SB 6.18.53

striyo vīravatīś cārcet
 srag-gandha-bali-maṇḍanaiḥ
patiṁ cārcyopatiṣṭheta
 dhyāyet koṣṭha-gataṁ ca tam
Synonyms: 
striyaḥ — women; vīra-vatīḥ — possessing husbands and sons; ca — and; arcet — she should worship; srak — with garlands; gandha — sandalwood; bali — presentations; maṇḍanaiḥ — and with ornaments; patim — the husband; ca — and; ārcya — worshiping; upatiṣṭheta — should offer prayers; dhyāyet — should meditate; koṣṭha-gatam — situated in the womb; ca — also; tam — upon him.
Translation: 
With flower garlands, sandalwood pulp, ornaments and other paraphernalia, a woman following this vow should worship women who have sons and whose husbands are living. The pregnant wife should worship her husband and offer him prayers. She should meditate upon him, thinking that he is situated in her womb.
Purport: 

The child in the womb is a part of the husband’s body. Therefore the husband, through his representative, indirectly remains within the womb of his pregnant wife.