7. Amnionic Fluid.pptx

FETOLOGY

1. Amnionic Fluid Themba Hospital FCOG(SA) Part 1 Tutorials By Dr N.E Manana

2. Intro Amnionic fluid serves several roles during pregnancy . It creates a physical space for fetal movement , which is necessary for normal musculoskeletal development It permits fetal swallowing —essential for gastrointestinal tract development , and fetal breathing —necessary for lung development . Amnionic fluid guards against umbilical cord compression and protects the fetus from trauma It even has bacteriostatic properties

3. NORMAL AMNIONIC FLUID VOLUME Amnionic fluid volume increases from approximately 30 mL at 10weeks to 200 mL by 16weeks and reaches 800 mL by the mid-third trimester This fluid is approximately 98-percent water . A full-term fetus contains roughly 2800 mL of water , and the placenta another 400 mL , such that the term uterus holds nearly 4 liters of water Abnormally decreased fluid volume is termed oligohydramnios , whereas abnormally increased fluid volume is termed hydramnios or polyhydramnios

4. Physiology Early in pregnancy , the amnionic cavity is filled with fluid that is similar in composition to extracellular fluid During the first half of pregnancy, transfer of water and other small molecules takes place across the amnion — transmembranous flow, across the fetal vessels on placental surface—intramembranous flow, and across fetal skin Fetal urine production begins between 8 and 11weeks , but it does not become a major component of amnionic fluid until the second trimester. This latter observation explains why fetuses with lethal renal abnormalities may not manifest severe oligohydramnios until after 18 weeks

5. Table 11.1

6. Measurement The actual volume of amnionic fluid is rarely measured outside of the research setting Amnionic fluid volume evaluation is a component of every standard sonogram performed in the second or third trimester Volume is typically assessed semiquantitatively , by measuring either a single pocket or the amnionic fluid index —AFI

7. Single Deepest Pocket This is also called the maximum vertical pocket . The ultrasound transducer is held perpendicular to the floor and parallel to the long axis of the pregnant woman In the sagittal plane , the largest vertical pocket of fluid is identified, the fluid pocket may contain fetal parts or loops of umbilical cord , but these are not included in the measurement The normal range for single deepest pocket that is most commonly used is 2 to 8 cm , with values above and below this indicating hydramnios and oligohydramnios , respectively

8. Amnionic Fluid Index (AFI) This was described by Phelan and coworkers (1987) more than 25 years ago, and it remains one of the most commonly used methods of amnionic fluid volume assessment The uterus is divided into four equal quadrants —the right- and left-upper and lower quadrants . The AFI is the sum of the single deepest pocket from each quadrant . A fluid pocket may contain fetal parts or umbilical cord loops , but these are not included in the measurement.

9. HYDRAMNIOS This is an abnormally increased amnionic fluid volume, and it complicates 1 to 2 percent of pregnancies Also termed polyhydramnios , hydramnios may be suspected if the uterine size exceeds that expected for gestational age . Hydramnios may be further categorized according to degree Mild hydramnios is the most common , comprising approximately two thirds of cases In general , severe hydramnios is far more likely to have an underlying etiology and to have consequences

10. HYDRAMNIOS: Aetiology Common underlying causes of hydramnios include fetal congenital anomalies in approximately 15 percent and diabetes in 15 to 20 percent Congenital infection and red blood cell alloimmunization are less frequent reasons Infections that may present with hydramnios include cytomegalovirus , toxoplasmosis , syphilis , and parvovirus Because the etiologies of hydramnios are so varied , hydramnios treatment also varies and is tailored in most cases to the underlying cause

11. Idiopathic Hydramnios When there is no obvious cause of hydramnios it is considered idiopathic, this accounts for up to 70 percent of cases Pregnancies with idiopathic hydramnios have been reported to have at least twice the likelihood of infant birthweight exceeding 4000g A rationale for this association is that larger infants have higher urine output Mild , idiopathic hydramnios is most commonly a benign finding , and associated pregnancy outcomes are usually good .

