Christianity Today’s her*meneutics blog has an article on natural family planning that’s not very flattering toward that practice at all:
Bethany and Sam Torode divorced in 2009 after nine years of marriage, during which they had four children. Early in their marriage, the couple wrote a book called Open Embrace: A Protestant Couple Rethinks Contraception, in which they argued that natural family planning (NFP) is the healthiest, most spiritually enriching contraceptive approach for Christians. …Oh well. One can be assured that Andronikos and Junia didn’t practice NFP.
The Torodes, as other NFP supporters do, argued in their book and here at Christianity Today that not only is NFP as effective as medical forms of birth control when done correctly (which admittedly requires knowledge and practice), but also makes for healthier marriages that more closely align with God’s purposes for husbands and wives. They believe NFP honors our God-given bodies and fertility cycles rather than manipulating them to suit our preferences. It makes each act of intercourse truly open to God’s procreative purpose for marriage. ...
The Torodes’ marriage did not last. But even before they divorced, they renounced NFP in a 2006 statement. They said that NFP can lead to guilt and frustration when the couple desires sex, but has to abstain, particularly given that many women are particularly interested in sex during ovulation. They argued that, rather than embracing God’s gift of the body, NFP can lead couples to reject physical intimacy, either because they don’t want to conceive, or because they are exhausted by raising children whose births may have been unplanned. (The statement is no longer easily accessible on the Internet, so I am paraphrasing based on a variety of sources that quote from it.)