4. Obstetrics p92-97 (Normal Growth and Development)

Question 1

Foetal growth (5)

Answer 1

4 standard measurements of foetal growth used in 2nd and 3rd trimesters
- Biparietal diameter
- Head circumference
- Abdominal circumference
- Femur length

Question 2

Biparietal diameter (2)

Answer 2

Recorded at level of thalamus, from outermost edge of near skull to inner table of far skull.
Affected by shape of foetal skull (false large from brachycephaly, false small from dolichocephaly)

Question 3

Head circumference (2)

Answer 3

Recorded at same slice as BPD. Does NOT include skin.
Affected less by head shape.

Question 4

Abdominal circumference (2)

Answer 4

Recorded at level of junction of umbilical vein and left portal vein.
Does NOT include subcutaneous soft tissues.

Question 5

Femur length (2)

Answer 5

Longest dimension of the femoral shaft.
Femoral epiphysis NOT included.

Question 6

Estimated foetal weight. (2)

Answer 6

Calculated by machine based on
- BPD and AC
OR
- AC and FL

Question 7

Gestational age (GA) (3)

Answer 7

USS estimates gestational age are most accirate in early pregnancy (becoming less precise in later portions).
Age in first trimester is made from crown rump length (accurate to 0.5 weeks)
Second and third trimester estimates are usually done using BPD, HC, AC and FL (referred to as composite GA). Accurate to 1.2 weeks (12-18 weeks) or 3.1 weeks (36-42 weeks)

Question 8

Intrauterine growth restriction - suggestive features (6)

Answer 8

Estimated fetal weight below 10th centile
Femur length/Abdominal circumference ratio (F/AC) >23.5
Umbilical artery systolic/diastolic ratio >4.0

If above but doppler is normal, mostly the child is OK just small.
If measuring small + oligohydramnios (AFI < 5) or polyhydramnios, prognosis is poor.
Commonest cause of oligohydramnios during third trimester = foetal growth restriction associated with placental insufficiency.

Question 9

Asymmetrical IUGR (4)

Answer 9

Restriction of weight followed by length. More common than symmetrical.
Normal size head, body is small, sometimes called “head sparing” as body tries to preserve the brain.
Seen mainly in 3rd trimester due to extrinsic factors.
Classic Hx of normal growth in first 2 trimesters, then normal head and small body in 3rd, with mother having high BP/pre-eclampsia.
Causes include HTN, Malnutrition, Ehler-Danlos

Question 10

Symmetric IUGR (7)

Answer 10

Global growth restriction, does NOT spare head.
Seen throughout pregnancy, including 1st trimester.
Head and body both small.
Much worse prognosis as brain doesn’t develop normally.
Causes:
- TORCH
- Fetal alcohol syndrome/drug abuse
- Chromosomal abnormalities
- Anaemia

Question 11

Biophysical profile (6)

Answer 11

Initially developed to look for acute and chronic hypoxia.
2 points for normal, 0 for abnormal. Score of 8-10 is normal. Abnormal must be so for 30 mins.
Components (normal):
Amniotic fluid: At least one pocket that measures 2cm or more in a vertical plane.
Fetal movement: 3 discrete movements.
Fetal tone: 1 episode of fetal extension from flexion
Fetal breathing: 1 episode of breathing motion lasting 30 seconds.
Non-stress test: 2 or more fetal heart rate accelerations of at least 15 beats per minute and/or 30 seconds or longer

Question 12

Umbilical artery systolic/diastolic ratio (4)

Answer 12

Resistance should progressively decrease with age. Should be 2-3 at 32 weeks, should not be >3 at 34 weeks.
Elevated ratio means high resistance.
High resistance is seen in pre-eclampsia and IUGR.
Absent or reversed diastolic flow is associated with very poor prognosis.

Question 13

Macrosomia (3)

Answer 13

Babies too big (>90th centile).
Maternal diabetes (usually gestational) is common cause. T1DM mothers can also have babies too small due to hypoxia from microvascular disease of placenta.
Complications during delivery (shoulder dystocia, brachial plexus injury) and after delivery (neonatal hypoglycaemia, meconium aspiration).

Question 14

Erb’s palsy (2)

Answer 14

Injury to upper trunk of brachial plexus (C5-6) most commonly seen in shoulder dystocia. Macrosomia is a risk factor.
Aplastic or hypoplastic humeral head/glenoid in kid, think about this.

Question 15

Amniotic fluid (4)

Answer 15

Early on, the amniotic and chorionic fluid is due to filtrate from membranes.
After 16 weeks, fluid is made by fetus (urine).
Balance between too much and too little is controlled by swallowing urine and renal function, i.e. polyhydramnios caused by GI/swallowing issue, oligohydramnios caused by poor renal function.
Common cause of polyhydramnios is also high maternal sugars.
Fine particulate in the fluid is normal, especially 3rd trimester.

Question 16

Amniotic fluid index (3)

Answer 16

Measures vertical height of deepest pocket in each quadrant of the uterus, then summing them.
Normal is 5-20.
Oligohydramnios defined as AFI < 5cm. Poly defined as AFI >20cm or single pocket >8cm.

Question 17

Normal development - brain (2)

Answer 17

Choroid plexus is large and echogenic. Should be <3mm separation of choroid plexus from medial wall of lateral ventricle (more suggests ventriculomegaly).
Cisterna magna should be 2-11mm (small suggests Chiari II, large suggests Dandy Walker)

Question 18

Normal development - face and neck

Answer 18

“Fulcrum” of upper lip is normal, should not be called cleft lip

Question 19

Normal development - Lungs

Answer 19

Normally homogenously echogenic, similar in appearance to liver.

Question 20

Normal development - Heart (2)

Answer 20

Papillary muscle can calcify (echogenic foci in ventricle).
No significance in itself but associated with increased risk of Downs

Question 21

Normal development - abdomen (3)

Answer 21

Only one artery adjacent to the bladder = 2 vessel cord.
Bowel should be <6mm in diameter. Can be moderately echogenic in 2nd and 3rd trimester, not more than bone.
Adrenals are large in newborns, 20x their relative adult size.

Question 22

2 vessel cord (2)

Answer 22

2 main ways to be shown:
Single vessel running lateral to the bladder, down by cord insertion.
Cord in cross section with 2 vessels.

Question 23

Cystic rhombencephalon (2)

Answer 23

Normal rhombencephalon is present as cystic structure in posterior fossa around 6-8 weeks.
Not a Dandy Walker malformation

Question 24

Physiologic mid gut herniation (2)

Answer 24

Midgut normally herniates into umbilical cord around 9-11 weeks. NOT an amphalocele