ASSESSMENT OF FETAL GROWTH AND DEVELOPMENT

 

New technology has allowed better assessment of the fetus

 

Modalities to Assess Fetal Status

 

I.                 Ultrasonography Ė a safe method of visualizing fetal organs and tissues

a.   Definitions

                                                            i.      Transabdominal Ultrsound

1.   after first trimester

                                                         ii.      Transvaginal Ultrasound

1.   during first trimester

b.   Clinical applications

                                                            i.      Identification of pregnancy

                                                         ii.      Identification of multiple fetuses

                                                      iii.      Determination of fetal age, growth and maturity

                                                      iv.      Observation of polyhydramnios and oligohydramnios

                                                         v.      Detection of fetal anomalies

                                                      vi.      Determination of placenta previa

                                                   vii.      Identification of placental abnormalities

                                                viii.      Location of the placenta and fetus for amniocentesis

                                                      ix.      Determination of fetal position

                                                         x.      Determination of fetal death

                                                      xi.      Examination of fetal heart rate and respiratory effort

                                                   xii.      Detection of incomplete miscarriages and ectopic pregnancies

II.             Amniocentesis

a.   the obtaining of a sample of amniotic fluid

b.   Timing

                                                            i.      early is done prior to 15 weeks gestation

                                                         ii.      mid-trimester is done during the 2nd and 3rd trimester

1.   most common

c.    Procedure

                                                            i.      A 3.4-4.0 inch 20-22 gauge needle attached to a syringe is inserted into a pocket of amniotic fluid

                                                         ii.      20-30 mL of amniotic fluid is aspirated

                                                      iii.      amniotic fluid is placed in sterile tubes

                                                      iv.      the amniotic fluid and cellular elements are examined

d.   Tests

                                                            i.      L/S Ratio and presence of PG

                                                         ii.      Alpha-Fetoprotein (AFP)

1.   increased in neural tube defects, decreased in Downís Syndrome and in fetal death

                                                      iii.      Bilirubin

1.   hemolytic disease such as Rh incompatibility

                                                      iv.      Creatinine Levels

1.   determine fetal kidney maturity

                                                         v.      Meconium Staining

1.   green fluid (normally clear)

                                                      vi.      Cytology

1.   cells from skin, amnion, TB tree

2.   detect genetic and chromosomal disorders

3.   cultured and grown

a.   takes two weeks for results

III.         Fetal Heart Rate Monitoring

a.   Purpose

                                                            i.      correlates with fetal well-being

b.   Three ways to monitor FHR

                                                            i.      Doppler transducer on momís abdomen

                                                         ii.      ECG monitor on momís abdomen

                                                      iii.      Small electrode on fetal scalp

1.   membranes are ruptured so there is a risk of infection

c.    Patterns

                                                            i.      Baseline heart rate

1.   Measured over 10 minutes

2.   Normal range is 120 to 160 bpm

3.   An increase or decrease of 20 to30 bpm may be abnormal even if in normal range

                                                         ii.      Variability

1.   Fetus has a constantly changing heart rate (5-10 bpm)

2.   Decreased variability is caused by:

a.   CNS depression secondary to hypoxia

b.   fetal sleep

c.    immaturity

d.   maternal narcotic use

                                                      iii.      Bradycardia

1.   Heart rate < 100 bpm or a drop of 20 bpm from baseline

2.   Causes

a.   Fetal asphyxia

                                                                                                                                    i.      most dangerous cause

                                                                                                                                 ii.      treat by giving mom O2

b.   congenital heart defects

c.    hypothermia

                                                      iv.      Tachycardia

1.   Heart rate > 180 consistently

2.   Causes

a.   maternal fever

b.   most common cause

c.    infection

d.   dehydration

e.   anxiety, asphyxia

f.     sympathomimetics

g.   parasympatholytics

                                                         v.      Acceleration

1.   Fetal heart > 160 for < 2 minutes

2.   Fetus is reacting to a contraction in a positive way

                                                      vi.      Decelerations

1.   Fetal heart rate < 120 bpm for < 2 minutes

2.   May be threatening or harmless, depending on the type of deceleration.

3.   Types of Decelerations

a.   Type I Decelerations(Early)

                                                                                                                                    i.      Closely follow uterine contractions in onset and duration

                                                                                                                                 ii.      Heart rate decreases to 60-80 bpm during the contraction, then rapidly returns to baseline after the contraction

                                                                                                                              iii.      Caused by compression of the fetal head against the cervix during the contraction (vagal response)

                                                                                                                              iv.      Benign, it doesnít indicate hypoxia

b.   Type II Decelerations (Late)

