Flashcards in Session 9 - Group work Deck (31)
List some factors that have an impact on fetal growth.
Maternal nutrition and health
Efficiency of placenta
Adequate utero-placental blood flow
Maternal parity (primaparous mothers have smaller babies than multiparous)
Maternal habits (smoking, drug abuse etc)
Also, race, maternal height, weight,
If a fetal growth restriction is caused by compromise of the uteroplacental circulation
(e.g., due to blood clots or hypertension), how may uteroplacental or fetoplacental
circulations be investigated?
9.3 An expectant women has her first (and sometimes only) ultrasound scan at 20
weeks. How are these measurements used at a later date?
The measurements are used to confirm earlier dating and form a reference point for later
Some but not all fetal anomalies may be excluded at this stage.
9.4 Suggest three reasons why this is a good time in pregnancy to have this procedure?
i. At this stage of pregnancy the organ systems are developed and can be visualised
and anomalies can be identified.
ii. If anomalies are seen, the pregnancy is still early enough for possible intervention or
termination if appropriate.
iii. The inherent error in these measurements increases with gestational age such that
as a dating tool ultrasound becomes less accurate as the pregnancy proceeds.
1st Trimester ± 1 week
2nd Trimester ± 2 weeks
3rd Trimester ± 3 weeks
List some further uses of ultrasound in obstetrics
A comprehensive list:
Determine presence or absence of intrauterine pregnancy (or ectopic pregnancy)
Determine gestational age and measure fetal growth (when compared against standard
e.g., abdominal circumference (AC)
biparietal diameter (BPD)
crown-rump length (CRL)
femur length (FL)
head circumference (HC)
Estimate fetal weight
Identify multiple pregnancies
Detect fetal anomalies (e.g., neural tube defects), placental anomalies (e.g., placenta
Measurement of amniotic fluid
(Identify maternal pelvic anomalies)
(Guide for needle in amniocentesis)
At this early stage, why is transvaginal ultrasound used to reassure the mother that
the pregnancy is well established?
Transvaginal ultrasound to see fetal cardiac activity in the uterus is very reassuring . It rules
out ectopic pregnancy and early causes of loss such as blighted ovum
Why have dietary supplements of folic acid been recommended?
Folic acid supplements may reduce the risk of neural tube defects. Routine blood tests for
alpha-fetoprotein are taken between 15-19 weeks gestation (when levels are at their
highest). If elevated, it can be indicative of an open neural tube defect. Ultrasound study with
optional amniocentesis is indicated. Raised alpha-fetoprotein levels, however, may 'simply'
indicate a multiple pregnancy.
Identification of fetal cardiac activity is an assurance of the diagnosis of pregnancy.
(The fetal heart beat can be seen with transvaginal ultrasound as early as 5-6
weeks). Predict when you can you hear the fetal heartbeat with (i) a Doppler
stethoscope and (ii) a plain stethoscope?
(i) Doppler stethoscope (10-12 weeks)
(ii) Plain stethoscope (18-20 weeks)
What is the average fetal heart rate at term?
140 - 160 beats per minute
At what stage are fetal respiratory movements evident by sonography?
From about 12 weeks fetal respiratory movements are seen by sonographic evaluation.
By 34 weeks they occur in irregular bursts, with rates up to 40-60/min, punctuated with
periods of apnoea (including hiccups). Fetal respiratory movements are diaphragmatic and
cause movement of amniotic fluid into and out of the lungs.
Which cells secrete surfactant? At what gestational age does surfactant production
begin and how is this significant in prematurity?
Type II ALVEOLAR CELLS produce surfactant beginning at about 20 weeks but increases
dramatically after 30mwekks, reaching significant levels at about 34weeks.
A deficiency of surfactant leads to respiratory distress syndrome of the newborn – a high risk
in prematurity. Steroid therapy, given antenatally to women at risk of pre-term delivery, may
reduce the risk of RDS by 50%, by promoting the production of surfactant
You next see her at 16 weeks and measure the symphysis–fundal height. The
symphysis-fundal is a simple but very common method of monitoring fetal growth is
height. What is this and how is it measured?
The uterus becomes an abdominal organ at about 12 weeks so the fundus is now palpable.
The height from top of symphysis pubis to top of fundus (in cm) correlates with the number
of weeks of gestation.
Distance between symphysis pubis to top of uterus (i.e., fundus). It can be measured with a
tape measure (e.g., 20cm at 20 weeks, 36 cm at 36weeks then, plateaus). Alternatively, the
height of the fundus is assessed in relation to other structures such as the umbilicus or
xiphisternum. The uterus is palpable above the pelvis after gestational week 12. A lag of 4
cm or more of the fundal height is suggestive of intrauterine growth restriction/fetal growth
Predict the sources of error for this assessment?
Measurements are dependent on the number of fetus, volume of amniotic fluid, extent of
engagement of head and the lie of the fetus.
At her 20 week visit, what question will you ask the mother which will be an indication
of fetal well-being?
As about fetal movements; the mother should be noticing fetal movements (also called
‘quickening’), which feel like fluttering.
