US:

1. Screen all pregnancies
2. Date pregnancies + chart antenatal growth of fetus.
3. Identifies Congenital abnormalities
4. Color & Doppler US identifies Placental + fetal blood vessels & provides information on placental function + fetal circulatory response to hypoxia.
5. Continuous wave Doppler US: Continuous tracings for fetal heart rate.

MI + 3 dimensional US for further information.

TRANSVAGINAL US:

Useful in early pregnancy
Examines cervix in late pregnancy
Identifies lower edge of placenta
Diagnosis of disorders of early pregnancy ( missed miscarriage, blighted over where no fetus is present, ectopic pregancy)
Missed miscarriage: fetus can be identified + absent fetal heart in a blighted ovum. Empty gestational sac.
Ectopic pregnancy: positive pregnancy test + US which doesn't identify gestational sac within the uterus, adnexal mass with or without fetal pole, fluid in the pouch of Douglas. Dress Affordable light blue color wedding selections

Abdominal US used later in pregnancy.

CLINICAL APPLICATIONS OF US:

1. Diagnosis + confirmation of viability in early pregnancy:

Gestational sac visualized at 4-5 weeks
Yolk sac at 5 weeks
Embryo observed + measured at 5-6 weeks
Heartbeat at 6 weeks.

2. Determination of gestational age + assessment of fetal size and growth:

For assessment of age:
CRL
HC
BPD (Bipareital diameter)
FL (femur length)

Later in pregnancy for size + growth:
AC (Abdominal circumference)
HC

3. Multiple pregnancy:

US most common way to diagnose.
Twin peak or lambda sign seen in 1st trimester.
Determination at 9-10 weeks.

4. Diagnosis of fetal abnormalities: before 20 weeks

5. Placental localization: at 20 weeks to identify women who have low lying placenta.

6. Amniotic fluid volume assessment:

7. Assessment of fetal well being: by evaluating fetal movements, tone, breathing in Biophysical profile.

8. Measurements of cervical length: women with short cervix deliver before 34 weeks.

9. Other uses:
Confirmation of intra uterine death.
Confirmation of fetal presentation.
Diagnosis of uterine and pelvic abnormalities.

US IN ASSESSMENT OF FETAL WELL BEING:

1. AMNIOTIC FLUID VOLUME

2. CTG: Continuous tracing of fetal heart rate to assess fetal well being.

Assessment of 4 things:

1. Baseline rate: normal is 110-150 bpm.
Fetal tachycardia in fetal infections, Acute fetal hypoxia, fetal anemia, drugs (adrenoreceptor agonists: ritodrine)
Best determined over 5-10 mins. Prior to term 160 bpm as upper limit of normal.

2. Baseline variability: interval between successive heart beats (beat to beat variability) known as short term variability.

Longer term fluctuations in heart rate occurring between 2-6 times per min: known as Baseline variability.

Normal Baseline variability: normal fetal autonomic nervous system.

Abnormal if less than 10 bpm.

3. Acceleration: increase in the Baseline fetal hear rate of atleast 15 bpm lasting for atleast 15 seconds.

Presence of 2 or more accelerations indicative of reactive trace and non hypoxic fetus.

4. Deceleration: transient reduction in fetal heart rate of 15 bpm or more lasting for more than 15 secs.

Indicative of fetal hypoxia of umbilical cord compression.

Pregnant woman should be in left lateral position to avoid compression of IVC.

Recordings for atleast 30 mins. Two lines are traced: one of fetal heart rate, second of uterine activity.

Biophysical profile:

Long (30 mins) ultrasound scan which observes:
Fetal behavior
Measures amniotic fluid
Includes CTG

Score of 8 or 10: normal
Score of 0, 2, 4: abnormal
Score of 6: repeat.

Limitations of Biophysical profile:

1. Fetus spend approximately 30 % of their time asleep and in this time breathing movements are not exhibited.

2. When abnormal score is found, most fetuses are severely hypoxic.

Doppler US: Umbilical artery + fetal vessels for fetal hypoxia assessment.

US guided invasive procedures:
Amniocentesis
CVS
Cordocentesis
Insertion of fetal bladder shunts or chest drains

Early pregnancy scan: 11 - 14 weeks: MNEMONIC CADIS

1. Confirm fetal viability
2. Accurate EDD
3. Diagnose multiple gestations
4. Identify markers of increased fetal chromosomal abnormalities
4. Identify structural abnormal

20 week scan (18-22 weeks) MNEMONIC: PAD

1. Accurate EDD if not previously done
2. Detailed fetal anomaly scan
3. Locate and identify placenta
4. Estimate amniotic fluid volume
5. Doppler for Maternal uterine arteries
6. Measure cervical length to assess Preterm risk.

US in 3rd trimester:

1. Assess fetal growth
2. Assess fetal well being.