The fifth house in a horoscope pertains to one's progeny or children. If Rahu or Ketu is in the 5th house, there are difficulties in conceiving as a general occurrence. However, at times, only delay in conceiving may take place due to beneficial aspects or strength of the 4th lord.
Astrology can forecast birth or existence of children based on a detailed analysis of the horoscopes of the parents read in conjunction. According to Nadi Astrology, a lot of importance is given to Venus. Consideration is also given to aspects on the luminaries i.e., Sun and Moon. The Karaka planet is Jupiter as per Vedic Astrology.
A strong lagna or ascendant (rising sign at birth) and 4th lords can mitigate the problems of childlessness to a great extent. Of course, the operating dasa (planetary period) too needs to be examined with reference and relation to the 5th and 4th house occupier(s), lord, aspects etc.