Miscarriage on the 19th week

Hi to all,

We had a miscarriage on the 19th week of our pregnancy. It was a shock. 

They were twins initially, the first was lost during the 1st month. 

The same exactly happened to us 3 years ago. With the same exactly frequency. Unbelievable. 

Between the first and the second miscarriage we had a normal pregnancy that gave us our 2 years old daughter. 

Can someone advise why after loosing from a twins the first then the risk for losing the second is high? In our case this was a fact unfortunately. 

Thank you in advance. Take care all.

T