The document discusses the importance of third trimester scanning for assessing fetal health, placenta, and amniotic fluid conditions. It covers various abnormalities such as oligohydramnios and polyhydramnios, their causes, clinical features, and consequences on fetal well-being. It emphasizes the role of ultrasound in diagnosing these conditions and outlines potential treatment options and complications associated with each condition.

1. Third trimester
scanning,
Placenta and
Amniotic fluid
abnormalities
Mini Sood

2. Contents
 Third trimester scans
 Placenta-Normal and abnormal
 Liqour amnii normal and abnormal

3. Third trimester scanning
 Indications
 Dating
 Fetal well-being
 Estimation of fetal weight
 Placental localization
 Amniotic fluid index

4. Dating in third trimester
 Bi-parietal diameter
 Accuracy-95%
 Head circumference
Accuracy- 93%
 Abdominal circumference
Accuracy-85%
 Femur length- accuracy-
95%
Estimated fetal weight-Accuracy
500gms
-

5. Fetal wellbeing assessment
 Manning score
 Five parameters- Fetal movements, fetal tone, AFI , NST and fetal breathing movements.
 All recorded over a 20-30 minute period and scored as 2 or 0 based on presence or absence.
 Total score over 8 considered good fetal well-being,
 Score between 6-8 considered equivocal and
 Score less than 4 considered fetal hypoxia.
 Modified Manning score or Planning score
Combination of AFI and NST (Non stress test)

6. Physiology of amniotic fluid: functions
 Derived almost entirely from the fetus
 Protects fetus from trauma
 Cushions the umbilical cord from compression
 Antibacterial properties
 Reservoir of fluid, nutrients for the fetus
 Provides growth factors for development of systems (esp. lungs, musculoskeletal,
gastrointestinal)

7. Physiology of amniotic fluid: source
 Produced from fetal urination, nasal and oral secretions, placental and
amniotic membrane surfaces, intramembranous and trans membranous flow
and fetal lung secretions
 The entire amniotic fluid recycles in three hours.
 Derangements in volume adversely affect pregnancy, both when it is i or h,
or if it is meconium stained
 The amniotic fluid is 98-99% water and 1-2% solids like proteins,
carbohydrates lipids , phospholipids, enzymes, hormones, pigments and
chemicals like urea, uric acid, creatinine and electrolytes
 There many be fetal cells, amnion cells, hair, blood cells and meconium as
well

8. Physiology of amniotic fluid: content
 Daily amniotic volume flows in the near term fetus are:
 Fetal urine 800-1200ml/day
 Fetal lung liquid secretions-170ml/day
 Fetal swallowing-500-1000ml/day
 Intramembranous flow 200-400ml/day
 Oral-nasal secretions -25ml/day
 Trans-membranous flow- 10ml/day

9. Physiology of amniotic fluid: normal levels
 Amniotic volume increases to 1L or more by 36 wks
 In post-term there may by only 100-200 ml
 Normal volume varies with the duration of pregnancy
 Average 12 weeks: 50 ml
24 weeks: 500 ml
36 weeks: 1000 ml, and decreases thereafter
 Term: normally (singleton pregnancy): 500-1500 ml

10. Oligohydramnios
Definition
 Deficiency of the amniotic volume (< normal)
Incidence
 0.5-5% of all pregnancies
 Usually develops late in pregnancy. Early
onset: worse prognosis

11. causes
 Placental causes
 Abruption
 IUGR
 Post-term
 PROM
 Twin-twin transfusion
 Utero-placental insufficiency
 Maternal causes
 Fetal causes

12. causes
 Placental causes
 Maternal causes
 Hypertension, diabetes
 Infections, fevers
 Drugs
 Prostaglandin synthetase inhibitors,
 Angiotensin converting enzyme inhibitors
 Idiopathic
 Fetal causes

13. causes
 Placental causes
 Maternal causes
 Fetal causes
 Chromosomal abnormalities
 Congenital anomalies
 Fetal death

14. clinical picture
 Uterus is small for date
 Fetus
 Easily felt & immobile
 FHS easily heard
 U/S
 Vertical pocket <1cm or <2cm
 AFI <5 cm

15. Oligohydramnios: complications
 During pregnancy
 Fetal hypoxia (cord compression)
 Persistent position of the fetus
 Limb deformities:(pressure or amniotic bands)
 Talipes (clubfoot)
 Ankylosis of joins
 Pulmonary hypoplasia
 During labor
Increased variable deceleration
Increased cesarean section rate

16. Oligohydramnios: treatment
 Amnio-infusion: infusion of saline into the uterine cavity
 through the abdominal wall by a spinal needle
 To increase the AFV
 To dilute meconium
 Prognosis
 Fetal outcome is poor with early-onset
oligohydramnios

