Foetus is made up of four set of four mahabhutas (i.e., of all except akasha), i.e., one set each from the mother, the father, from nutrition provided by the mother, and from the self only.
Out of these factors, the past deeds of the soul and the parents significantly influence the physical and psychological traits of the progeny. Like-wise, resemblance is also determined by the deeds of past life.
कस्मात् प्रजां स्त्री विकृतां प्रसूते हीनाधिकाङ्गीं विकलेन्द्रियां वा| देहात् कथं देहमुपैति चान्यमात्मा सदा कैरनुबध्यते च ||२८||
Why does a woman deliver an abnormal child with deficiencies or excess of organs or deranged sense organs? How does the soul transmigrate from one body to another and what is always associated with it?
Due to defects in the sperm/ovum, past deeds of the soul, uterus, time and mother’s food and behavior, doshas get vitiated causing various abnormalities in shape, complexion and sense organs.
Just as in the rainy season, wood, stone pieces and water current cause derangements in a tree situated in the river stream, doshas cause abnormalities in fetus situated in the womb.