Zeir Anpin’s Mental Powers… i.e. his inner soul – Heb. pnimiyut – because it is impossible to have neither interiority nor externality. Thus even during Pregnancy there are Mental Powers.
…in this period are at their lowest possible degree of strength. As discussed earlier, the strength of the body is according to the strength of the Mental Powers. Accordingly, when the Mental Powers are at minimum strength, the body also remains concealed and powerless. (Thus in Pregnancy, only Netzach-Hod-Yesod of the body are revealed, while the head – Chochmah-Binah-Daat – and chest – Chessed-Gevurah-Tiferet—are folded up behind them “three within three”.)