Fetal Biometry

Embryonic/fetal growth 1st trimester

• Crown rump lengthCrown rump length best index of gestational best index of gestational lengthlength

• Phase of most rapid growth in length (up to first ½ preg.)• Time when growth influenced most by

genome aneuploidyaneuploidyexternal influences infection

drugs

Stage being set for later effects Stage being set for later effects smokingsmoking maternal nutritionmaternal nutrition uterine circulationuterine circulation

Fetal Growth 2nd – 3rd trimestersWhy has it happened what will be the best tests?

• Environment (diff. populations and over time)maternal factor small maternal size (customise)small maternal size (customise)

smoking-dose dependent (200gsmoking-dose dependent (200g))

parityparity

preeclampsiapreeclampsia

previous FGRprevious FGR

glucose concentrationsglucose concentrations

Measurement of BPD

• Short midline, 90 degrees to the beam

• Oval shape

• Thalami

• NO cerebellum or orbits

• Cavum septum pellucidi

• Measure from outer bone to inner bone at widest point (parietal eminence)

Measurement of BPD

Measurement of HC

• Short midline, 90 degrees to the beam

• Oval shape

• Thalami

• NO cerebellum or orbits

• Cavum septum pellucidi

• Measure circumference of outer bone (usual to put calipers at occiput then sinciput)

Measurement of AC

• Transverse section through abdomen• As round as possible• Transverse spine and short length 1 rib• Stomach• Short length umbilical vein and right portal

vein approximatly 1/3 from anterior abdominal wall

• NO kidney, bladder, heart. Adrenal allowed

Measurement of AC

Measurement of FL

• Full length femur

• Bone 90 degrees to the beam

• Both ends clearly seen

• Skin line separate and beyond bone end

• Measure from bottom of ‘U’ either end

• Bring in calipers from wider point to end

Measurement of FL

Summary of fetal growthSummary of fetal growthprediction of IUGRprediction of IUGR

• Poor predicitors of IUGR

Single estimates of fetal size

AFV

Umbilical artery resistance (doppler)• Useful

fetal abdominal area (AC)fetal abdominal area (AC)

fetal growth velocitiesfetal growth velocities

• Owen et al BJOG 2003; 411-415

www.gestation.netl.mccowan@auckland.ac.nz

Pathophysiological factors and clinical conditions

• Placental FailureReduced utero/plac blood

flowSmall surface area• Altered Maternal

SubstrateHypoglycaemiaHypoxia

Preeclampsia FGRAPS,uterine abns,plac

infarct

MalnutritionAltitude, anaemia,cyanosis

• Reduced fetal driveChromosomal

anomaliesGene defectsEndocrine disordersFetal anomalies• Extnal/int.growth

inhibitionDrugs, smoking age,

infections

Aneuploidy, Chr15 IGF-1r loss

PKUPancreatic,thyroidRenal, cong.heart

Cytotoxics,radiation,rubella,CMV, mat age extremes

Twin growth

• Discordancy defined as >15% difference

• Search for cause of discordancy FGR

abnormality

TTTS

• Controversy over twin growth rates

use of singleton charts

50th birthweight percentiles

Alexander et al Clinical Obstet Gynecol 41:1;115-125

Placental Localisation

• Identify placenta previa– Major previa– Minor previa

• Identify succenturiate lobes

• Identify vasa previa

TA- Sagittal midline suprapubic image

PosteriorPlacenta Praevia

Placental Localisation

• When to rescan if identified at:– 14 weeks?– 20 weeks?– 32 weeks?– 37 weeks?

• Placenta accreta

Cervical length Assessment

• TA, TL or TV

• Indications– Previous cervical surgery– Previous midtrimester losses (14-24 weeks)– Previous PPROM– Previous PTL

• Timing– 14-18 weeks

Cervical length at 18 weeks and risk of Cervical length at 18 weeks and risk of preterm delivery preterm delivery 32 weeks 32 weeks

10 29 (11-76) 48% 15 24 (13-46) 41% 20 18 (11-31) 32% 25 13 (8-21) 30 3 (2.4-4)

Hassan et al. Am J Obstet Gynecol 2000; 182: 1458-67.

Cervical Length(mm)

RR(95%CI) PPV

BulgingBulgingmembranesmembranes