Amniotic Fluid and Fetal Membranes

OB2

Amniotic fluid allows the fetus to move freely while

maintaining intrauterine temperature

protecting the developing fetus from injury

Abnormalities with the amniotic fluid may

interfere with normal fetal development

cause structural abnormalities

represent indirect sign of underlying anomaly

neural tube defect

GI disorder

Amniotic fluid is protected by

umbilical cord and membranes

lungs

skin

kidneys

As the fetus and placenta mature, fluid production and consumption change to include movement of fluid across

chorion frondosum

fetal skin

fetal urine output

fetal swallowing

gastrointestinal absorption

Amniotic fluid functions

acts as a cushion to protect the fetus

allows embryonic and fetal movements

prevents adherence of amnion to embryo

allows symmetrical growth

maintains a constant temperature

acts as a reservoir to fetal metabolites before their excretion by the maternal system

Chorion frondosum

portion of the chorion that develops into the fetal portion of the placenta

site where water is exchanged freely between the fetal blood and amniotic fluid across the amnion

When does fetal production of urine and the ability to swallow begin?

8-11 weeks

What accounts for nearly all of the total volume of amniotic fluid by the second half of the pregnancy?

fetal urination

directly related to kidney function

In addition to the fetal kidneys, the amount of fluid is also regulated by:

removal of the fluid by swallowing

fluid exchange within the lungs

membranes and cord

When does the amount of amniotic fluid appear generous

20-30 weeks

by 20 weeks gestation, AF volume increases by 10 ml/day

Vernix caseosa

fatty material found on fetal skin and in amniotic fluid late in pregnancy

What are the different assessments of measuring amniotic fluid

subjective assessment

four quadrant assessment

measurement of the single deepest pocket of fluid

A subjective assessment of AF is an “eyeball” assessment of

fluid present

fetal lie

placenta position

AF volume progressively increases until about:

33 weeks gestation

When looking at the AF volume, always check the:

kidneys

Four quadrant assessment

evaluating and quantifying the AF volume in 4 quadrants

measure the largest vertical pocket in each quadrant

exclude limbs and cord

Sum of the four quadrants =

the amniotic fluid index

Normal amount of AF

10-20 cm

Oligo

< 5 cm

Poly

>24cm

When measuring the AF do not include:

the thickness of the maternal uterine wall

Single pocket assessment

find the largest pocket and measure the max vertical depth

Single pocket categories

< 2 cm - oligo

2-8 cm - normal

>8cm - poly

Two-diameter pocket assessment

two dimensional determination

largest pocket and measure the vertical and horizontal dimensions

multiply both dimensions to obtain a single volume

between 15-50 cm is normal

AF in twin pregnancies

multiple gestations will have a smaller AFI

Polyhydramnios

AF volume of >2000ml

Increased perinatal mortality and morbidity and maternal complications

Polyhydramnios can lead to

preterm labor

variety of other maternal symptoms

painful

compress other organs and vascular structures

cause hydronephrosis of the kidneys

SOB from compression of the organs on the diaphragm

fetal hydrops

skeletal anomalies

renal disorders

fetal macrosomia

Rh isoimmunization

Poly is associated with

CNS disorders that cause depressed swallowing

Maternal conditions associated with polyhydramnios

DM

obesity

Rh incompatibility

anemia

CHF

Anomalies associated with oligo

pulmonary hypoplasia

abnormal facial features

abnormal limb development

Causes of oligo

congenital anomalies (renal)

IUGR

post-term pregnancies

ruptured membranes

iatrogenesis

Maternal conditions associated with oligo

hypertension

preeclampsia

chronic cardiac or renal disease

connective tissue disorders

receiving indomethacin

IUGR

4x risk of growth delay with oligo

placental insufficiency

fetal hypoxia

COMMON complication of post-term pregnancies

oligohydramnios

Iatrogenic causes of oligo

medications

insensible fluid loss

maternal intravascular fluid depletion

prior procedures like a CVS

What is one way to combat oligo?

maternal hydration

does not work if membranes are ruptured

If oligo is present, you must doppler

umbilical cord

placenta

cerebral vascular system

LOOK OUT FOR CORD COMPRESSION

Premature ruptured fetal membranes

when the membranes rupture abnormally

“water breaking”

Nitrazine paper and fern paper test determine the presence of AF in vaginal secretions

PROM associated with

preterm delivery

fetal and neonatal death

neonatal respiratory distress

prolapsed umbilical cord

chorioamnionitis

placental abruption

Amniotic band syndrome

common nonrecurrant cause of various fetal malformations involving the limbs, craniofacial region and trunk

Cause of amniotic band syndrome

rupture of amnion during early pregnancy development that leads to the entanglement of various embryonic or fetal parts

Common findings of amniotic band syndrome

facial clefts

asymmetric encephaloceles

constriction or amputation defects of the extremities

clubfoot deformities

Amniotic sheets / synechiae

folds identified as echogenic, nonfloating bands crossing through the amniotic cavity

believed to be caused by uterine scars from c-sections, D&Cs, and endometritis

Asherman’s syndrome

patients who present with uterine synechiae and infertility

Hydrops fetalis

disparity seen between the amount of serous fluid being produced and that of which is absorbed

leads to placental edema

Hydrops leads to the accumulation of fluid in at least 2 areas like:

pleural effusions

ascites

cardiac effusions

skin edema

anasarca

Hydrops is associated with:

enlarged umbilical cord

polyhydramnios

placental edema

enlarged liver or spleen

high incidence of mortality

MOST COMMON cause of nonimmune hydrops

cardiac insufficiency

Mirror syndrome

Ballantyne syndrome or pseudotoxemia

mirrors preeclampsia

leads to fetal and maternal death

Mirror syndrome triad

fetal hydrops

placental edema

maternal edema