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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
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