שובבים ת"ת

The original תקנה of שובבים ת"ת,( fasting & Tikunim  the 8 weeks starting from Parshas שמות) was intended only
for leap years. (This year)

The Levush O. Ch. 685 writes," one of the reasons we fast  on שובבים ת" ת, so that pregnant women wouldn’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 a miscarriage) . It is appropriate to start on Parshas Shemos, where it says ובני ישראל פרו וישרצו