Kenneth F. Trofatter, Jr., MD, PhDPregnancy and Childbirth
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Amniotic Fluid - 6 - Polyhydramnios: Causes of Too Much Amniotic Fluid

Kenneth F. Trofatter, Jr., MD, PhD
Polyhydramnios (excessive amniotic fluid), also termed hydramnios, is usually defined by vertical pockets of amniotic fluid > 8 cm or as a 4-quadrant amniotic fluid index (AFI) > 95th percentile for the gestational age. Polyhydramnios has a multitude of causes and associations but is seen in only about 1-2% of all pregnancies. It can occur gradually or rapidly depending on the underlying etiology. About 50-60% of polyhydramnios is ‘idiopathic’ which means we haven’t been smart enough to figure out why there is too much fluid. It is not necessarily associated with increased urine production by the baby, but it may have a genetic basis because it can recur in sequential pregnancies, even without an etiology being identified. In some instances there is just excessive fluid and it doesn’t necessarily increase significantly over time and in other cases, it gets progressively worse and may cause both fetal and maternal complications.

There are some specific conditions in which polyhydramnios is frequently associated. The easiest to understand are the fetal anomalies that inhibit or prevent fetal swallowing or block the passage of fluid through the fetal bowel. (Recall, much of the amniotic fluid around the baby is urine and the baby must be able to swallow that and move it through the bowel to the colon where it can be reabsorbed). Common structural gastrointestinal abnormalities that are accompanied by polyhydramnios include esophageal atresia (incomplete development of the esophagus), tracheoesophageal fistulas (aberrant connections, sometimes ending in ‘blind pouches’, between the trachea and the esophagus), duodenal atresia with the classic “double bubble” seen by ultrasound in the upper abdomen (and at least 30% of these associated with Down syndrome – trisomy 21), other small bowel atresias and obstructions (the lower in the small bowel the obstruction, the greater the number of fluid-filled loops of bowel), gastroschisis (a condition in which much of the small bowel is outside the abdomen through a small defect adjacent to the fetal umbilical cord insertion site), gastrointestinal ‘malrotations’ and ‘midgut volvulus’.

Other fetal anomalies associated with polyhydramnios probably have different reasons for contributing to the excessive fluid. Large neural tube defects and certain neuromuscular disorders (such as myotonic dystrophy), for example, probably exert their effects by impairing the ability of the baby to actually swallow fluid, even if the esophagus and gastrointestinal tract are patent. Certain cardiac defects and fetal arrhythmias may contribute by virtually putting the baby into congestive heart failure. Heart failure is also likely to be a major contributing factor when the baby has severe anemia secondary to maternal isoimmunization, a fetal hemoglobinopathy, or bone marrow suppression of red blood cell synthesis as is seen with congenital Parvovirus B19 infections.

Other congenital infections (e.g., syphilis, toxoplasmosis, cytomegalovirus) may also result in excessive amniotic fluid although the actual causes of this may be different depending on the organism involved. Indeed, any condition that results in immune or nonimmune fetal hydrops, including chromosomal abnormalities and inborn errors associated with severe metabolic or cardiac dysfunction, may be accompanied by polyhydramnios. One of the more unusual conditions that is associated with polyhydramnios and fetal hydrops is the so-called “mirror syndrome” that occurs in some cases of severe maternal preeclampsia. Lithium toxicity appears to cause polyhydramnios by causing the baby to have a condition called diabetes insipidus which results from inadequate vasopressin (antidiuretic hormone – ADH) secretion by the posterior pituitary gland and, subsequently, massive production of very dilute (unconcentrated) urine.

The most common clinical condition that is often accompanied by polyhydramnios is diabetes, particularly, gestational diabetes and type 2 diabetes. It is much less likely to be found in long-standing diabetics, particularly, if they have significant kidney, cardiac, or vascular disease. In diabetics, polyhydramnios is more common if the diabetes is poorly-controlled and/or the baby is macrosomic. At times, even improving the diabetic control will not reduce the increased amniotic fluid. The etiology of the increased fluid in certain diabetics is unclear, but when present, it increases the risk for a poor fetal outcome.