A multiparous woman may detect fetal movements earlier
An expectant mother presents at 30 weeks, she has previously been doing well. Her
symphysis-fundal height today shows a lag and is only measuring 25cm. An
ultrasound is ordered. Fetal abdominal circumference is measured below that which
is predicted for gestational age (head circumference and biparietal diameter are
normal). What sort of pattern of growth restriction would you expect to be occurring
at this stage in a pregnancy
Asymmetric growth retardation in which there is "brain sparing". The head (and indeed
femur) continues to grow but abdominal fat and glycogen is diminished as fetus is
compromised. Asymmetrical growth retardation is associated with poor maternal nutrition or
decline in nutrient delivery to the fetus in the latter stages of pregnancy. This may be due to
maternal or fetal factors but most often reflects compromise to the utero-placental unit. The
growth restriction shows up mainly in the third trimester when nutritional demands and fetal
growth are most rapid
Growth retardation earlier in pregnancy is more often related to genetic, or congenital
problems or isolated insults to the development of the fetus.
Why is fetal abdominal circumference a valuable measurement?
Measurement of fetal waist (at level of the umbilical vein) provides assessment of growth of
fetal liver and amount of sub-cutaneous fat etc. Glycogen laid down in the fetal liver
accounts for much of this growth.
Patients carrying a fetus with growth restriction are usually seen more often and the
biophysical parameters are checked. One method is the BioPhysical Profile( BPP).
The BPP uses ultrasound and electrocardiography to document 5 parameters of fetal
well-being relating to development and function of fetal organ systems and used to
determine whether early delivery is required
Which organ systems are being assessed by each test?
fetal movement Musculoskeletal
fetal breathing movement musculoskeletal /respiratory
fetal tone Musculoskeletal
amniotic fluid volume Renal
fetal heart rate response to movement in the
NON-STRESS TEST (NST)
Autonomic nervous system
The first four are assessed by ultrasound. Many factors may cause a reduction in the scores
achieved including fetal sleep cycles, maternal dehydration or hunger, maternal sedation
and fetal alcohol syndrome, as well as fetal compromise due to hypoxemia. The results have
to be viewed in context of risk factors, earlier studies and sometimes repeat evaluations to
determine whether urgent and /or early delivery is required.
Normal CNS development is dependent on the production of which fetal hormone(s)
which if deficient cause cretinism in children?
Thyroid hormones (secreted from 12 weeks onwards, very little is derived from the mother)
At 34 weeks of pregnancy, the fundal height is only 29cm. An ultrasound study
shows asymmetrical growth restriction with reduced amniotic fluid (AF) volume
(oligohydramnios). Uteroplacental circulation is compromised (Doppler ultrasound).
Why is oligohydramnios associated with this pattern of growth restriction?
Nutritional deprivation / utero-placental insufficiency leads to decreased fetal urine
What factors must you consider in deciding whether to allow a compromised fetus to
remain in utero?
Risks of compromise v risks of prematurity, particularly respiratory problems. In this case, at
34 weeks, the fetus should be producing surfactant that will help reduce respiratory distress.
Prior to week 8, how is amniotic fluid produced?
Passage of fluid across the amnion and fetal skin (transudation)
Fetal urine contributes to the volume of amniotic fluid. At what stage is urine first
9.23 Amniotic fluid volume increases proportionately with fetal growth until late pregnancy
when it begins to decline. Most of the amniotic fluid in the last half of pregnancy
consists of fetal urine and amniotic fluid volume is a reflection of fetal renal function
and hence fetal metabolism.
Consider how amniotic fluid volume might be altered in the following situations.
• Fetal kidney malfunction
• Maternal hypertensive disorders
• Premature rupture of membranes
• Fetal bladder outlet obstruction
• Premature leakage of amniotic fluid
All would lead to an abnormally low volume of amniotic fluid. (oligohydramnios )
4 As the fetus swallows and digests amniotic fluid. Identify a fetal GI tract defects that
might lead to excessive amniotic fluid volume (polyhydramnios)
(Also, diaphragmatic hernia, anencephaly, inencephaly, hydrocephaly)
At 36 weeks, the fetal abdominal circumference reading is high in relation to head
circumference. What maternal condition might cause these abnormal readings?
Poorly controlled maternal diabetes. A rise in maternal blood glucose levels raises the
availability of glucose to the fetus. Much of this glucose will be laid down as glycogen in the
fetal liver (hence increase in fetal abdominal measurement).
What term is used to describe such a fetus?
Fetal macrosomia; birth weight >4000 or 4500g
(There are other causes of fetal macrosomia including post-term pregnancy and maternal
In certain pregnancies, especially near to term, a fetus may be classified as 'at-risk',
and will require special monitoring such as a non-stress tests and biophysical profile.
In what instances might the fetus be classified as at-risk?
• maternal heart or liver disease
• multiple gestation
• maternal diabetes
• where there is evidence of fetal growth retardation
• suspected oligohydramnios
• presence of placental abnormality
• post-dated pregnancy
In a non-stress test, 3 or more fetal movements should be accompanied by a rise in
fetal heart rate. Over a 30-minute period you record neither fetal movement nor-
change in heart rate. Should you be concerned?
The fetus may be sleeping. Repeat later, e.g., after a meal
9 The presence of meconium in the amniotic fluid is a sign of fetal stress and asphyxia.
What is meconium and how is it formed?
Typically, meconium are the first stools of a newborn baby – green, dark and sticky and
composed of cellular debris, mucous and bile pigments. It is formed from the digestion
products of amniotic fluid (cells and protein) the fetus has swallowed. The presence of
meconium in the amniotic fluid is an indicator that the fetus has had an episode of distress.
Apart from ultrasound, how can you decide on the lie and presentation of a fetus in