No miscarriages

The original תקנה of שובבים ת"ת (fasting & Tikunim  the

8 weeks starting from Parshas שמות) was intended only

for leap years.

The Levush O. Ch. 685 writes," one of the reasons we fast  on

שובבים ת"ת so that pregnant women shouldn’t miscarry.

During leap years, it is more common for women to miscarry.

We fast 8 times for the last 8 months of pregnancy.

(first month [40 days] is not considered a miscarriage) . 

It is appropriate to start on Parshas שמות, where it 

says    ובני ישראל פרו וישרצו "