17. Amniotic band syndrome
 Other names-Amniotic band disruption
complex, constriction band syndrome, amniotic
deformity, adhesions, mutilations complex
 Incidence: 0.89/10,000 births
 Cause: amniotic rupture occurring early in
pregnancy
 Vascular insults in early pregnancy also
implicated

18. Amniotic band syndrome
 Seen in chronic oligohydramnios
 Adhesions in the amniotic sac walls, interfere with
fetal development, causing limb defects or even
growth restriction, due to these fibrous bands.
 Bands may amputate part of the limb or digit
 Can be detected on scanning antenatally.
 Range from simple band constrictions to major
craniofacial and visceral defects.
 Can cause significant neonatal morbidity

19. Amniotic band syndrome
 Prenatal diagnosis is essential for
counselling and management
 Can mimic genetic syndromes
 Risk of recurrence of is low

20. Polyhydramnios: definition
 Amniotic fluid volume (AFV) >2 L
 Incidence: 1-4% pregnancies.
Differential diagnosis
 Twins
 Ovarian cyst
 Full bladder
 Hydatidiform mole
 Ascitis
 (All are resolved by U/S)

21. Polyhydramnios: acute and chronic
 Acute
 Excess fluid accumulates more quickly & it occurs
earlier in pregnancy. It is usually associated with
twin pregnancy
 Chronic
 Excess fluid accumulates gradually & it is only
noticed after the 30th of pregnancy. It is 10 times
more common than acute PH.

22. Polyhydramnios: fetal causes
 Multiple pregnancy
 Hydrops fetalis
 Anomalies: Neural tube defects (anencephaly,
spina bifida), duodenal atresia, tracheo-
esophageal fistula
 Increased transudation of CSF
 Excessive urination
 Stimulation of cerebrospinal centers, poor
arginine vasopressin secretion


23. Double bubble of duodenal atresia

24. Polyhydramnios: maternal causes
 Diabetes mellitus
 Maternal hyperglycemia
 Fetal hyperglycemia
 Osmotic diuresis
 Pre-eclampsia
 Heart or renal failure
 *Idiopathic

25. Polyhydramnios: severity
With sonography:
 Mild 8-11cm 80%
 Moderate 12-15cm 15%
 Severe >16cm 5%

26. Polyhydramnios: clinical features
 Dyspnea
 Edema
 Oliguria
 Dyspepsia

27. Polyhydramnios: diagnosis
 Uterine enlargement (> period of pregnancy)
 Difficulty in palpating fetal parts
 Difficulty in hearing fetal heart
 Sonography
 *assess severity by measurement of single
deepest pocket on US
 Detect the cause when possible

28. Polyhydramnios: treatment
 Amniocentesis - 1500-2000 ml/day
 Indomethacin
 Decreases lung liquid production
 Decreases fetal urine production
 Increases fluid movement across fetal membranes
 Mild polyhydramnios rarely requires treatment
 Moderate: can usually manage until labor
 Severe (dyspnea, abdominal pain, ):  higher
perinatal mortality rate  hospitalization

29. Hyperechoic liquor
 Hyperechoic liquor (on US) with haziness
surrounding fetus: meconium stained
liquors. Results from passage of
meconium as a result of distress
 This could be seen in the third trimester or
even when the scan is done during labor

30. Hyperechoic liquor
 When hazy liquor is detected, try to find the
underlying cause
 Amnioscopy (if the cervix is dilated), can
confirm the diagnosis of meconium.
 Delivery on an urgent basis to rescue the
fetus.

31. Placenta - Normal

32. Placenta Previa-placenta in the lower
uterine segment

33. Placenta abruption- separation of a normally
situated placenta with bleeding

34. Placenta accrete- Placenta embedding into the
myometrium or beyond it

35. Placental tumors-Chorioangioma
Placental tumors

36. Abnormalities of placenta
 Circumvallate Placenta
 Succenturiate lobe

37. Conclusions
 Liquor abnormality is a common US feature.
 Amniotic fluid abnormalities can increase perinatal mortality and morbidity.
 Oligohydramnios can be due to infections, preterm membrane rupture, or fetal anomaly. It
leads to fetal lung hypoplasia, amniotic band syndrome, preterm labor, fetal demise
 Polyhydramnios can result from maternal diabetes or fetal anomaly. It causes maternal and fetal
complications.
 Meconium stained liquor is a consequence of acute or chronic fetal distress and results in
meconium aspiration syndrome with respiratory distress in the newborn and can be fatal.
 The ultrasonic evaluation of fetal wellbeing includes the assessment of the amniotic fluid index.
It accurately detects fetal distress, and diagnoses oligohydramnios as well as polyhydramnios

38. Conclusions
 Placenta Previa minor and major are detected by ultrasound with an over 99% accuracy.
 Associated placenta accrete can be detected and when there is a doubt an MRI can be done
to confirm accrete.
 Placental abruption is recognized by the presence of the retro-placental clot along with the
clinical picture.
 Rare placenta structural defects and tumors too can be accurately diagnosed.