Commentary for Kiddushin 69:1
ולרבי יוחנן בן ברוקא דאמר על שניהם הוא אומר (בראשית א, כב) ויברך אותם אלהים פרו ורבו מאי איכא למימר משום דהוה ת"ת ופדיון הבן שני כתובים הבאים כאחד וכל שני כתובים הבאים כאחד אין מלמדין
But according to R'Johanan B'Beroka, who maintained, Concerning both [Adam and Eve] it is said: And God blessed them: and God said unto them, Be fruitful and multiply,<span class="x" onmousemove="('comment',' Gen. I, 28; this is the command of procreation.');"><sup>1</sup></span> what can be said? - Because the study of the Torah and redemption of the firstborn are two verses with one purpose, and such do not illumine [others]. But according to R'Johanan B'Beroka too, let procreation and fear be regarded as two verses with one purpose,<span class="x" onmousemove="('comment',' Viz., both are affirmative precepts not occasioned by time and both are incumbent upon women.');"><sup>2</sup></span>
Daf Shevui to Kiddushin
The answer—there is another PNTB commandment for which they are exempt—redeeming the first born. Only the father is obligated to redeem his first born.