Birth means the appearance of the five aggregates in the mother's womb.The five aggregates (Panca khandha) are;Material form (Rnpa-khandha), Feeling (Vedhana-khandha), Perception(Sanna-khandha),Kamma-Formation (Sankhara khandha) and Consciousness(Vinnana-khandha)
Birth,as one might expect,is shown as a mother in the process of childbirth.a painful business and a reminder of how dukkha cannot be avoided in any life Whatever the future life is to be,if we are not able to bring the wheel to a stop in this life,certainly that future will arise conditioned by the kamma made in this life But it is no use thinking that since there are going to be future births,one may as well put off Dhamma practice until then for it is not sure what those future births will be like. And when they come around,they are just the present moment as well.So no use waiting,
Naturally where there is Birth, is also Decay and Death