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NeoReviews Vol.7 No.6 2006 e305
© 2006 American Academy of Pediatrics

Polyhydramnios/Oligohydramnios in Twin Pregnancy

^* Professor and Vice Chairman, Department of Obstetrics and Gynecology, University of Missouri-Kansas City School of Medicine; Director of Medical Affairs, Saint Luke’s Hospital of Kansas City, Kansas City, Mo

The first 300 words of the full text of this article appear below.

	Objectives

 
After completing this article, readers should be able to:

1. Describe the morbidity and mortality associated with monochorionic twin gestations.
   
2. List the causes of polyhydramnios/oligohydramnios in twins.
   
3. Recognize the complex pathophysiology of twin-to-twin transfusion syndrome.
   
4. Delineate the treatment options currently available for polyhydramnios/oligohydramnios and the relative value of each.
   
5. Know the importance of prenatal understanding of zygosity and placentation in twin gestations.
   

	Introduction

 
The discovery of increased amniotic fluid in the gestational sac of one twin and decreased amniotic fluid in the amniotic sac of the second twin should generate an immediate clinical suspicion of twin-twin transfusion syndrome (TTTS). This relatively uncommon condition occurs when twins sharing a single placenta develop significant vascular anastomoses that result in a unidirectional shunt from one twin to the other. Although independent diagnoses could be affecting each twin simultaneously, leading to separate abnormalities in amniotic fluid volume, the possibility of such clinical coincidence is rare. Indeed, if the clinician recognizes that the placentation is monochorionic, the leading consideration in the differential diagnosis must be TTTS.

	Incidence and Frequency

 
TTTS is unique to monozygotic (one egg), monochorionic (one placenta) twin gestations. It has been recognized for some time that monochorionic twins experience greater morbidity and fetal loss than do dichorionic twins. Fortunately, only 30% of twins are monochorionic (Table 1). Of those, up to 15% may demonstrate some degree of TTTS. Thus, for all spontaneous twin gestations, the risk of TTTS is 4.5%.

Table 1. The Frequency of Placentation in Twin Pregnancies

Type of Placentation Frequency Dichorionic/Diamnionic, fused* 34.0% Dichorionic/Diamnionic, separated* 35.2% Monochorionic/Diamnionic** 29.6% Monochorionic/Monoamnionic** 1.2%

^* Monozygotic or dizygotic

^** Monozygotic only

It is estimated that 15% of perinatal mortality for twins is due to TTTS. Death may occur in either the donor (oligohydramnios) twin or the recipient (polyhydramnios) twin. Although perinatal mortality was nearly 100% with this diagnosis as recently as 25 years ago, improvements in outcome have resulted from better management options. In addition, . . . [Full Text of this Article]