SB 6.18.53
striyo viravatis carcet
srag-gandha-bali-mandanaih
patim carcyopatistheta
dhyayet kostha-gatam ca tam
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
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 by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
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.