A wife's child in a valid marriage is attributed to her husband on two conditions: that the minimum pregnancy period has passed since the marriage contract, and that it is not proven that contact between the spouses was impossible due to a physical barrier from the contract date to birth, or one arising after marriage and lasting more than three hundred and sixty-five days (art. 169). The minimum pregnancy period is six lunar months and the maximum is three hundred and sixty-five days (art. 166).
If a revocably divorced wife gives birth during her waiting period, paternity is established to the divorcer (art. 170). Paternity cannot be established by adoption, even if the adopted child is of unknown lineage (art. 167).
As for denial, in cases where paternity is established by the marital bed, the man may deny the child's paternity within seven days of the birth or of learning of it, provided he has not acknowledged paternity expressly or implicitly (art. 176). The li'an (mutual cursing) proceedings must be initiated within fifteen days of the birth or learning of it (art. 177). If li'an takes place, the judge negates the child's paternity from the man and the child is attributed to the mother (art. 178).
This is general legal information, not legal advice. For advice on your specific situation, consult a lawyer licensed in Kuwait.