                                                                                                                                    i.      Occur 10-30 after start of contraction with a slow return to baseline

                                                                                                                                 ii.      Even a small decrease of 10-20 bpm indicates a problem

                                                                                                                              iii.      Secondary to uteroplacental insufficiency

                                                                                                                              iv.      †Caused by compression of the vessels of the uterus and placenta during the contraction

                                                                                                                                 v.      †Leads to decreased transfer of O2 to the fetus and fetal asphyxia

c.    Type III Decelerations (Variable)

                                                                                                                                    i.      Decelerations independent of contractions

                                                                                                                                 ii.      Random in onset, duration and severity

                                                                                                                              iii.      Caused by compression of the umbilical cord

1.   Umbilical cord wrapped around the fetuses neck or compressed between the pelvis and body part

                                                                                                                              iv.      Danger depends on frequency and severity

                                                                                                                                 v.      Turn mom side to side or place in knees to chest position to alleviate cord compression

IV.          Fetal scalp pH

a.   Purpose

                                                            i.      Used in conjunction with fetal heart monitoring

b.   Indications

                                                            i.      Absence of baseline variability

                                                         ii.      Late decelerations with decreasing variability

                                                      iii.      Abnormal FHM tracings

c.    Procedure

                                                            i.      Mother placed in lithotomy position

                                                         ii.      Fetal head visualized through the cervix

                                                      iii.      Scalp incision made

                                                      iv.      Blood collected in heparinized capillary tube

d.   Poor gas exchange leads to increased PaCO2 and lactic acidosis (mixed acidosis)

e.   Interpretation of Fetal Scalp pH

†††††††††††††

pH

Interpretation

7.25

Normal

7.20-7.24

Slight asphyxia

< 7.20

Severe

 

 

Estimating the Delivery Date

 

I.                 Nageleís Rule

a.   Three months are subtracted from the first day of the last menstrual period, then seven days are added to the result

b.   For example, if the first day of the last menstrual period is May 15, subtracting 3 months would arrive at February 15.† Adding 7 days gives an EDC as February 22

c.    Requires a regular cycle of 28 days, use of oral contraceptives or irregular cycle reduces the accuracy

II.             Fundal Height

a.   Fundus is the portion of the uterus opposite the cervix

b.   The distance from the symphysis pubis and the top of the fundus is measured

c.    The distance in centimeters is equal to the gestational age (20cm = 20 weeks)

d.   Correlates during the first two trimesters

III.         Quickening

a.   Sensation of fetal movement

b.   Usually occurs at 16-22 weeks

c.    Very rough estimate of gestational age

IV.          Determination of Fetal Heartbeat

a.   The fetal heartbeat is heard between 16-20 weeks gestation

b.   As early as 8 weeks with a Doppler device

c.    Rough estimate of gestation age

V.              Ultrasonagraphy

a.   Discussed earlier

 

 

Biophysical Tests of Well Being

 

I.                 Contraction stress test (CST)

a.   CST assesses fetal response to contractions

b.   Determines the presence of uteroplacental insufficiency

c.    Fetus is stressed during contractions

d.   Positive CST

                                                            i.      50% of contractions have Type II FHR decelerations

e.   Negative CST

                                                            i.      no deceleration in FHR

f.     Most tests fall somewhere in between

g.   Can fetus tolerate normal labor and delivery or is Cesarian section needed?

h.   Variation of CST

                                                            i.      Oxytocin Contraction Test (OST)

1.   IV is used to start contractions

2.   Positive CST indicates induction for delivery

II.             The Non-Stress Test (NST)

a.   The response of FHR to movement is observed

b.   FHR increases 15 bpm > baseline for at lest 15 seconds

c.    Positive NST

                                                            i.      at least 2 accelerations over a 20 minute period

d.   Negative NST

                                                            i.      no accelerations over a 20 minute period

e.   Fetal monitor is placed on momís abdomen

                                                            i.      Mom presses a button when the baby moves

f.     Simple to perform, less time consuming, little risk

III.         Interpretation of CST and NST

                                                            i.      Positive CST and Negative NST

1.   Fetus with hypoxia

                                                         ii.      Negative CST and Negative NST

1.   Fetal sleep

2.   CNS depression

IV.          Acoustic Stimulation

a.   Buzzer against momís abdomen

b.   FHR monitored for accelerations

c.    Failure to accelerate indicates that the fetus is compromised and further testing is required