In the next post, we will continue with a discussion of polyhydramnios – pregnancy complications, evaluation, and management….

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6 Comments:

  • At Tue May 20, 09:19:00 AM 2008, Anonymous Lori said…

    Hello! I am posting about an unrelated topic - I hope that is ok. Long story short, I have had two early miscarriages in the last year and a half. Since then, I have been diagnosed with Lupus Anticoagulant, MTHFR, and Asherman's syndrome. I had surgery for the Asherman's and am on Lovenox, baby aspirin and Folgard for the LAC and MTHFR - and I just found out I am pregnant. My doc thinks one or more of the above issues are what caused my miscarriages but obviously doesn't know for sure. So now my two questions: 1) He wants to put me on erythromycin for 6 weeks to ensure I don't have and don't get an infection. He said infection *could* have played a part in my miscarriages. First off, are antibiotics ok during the first trimester - I have read varying thoughts on the matter. And if yes, is 6 weeks really necessary just as a preventitive measure? My second question is - my progesterone level on day 28 came back at 79, which is very good from what I have read, but my doc still wants to give me weekly progesterone injections. Is this necessary? Is it ever possible to have your progesterone be too high? Thank you so much for your insight! Lori

     
  • At Sun May 25, 05:51:00 PM 2008, Blogger Kenneth F. Trofatter, Jr., MD, PhD said…

    Hi Lori: Personally, I would have preferred to treat you with the erythromycin prior to the pregnancy if at all. It sounds like you are in good hands though. At that progesterone level, you will probably get limited benefit from supplemental progesterone, but it should't be "too much" either. Soon the placenta will be making more than we can routinely give you anyway. Good luck and let us know how things turn out. Dr T

     
  • At Wed Jun 04, 05:36:00 PM 2008, Anonymous Jennifer said…

    I have been diagnosed with polyhydramnios and my doctor thinks that our baby may have duodenal atresia. I am waiting to see a specialist but am already 34 weeks pregnant. Is this something that should have been seen earlier in my pregnancy? Also, should I be taking it easy and not exercising? Another article I read on this topic said polyhydramnios puts you at risk for preterm labor. Also, how soon after birth do they do the surgery to correct the atresia? Any answers would be greatly appreciated ad I am extremely worried.

     
  • At Sat Jun 07, 07:26:00 AM 2008, Blogger Kenneth F. Trofatter, Jr., MD, PhD said…

    To Jennifer: As I am sure you have read by now, about half of babies with duodenal atresia have trisomy 21 (Down syndrome). I have been involved in many cases where this was found late in pregnancy only after polyhydramnios developed. If you had not had an ultrasound since earlier in midtrimester it could have beeen easily missed. The repair is usually done shortly after birth if the baby is stable from other respects, but ask your doctor to arrange a consultation with a neonatalogist and a pediatric surgeon to give you the full idea of the evaluation and management options following delivery. Best of luck to you and please let us know how things turn out! Dr T

     
  • At Tue Jul 01, 08:15:00 AM 2008, Blogger Monica said…

    I miscarried at 22 wks in June 06, all test revealed nothing. The only issues was that I had excess amniotic fluid. I am now 20 wks pg and have been diagnosed with Polyhydramnios again, volume of liquor is 26cm. I am really worried, they have referred me to UCH for a more detailed scan on Friday

     
  • At Tue Jul 01, 06:39:00 PM 2008, Blogger Kenneth F. Trofatter, Jr., MD, PhD said…

    To Monica: Idiopathic polyhydramnios recurs about 50% of the time, we are just too stupid to figure out why! I hope they look at your cervix while they are evaluating the baby and the fluid. You could have cervical incompetence as well. Best of luck and let us know what you find out! Dr T

     

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