12. Complications Unless hydramnios is severe or develops rapidly , maternal symptoms are infrequent Symptoms may arise from pressure upon adjacent organs When distention is excessive , the mother may suffer dyspnea and orthopnea Edema may develop as a consequence of major venous system compression , and it tends to be most pronounced in the lower extremities , vulva , and abdominal wall Maternal complications associated with hydramnios include placental abruption , uterine dysfunction , and postpartum hemorrhage

13. Pregnancy Outcomes Some outcomes that have been reported to be increased with hydramnios include cesarean delivery rate , birthweight > 4000g , and i mportantly , perinatal mortality rate The cesarean delivery rate is increased approximately threefold When hydramnios has been identified , and the perinatal mortality rate rises approximately fourfold

14. Management Occasionally, severe hydramnios may result in early preterm labor or the development of maternal respiratory compromise . In such cases, large-volume amniocentesis —termed amnioreduction —may be needed Approximately 1000 to 1500 mL of fluid is slowly withdrawn during approximately 30 minutes , depending on the severity of hydramnios and gestational age The goal is to restore amnionic fluid volume to upper normal range Subsequent amnioreduction procedures may be required as often as weekly or even semi-weekly

15. OLIGOHYDRAMNIOS Oligohydramnios complicates approximately 1 to 2 percent of pregnancies Unlike hydramnios , which is often mild and confers a benign prognosis in the absence of an underlying etiology , oligohydramnios is a cause for concern When no measurable pocket of amnionic fluid is identified, the term anhydramnios may be used. The sonographic diagnosis of oligohydramnios is usually based on an AFI ≤ 5 cm or on a single deepest pocket of amnionic fluid ≤ 2 cm

16. Aetiology Include those in which the amnionic fluid volume has been severely decreased since the early second trimester and those in which the fluid volume was normal until near-term or even full-term. The prognosis depends heavily on the underlying etiology Early-Onset Oligohydramnios: it may reflect a fetal abnormality that precludes normal urination , or it may represent a placental abnormality severe enough to impair perfusion Oligohydramnios after Midpregnancy : it more likely is associated with fetal -growth restriction , a placental abnormality , or a maternal complication such as preeclampsia or vascular disease

17. Congenital Anomalies Among those with fetal abnormalities , most cases of severely decreased amnionic fluid volume beginning early in gestation are secondary to genitourinary anomalies Anomalies of other organ systems , aneuploidy , and other genetic syndromes also have the potential to cause oligohydramnios indirectly, either from fetal decompensation , FGR , or an accompanying placental abnormality Overall, approximately 3 percent of newborns with congenital anomalies have oligohydramnio s found during prenatal sonography

18. Medication Oligohydramnios has been associated with exposure to drugs that block the renin-angiotensin system . These include ACE inhibitors and NSAIDs. When taken in the second or third trimester , ACE inhibitors and angiotensin-receptor blockers may create fetal hypotension , renal hypoperfusion , and renal ischemia , with subsequent anuric renal failure

19. Pregnancy Outcomes Oligohydramnios is associated with increased risk of adverse pregnancy outcomes, more likely than those with AFIs > 5 cm to have malformations Even in the absence of malformations , higher rates of fetal stillbirth , growth restriction , nonreassuring heart rate pattern, and meconium aspiration syndrome were noted Chauhan and coworkers (1999) found that women with oligohydramnios had a twofold increased risk for cesarean delivery for fetal distress and a fivefold risk for an Apgar score < 7 at 5 minutes

20. Pulmonary Hypoplasia When decreased amnionic fluid is first identified before the mid-second trimester , particularly before 20 to 22weeks, pulmonary hypoplasia is a significant concern The underlying etiology is a major factor in the prognosis Severe oligohydramnios secondary to a renal abnormality generally has a lethal prognosis If a placental hematoma or chronic abruption is severe enough to result in oligohydramnios

21. Management As with hydramnios , management targets the underlying etiology when feasible . Initially, an evaluation for fetal anomalies and growth is essential . In a pregnancy complicated by oligohydramnios and FGR , close fetal surveillance is important In many cases , evidence for fetal or maternal compromise will override potential complications from preterm delivery Oligohydramnios detected before 36 weeks in the presence of normal fetal anatomy and growth may be managed expectantly in conjunction with increased fetal surveillance

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