 weeks.

AC

Femur length One-dimensional measurement Long bone of choice due to ease of measurement Normal femur demonstrates a straight border and a curved medial border Measure parallel to the femoral shaft placing calipers at the level of the femoral head cartilage and the distal femoral condyle.

Best obtained with linear array transducer Measure anterior (upside) femur to reduce artifactual bowing Includes only ossified diaphysis, excludes epiphyseal cartilage. If femur length falls more than 2 SD below the mean, skeletal dysplasia may be present, and other long bones should be measured.

Femur Length

FL

Second Trimester Assessment Is there a Heart Beat? How many? Presentation? Where is the Placenta? How much amniotic fluid? Fetal measurements Fetal anatomy

Harry’s rule: Start with the heart. Is there viability? M-mode to establish BPM (use 120 as normal, below 100 and above 180 as abnormal) Establish the heart’s position in the chest. Obtain the standard 4-chamber view. Obtain the outflow tracks: Pulmonary Vein ascends from the right Ventricle The Aortic ascends from the left Ventricle

4 chamber heart

M (Motion) mode

Second Trimester Anatomy Start with the head and move down to the feet. Eyes Lips Profile Chin Ears Etc…

Tangential View of the lips

Binocular Distance

Umbilical Cord-Umbilical Cord insertion site Bladder Fetal Gender Chest Heart 4 chamber view and outflow tracks Lungs Diaphragm Abdomen Stomach Kidneys Bowel Umbilical Cord-Umbilical Cord insertion site Bladder Fetal Gender

Diaphragm/Fetal bladder

Diaphragm

Fetal Kidneys

Cord insertion into the fetus

Umbilical Cord/Cross section Two arteries and a Vein

Normal Fetal bowel

Fetal Bowel obstruction

Fetal Gender Girl

Fetal bladder

Arms Hands Legs Feet Spine Cervical Thoracic/Dorsal Lumbar/Sacral

Hands Both hands? How many fingers?

Feet Both feet? Count toes.

Radius Ulna

Longitudinal Spine Cervical area

Longitudinal Lumbosacral (L/S) spine

Fetal Spine Transverse

Third-Trimester measurements 28-42 weeks

Biparietal Diameter BPD Head Circumference HC Abdominal Circumference AC Femur Length FL

Amniotic Fluid Volume (Index) Uterus is divided into four quadrants Vertical (AP) measurement of fluid in each quadrant is obtained. Quadrants are added to obtain the AFI A progressive increase in AFI is noted until approximately 28 weeks, after which time the AFI slowly decreases NORMAL AFI range is between 5 – 22 cm

AFI divide the uterus into 4 sections

Transcerebellar distance Measured from lateral aspects of the cerebellum in the axial plane. May be useful in assessing Gestational age in IUGR, or when other head measurements are impossible to obtain.

Cerebellum Posterior Fossa

Cerebellum

Head-Circumference to abdominal-Circumference ratio (HC/AC) During the early third trimester, the head circumference is slightly larger than the circumference of the abdomen During the late third trimester, with the increase of fetal body fat, the abdominal circumference is typically equal to or slightly larger than the head circumference.

OTHER PARAMETERS Long bone length such as radius, ulna, tibia, fibula Humeral length Foot length Binocular distance: Measured from lateral orbital rim to lateral orbital rim. May be useful in assessing gestational age in IUGR or when obtaining other measurements is impossible doe to fetal position or malformations.

Estimated fetal weight Most commonly calculated using the Biparietal diameter, femur length, and abdominal Circumference. Overall accuracy falls within 18% of the fetal actual weight in 95% of the cases. Changes in weight from previous sonograms may be used as an indicator of fetal growth. Significant variation in normal fetal weight exists, especially in the 3rd trimester

Third Trimester Anatomy Same as second trimester + check for placenta previa + check for fetal lie (Presentation) L/S ratio for fetal lung maturity? BPP (Bio-Physical Profile) AFI Fetal Movement Fetal Breathing Fetal tone Not part of BPP but check for placental grade 0-3

NST Non-Stress test is the non-ultrasound component of the BPP

Cervical evaluation > 3cm

Complete Placental Previa

Placental Location

Placental Location

Fetal Positions

Final thoughts Allow 20 minutes for a complete first trimester exam Allow 40 minutes for a complete 2nd or 3rd trimester exam If BPP, one hour for complete exam. Scan sitting down…a tired tech makes for sloppy films. Your communication skills (verbal and non-verbal) will be on display!!!

Fetal tragedies are hard on everyone. Get used to them. If you get upset, everyone gets upset. BUT, if you appear indifferent, you may come off as non-caring. Perfect the art of being a professional!! Whatever that is…