לֹ֥א תִהְיֶ֛ה מְשַׁכֵּלָ֥ה וַעֲקָרָ֖ה בְּאַרְצֶ֑ךָ אֶת־מִסְפַּ֥ר יָמֶ֖יךָ אֲמַלֵּֽא׃
None shall miscarry, nor be barren, in thy land; the number of thy days I will fulfil.
Rashi on Exodus
לא תהיה משכלה THERE SHALL NOTHING BE BEREAVED OF YOUNG, if you will act according to My will.
Sforno on Exodus
לא תהיה משכלה ועקרה, so that you will have an opportunity to teach the children that have been born to you.
Rashbam on Exodus
לא תהיה משכלה, even when the baby has gown up it will not die in adolescence, but, את מספר ימיך אמלא, they will all reach ripe old age.