Our Gemara on Amud Aleph questions the Mishna’s declaration of a general rule regarding women not being obligated in time-bound mitzvos:
וּכְלָלָא הוּא? הֲרֵי מַצָּה, שִׂמְחָה, הַקְהֵל, דְּמִצְוַת עֲשֵׂה שֶׁהַזְּמַן גְּרָמָא, וְנָשִׁים חַיָּיבוֹת! וְתוּ: וַהֲרֵי תַּלְמוּד תּוֹרָה, פְּרִיָּה וּרְבִיָּה, וּפִדְיוֹן הַבֵּן דְּלָאו מִצְוַת עֲשֵׂה שֶׁהַזְּמַן גְּרָמָהּ הוּא – וְנָשִׁים פְּטוּרוֹת!
The Gemara asks: But is this an established principle? But there are the mitzvos of eating matzah on the first night of Passover (Exodus 23:15), of rejoicing on a Festival (Deuteronomy 16:9–11), and assembly on Sukkot following the Sabbatical Year (Deuteronomy 31:10–13). And each of these is a positive, time-bound mitzva, and yet women are obligated in them. And furthermore, one can raise a difficulty as follows: But there are the mitzvos of Torah study (Deuteronomy 6:7), procreation (Genesis 1:28), and redemption of the firstborn (Exodus 13:12–13), each of which is not a positive, time-bound mitzva, and yet women are exempt from them.
Rav Yosef Engel (Beis Haotzar Klal 48, and אתוון דאורייתא כלל כב) asks why the commandment of peru urevu is considered not time-bound. On Yom Kippur, it is forbidden to engage in marital relations; therefore, ipso facto one is not obligated that night. Rav Engel uses that question as proof of the idea that if one is missing only one day out of the year, it is not considered missing, and it has various halakhic implications. While he brings many proofs to this idea, regarding his proof, from this particular question, I believe that another answer is possible.
The question is posed from the wrong direction. If we looked at it differently, and we imagined women are obligated in the commandment to be fruitful and multiply, then they actually would be able to fulfill the commandment even on Yom Kippur. This is because the act of carrying the baby would be part of the fulfillment of the mitzvah. The proof for this comes from an analogous case, in regard to returning a lost object. The General Bava Kama (56b) discusses the idea that because one who is involved in one mitzvah is exempt from performing another, therefore, somebody who is involved in tending to a lost object will be exempt from giving Tzedaka to a beggar if he is solicited during that time of occupation with the mitzvah. Let us keep in mind, the real mitzvah is to actually return the lost object to the owner. Watching the object, seeking the owner, etc. is not the fulfillment of the ultimate purpose, yet it still considered being involved in the mitzvah. So too, we can argue that while a woman is pregnant, and therefore tending to her unborn baby, she also is fulfilling the mitzvah of being fruitful and multiply. And, this obviously could be done on Yom Kippur. Now it turns out for technical and separate reasons, women are exempted from that mitzvah, however, the point is that if they were obligated, part of the fulfillment would be carrying the baby and therefore could be done even on Yom Kippur.
Aside from this being an interesting lomdishe argument, it is also an important reminder that though women may not be obligated in the mitzvah of bearing children, carrying the baby, and managing the pregnancy, is certainly fulfillment of a Mitzvah, obligation, or not.
Translations Courtesy of Sefaria, except when, sometimes, I disagree with the translation 
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