The Role of Ultrasound in Obstetric and Gynaecology

Max Brinsmead PhD FRANZCOGMay 2006

Potential uses for ultrasound in obstetrics 1:

Locate the pregnancy – exclude ectopic Assess viability – assessment of threatened miscarriage Determining gestation & dates

Crown rump length

Diagnosis of twins – the importance of zygosity Assessment of other pelvic masses

e.g. fibroids, functional ovarian cysts & neoplasms

Screening for abnormalities first trimester Nuchal fold measure, anencephaly etc.

Assisting CVS and amniocentesis Diagnosis of molar pregnancy

Potential uses for ultrasound in obstetrics 2:

Second trimester dating (+/- 10 days) Biparietal diameter, head & abdominal circumference, femur length

Screening for abnormalities e.g. spina bifida, cardiac, renal

Screening for placenta previa Cervical length monitoring

>30 mm before 18w & >25 mm before 28 w = low risk of pre term delivery

Assessment of APH Assessment of fetal growth

Asymmetrical and symmetrical

Evaluation of polyhydramnios and hydrops

Potential uses for ultrasound in obstetrics 3: Assessment of fetal welfare

Amniotic fluid index or deepest pool Fetal breathing Fetal movements and tone (the Biophysical Profile)

Doppler flow studies In umbilical arteries Fetal middle cerebral artery Uterine arteries

Diagnosis and management of malpresentation Breech and unstable or transverse lie

Directing intrauterine interventions e.g. transfusion for hydrops, catheter for urethral stricture

Placental grading (of doubtful value) Assessment of the postpartum uterus

Proven uses for ultrasound in pregnancy:

Dating the gestation 30% of women cannot provide a LMP Another 25% have a LMP that is >2w different from USS dates When dates are known aneuploidy screening is accurate and errors

of delivery are avoided, fewer inductions for post dates etc.

Identification of multiple pregnancy Twins have a perinatal mortality that is 2-4x singletons Monitoring for discordant growth with Doppler reduces risk

Identification of breech in the third trimester ECV reduces the rate of Caesarean section

Few RCTs of routine ultrasound have shown any effect on overall perinatal mortality and morbidity

Unproven uses for ultrasound in pregnancy:

Screening for Aneuploidy Cost effectiveness of universal screening debated Ethical issues and patient choice involved

Screening for structural malformations Sensitivity is 13 – 50% depending on expertise & equipment And only half of these before 20 w gestation False positives occur

Screening for IUGR in the 3rd trimester Sensitivity is 80-90% But the positive predictive value of neonatal morbidity is only 25-

50% The rest have constitutional smallness

Harmful Effects of ultrasound in pregnancy:

It is not ionising radiation

However, thermal effects and cavitation can occur in tissues exposed to high power ultrasound

One RCT of repeated routine ultrasound with Dopplers in the 3rd trimester found a small but significant decrease in birth weight in the exposed cohort

Potential uses for ultrasound in gynaecology 1:

Assessment of adnexal pelvic masses Compound B scan Doppler vessel studies

Diagnosis of polycystic ovaries Investigation of postmenopausal bleeding

Imaging and measure of endometrial thickness Investigation of menorrhagia

Fibroids and adenomyosis Monitoring of follicle number and growth for IVF Egg recovery for IVF and ICSI Evaluation of pelvic pain

A limited role Screening for ovarian cancer

Too many false positives

Potential uses for ultrasound in gynaecology 2:

IUCD and Implanon location

Treatment of ovarian cysts (aspiration) and ectopic pregnancy (methotrexate)

Saline hysterography for delineation of the uterine cavity

Tubal patency studies in infertility

Evaluation of primary amenorrhoea