V.              Monitoring Fetal Movement

a.   Indirect measurement of CNS function

b.   Momís observation or ultrasound

c.    Greatest activity between 28-34 weeks

d.   First detected between 16-20 weeks

e.   < 10 movements per hour require further testing

f.     Inactivity is associated with fetal distress and stillbirth

VI.          The Biophysical Profile

a.   Fetal breathing

b.   Fetal movement

c.    Fetal limb tone

d.   NST

e.   Amniotic fluid volume

f.     Normal score is 8-10

g.   May be best overall method of fetal risk determination

VII.      Meconium Presence in Amniotic Fluid

a.   Thick, dark greenish stool found in the fetal intestine

b.   Occurrence

                                                            i.      Present in 40% of post-term fetuses > 42 weeks

                                                         ii.      Present in 10% of term fetuses 38-42 weeks

                                                      iii.      Present in 3-5% of pre-term fetuses < 38 weeks

c.    Determined by amniocentesis or visualized when sac ruptures

d.   May result from fetal asphyxia

                                                            i.      relaxation of the anal sphincter and increased peristalsis

e.   May cause Meconium Aspiration Syndrome

VIII.  Chorionic Villus Sampling

a.   Indications

                                                            i.      Advanced maternal age

                                                         ii.      Previous child with chromosomal anomalies

                                                      iii.      Parent carrier

b.   Done at 9-12 weeks gestation

c.    Examined for chromosomal abnormalities

d.   Contains fetal blood and tissue

                                                            i.      Provides a larger DNA sample than amniocentesis

e.   With USN fetal loss rate < 1%

IX.          Cordocentesis

a.   In utero sampling of fetal umbilical cord blood

b.   Under ultrasound, the umbilical cord is punctured with a 22 gauge needle and blood samples are drawn into tuberculin syringes

c.    Samples checked for sickle-cell, hemophilia, fetal infection, metabolic disease, congenital defects, PO2 and acid-base status

d.   Fetal and maternal risk is < 1%

X.              Biochemical Methods of Assessment

a.   Maternal Estriol

                                                            i.      Secreted in high quantities by the placenta in the latter half of pregnancy

                                                         ii.      Normal levels depend on properly functioning fetal liver and adrenal glands

                                                      iii.      Levels are decreased in growth retardation, fetal distress, and placental insufficiency

                                                      iv.      Maternal blood and /or urine is collected several times a week

                                                         v.      Fetal distress is indicated by a 50-60%† drop from previous tests or ongoing drop

                                                      vi.      Inconvenient, high number of false negatives

b.   Human Placental Lactogen (HPL)

                                                            i.      Produced by the placenta, excreted in maternal blood

                                                         ii.      Prepares breasts for milk production

                                                      iii.      Levels increase until 37 weeks then remains same or decreases slightly

                                                      iv.      Serum levels are evaluated weekly

                                                         v.      Normal range (term) 5.4-7.0 ug/mL

                                                      vi.      HPL< 4 ug/mL after 30 weeks gestation may indicate fetal compromise

                                                   vii.      Less popular in recent years, inconvenient

XI.          Magnetic Resonance Imaging

a.   Used to assess the status of soft tissue structure and function

b.   Indicated when ultrasound is insufficient

c.    Used to detect placental and fetal abnormalities

d.   Assess development of the fetal lungs and brain

e.   No risk of damage to the fetus

 

 

Factors Identifying a High-Risk Pregnancy

 

I.                 It is important to identify a high risk fetus

II.             High-Rick Pregnancy Indicating Factors (see text for complete list)

a.   Socioeconomic factors

                                                            i.      Low income and poor housing

                                                         ii.      Unwed status, especially adolescent

                                                      iii.      Poor nutritional status

b.   Demographic factors

                                                            i.      Maternal age under 16

                                                         ii.      Obese or underweight before pregnancy

                                                      iii.      Familial history of inherited disorders

a.   Medical factors

                                                            i.      Obstetric History

1.   history of miscarriage

2.   previous multiple gestations

3.   history of premature labor

                                                         ii.      Maternal medical history

1.   maternal diabetes

2.   maternal pulmonary disease

3.   maternal hypertension

                                                      iii.      Current obstetric status

1.   absence of prenatal care

2.   polyhydramnios or oligohydramnios

3.   placenta previa

                                                      iv.      Habits

1.   smoking

2.   alcohol

3.   drug use

††††††

Definitions

 

1.   Para Ė the number of births (alive or not) with a viable infant > 20 weeks and at least 500 grams

2.   Gravida Ė the number of pregnancies

3.   Pre-eclampsia (toxemia)

a.   Usually occurs at > 24 weeks gestation

b.   Acute hypertension, edema, renal impairment (proteinuria), sudden weight gain

c.    Occurs in 7% of pregnancies

d.   More common in low socioeconomic groups

4.   Eclampsia

a.   Toxemia, seizures, coma, convulsions, hemolysis, renal failure

b.   5% of women with pre-eclampsia develop eclampsia

c.    15% die from complications

d.   Associated with high fetal mortality due to premature delivery