There is no reference to birth control in the extensive writings of Bahá'u'lláh, the Founder of the Bahá'í Faith. Guidance is provided for just about every other material and spiritual issue, so I have often wondered what exactly is going to happen to prevent the need for ways to deal with overpopulation.
Will one of the thousands of unnamed and so far unresearched diseases wipe out a larger portion of humanity than AIDS has to date? Will one of the many disasters presently predicted actually come about, even if we don't buy the latest remedy?
Most likely, Bahá'ís believe, people will learn to live together "on Earth as in Heaven"--as has been promised by religion for millennia. That is certainly the promise and purpose of the Bahá'í Faith: to produce such a golden age in the near future. Its laws are designed to guide mankind towards recognition and acceptance that it is one diverse human family, worshipping one God, calling the entire planet one home.
In the meantime, however, "Abortion and surgical operations for the purpose of preventing the birth of unwanted children are forbidden...unless there are circumstances which justify such actions on medical grounds, in which case the decision is left to the consciences of those concerned who must carefully weigh the medical advice in light of the general guidance given in the teachings. Beyond this nothing has been found in the Writings concerning specific methods or procedures to be used in family planning." However, since Bahá'í teaching is that the soul appears at conception, it would be improper to use a method such as the IUD that aborts the process even so shortly after conception has taken place. - Lights of Guidance , p. 344
Lacking specifics of birth control in the Writings, "The utmost we can say is by way of reference from what Bahá'u'lláh has revealed regarding the nature, purpose and character of marriage. We, as Bahá'ís, are not therefore in a position either to condemn the practice of birth control or to confirm it. Birth control, however, when exercised in order to deliberately prevent the procreation of any children is against the spirit of the law of Bahá'u'lláh, which defines the primary purpose of marriage to be the rearing of children and their spiritual training..." ibid, p. 346
This does not mean that Bahá'ís are obliged to have baby after baby when they marry, but only to raise the one(s) they do produce to know and love God and be good citizens. There are instructions as to the importance of educating each child, so ideally, a couple planning to marry is concerned with more than just the material aspects of raising a family.
When asked whether the Bahá'í Writings offer guidance specific to the problem of too many people, the Universal House of Justice said this: "We have not discovered any specific reference in the texts to the problems of population explosion in its relation to birth control. This question, of course is a matter which is currently a subject of concern and speculation by many. A study of our teachings, however, indicates that in the future there will no doubt be a general improvement of standards of life and of health, but there will also be the full exploitation of unused and as yet unsuspected resources of the planet along with the control and tapping of its sources of raw material, with a great increase in productivity." - Baha'i World, Volume 16, p. 343
So, no, the Bahá'í Faith does not concern itself with the problem of too many people, or ways to prevent making more. Rather, Bahá'u'lláh focused on treating the spiritual illness whose resulting attitudes and behaviors cause humanity's problems. The planet will support many, many more people than it does today--when more of us behave better. That sort of paradigm change demands the faith, commitment and sacrifice which religion has supplied across generations.