Anatomia

Vasa previa e inserzione velamentosa del cordone ombelicale

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I vasa previa sono vasi sanguigni fetali del cordone ombelicale, privi di guaina protettiva e gelatina di Wharton,  che attraversano o sono prospicienti all’orificio uterino interno. Possono presentarsi come unica anomalia placentare o essere associati ad altre con anomalie annessiali, come inserzione velamentosa del cordone, placenta previa, distacco di placenta. 

L’inserzione velamentosa del cordone imita un po’ la situazione dei  vasa previa in quanto i vasi del cordone ombelicale, in prossimità dell’inserzione placentare, si suddividono in numerosi vasi privi di protezione che raggiungono il corpo placentare percorrendo anche diversi centimetri privi della guaina propria del cordone ombelicale.   

La prevalenza dei vasa previa è di circa 1/2500 su 5000 parti e la loro frequenza è aumentata dopo l’introduzione delle tecniche di fecondazione in vitro. Il tasso di mortalità fetale può avvicinarsi al 60% se i vasa previa non vengono diagnosticati prima della nascita.

Sintomatologia dei vasa previa

La presentazione classica dei vasa previa è costituita da un sanguinamento vaginale indolore, rottura delle membrane, e bradicardia fetale.

Diagnosi

  • Ecografia transvaginale: I vasi fetali possono essere visualizzati come se le membrane passassero direttamente sopra o vicino l’orifizio uterino interno sono facilmente individuabili con eco color-Doppler.

Diagnosi ecografica differenziale – I vasa previa devono essere distinti dalla presentazione funicolare (procidenza del cordone ombelicale tra la parte presentata e l’orifizio uterino interno a membrane integre), in cui i vasi del sangue fetale avvolti dalla gelatina di Wharton possono essere visti come se coprissero il collo dell’utero. Nella presentazione funicolare il cordone ombelicale si allontana dalla cervice durante la valutazione ecografica; nei vasa previa, il cordone è fisso sul posto. La procidenza del cordone va distinta dal prolasso del cordone, condizione in cui il funicolo si interpone fra la parte presentata e la cervice uterina dopo la rottura delle membrane amnio-coriali. Il cosiddetto prolasso occulto del cordone invece è dato dall’interposizione laterale del cordone fra la parte presentata e la pelvi materna.

  • CTG: alterazioni del tracciato cardiotocografico al comparire del travaglio

Complicanze: in caso di rottura delle membrane amniotiche i vasa previa facilmente si lacerano con notevole emorragia. Tale emorragia è a totale carico della circolazione fetale con rapida anemizzazione e frequente morte fetale. 

Management:

1. Monitoraggio con non-stress test due volte alla settimana iniziando dalla 28a fino alla 30a settimana e più frequentemente a circa 30-32 settimane per evidenziare precocemente la compressione del cordone ombelicale

2. programmazione del parto – 

Il parto cesareo d’emergenza di solito è indicato se si verifica qualsiasi delle seguenti situazioni:

  1. rottura prematura delle membrane.
  2. sanguinamento vaginale continuo
  3. segni di distress fetale 

Se non è presente nessuno di questi problemi e non si è verificato il travaglio, si può programmare un taglio cesareo di elezione avendo cura di Somministrare di corticosteroidi per accelerare la maturità polmonare fetale.

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